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Spectacle and Contact Lens Wearing Six Years after Radial Keratotomy in the Prospective Evaluation of Radial Keratotomy Study
Spectacle and Contact Lens Wearing Six Years after Radial Keratotomy in the Prospective Evaluation of Radial Keratotomy Study Linda B. Bourque, PhD/ Michael]. Lynn, MS, 2 George O. Waring III, MD,3 Ceretha Cartwright, Dr PH,3 The Prospective Evaluation of Radial Keratotomy Study Group Background: Patients in the Prospective Evaluation of Radial Keratotomy (PERK) Study stated that a major reason for obtaining radial keratotomy was to see without dependence on corrective lenses . The authors examined lens-wearing patterns 6 years after surgery. Methods: Of the 435 patients in the PERK Study, the authors analyzed the responses of 328 (75.4%) who elected to have surgery on both eyes, who completed a questionnaire at 6 years, and for whom visual acuity and cycloplegic refraction were available. Resufts: Sixty-four percent (106/167) of patients younger than 40 years of age and 38% (64/161) of patients older than 40 years of age wore no lenses for distance or near vision. The proportion of time lenses were wom increased with age for those who wore them for close work only (from 18% younger than 40 years of age to 25% older than 40 years of age) and decreased with age for those who wore them for distance only (from 41% to 27%). The authors examined the visual acuity and refractive error criteria for patients to be free of distance lenses. Of the 359 patients who saw 20/20 or better uncorrected in one or both eyes, 77% (n = 198) wore no distance correction, whereas of the 53 patients who saw 20/25 to 20/40 in both eyes or their best eye, only 34% (n = 18) wore no distance correction. Of the 72 patients with a residual refractive error of ±0.50 diopters (D) in both eyes, 85% (n = 61) wore no distance correction, whereas of the 87 patients with ±1 .00 D in both eyes, only 39% (n = 34) wore no distance correction. Of the 328 patients, 60% (n = 197) were highly satisfied with the results of surgery, and satisfaction was primarily predicted by having a visual acuity 20/20 or better in at least one eye and not wearing spectacles for distance vision. Before surgery, 57% of patients reported worrying about their eyesight and 47% reported restrictions in activities because of their eyes; these rates dropped to 31% and 9% , respectively, at 6 years. Of the 328 patients, 74% (n = 243) said their preoperative goals were completely met and 94% (n = 308) said they would have radial keratotomy again. Conclusion: The use of 20/40 uncorrected visual acuity and a residual refractive error of ±'1.00 D were insensitive criteria for evaluating distance spectacle independence. The ability to function without lenses increased substantially only when patients had an uncorrected visual acuity of 20/20 or better in at least one eye, and a refractive error within ±0.50 D. Ophthalmology 1994;100:421-431
Originally received: January 25, 1993. Revision accepted : September 3, 1993. I University of California, Los Angeles, School of Public Health, Los Angeles.
2 Division of Biostatistics, Emory Un iversity School of Public Health , Atlanta. 3 Department of Ophthalmology, Emory University School of Medicine, Atlanta .
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Radial keratotomy is a surgical procedure performed on anatomically normal eyes with the objective of reducing myopia and allowing the patient to function without wearing corrective lenses, especially for distance vision.' The Prospective Evaluation of Radial Keratotomy (PERK) Study is a nine-center, monitored, prospective clinical trial of a single standardized technique of radial keratotomy. Bourque et al2 reported that 65% of patients in the PERK Study sought radial keratotomy primarily to see well without corrective lenses. Four years after surgery, Waring et al3 reported that 64% of 323 patients in the PERK Study with bilateral radial keratotomy were lens-free. In the current study, we used both self-administered questionnaires and clinical examinations 6 years after surgery to answer the following seven questions about 328 patients who had bilateral surgery: I. What proportion of patients wore no corrective lenses? 2. What proportion of patients wore lenses for near vision only, distance vision only, and both near and distance vision? 3. To what extent was lens wearing correlated with patients' age, sex, uncorrected visual acuity, cycloplegic spherical equivalent refraction, and symmetry of refraction? 4. What kinds of lenses (spectacles or contact lenses) were being worn and for what proportion of time? 5. How did the ability to read newsprint or to recognize a friend across the street without lenses vary with lens-wearing status? 6. Did current perceptions of health status or quality of life vary with lens-wearing status? 7. Did patient satisfaction with radial keratotomy, satisfaction with the PERK Study, and self-reported concern about vision vary with whether lenses were worn and with the reason for wearing lenses?
Patients and Methods Surgery was done on the first eye of 435 patients between March 1982 and October 1983. The overall objectives of the PERK Study are to ascertain the extent to which the PERK technique of radial keratotomy reduces myopia between -2.00 and -8.00 diopters (D), including stability of the correction, complications, and the patient's subjective assessment of the results. Patients were required to wait 1 year between surgery on their first and second eyes. Detailed descriptions of the study design and the results up to 5 years after surgery have been reported elsewhere."?" Supported by grants EY03761, EY03756, EY03755, EY03764, EY03753, EY03751, EY03767, EY04176, EY03752, and EY03765 from the National Eye Institute , Bethesda, Maryland . Reprint requests to Linda B. Bourque, PhD, University of California , Los Angeles, School of Public Health , 10833 Le Conte Avenue, Los Angeles, CA 90024-1772.
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Population Studied Clinical measurements and data regarding patients ' lenswearing were gathered 6 years after the initial surgery on the first eye and 5 years after eligibility for surgery on the second eye. A total of 435 patients, 43 to 50 patients at each of the nine clinical centers, entered the PERK Study. All 435 patients were eligible for this report. Consistent with most earlier reports of patients in the PERK Study, and because lens-wearing and satisfaction are onlv mean ingful for clinicians in patients with bilateral surgery, 77 people who did not have surgery on their second eye were excluded from these analyses. We also excluded 30 people who were unavailable for the 6-year psychometric questionnaire. These analyses were conducted on the remaining 328 patients who had bilateral surgery, completed a questionnaire, and had visual acuity and refraction data available within 3 years of the questionnaire's administration. Repeated operations were done on 13% (84/656) of eyes of73 patients (22%).
Six-year Postoperative Psychometric Questionnaire Patients filled out a questionnaire (173 questions), without assistance from clinical coordinators, that took an average of 25 minutes to complete. We mailed 32% of the questionnaires to patients for completion and return. Questionnaires were processed and analyzed at the PERK Psychometric Center. Items in the 6-year questionnaire replicated, built upon , and supplemented prior studies with patients in the PERK Study.j? Assessment of Lens Wearing, Nine questions replicated questions asked in RAND's Health Insurance Experiment and in the baseline PERK questionnaire (Table I). These, plus nine new questions, were the major source of information on assessed patients' current lens-wearing status, the proportion of waking hours they wore lenses, and their perceptions of their ability to see without lenses. The reliability of questionnaire responses was tested by comparing them to a separate set of five questions asked by the coordinator during each clinical examination (Table 2). The two sources of information were in complete agreement for 88% (n = 289) of the patients. The remaining 39 patients gave inconsistent answers. (For example , one patient reported no use of any kind of lenses in the questionnaire and at the 5- and 6-year clinical examinations; however, he reported using spectacles for I eye at the 4-year clinical examination.) Discrepancies of this sort were resolved by examining all the information available on these patients and assigning them to lenswearing groups on the basis of the preponderance of the evidence available. The patient in the example was assigned to the non-lens-wearing group on the basis of the preponderance of the available information. Satisfaction with Radial Keratotomy. Ten questions used in earlier questionnaires to assess overall satisfaction were used to create a satisfaction index." Patients also were asked what they had originally expected from radial keratotomy, whether their goals were met, whether they
Bourque et al . Spectacle and Contact Lens Wearing in PERK Table 1. Written Questions Used to Assess Lens Wearing and Visual Function 1. With glasses or contact lenses, if you wear them, how well can you see as compared with most persons your age? Would you say: better than most, about the same as most, or not as well as most?* 2. Without glasses or contacts, can you read ordinary newsprinti'[ 3. Without glasses or contacts, can you recognize a friend across the srreetr[ 4. What proportion of the time that you are awake do you wear glasses in either or both eyes?t 5. During the last 3 months, how much pain have your eyes caused you?t 6. During the last 3 months, how much have eyesight problems worried or concerned your] 7. During the last 3 months, how much of the time have eyesight problems kept you from doing the kinds of things other people your age dolt 8. In comparison to other people who are near-sighted/farsighted, would you say that your eyesight is much worse, somewhat worse, about average, somewhat better, or much better?" 9. In comparison to your own vision before surgery, would you say that your eyesight is much worse, somewhat worse, about average, somewhat better, or much better?* 10. Do you currently wear glasses or contact lenses in either eye to improve your eyesight?t A. Do you wear these all the time or only sometimes? B. When you wear corrective lenses, what are your main reasons for wearing them? 11. Do you wear them for reading and close work or for seeing things at a distance, or for both?t 12. Please describe what kind of lenses you currently wear. Do you wearr] A. Glasses with a correction for both eyes? B. Glasses with a correction for the right eye? C. Glasses with a correction for the left eye? D. Contacts in both eyes? E. Contact in right eye? F. Contact in left eye? G. Other? • Question was administered to patients in the Prospective Evaluation of Radial Keratotomy study at baseline and/or original follow-up."
t Question was administered to patients in the Prospective Evaluation of Radial Keratotomy at baseline and was adapted from questionnaires used in RAND's Health Insurance Experiment. 10 t
Question was developed for 6-year follow-up questionnaire.
would have radial keratotomy if they had it to do over, and whether they would participate in the PERK Study again. Health Status and Quality of Life. An early version of the Medical Outcomes Study 20-Item Short-Form Health Survey 1 1-13 was used to create three indices with Cronbach's alphas" more than 0.80 that assessed how the general health status and quality of life of patients in the PERK Study at 6 years compared with that of a national
sample studied by Ware et a1 15• 16 and whether it differed with patients' lens-wearing status at 6 years. Clinical Examinations An ophthalmologist-examiner who was not the surgeon and a coordinator-technician gathered all clinical data. Cycloplegic refractions were measured by the technician and verified by the ophthalmologist. Uncorrected visual acuity was measured at a distance of 4 m under standardized illumination. To reduce the chance that patients would memorize the letters, three different specially designed National Eye Institute-PERK Snellen charts were used.":" Visual acuity was recorded as the number ofletters correctly read and was converted into Snellen notation. Near visual acuity was not measured. Clinical examinations were available within 1 year of questionnaire administration for 309 patients. Cycloplegic refractions done within 3 years were used for 321 patients, and manifest refractions were used for three patients. No refractions within the 3-year window were available on the first eyes of three patients and the second eye of one patient; these four patients were eliminated from all analyses in which data on refractions were used. Selection of Variables and Analysis Data are presented in contingency tables, and chi-square tests, paired Student's t tests, and analysis of variance were used. In most instances, bivariate cross-tabular analyses are reported, but some two- and three-way analyses of variance were examined. To control for decreased accommodation with increasing age, tables frequently separate patients 40 years of age and older from patients younger than 40 years of age.
Results Population and Refractive Results The population contained 51% males with an average age of 39.8 ± 6.7 years (range, 28-65 years). The average reTable 2. Questions about Lens Wearing Asked by the Coordinators during Clinical Examinations 1. What kinds of optical correction do you use for your eyes? 2. Which do you wear most frequently? Which next most frequently? 3. How many days per week do you wear your spectacles, hard contact lenses, soft contact lenses? 4. On each day that you wear your spectacles, hard contact lenses, soft contact lenses, estimate the average number of hours you wear them. 5. Obtain the prescription for each type of correction worn, and record it in the space provided.
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fraction at baseline was -4.08 ± 1.39 D (range, -2.00 to -8.00 D) in the first eye and -4.01 ± 1.35 D (range, -2.0 to -7.75 D) in the second. At 6 years, the average refraction was +0.13 ± 1.42 D (range, -4.25 to +6.75 D) in the first eye and -0.14 ± 1.40 D (range, -6.38 to +7.00 D) in the second. Questionnaires were completed an average of 6.6 years after surgery on the first eye and 5.2 years after surgery on the second. Twenty-two percent (n = 144) ofeyes had a refractive error within ±0.50 D; 66% (n = 430) of eyes were within ± 1.00 D; 16% (n = 105) were overcorrected more than 1.00 D; 18% (n = 117) were undercorrected more than 1.00 D.
Distance Only, 59 (18%)
Both, 51 (16%)
Close Only, 48 (15%)
Lens-wearing Pattern and Age Fifty-two percent (n = 170) of the patients reported that they were wearing no lenses of any kind (Fig 1). The remaining 158 (48%) patients were approximately evenly divided among 48 (15%) who wore lenses for reading and close work only, 59 (18%) who wore lenses for distance only, and 51 (16%) who wore lenses for both near and distance vision. Twelve (4%) patients reported needing a lens for only one eye. Lens-wearing did not differ with gender but differed significantly with age (P < 0.0001). Sixty-four percent (n = 106) of the 167 people younger than 40 years of age wore no lenses, in contrast to 40% (n = 64) of the 161 people who were 40 years of age or older (Fig 1).
A
No Lens, 170 (52%) Distance Only , 31 (19%)
Close Only, 6 (4%)
Both, 24 (14%)
Relation of Lens Wearing and Residual Refractive Error Whether lenses were worn and the type of lenses worn varied with the residual refractive error (Table 3), with uncorrected visual acuity (Table 4), and with age. Of the 162 people younger than 40 years of age, 64% (n = 104) wore no lenses, 19% (n = 30) wore lenses for distance vision only, and 14% (n = 23) wore lenses for both near and distance vision. Eighty-eight percent (33/43) ofpeople younger than 40 years of age who had bilateral refractive errors within 0.5 D of emmetropia were lens-free (Table 3). Of the 155 people older than 40 years of age, 39% (n = 60) wore no lenses, and 27% (n = 42) wore lenses for near vision only (Table 3). Fifty-five percent (16/29) of people older than 40 years of age with residual refractive error of ±0.50 D in both eyes wore no lenses (Table 3). Comparing the lens-wearing status of all patients who had a residual refractive error in both eyes of ±0.50 D with those who had ± 1.00 D in both eyes showed that 85% (n = 61) of the 72 patients with ±0.50 D wore no distance correction and that 39% (n = 34) of the 87 patients with ± 1.00 D wore no distance correction (Table 3).
Relation of Lens Wearing and Uncorrected Distance Visual Acuity Three hundred seven (94%) patients had an uncorrected visual acuity of 20/40 or better in both eyes, and 259
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B
No Lens, 106 (64%)
Distance Only , 28 (17%)
Both, 27 (17 %)
Close Only, 42 (26%) /
/
,
\
C
No Lens, 64 (40%)
Figure 1. Lens-wearing status 6 years after bilateral radial keratotomy for 328 patients in the Prospective Evaluation of Radial Keratotomy Study. A, overall (n = 328); B, age < 39 years (n = 167); C, age> 40 years (n = 161).
Bourque et al . Spectacle and Contact Lens Wearing in PERK
Table 3. Corrective Lens-wearing Status by Spherical Equivalent Cycloplegic Refractions in Both Eyes, Controlling for Age, at 6 Years in the Prospective Evaluation of Radial Keratotomy Study" Both Eyes ± 0.50 D Lens-wearing Status
No . of Patients (%)
Both Eyes within
±1.0
1 Eye
Dt
No. of Patients (%)
-<1.0 DT
> +1.0 D§
1 Eye
Both Eyes <-1.0 D
Both Eyes >+1.0 D
No . of Patients (%)
No. of Patients (%)
No . of Patients (%)
No. of Patients (%)
Total No. of Patients (%)
21 3 (14) 2 (10) 8 (38) 8 (38)
6 4 (67) 0 2 (33) 0
162 104 (64) 5 (3) 30 (19) 23 (14)
9 1 (11) 0 4 (44) 4 (44)
16 4 (25) 7 (44) 1 (6) 4 (25)
155 60 (39) 42 (27) ~7 (17) 26 (17)
Younger Than 40 Yrs of Age (P < O.OOOm
No. of patients No lenses Near only Distance only Both
43 38 (88) 0 3 (7) 2 (5)
37 25 (67) 0 8 (22) 4 (11)
26 9 (34) 1 (4) 8 (31) 8 (31)
29 25 (86) 2 (7) 1 (3) 1 (3)
40 Yrs of Age or Older (P < 0.0001)
No. of patients No lenses Near only Distance only Both
29 16 (55) 7 (24) 2 (7) 4 (14)
50 21 (42) 12 (24) 13 (26) 4 (8)
18 7 (39) 0 3 (17) 8 (44)
33 11 (33) 16 (49) 4 (12) 2 (6)
D = diopter. • Deletes four patients for whom refractions in one or both eyes were missing at 6 years and one 37-year-old man with cycloplegic equivalent refractions of + 2.38 and - 2.0 who stated he wore spectacle s 100% of the time for distanc e vision onl y.
t Thirty-nine of these 87 patients had one eye within ±0.5 D of emmetropia and the other eye between - 0.5 an d -1.0 D; 26 of the 87 patients had one eye within ±0.5 D of emmetropia and the other eye between ±0.5 and + 1.0 D.
t Twenty-two of these 44 patients had one eye within ±0.5 D of emmetropia. § Twenty-nine of these 62 patients had on e eye within ±0.5 D of emmetropia and the other eye between 0.55 D and 2.0 D; 15 of the 62 patients h ad one eye within ±0.5 D of emmetropia and the other eye greater than ± 2.0 D. ~
Significance level for chi-square test of lens -wearing status by refract ive error withi n the indicated age group.
(79%) had at least one eye with an uncorrected visual acuity of 20/20 or better (Table 4). Lens use increased dramatically when the uncorrected visual acuity in both eyes or the best eye was worse than 20/20 and when the patient was older than 40 years of age (Table 4). Comparing the lens-wearing status of all patients who had an uncorrected visual acuity of 20/20 or better in at least one eye with those who had 20/25, 20/30, or 20/40 in both eyes or their best eye showed that 77% (n = 198) of the 259 patients in the 20/20 group wore no distance correction and that 34% (n = 18) of the 53 patients in the 20/25 to 20/40 group wore no distance correction (Table 4). Whereas only 2% (n = 3) of those younger than 40 years of age with 20/20 visual acuity in at least one eye wore lenses for near vision and 8% (n = 10) wore lenses for both near and distance vision , 26% (n = 34) of those older than 40 years of age wore lenses for near vision and 18% (n = 14) wore lenses for both near and distance vision. Even with age, however , many patients were able to remain lens-free or to use lenses only for near vision as long as the visual acuity in at least one eye was 20/20 or better (Table 4). Fifty-six percent (n = 25) of those patients younger than 40 years of age and 33% (n = 18)
of those older than 40 years of age who had an uncorrected visual acuity of 20/20 or better in their best eye wore no lenses. In contrast, only 21 % (n = 3) of those younger than 40 years of age and 15% (n = 2) of those older than 40 years of age whose best eye or both eyes had uncorrected visual acuities between 20/20 and 20/ 25 were lens-free. Sensitivity and Specificity of the 20/40 Criteria. To examine this finding in more detail, we examined the specificity and sensitivity of the traditionally used 20/40 ("driver's license visual acuity") cutoff as a criterion for determining the need for lenses. When the full population was examined, we obtained a sensitivity rate of 88% and a specificity rate of only 54%. In other words, of the 16 people whose visual acuity was worse than 20/40 in both eyes, 88% (n = 14) used lenses. Conversely, of the 312 patients whose acuity was better than 20/40 in both eyes, 46% (n = 144) wore lenses. When we eliminated those who wore lenses only for near vision (n = 48) from the calculations, the specificity rate rose to 64% and the sensitivity rate remained at 88%. Similarly, restricting the population to those older than 40 years of age (n = 161) reduced the specificity rate to 56% but increased the sensitivity rate to 90%.
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Table 4. Corrective Lens-wearing Status by Uncorrected Distance Visual Acuity in Both Eyes, Controlling for Age, at 6 Years in the Prospective Evaluation of Radial Keratotomy Study
Lens-wearing Status
Both Eyes 20/20 or Better
Best Eye 20/20 or Better
No. of Patients (%)
No. of Patients (%)
Both or Best Eye(s)
Both or Best Eye(s)
Both or Best Eye(s)
Both Eyes Worse Than
No. of Patients (%)
No. of Patients (%)
No. of Patients (%)
No. of Patients (%)
Total No. of Patients
5 2 (40) 0(0) 0(0) 3 (60)
8 1 (13) 0(0) 3 (38) 4 (50)
167 106 (64) 6 (4) 31 (19) 24 (14)
2 0(0) 0(0) 1 (50) 1 (50)
8 1 (13) 0(0) 2 (25) 5 (63)
161 64 (40) 42 (26) 28 (17) 27 (17)
20/25
20/32
20/40
20/40
Younger Than 40 Years (P < O.OOOIt No . of patients No lenses Near only Distance only Distance and near
87 75 (86) 2 (2) 5 (6) 5 (6)
14 3 (21) 3 (21) 4 (29) 4 (29)
45 25 (56) 1 (2) 14 (31) 5 (11)
8 0(0) 0(0) 5 (63) 3 (38)
40 Years of Age or Older (P < 0.001) No . of patients No lenses Near only Distance only Distance and near
72 43 (60) 17 (24) 7 (8) 5 (7)
13 2 (15) 4 (31) 3 (23) 4 (31)
55 18 (33) 17 (31) 11 (20) 9 (16)
11 0(0) 4 (36) 4 (36) 3 (27)
• Significance level for chi-square test of lens-wearing status by refractive error within indicated age group .
Proportion of Time Lenses Worn Patients who reported wearing lenses for both near and distance vision wore them 73% of the time they were awake, on average, and there was no change with age (Table 5). In contrast, patients who wore lenses for distance only decreased their use with age from 41% to 27% of the time. Use of lenses for near vision increased from 18% to 25% with age.
Use of Contact Lenses Seven patients (2%) reported using only contact lenses; four wore them for both near and distance vision an average of 89% of the time they were awake, and three wore
them for distance only an average of 68% of the time. Sixteen reported wearing both contacts and spectacles. The use of contact lenses is probably artificially low because the investigators discouraged patients from wearing contact lenses to avoid influencing the natural postoperative course of radial keratotomy by such conditions as corneal warpage and keratitis.
Need for Lenses Two questions traditionally have been used to assess the need for lenses: "Without glasses or contacts, can you read ordinary newsprint"," and "Without glasses or contacts, can you recognize a friend across the street?" Six years after surgery, only five patients stated that they could
Table 5. Mean Percent of Waking Time Lenses Worn by Lens-wearing Status, Controlling for Age, at 6 Years in the Prospective Evaluation of Radial Keratotomy Study" Lens-wearing Status Near vision only Distance vision only Distance and near
Younger Than 40 Years
40 Years of Age or Older
No. of Patients
Mean % Time
No. of Patients
Mean % Time
Total No. of Patients'[
Mean % Time
6 31
18 41
24
72
42 28 27
25 27 74
48 59 51
24 34 73
• In a two-way analysis of variance, the effect for "reason lenses worn" was significant at P < O.OOl.
t
The remaining 170 patients reported no use of lenses at 6 years.
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Bourque et al . Spectacle and Con tact Lens Wearing in PERK neither read newsprint nor recognize a friend. Because 48% (n = 158) of these patients wore lenses, these two quest ions were not a dependable indication of whether mildly visually disabled people need lenses to function well in their daily lives. As with the sensitivity and specificity of the 20/40 criterion, we found that the sensitivity and specificity of these two questions varied substantially depending on how we restricted the population.
Satisfaction and Lens-wearing Status Ninety-five percent of patients who did not wear lenses and 84% of those who wore lenses stated that their "eyesight was much better" than before surgery (Table 7). Satisfaction varied across the lens-wearing groups with 82% of those who wore no lenses expressing high satisfaction but only 22% of those who wore lenses for both near and distance vision expressing high satisfaction. Younger patients were slightly more satisfied (r = -0.11; P < 0.05), and the percent of time lenses were worn was inversely associated with satisfaction (r = -0. , 8; P < 0.001 ). Satisfaction also was associated with having experienced no eye pain (r = 0.18; P < 0.05), no WoITy about one's eyes (r =0.39; P < 0.001), and reporting no restrictions in activities (r = 0 .3 1; P < 0.00 I). To summarize how visual functioning, age, and concern about eyes combined to predict satisfaction 6 years after surgery, scores on the satisfaction index were regressed on the full set of variables included in these analyses. Three factors explained 47% of the variance in satisfaction at 6 years: (I) reporting no worry, pain , or restrictions in activities because of one's eyes; (2) not having to wear lenses for distance vision or both distan ce and near Vision; and (3) having a visual acuit y of 20/20 or better in both eyes. Also, contributing to satisfaction were reports of being restricted in activities by eyesight at baseline. Age was not a pred ictor of satisfaction once other variables were controlled. Although responses differed across lens-wearing groups (P < 0.0001), 74% (n = 243) of the total sample reported that their goals were completely met , and 94% of the pa-
Health Status at Six Years Reports of the physical, mental, and general health status of patients in the PERK Stud y at 6 years did not differ appreciably from that of a national sample." Nor did health status among patients in the PERK Study vary with age or lens-wearing status .
Side Effects and Problems Before surgery, patients in the PERK Study-all of whom wore spectacles or contact lenses-reported substantially more worry about their eyes and restrictions in activities because of their eyes than did those with myopia in RAND's Health Insurance Experiment (Table 6).2 At 6 years, overall concerns about eyes and reports of restrictions because of vision had declined substantially, regardless oflens-wearing status. Reports ofworrying about eyesight within the last 3 months declined from 57% preoperatively (n = 187) to 31% (n = 103) at{) years; reports of some restriction in activities because of eyes declined from 47% (n = 154) to 9% (n = 30).
Table 6. Comparison of Reported Problems of Patients from the Prospective Evaluation of Radial Keratotomy by Lens-wearing Group at 6 Years with Their Own Reports before Surgery and with Those of RAND Patients Myopia* PERK Study-lens-wearing Status
No Lenses RAND
Distance Only (n = 59)
Distan ce and N ear (n = 51)
Study
Baseline
6 Ye ars
Baseline
6 Y ears
Baseline
6 Years
Baselin e
6 Years
No . of Pat ients (%)
N o. of Patients (%)
N o. of Pat ients (%)
N o. of Pat ients (%)
N o. of Patients (%)
N o. of Patients (%)
No . of Patients (%)
N o. of Patients (%)
No . of Pa tients (%)
56 (13)
75 (44)t
9(5)
23 (48)t
6 (12)
27 (45)t
6 (10)
23 (45)t
150(35)
47 (56)t
46 (27)
11 (57)t
17 (35)
13 (56)t
18 (30)
90 (21)
23 (14)
17 (10)
4 (9)
4 (8)
4 (7)
4 (7)
--
Eye problem s that have caused some restriction in activities in last 3 mos Some worry about eyesigh t during the last 3 mos Som e pain in the eyes during th e last 3 mos
(n = 170)
Near Only (n = 48)
Total PERK (n = 328) Baseline
6 Y ears
N o. of Patients (%)
No . of Patien ts (%)
7 (14)
154(47)t
30(9)
11 (43)
22 (43)
82 (57)t
102 (31)
10(20)
9 (18)
41 (15)
33 (10)
- - -
* Data for RAND patients myopia and for those in the PERK stud y before sur gery taken from Table 1 of Bourque et aU
t Paired Student's t tests comp arin g patients in the PERK stud y before and after su rgery are significant at P < 0.05.
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Volume 101, Number 3, March 1994
7. Reported Satisfaction with Radial Keratotomy by Lens-wearing Status
Eyesight is much better than before surgery" Expressed high satisfaction (>5)t Mean score on satisfaction index (range, 1-7)" Preoperative goals were completely met" Would have radial keratotomy again" Would enroll in the PERK Study again"
(% of patients)
No Lenses (n = 170)
Near Only (n = 48)
Distance Only (n = 59)
Distance and Near (n = 51)
No. of Patients (%)
No. of Patients (%)
No. of Patients (%)
No. of Patients (%)
Total No. of Patients (%) (n = 328)
161 (95) 137 (82) 5.8 148 (93) 155 (97) 156 (98)
40 (83) 28 (58) 5.1 36 (77) 45 (96) 46 (98)
50 (85) 18 (31) 4.4 33 (57) 52 (90) 52 (90)
39 (83) 11 (22) 4.3 26 (51) 44 (86) 44 (86)
289 (89) 194 (60) 5.2 243 (74) 296 (94) 298 (94)
"P < 0.05. t On ten-item satisfaction index (range, 1-7) (P < 0.001).
tients stated that they would have radial keratotomy again and that they would enroll in the PERK Study again. Responses to these questions did not differ with the patient's age. Symmetry of Vision We previously reported that symmetry of refraction decreased slightly after radial keratotomy." We were interested in ascertaining whether there was any association between symmetry of refraction and use of lenses. Anisometropia Greater Than or Equal to 3.00 Diopters. Twelve patients had refractions in the two eyes that differed by 3.00 D or more. Six of these patients had near emmetropia (±0.50 D) in one eye and hyperopia (+2.88 to +6.75 D) in the other. Three patients had near emmetropia (±0.50 D) in one eye and residual myopia (-2.60 to -6.40 D) in the other. The last three patients had hyperopia (+ 1.63 to +2.38 D) in one eye and myopia (-1.40 to -2.00 D) in the other. These 12 patients did not differ significantly from the rest of the 316 patients in sex ratio, age, preoperative refraction, lens wearing at 6 years, use of spectacles, mental health, role and physical functioning, concern about their eyes, satisfaction with the outcome of surgery, or mental or physical health. They did differ from other patients in uncorrected visual acuity, the percent oftime lenses were worn, whether they could recognize a friend across the street, and current perceptions of their health. Six (50%) of these patients wore lenses and reported using them more of the time than other lens-wearing patients in the PERK Study (76% versus 25%). Nine (75%) considered their vision "much better" than before surgery; none considered their vision worse than before surgery. When asked what the worst thing was that happened as a result of surgery, the 12 patients responded as follows: must wear reading glasses(n = 1); visual acuity is not 20/ 20 (n = 1);visual acuity is worse (n = 2); trouble focusing
428
(n
=
1); glare or light sensitivity (n
=
.1); glare at night (n
= 1); "star" images (n = 1); and four reported no "worst
thing." The remarkable ability of these 12 patients to adjust to 3.00 D or more of anisometropia suggested that the whole topic of monovision should be studied in more detail in this population. Monovision. We defined monovision as persons who had emmetropia (±0.50 D) in one eye with -0.55 to -2.00 D of myopia in the other eye-a total of 53 patients (Table 8). In general, with age, these patients wore lenses fur less time than did those who did not have potential monovision. The 12 patients older than 40 years of age with one emmetropic eye whose second eye was mildly myopic (-0.55 to -2.00 D) and who reported wearing lenses for distance only (n = 7) or both distance and near vision (n = 5) reported wearing their lenses an average of 11% and 22% of the time, respectively. The 43 comparably aged patients who needed distance lenses and who were not candidates for monovision reported wearing distance lenses an average of 59% ofthe time. The two patients older than 40 years of age who were candidates for monovision who wore lenses only for near vision reported wearing them 8% of the time as contrasted to the 40-year-old patients with non-monovision who reported wearing lenses an average of 26% of the time.
Discussion The major reason patients gave for having radial keratotomy was to be free of dependence on spectacles and contact lenses, especially for distance vision. Four years after surgery, 64% of those who had radial keratotomy on both eyes were lens-free for both distance and near vision.' By 6 years, 52% were lens-free, a decline explained by increasing age and the onset of presbyopia. More patients younger than 40 years of age remained totally lens-free (64%) than those older than 40 years
Bourque et al . Spectacle and Contact Lens Wearing in PERK Table 8. Lens-wearing Status and Mean Percent of Time Lenses Worn by Potential for and Type of Monovision, Controlling for Age" Lens-wearing Status
Refraction: 1 Eye ± 0.50 D; Other Eye: Not Monovision
<-2.0 D
-0.55
to
-2.00 D
0.55 to 2.00 D
>2.00 D
Younger Than 40 Yrs of Age
No. of patients No lenses No. of patients (%) % timet Near only No. of patients % timet Distance only No. of patients (%) % timet Distance and near No. of patients (%) % timet
105
4
32
19
7
62 (59) 2t
2 (50) 0
17 (53) 0
18 (95) 0
7 (100) 0
3 (3) 10
1 (25) 60
2 (6) 10
23 (22) 43
1 (25) 90
6 (19) 19
17 (16) 76
7 (22) 61
0
0 1 (5) 90
0 0
0
0
36
11
40 Yrs of Age or Older
No. of patients No lenses No. of patients (%) % timet Near only No. of patients (%) % timet Distance only No. of patients (%) % timet Distance and near No. of patients (%) % timet
89
4
33 (37) 0
1 (25) 0
7 (33) 0
20 (56) It
3 (27) lOt
23 (26) 26
0
2 (10) 8
12 (33) 19
5 (46) 41
7 (33)
3 (8) 8
2 (18) 50
5 (24) 22
1 (3) 100
1 (10) 100
15 (17) 30
1 (25) 95
18 (20) 82
2 (50) 100
21
11
P = 0.01.
• In a three-way analysis ofvariance predicting the percent oftime lenses are worn, the main effects for the reason lenses are worn, andthe type of monovision, the interaction between the two- andthe three-way interaction with age issignificant at P < 0.01. t Some patients reported using magnifiers or otherpeople's spectacles on occasion.
of age (39%). An additional 4% (n = 6) of patients younger than 40 years of age and 27% (n = 42) of patients older than 40 years of age reported needing lenses for near vision only. The remaining 32% (n = 55) of patients younger than 40 years of age and 34% (n = 55) of those older than 40 years of age reported wearing lenses for distance vision or both distance and near vision for some proportion of the time they were awake. As patients aged, the proportion of time lenses were worn increased for near vision from 18% to 25% of the time but decreased for distance vision from 41 % to 27% of the time. Refraction, Age, and Lens Wearing Patients with symmetric postoperative residual myopia were most likely to be wearing lenses for distance vision.
The greater the residual myopia and the younger the patient, the more likely the patient was to report using lenses for both distance and near vision. When radial keratotomy resulted in symmetric emmetropia or slight hyperopia, patients reported little use of lenses until they reached 40 years of age. At that time, the use of lenses for near vision increased, as expected in a group with presbyopia. Although both the proportion of patients with bilateral emmetropia (±0.50 D) who wore lenses and the proportion of time they wore lenses increased with age, the proportion of time that patients with mild myopia (those with 1 or both eyes between -1.00 and -2.00 D) wore lenses decreased with age. We think that younger people with mild myopia tended to leave their lenses on when it was not necessary, as long as they were able to accommodate for near work but, with age, they discovered that minus lenses interfered with their ability
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Volume 101, Number 3, March 1994
to see close work, and they began to remove their lenses. Often, we speculate, these people discovered that they could see much better at a distance without their lenses than they realized and, as a result, their overall dependence on lenses declined.
surgery, both groups were free oflenses for a majority of the time they were awake. Because we assume both groups wore lenses all the time they were awake before surgery, the need for lenses in both groups declined substantially as a result of radial keratotomy.
Uncorrected Visual Acuity as a Predictor of Distance Lens Wearing
Reading Newsprint and Recognizing a Friend
Lens wearing also varied with postoperative uncorrected visual acuity, but not in ways that might be expected when traditional visual acuity screening criteria were used. A Snellen visual acuity of 20/40 or better is widely assumed to indicate adequate functional distance vision because it is the level at which a driver's license is issued without restriction in many states. The overwhelming majority (88%) of patients in the PERK Study saw 20/40 or better without correction in both eyes after surgery, but almost half of these patients (46%) wore lenses for either distance vision alone or both distance and near vision (Table 4). Therefore, visual acuity of 20/40 was not a specific criterion for estimating whether a person in the PERK population would be lens-free. Many patients whose visual acuity in both eyes was better than 20/40 reported using distance lenses some or all of the time (Table 4), and the 20/40 criterion for determining whether or not a person can function without distance lenses was neither appropriate nor efficient. In the entire PERK population, both the highest sensitivity (98%) and the highest specificity (88%) in predicting need for distance lenses from uncorrected visual acuity was obtained when we used 20/20 or better in both eyes as the criterion and eliminated those who reported using lenses only for near vision from our calculations. That is, 98% ofthose who had 20/20 or better visual acuity in both eyes did not wear lenses to see at a distance; 88% of those whose visual acuity in at least one eye was poorer than 20/20 did wear lenses for distance vision at least part of the time. To summarize, a person with worse than 20/40 visual acuity in both eyes is highly likely to wear lenses some of the time; however, knowing that persons have 20/40 or better visual acuity in both eyes does not mean that they do not need lenses for distance. Using 20/20 or better uncorrected visual acuity as the criterion (i.e., 20/20, 20/ 16, 20/12, or 20/ 10) results in the most efficient screening for the need for distance lenses.
Proportion of Waking Time Lenses Were Worn Although 15% (48/328) of patients reported using lenses for near vision only and 18% (59/328) reported using lenses for distance vision only, the actual proportion of waking hours that such lenses were used was quite low (Table 5). Persons who used lenses for near vision only reported using them an average of 24% of the time the y were awake , with the percent oftime increasing from 18% to 25% with age. Those who used lenses for distance vision only reported using lenses an average of 34% of the time with use declining from 41% to 27% with age. Thus, after
430
In 1963-64, six questions were added to the National Health Interview Survey to collect detailed information on functional loss of vision." For reasons unknown to us, two of these questions have been used in numerous situations to screen for a wide range of visual functions, including myopia, hyperopia, and presbyopia: 1. Without glasses or contacts, can you read ordinary newsprint? 2. Without glasses or contacts, can you recognize a friend across the street? The questions assume that people who cannot read newsprint without lenses have severe hyperopia or presbyopia and require reading glasses and that people who cannot recognize a friend across the street have myopia and require distance lenses. No refractions, visual acuities , or other traditional ophthalmic tests were administered to the sample, so it was not possible to validate the set of questions against traditional clinical measures of visual function. At 6 years, we found that neither of these questions was an efficient screen for population-based studies of myopia and presbyopia. These findings do not surprise us because earlier studies have demonstrated the inadequacy of similar questions, and it is well known in the psychometric literature that single questions rarely provide a reliable or valid measure of a construct. i'r'" Monovision. We found that patients with asymmetric refractions were no more likely than other patients to wear lenses and were as satisfied as others with the results of radial keratotomy. We suggest that patients with a nearly emmetropic refraction in one eye and a myopic refraction in the other can, if they desire, learn to use the first eye for distance vision and the second eye for near, and go lens-free for substantial amounts of time (Table 8). General Health. We can say with some confidence that having radial keratotomy did not affect the general health and well-being of patients in the PERK Study, nor did a need to wear lenses result in a poorer general quality of life. When compared with a more representative national sample, the postoperative distribution of patients in the PERK Study on measures ofgeneral health, mental health, and role functioning was identical to that of the general population. In addition, concerns of patients in the PERK Study about their eyes declined substantially after having radial keratotomy, which suggests that radial keratotomy increased patients' visual quality oflife while not resulting in deterioration of general quality of life. Determinants of Satisfaction. Patients who told us that their eyesight restricted their activities at baseline but not at 6 years, who had 20/20 or better visual acuity in both eyes, and who either wore no lenses or wore lenses
Bourque et al . Spectacle and Contact Lens Wearing in PERK only for close work were most satisfied at 6 years. Other concerns at baseline, the amount of refractive error at 6 years, the percent of time lenses were worn, a patient 's age, sex, health status, and ability to recognize a friend across the street or read newsprint did not contribute to patient satisfaction once the above variables were controlled. Distance visual acuity was a better predictor of satisfaction than refractiveerror. For this group of patients, however, having a visual acuity of 20/40 or better in both eyes was not sufficient; both ability to function without lenses and satisfaction increased substantially only when patients had a visual acuity of20/20 in their best eye. With few exceptions, the patients in the PERK Study stated that their goals were met, they would have radial keratotomy again, and they would enter the PERK Study again. These results are not surprising, given the strong desire among patients in the PERK Study to reduce their dependence on distance lenses. Beforesurgery, all patients in the PERK Study needed lenses all the time to see at a distance. At 6 years, most patients in the PERK Study could see at a distance without lenses even if they were not completely lens-free. Increased need for lenses for near vision with age does not offset this improvement. It was, after all, improved distance vision that patients in the PERK Study hoped to achieve and did achieve with radial keratotomy.
Participating Personnel A list of PERK investigators appears at the end of the article by Waring GO III, et al. "Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study Five Years after Surgery" (Ophthalmology J99 J;98:JJ64- 76).
References 1. Waring GO III. Refractive Keratotomy for Myopia and Astigmatism. St. Louis: Mosby Yearbook, 1992. 2. Bourque LB, Rubenstein R, Cosand B, et al. Psychosocial characteristics of candidates for the Prospective Evaluation of Radial Keratotomy (PERK) Study. Arch Ophthalmol 1984;102:1187-92. , 3. Waring GO III, Lynn MJ, Fielding B, et al. Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study 4 years after surgery for myopia. JAMA 1990;263:108391. 4. Waring GO III, Lynn MJ, Nizam A, et al. Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study five years after surgery. Ophthalmology 1991;98:1164-76. 5. Holladay JT, Lynn MJ, Waring GO III, et al. The relationship of visual acuity, refractive error, and pupil size after radial keratotomy. Arch Ophthalmol 1991;109:70-6. 6. Santos VR, Waring GO III, Lynn MJ, et al. Morning-toevening change in refraction, corneal curvature, and visual acuity 2 to 4 years after radial keratotomy in the PERK Study. Ophthalmology 1988;95:1487-93 .
7. Bourque LB, Cosand BB, Drews C, et al. Reported satisfaction, fluctuation of vision, and glare among patients one year after surgery in the Prospective Evaluation of Radial Keratotomy (PERK) Study. Arch Ophthalmol 1986;104: 356-63. 8. Waring GO III, Moffitt SD, Gelender H, et al. Rationale for and design of the National Eye Institute Prospective Evaluation of Radial Keratotomy (PERK) Study. Ophthalmology 1983;90:40-58. 9. Waring GO III, Lynn MJ, Strahl man ER, et al. Stability of refraction during four years after radial keratotomy in the Prospective Evaluation of Radial Keratotomy Study. Am J Ophthalmol 1991;111:133-44. 10. Lynn MJ, Waring GO III, Sperduto RD, PERK Study Group. Factors affectingoutcome and predictability of radial keratotomy in the PERK study. Arch Ophthalmol 1987; I05: 42-51. 11. Stewart AL, Ware JE Jr, eds. Measuring Functioning and Well-Being:The Medical Outcomes Study Approach. Durham, NC: Duke University Press, 1992. 12. Ware JE Jr. Incorporating health status measures into clinical trials. In: Drummond ME, ed. Measuring the Quality of Life of People With Visual Impairment. Proceedings of a Workshop. [Bethesda]: U.S. Depart of Health and Human Services, 1990;51-8. (NIH Publ. No. 90-3078). 13. Stewart AL, Hays RD, Ware JE Jr. The MOS short-form general health survey. Reliability and validity in a patient population. Med Care 1988;26:724-35. 14. Cronbach U . Coefficient alpha and the internal structure of tests. Psychometrika 1951;16:297-334. 15. Ware JE, Sherbourne CD, Davies AR. Developing and Testing the MOS 20-Item Short-Form Health Survey: A General Population Application. In: Stewart AL, Ware JE Jr, eds. Measuring Functioning and Well-Being: The Medical Outcomes Study Approach . Durham, NC: Duke University Press, 1992;277-303. 16. McHorney CA, Ware JE Jr, Rogers W, et al. The validity and relative precision of MOS short- and long-form health status scales and Dartmouth COOP charts. Results from the Medical Outcomes Study. Med Care 1992;30(Suppl 5): MS253-65 . 17. Ferris FL III, Sperduto RD. Standardized illumination for visual acuity testing in clinical research. Am J Ophthalmol 1982;94:97-8. 18. Ferris FL III, Kassoff A, Bresnick GH, Bailey I. New visual acuity charts for clinical research. Am J Ophthalmol 1982;94:91-6. . 19. Lynn MJ, Waring GO, Nizam A, et al. Symmetry of refractive and visual acuity outcome in the Prospective Evaluation of Radial Keratotomy (PERK) Study. Refract Corneal Surg 1989;5:75-81. 20. Wilson RW. Characteristics of Visually Impaired Persons: United States, July 1963-June 1964. Washington, DC: US Public Health Service, 1968;1-3. (Vital & Health Statistics. Ser. 10, no. 46.) 21. Bourque LB, Clark VA. Processing Data: The Survey Example. Newbury Park, CA: Sage, 1992. 22. Stone DH , Shannon DJ. Screening for impaired visual acuity in middle age in general practice. BMJ 1978;2:859-61. 23. Cullinan T. The Epidemiology of Visual Impairment (Pari 2). Canterbury: Health Services Research Unit, University of Kent, 1976.
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Originally received: January 25, 1993. Revision accepted : September 3, 1993. I University of California, Los Angeles, School of Public Health, Los Angeles.
2 Division of Biostatistics, Emory Un iversity School of Public Health , Atlanta. 3 Department of Ophthalmology, Emory University School of Medicine, Atlanta .
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Radial keratotomy is a surgical procedure performed on anatomically normal eyes with the objective of reducing myopia and allowing the patient to function without wearing corrective lenses, especially for distance vision.' The Prospective Evaluation of Radial Keratotomy (PERK) Study is a nine-center, monitored, prospective clinical trial of a single standardized technique of radial keratotomy. Bourque et al2 reported that 65% of patients in the PERK Study sought radial keratotomy primarily to see well without corrective lenses. Four years after surgery, Waring et al3 reported that 64% of 323 patients in the PERK Study with bilateral radial keratotomy were lens-free. In the current study, we used both self-administered questionnaires and clinical examinations 6 years after surgery to answer the following seven questions about 328 patients who had bilateral surgery: I. What proportion of patients wore no corrective lenses? 2. What proportion of patients wore lenses for near vision only, distance vision only, and both near and distance vision? 3. To what extent was lens wearing correlated with patients' age, sex, uncorrected visual acuity, cycloplegic spherical equivalent refraction, and symmetry of refraction? 4. What kinds of lenses (spectacles or contact lenses) were being worn and for what proportion of time? 5. How did the ability to read newsprint or to recognize a friend across the street without lenses vary with lens-wearing status? 6. Did current perceptions of health status or quality of life vary with lens-wearing status? 7. Did patient satisfaction with radial keratotomy, satisfaction with the PERK Study, and self-reported concern about vision vary with whether lenses were worn and with the reason for wearing lenses?
Patients and Methods Surgery was done on the first eye of 435 patients between March 1982 and October 1983. The overall objectives of the PERK Study are to ascertain the extent to which the PERK technique of radial keratotomy reduces myopia between -2.00 and -8.00 diopters (D), including stability of the correction, complications, and the patient's subjective assessment of the results. Patients were required to wait 1 year between surgery on their first and second eyes. Detailed descriptions of the study design and the results up to 5 years after surgery have been reported elsewhere."?" Supported by grants EY03761, EY03756, EY03755, EY03764, EY03753, EY03751, EY03767, EY04176, EY03752, and EY03765 from the National Eye Institute , Bethesda, Maryland . Reprint requests to Linda B. Bourque, PhD, University of California , Los Angeles, School of Public Health , 10833 Le Conte Avenue, Los Angeles, CA 90024-1772.
422
Population Studied Clinical measurements and data regarding patients ' lenswearing were gathered 6 years after the initial surgery on the first eye and 5 years after eligibility for surgery on the second eye. A total of 435 patients, 43 to 50 patients at each of the nine clinical centers, entered the PERK Study. All 435 patients were eligible for this report. Consistent with most earlier reports of patients in the PERK Study, and because lens-wearing and satisfaction are onlv mean ingful for clinicians in patients with bilateral surgery, 77 people who did not have surgery on their second eye were excluded from these analyses. We also excluded 30 people who were unavailable for the 6-year psychometric questionnaire. These analyses were conducted on the remaining 328 patients who had bilateral surgery, completed a questionnaire, and had visual acuity and refraction data available within 3 years of the questionnaire's administration. Repeated operations were done on 13% (84/656) of eyes of73 patients (22%).
Six-year Postoperative Psychometric Questionnaire Patients filled out a questionnaire (173 questions), without assistance from clinical coordinators, that took an average of 25 minutes to complete. We mailed 32% of the questionnaires to patients for completion and return. Questionnaires were processed and analyzed at the PERK Psychometric Center. Items in the 6-year questionnaire replicated, built upon , and supplemented prior studies with patients in the PERK Study.j? Assessment of Lens Wearing, Nine questions replicated questions asked in RAND's Health Insurance Experiment and in the baseline PERK questionnaire (Table I). These, plus nine new questions, were the major source of information on assessed patients' current lens-wearing status, the proportion of waking hours they wore lenses, and their perceptions of their ability to see without lenses. The reliability of questionnaire responses was tested by comparing them to a separate set of five questions asked by the coordinator during each clinical examination (Table 2). The two sources of information were in complete agreement for 88% (n = 289) of the patients. The remaining 39 patients gave inconsistent answers. (For example , one patient reported no use of any kind of lenses in the questionnaire and at the 5- and 6-year clinical examinations; however, he reported using spectacles for I eye at the 4-year clinical examination.) Discrepancies of this sort were resolved by examining all the information available on these patients and assigning them to lenswearing groups on the basis of the preponderance of the evidence available. The patient in the example was assigned to the non-lens-wearing group on the basis of the preponderance of the available information. Satisfaction with Radial Keratotomy. Ten questions used in earlier questionnaires to assess overall satisfaction were used to create a satisfaction index." Patients also were asked what they had originally expected from radial keratotomy, whether their goals were met, whether they
Bourque et al . Spectacle and Contact Lens Wearing in PERK Table 1. Written Questions Used to Assess Lens Wearing and Visual Function 1. With glasses or contact lenses, if you wear them, how well can you see as compared with most persons your age? Would you say: better than most, about the same as most, or not as well as most?* 2. Without glasses or contacts, can you read ordinary newsprinti'[ 3. Without glasses or contacts, can you recognize a friend across the srreetr[ 4. What proportion of the time that you are awake do you wear glasses in either or both eyes?t 5. During the last 3 months, how much pain have your eyes caused you?t 6. During the last 3 months, how much have eyesight problems worried or concerned your] 7. During the last 3 months, how much of the time have eyesight problems kept you from doing the kinds of things other people your age dolt 8. In comparison to other people who are near-sighted/farsighted, would you say that your eyesight is much worse, somewhat worse, about average, somewhat better, or much better?" 9. In comparison to your own vision before surgery, would you say that your eyesight is much worse, somewhat worse, about average, somewhat better, or much better?* 10. Do you currently wear glasses or contact lenses in either eye to improve your eyesight?t A. Do you wear these all the time or only sometimes? B. When you wear corrective lenses, what are your main reasons for wearing them? 11. Do you wear them for reading and close work or for seeing things at a distance, or for both?t 12. Please describe what kind of lenses you currently wear. Do you wearr] A. Glasses with a correction for both eyes? B. Glasses with a correction for the right eye? C. Glasses with a correction for the left eye? D. Contacts in both eyes? E. Contact in right eye? F. Contact in left eye? G. Other? • Question was administered to patients in the Prospective Evaluation of Radial Keratotomy study at baseline and/or original follow-up."
t Question was administered to patients in the Prospective Evaluation of Radial Keratotomy at baseline and was adapted from questionnaires used in RAND's Health Insurance Experiment. 10 t
Question was developed for 6-year follow-up questionnaire.
would have radial keratotomy if they had it to do over, and whether they would participate in the PERK Study again. Health Status and Quality of Life. An early version of the Medical Outcomes Study 20-Item Short-Form Health Survey 1 1-13 was used to create three indices with Cronbach's alphas" more than 0.80 that assessed how the general health status and quality of life of patients in the PERK Study at 6 years compared with that of a national
sample studied by Ware et a1 15• 16 and whether it differed with patients' lens-wearing status at 6 years. Clinical Examinations An ophthalmologist-examiner who was not the surgeon and a coordinator-technician gathered all clinical data. Cycloplegic refractions were measured by the technician and verified by the ophthalmologist. Uncorrected visual acuity was measured at a distance of 4 m under standardized illumination. To reduce the chance that patients would memorize the letters, three different specially designed National Eye Institute-PERK Snellen charts were used.":" Visual acuity was recorded as the number ofletters correctly read and was converted into Snellen notation. Near visual acuity was not measured. Clinical examinations were available within 1 year of questionnaire administration for 309 patients. Cycloplegic refractions done within 3 years were used for 321 patients, and manifest refractions were used for three patients. No refractions within the 3-year window were available on the first eyes of three patients and the second eye of one patient; these four patients were eliminated from all analyses in which data on refractions were used. Selection of Variables and Analysis Data are presented in contingency tables, and chi-square tests, paired Student's t tests, and analysis of variance were used. In most instances, bivariate cross-tabular analyses are reported, but some two- and three-way analyses of variance were examined. To control for decreased accommodation with increasing age, tables frequently separate patients 40 years of age and older from patients younger than 40 years of age.
Results Population and Refractive Results The population contained 51% males with an average age of 39.8 ± 6.7 years (range, 28-65 years). The average reTable 2. Questions about Lens Wearing Asked by the Coordinators during Clinical Examinations 1. What kinds of optical correction do you use for your eyes? 2. Which do you wear most frequently? Which next most frequently? 3. How many days per week do you wear your spectacles, hard contact lenses, soft contact lenses? 4. On each day that you wear your spectacles, hard contact lenses, soft contact lenses, estimate the average number of hours you wear them. 5. Obtain the prescription for each type of correction worn, and record it in the space provided.
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fraction at baseline was -4.08 ± 1.39 D (range, -2.00 to -8.00 D) in the first eye and -4.01 ± 1.35 D (range, -2.0 to -7.75 D) in the second. At 6 years, the average refraction was +0.13 ± 1.42 D (range, -4.25 to +6.75 D) in the first eye and -0.14 ± 1.40 D (range, -6.38 to +7.00 D) in the second. Questionnaires were completed an average of 6.6 years after surgery on the first eye and 5.2 years after surgery on the second. Twenty-two percent (n = 144) ofeyes had a refractive error within ±0.50 D; 66% (n = 430) of eyes were within ± 1.00 D; 16% (n = 105) were overcorrected more than 1.00 D; 18% (n = 117) were undercorrected more than 1.00 D.
Distance Only, 59 (18%)
Both, 51 (16%)
Close Only, 48 (15%)
Lens-wearing Pattern and Age Fifty-two percent (n = 170) of the patients reported that they were wearing no lenses of any kind (Fig 1). The remaining 158 (48%) patients were approximately evenly divided among 48 (15%) who wore lenses for reading and close work only, 59 (18%) who wore lenses for distance only, and 51 (16%) who wore lenses for both near and distance vision. Twelve (4%) patients reported needing a lens for only one eye. Lens-wearing did not differ with gender but differed significantly with age (P < 0.0001). Sixty-four percent (n = 106) of the 167 people younger than 40 years of age wore no lenses, in contrast to 40% (n = 64) of the 161 people who were 40 years of age or older (Fig 1).
A
No Lens, 170 (52%) Distance Only , 31 (19%)
Close Only, 6 (4%)
Both, 24 (14%)
Relation of Lens Wearing and Residual Refractive Error Whether lenses were worn and the type of lenses worn varied with the residual refractive error (Table 3), with uncorrected visual acuity (Table 4), and with age. Of the 162 people younger than 40 years of age, 64% (n = 104) wore no lenses, 19% (n = 30) wore lenses for distance vision only, and 14% (n = 23) wore lenses for both near and distance vision. Eighty-eight percent (33/43) ofpeople younger than 40 years of age who had bilateral refractive errors within 0.5 D of emmetropia were lens-free (Table 3). Of the 155 people older than 40 years of age, 39% (n = 60) wore no lenses, and 27% (n = 42) wore lenses for near vision only (Table 3). Fifty-five percent (16/29) of people older than 40 years of age with residual refractive error of ±0.50 D in both eyes wore no lenses (Table 3). Comparing the lens-wearing status of all patients who had a residual refractive error in both eyes of ±0.50 D with those who had ± 1.00 D in both eyes showed that 85% (n = 61) of the 72 patients with ±0.50 D wore no distance correction and that 39% (n = 34) of the 87 patients with ± 1.00 D wore no distance correction (Table 3).
Relation of Lens Wearing and Uncorrected Distance Visual Acuity Three hundred seven (94%) patients had an uncorrected visual acuity of 20/40 or better in both eyes, and 259
424
B
No Lens, 106 (64%)
Distance Only , 28 (17%)
Both, 27 (17 %)
Close Only, 42 (26%) /
/
,
\
C
No Lens, 64 (40%)
Figure 1. Lens-wearing status 6 years after bilateral radial keratotomy for 328 patients in the Prospective Evaluation of Radial Keratotomy Study. A, overall (n = 328); B, age < 39 years (n = 167); C, age> 40 years (n = 161).
Bourque et al . Spectacle and Contact Lens Wearing in PERK
Table 3. Corrective Lens-wearing Status by Spherical Equivalent Cycloplegic Refractions in Both Eyes, Controlling for Age, at 6 Years in the Prospective Evaluation of Radial Keratotomy Study" Both Eyes ± 0.50 D Lens-wearing Status
No . of Patients (%)
Both Eyes within
±1.0
1 Eye
Dt
No. of Patients (%)
-<1.0 DT
> +1.0 D§
1 Eye
Both Eyes <-1.0 D
Both Eyes >+1.0 D
No . of Patients (%)
No. of Patients (%)
No . of Patients (%)
No. of Patients (%)
Total No. of Patients (%)
21 3 (14) 2 (10) 8 (38) 8 (38)
6 4 (67) 0 2 (33) 0
162 104 (64) 5 (3) 30 (19) 23 (14)
9 1 (11) 0 4 (44) 4 (44)
16 4 (25) 7 (44) 1 (6) 4 (25)
155 60 (39) 42 (27) ~7 (17) 26 (17)
Younger Than 40 Yrs of Age (P < O.OOOm
No. of patients No lenses Near only Distance only Both
43 38 (88) 0 3 (7) 2 (5)
37 25 (67) 0 8 (22) 4 (11)
26 9 (34) 1 (4) 8 (31) 8 (31)
29 25 (86) 2 (7) 1 (3) 1 (3)
40 Yrs of Age or Older (P < 0.0001)
No. of patients No lenses Near only Distance only Both
29 16 (55) 7 (24) 2 (7) 4 (14)
50 21 (42) 12 (24) 13 (26) 4 (8)
18 7 (39) 0 3 (17) 8 (44)
33 11 (33) 16 (49) 4 (12) 2 (6)
D = diopter. • Deletes four patients for whom refractions in one or both eyes were missing at 6 years and one 37-year-old man with cycloplegic equivalent refractions of + 2.38 and - 2.0 who stated he wore spectacle s 100% of the time for distanc e vision onl y.
t Thirty-nine of these 87 patients had one eye within ±0.5 D of emmetropia and the other eye between - 0.5 an d -1.0 D; 26 of the 87 patients had one eye within ±0.5 D of emmetropia and the other eye between ±0.5 and + 1.0 D.
t Twenty-two of these 44 patients had one eye within ±0.5 D of emmetropia. § Twenty-nine of these 62 patients had on e eye within ±0.5 D of emmetropia and the other eye between 0.55 D and 2.0 D; 15 of the 62 patients h ad one eye within ±0.5 D of emmetropia and the other eye greater than ± 2.0 D. ~
Significance level for chi-square test of lens -wearing status by refract ive error withi n the indicated age group.
(79%) had at least one eye with an uncorrected visual acuity of 20/20 or better (Table 4). Lens use increased dramatically when the uncorrected visual acuity in both eyes or the best eye was worse than 20/20 and when the patient was older than 40 years of age (Table 4). Comparing the lens-wearing status of all patients who had an uncorrected visual acuity of 20/20 or better in at least one eye with those who had 20/25, 20/30, or 20/40 in both eyes or their best eye showed that 77% (n = 198) of the 259 patients in the 20/20 group wore no distance correction and that 34% (n = 18) of the 53 patients in the 20/25 to 20/40 group wore no distance correction (Table 4). Whereas only 2% (n = 3) of those younger than 40 years of age with 20/20 visual acuity in at least one eye wore lenses for near vision and 8% (n = 10) wore lenses for both near and distance vision , 26% (n = 34) of those older than 40 years of age wore lenses for near vision and 18% (n = 14) wore lenses for both near and distance vision. Even with age, however , many patients were able to remain lens-free or to use lenses only for near vision as long as the visual acuity in at least one eye was 20/20 or better (Table 4). Fifty-six percent (n = 25) of those patients younger than 40 years of age and 33% (n = 18)
of those older than 40 years of age who had an uncorrected visual acuity of 20/20 or better in their best eye wore no lenses. In contrast, only 21 % (n = 3) of those younger than 40 years of age and 15% (n = 2) of those older than 40 years of age whose best eye or both eyes had uncorrected visual acuities between 20/20 and 20/ 25 were lens-free. Sensitivity and Specificity of the 20/40 Criteria. To examine this finding in more detail, we examined the specificity and sensitivity of the traditionally used 20/40 ("driver's license visual acuity") cutoff as a criterion for determining the need for lenses. When the full population was examined, we obtained a sensitivity rate of 88% and a specificity rate of only 54%. In other words, of the 16 people whose visual acuity was worse than 20/40 in both eyes, 88% (n = 14) used lenses. Conversely, of the 312 patients whose acuity was better than 20/40 in both eyes, 46% (n = 144) wore lenses. When we eliminated those who wore lenses only for near vision (n = 48) from the calculations, the specificity rate rose to 64% and the sensitivity rate remained at 88%. Similarly, restricting the population to those older than 40 years of age (n = 161) reduced the specificity rate to 56% but increased the sensitivity rate to 90%.
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Table 4. Corrective Lens-wearing Status by Uncorrected Distance Visual Acuity in Both Eyes, Controlling for Age, at 6 Years in the Prospective Evaluation of Radial Keratotomy Study
Lens-wearing Status
Both Eyes 20/20 or Better
Best Eye 20/20 or Better
No. of Patients (%)
No. of Patients (%)
Both or Best Eye(s)
Both or Best Eye(s)
Both or Best Eye(s)
Both Eyes Worse Than
No. of Patients (%)
No. of Patients (%)
No. of Patients (%)
No. of Patients (%)
Total No. of Patients
5 2 (40) 0(0) 0(0) 3 (60)
8 1 (13) 0(0) 3 (38) 4 (50)
167 106 (64) 6 (4) 31 (19) 24 (14)
2 0(0) 0(0) 1 (50) 1 (50)
8 1 (13) 0(0) 2 (25) 5 (63)
161 64 (40) 42 (26) 28 (17) 27 (17)
20/25
20/32
20/40
20/40
Younger Than 40 Years (P < O.OOOIt No . of patients No lenses Near only Distance only Distance and near
87 75 (86) 2 (2) 5 (6) 5 (6)
14 3 (21) 3 (21) 4 (29) 4 (29)
45 25 (56) 1 (2) 14 (31) 5 (11)
8 0(0) 0(0) 5 (63) 3 (38)
40 Years of Age or Older (P < 0.001) No . of patients No lenses Near only Distance only Distance and near
72 43 (60) 17 (24) 7 (8) 5 (7)
13 2 (15) 4 (31) 3 (23) 4 (31)
55 18 (33) 17 (31) 11 (20) 9 (16)
11 0(0) 4 (36) 4 (36) 3 (27)
• Significance level for chi-square test of lens-wearing status by refractive error within indicated age group .
Proportion of Time Lenses Worn Patients who reported wearing lenses for both near and distance vision wore them 73% of the time they were awake, on average, and there was no change with age (Table 5). In contrast, patients who wore lenses for distance only decreased their use with age from 41% to 27% of the time. Use of lenses for near vision increased from 18% to 25% with age.
Use of Contact Lenses Seven patients (2%) reported using only contact lenses; four wore them for both near and distance vision an average of 89% of the time they were awake, and three wore
them for distance only an average of 68% of the time. Sixteen reported wearing both contacts and spectacles. The use of contact lenses is probably artificially low because the investigators discouraged patients from wearing contact lenses to avoid influencing the natural postoperative course of radial keratotomy by such conditions as corneal warpage and keratitis.
Need for Lenses Two questions traditionally have been used to assess the need for lenses: "Without glasses or contacts, can you read ordinary newsprint"," and "Without glasses or contacts, can you recognize a friend across the street?" Six years after surgery, only five patients stated that they could
Table 5. Mean Percent of Waking Time Lenses Worn by Lens-wearing Status, Controlling for Age, at 6 Years in the Prospective Evaluation of Radial Keratotomy Study" Lens-wearing Status Near vision only Distance vision only Distance and near
Younger Than 40 Years
40 Years of Age or Older
No. of Patients
Mean % Time
No. of Patients
Mean % Time
Total No. of Patients'[
Mean % Time
6 31
18 41
24
72
42 28 27
25 27 74
48 59 51
24 34 73
• In a two-way analysis of variance, the effect for "reason lenses worn" was significant at P < O.OOl.
t
The remaining 170 patients reported no use of lenses at 6 years.
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Bourque et al . Spectacle and Con tact Lens Wearing in PERK neither read newsprint nor recognize a friend. Because 48% (n = 158) of these patients wore lenses, these two quest ions were not a dependable indication of whether mildly visually disabled people need lenses to function well in their daily lives. As with the sensitivity and specificity of the 20/40 criterion, we found that the sensitivity and specificity of these two questions varied substantially depending on how we restricted the population.
Satisfaction and Lens-wearing Status Ninety-five percent of patients who did not wear lenses and 84% of those who wore lenses stated that their "eyesight was much better" than before surgery (Table 7). Satisfaction varied across the lens-wearing groups with 82% of those who wore no lenses expressing high satisfaction but only 22% of those who wore lenses for both near and distance vision expressing high satisfaction. Younger patients were slightly more satisfied (r = -0.11; P < 0.05), and the percent of time lenses were worn was inversely associated with satisfaction (r = -0. , 8; P < 0.001 ). Satisfaction also was associated with having experienced no eye pain (r = 0.18; P < 0.05), no WoITy about one's eyes (r =0.39; P < 0.001), and reporting no restrictions in activities (r = 0 .3 1; P < 0.00 I). To summarize how visual functioning, age, and concern about eyes combined to predict satisfaction 6 years after surgery, scores on the satisfaction index were regressed on the full set of variables included in these analyses. Three factors explained 47% of the variance in satisfaction at 6 years: (I) reporting no worry, pain , or restrictions in activities because of one's eyes; (2) not having to wear lenses for distance vision or both distan ce and near Vision; and (3) having a visual acuit y of 20/20 or better in both eyes. Also, contributing to satisfaction were reports of being restricted in activities by eyesight at baseline. Age was not a pred ictor of satisfaction once other variables were controlled. Although responses differed across lens-wearing groups (P < 0.0001), 74% (n = 243) of the total sample reported that their goals were completely met , and 94% of the pa-
Health Status at Six Years Reports of the physical, mental, and general health status of patients in the PERK Stud y at 6 years did not differ appreciably from that of a national sample." Nor did health status among patients in the PERK Study vary with age or lens-wearing status .
Side Effects and Problems Before surgery, patients in the PERK Study-all of whom wore spectacles or contact lenses-reported substantially more worry about their eyes and restrictions in activities because of their eyes than did those with myopia in RAND's Health Insurance Experiment (Table 6).2 At 6 years, overall concerns about eyes and reports of restrictions because of vision had declined substantially, regardless oflens-wearing status. Reports ofworrying about eyesight within the last 3 months declined from 57% preoperatively (n = 187) to 31% (n = 103) at{) years; reports of some restriction in activities because of eyes declined from 47% (n = 154) to 9% (n = 30).
Table 6. Comparison of Reported Problems of Patients from the Prospective Evaluation of Radial Keratotomy by Lens-wearing Group at 6 Years with Their Own Reports before Surgery and with Those of RAND Patients Myopia* PERK Study-lens-wearing Status
No Lenses RAND
Distance Only (n = 59)
Distan ce and N ear (n = 51)
Study
Baseline
6 Ye ars
Baseline
6 Y ears
Baseline
6 Years
Baselin e
6 Years
No . of Pat ients (%)
N o. of Patients (%)
N o. of Pat ients (%)
N o. of Pat ients (%)
N o. of Patients (%)
N o. of Patients (%)
No . of Patients (%)
N o. of Patients (%)
No . of Pa tients (%)
56 (13)
75 (44)t
9(5)
23 (48)t
6 (12)
27 (45)t
6 (10)
23 (45)t
150(35)
47 (56)t
46 (27)
11 (57)t
17 (35)
13 (56)t
18 (30)
90 (21)
23 (14)
17 (10)
4 (9)
4 (8)
4 (7)
4 (7)
--
Eye problem s that have caused some restriction in activities in last 3 mos Some worry about eyesigh t during the last 3 mos Som e pain in the eyes during th e last 3 mos
(n = 170)
Near Only (n = 48)
Total PERK (n = 328) Baseline
6 Y ears
N o. of Patients (%)
No . of Patien ts (%)
7 (14)
154(47)t
30(9)
11 (43)
22 (43)
82 (57)t
102 (31)
10(20)
9 (18)
41 (15)
33 (10)
- - -
* Data for RAND patients myopia and for those in the PERK stud y before sur gery taken from Table 1 of Bourque et aU
t Paired Student's t tests comp arin g patients in the PERK stud y before and after su rgery are significant at P < 0.05.
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7. Reported Satisfaction with Radial Keratotomy by Lens-wearing Status
Eyesight is much better than before surgery" Expressed high satisfaction (>5)t Mean score on satisfaction index (range, 1-7)" Preoperative goals were completely met" Would have radial keratotomy again" Would enroll in the PERK Study again"
(% of patients)
No Lenses (n = 170)
Near Only (n = 48)
Distance Only (n = 59)
Distance and Near (n = 51)
No. of Patients (%)
No. of Patients (%)
No. of Patients (%)
No. of Patients (%)
Total No. of Patients (%) (n = 328)
161 (95) 137 (82) 5.8 148 (93) 155 (97) 156 (98)
40 (83) 28 (58) 5.1 36 (77) 45 (96) 46 (98)
50 (85) 18 (31) 4.4 33 (57) 52 (90) 52 (90)
39 (83) 11 (22) 4.3 26 (51) 44 (86) 44 (86)
289 (89) 194 (60) 5.2 243 (74) 296 (94) 298 (94)
"P < 0.05. t On ten-item satisfaction index (range, 1-7) (P < 0.001).
tients stated that they would have radial keratotomy again and that they would enroll in the PERK Study again. Responses to these questions did not differ with the patient's age. Symmetry of Vision We previously reported that symmetry of refraction decreased slightly after radial keratotomy." We were interested in ascertaining whether there was any association between symmetry of refraction and use of lenses. Anisometropia Greater Than or Equal to 3.00 Diopters. Twelve patients had refractions in the two eyes that differed by 3.00 D or more. Six of these patients had near emmetropia (±0.50 D) in one eye and hyperopia (+2.88 to +6.75 D) in the other. Three patients had near emmetropia (±0.50 D) in one eye and residual myopia (-2.60 to -6.40 D) in the other. The last three patients had hyperopia (+ 1.63 to +2.38 D) in one eye and myopia (-1.40 to -2.00 D) in the other. These 12 patients did not differ significantly from the rest of the 316 patients in sex ratio, age, preoperative refraction, lens wearing at 6 years, use of spectacles, mental health, role and physical functioning, concern about their eyes, satisfaction with the outcome of surgery, or mental or physical health. They did differ from other patients in uncorrected visual acuity, the percent oftime lenses were worn, whether they could recognize a friend across the street, and current perceptions of their health. Six (50%) of these patients wore lenses and reported using them more of the time than other lens-wearing patients in the PERK Study (76% versus 25%). Nine (75%) considered their vision "much better" than before surgery; none considered their vision worse than before surgery. When asked what the worst thing was that happened as a result of surgery, the 12 patients responded as follows: must wear reading glasses(n = 1); visual acuity is not 20/ 20 (n = 1);visual acuity is worse (n = 2); trouble focusing
428
(n
=
1); glare or light sensitivity (n
=
.1); glare at night (n
= 1); "star" images (n = 1); and four reported no "worst
thing." The remarkable ability of these 12 patients to adjust to 3.00 D or more of anisometropia suggested that the whole topic of monovision should be studied in more detail in this population. Monovision. We defined monovision as persons who had emmetropia (±0.50 D) in one eye with -0.55 to -2.00 D of myopia in the other eye-a total of 53 patients (Table 8). In general, with age, these patients wore lenses fur less time than did those who did not have potential monovision. The 12 patients older than 40 years of age with one emmetropic eye whose second eye was mildly myopic (-0.55 to -2.00 D) and who reported wearing lenses for distance only (n = 7) or both distance and near vision (n = 5) reported wearing their lenses an average of 11% and 22% of the time, respectively. The 43 comparably aged patients who needed distance lenses and who were not candidates for monovision reported wearing distance lenses an average of 59% ofthe time. The two patients older than 40 years of age who were candidates for monovision who wore lenses only for near vision reported wearing them 8% of the time as contrasted to the 40-year-old patients with non-monovision who reported wearing lenses an average of 26% of the time.
Discussion The major reason patients gave for having radial keratotomy was to be free of dependence on spectacles and contact lenses, especially for distance vision. Four years after surgery, 64% of those who had radial keratotomy on both eyes were lens-free for both distance and near vision.' By 6 years, 52% were lens-free, a decline explained by increasing age and the onset of presbyopia. More patients younger than 40 years of age remained totally lens-free (64%) than those older than 40 years
Bourque et al . Spectacle and Contact Lens Wearing in PERK Table 8. Lens-wearing Status and Mean Percent of Time Lenses Worn by Potential for and Type of Monovision, Controlling for Age" Lens-wearing Status
Refraction: 1 Eye ± 0.50 D; Other Eye: Not Monovision
<-2.0 D
-0.55
to
-2.00 D
0.55 to 2.00 D
>2.00 D
Younger Than 40 Yrs of Age
No. of patients No lenses No. of patients (%) % timet Near only No. of patients % timet Distance only No. of patients (%) % timet Distance and near No. of patients (%) % timet
105
4
32
19
7
62 (59) 2t
2 (50) 0
17 (53) 0
18 (95) 0
7 (100) 0
3 (3) 10
1 (25) 60
2 (6) 10
23 (22) 43
1 (25) 90
6 (19) 19
17 (16) 76
7 (22) 61
0
0 1 (5) 90
0 0
0
0
36
11
40 Yrs of Age or Older
No. of patients No lenses No. of patients (%) % timet Near only No. of patients (%) % timet Distance only No. of patients (%) % timet Distance and near No. of patients (%) % timet
89
4
33 (37) 0
1 (25) 0
7 (33) 0
20 (56) It
3 (27) lOt
23 (26) 26
0
2 (10) 8
12 (33) 19
5 (46) 41
7 (33)
3 (8) 8
2 (18) 50
5 (24) 22
1 (3) 100
1 (10) 100
15 (17) 30
1 (25) 95
18 (20) 82
2 (50) 100
21
11
P = 0.01.
• In a three-way analysis ofvariance predicting the percent oftime lenses are worn, the main effects for the reason lenses are worn, andthe type of monovision, the interaction between the two- andthe three-way interaction with age issignificant at P < 0.01. t Some patients reported using magnifiers or otherpeople's spectacles on occasion.
of age (39%). An additional 4% (n = 6) of patients younger than 40 years of age and 27% (n = 42) of patients older than 40 years of age reported needing lenses for near vision only. The remaining 32% (n = 55) of patients younger than 40 years of age and 34% (n = 55) of those older than 40 years of age reported wearing lenses for distance vision or both distance and near vision for some proportion of the time they were awake. As patients aged, the proportion of time lenses were worn increased for near vision from 18% to 25% of the time but decreased for distance vision from 41 % to 27% of the time. Refraction, Age, and Lens Wearing Patients with symmetric postoperative residual myopia were most likely to be wearing lenses for distance vision.
The greater the residual myopia and the younger the patient, the more likely the patient was to report using lenses for both distance and near vision. When radial keratotomy resulted in symmetric emmetropia or slight hyperopia, patients reported little use of lenses until they reached 40 years of age. At that time, the use of lenses for near vision increased, as expected in a group with presbyopia. Although both the proportion of patients with bilateral emmetropia (±0.50 D) who wore lenses and the proportion of time they wore lenses increased with age, the proportion of time that patients with mild myopia (those with 1 or both eyes between -1.00 and -2.00 D) wore lenses decreased with age. We think that younger people with mild myopia tended to leave their lenses on when it was not necessary, as long as they were able to accommodate for near work but, with age, they discovered that minus lenses interfered with their ability
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to see close work, and they began to remove their lenses. Often, we speculate, these people discovered that they could see much better at a distance without their lenses than they realized and, as a result, their overall dependence on lenses declined.
surgery, both groups were free oflenses for a majority of the time they were awake. Because we assume both groups wore lenses all the time they were awake before surgery, the need for lenses in both groups declined substantially as a result of radial keratotomy.
Uncorrected Visual Acuity as a Predictor of Distance Lens Wearing
Reading Newsprint and Recognizing a Friend
Lens wearing also varied with postoperative uncorrected visual acuity, but not in ways that might be expected when traditional visual acuity screening criteria were used. A Snellen visual acuity of 20/40 or better is widely assumed to indicate adequate functional distance vision because it is the level at which a driver's license is issued without restriction in many states. The overwhelming majority (88%) of patients in the PERK Study saw 20/40 or better without correction in both eyes after surgery, but almost half of these patients (46%) wore lenses for either distance vision alone or both distance and near vision (Table 4). Therefore, visual acuity of 20/40 was not a specific criterion for estimating whether a person in the PERK population would be lens-free. Many patients whose visual acuity in both eyes was better than 20/40 reported using distance lenses some or all of the time (Table 4), and the 20/40 criterion for determining whether or not a person can function without distance lenses was neither appropriate nor efficient. In the entire PERK population, both the highest sensitivity (98%) and the highest specificity (88%) in predicting need for distance lenses from uncorrected visual acuity was obtained when we used 20/20 or better in both eyes as the criterion and eliminated those who reported using lenses only for near vision from our calculations. That is, 98% ofthose who had 20/20 or better visual acuity in both eyes did not wear lenses to see at a distance; 88% of those whose visual acuity in at least one eye was poorer than 20/20 did wear lenses for distance vision at least part of the time. To summarize, a person with worse than 20/40 visual acuity in both eyes is highly likely to wear lenses some of the time; however, knowing that persons have 20/40 or better visual acuity in both eyes does not mean that they do not need lenses for distance. Using 20/20 or better uncorrected visual acuity as the criterion (i.e., 20/20, 20/ 16, 20/12, or 20/ 10) results in the most efficient screening for the need for distance lenses.
Proportion of Waking Time Lenses Were Worn Although 15% (48/328) of patients reported using lenses for near vision only and 18% (59/328) reported using lenses for distance vision only, the actual proportion of waking hours that such lenses were used was quite low (Table 5). Persons who used lenses for near vision only reported using them an average of 24% of the time the y were awake , with the percent oftime increasing from 18% to 25% with age. Those who used lenses for distance vision only reported using lenses an average of 34% of the time with use declining from 41% to 27% with age. Thus, after
430
In 1963-64, six questions were added to the National Health Interview Survey to collect detailed information on functional loss of vision." For reasons unknown to us, two of these questions have been used in numerous situations to screen for a wide range of visual functions, including myopia, hyperopia, and presbyopia: 1. Without glasses or contacts, can you read ordinary newsprint? 2. Without glasses or contacts, can you recognize a friend across the street? The questions assume that people who cannot read newsprint without lenses have severe hyperopia or presbyopia and require reading glasses and that people who cannot recognize a friend across the street have myopia and require distance lenses. No refractions, visual acuities , or other traditional ophthalmic tests were administered to the sample, so it was not possible to validate the set of questions against traditional clinical measures of visual function. At 6 years, we found that neither of these questions was an efficient screen for population-based studies of myopia and presbyopia. These findings do not surprise us because earlier studies have demonstrated the inadequacy of similar questions, and it is well known in the psychometric literature that single questions rarely provide a reliable or valid measure of a construct. i'r'" Monovision. We found that patients with asymmetric refractions were no more likely than other patients to wear lenses and were as satisfied as others with the results of radial keratotomy. We suggest that patients with a nearly emmetropic refraction in one eye and a myopic refraction in the other can, if they desire, learn to use the first eye for distance vision and the second eye for near, and go lens-free for substantial amounts of time (Table 8). General Health. We can say with some confidence that having radial keratotomy did not affect the general health and well-being of patients in the PERK Study, nor did a need to wear lenses result in a poorer general quality of life. When compared with a more representative national sample, the postoperative distribution of patients in the PERK Study on measures ofgeneral health, mental health, and role functioning was identical to that of the general population. In addition, concerns of patients in the PERK Study about their eyes declined substantially after having radial keratotomy, which suggests that radial keratotomy increased patients' visual quality oflife while not resulting in deterioration of general quality of life. Determinants of Satisfaction. Patients who told us that their eyesight restricted their activities at baseline but not at 6 years, who had 20/20 or better visual acuity in both eyes, and who either wore no lenses or wore lenses
Bourque et al . Spectacle and Contact Lens Wearing in PERK only for close work were most satisfied at 6 years. Other concerns at baseline, the amount of refractive error at 6 years, the percent of time lenses were worn, a patient 's age, sex, health status, and ability to recognize a friend across the street or read newsprint did not contribute to patient satisfaction once the above variables were controlled. Distance visual acuity was a better predictor of satisfaction than refractiveerror. For this group of patients, however, having a visual acuity of 20/40 or better in both eyes was not sufficient; both ability to function without lenses and satisfaction increased substantially only when patients had a visual acuity of20/20 in their best eye. With few exceptions, the patients in the PERK Study stated that their goals were met, they would have radial keratotomy again, and they would enter the PERK Study again. These results are not surprising, given the strong desire among patients in the PERK Study to reduce their dependence on distance lenses. Beforesurgery, all patients in the PERK Study needed lenses all the time to see at a distance. At 6 years, most patients in the PERK Study could see at a distance without lenses even if they were not completely lens-free. Increased need for lenses for near vision with age does not offset this improvement. It was, after all, improved distance vision that patients in the PERK Study hoped to achieve and did achieve with radial keratotomy.
Participating Personnel A list of PERK investigators appears at the end of the article by Waring GO III, et al. "Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study Five Years after Surgery" (Ophthalmology J99 J;98:JJ64- 76).
References 1. Waring GO III. Refractive Keratotomy for Myopia and Astigmatism. St. Louis: Mosby Yearbook, 1992. 2. Bourque LB, Rubenstein R, Cosand B, et al. Psychosocial characteristics of candidates for the Prospective Evaluation of Radial Keratotomy (PERK) Study. Arch Ophthalmol 1984;102:1187-92. , 3. Waring GO III, Lynn MJ, Fielding B, et al. Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study 4 years after surgery for myopia. JAMA 1990;263:108391. 4. Waring GO III, Lynn MJ, Nizam A, et al. Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study five years after surgery. Ophthalmology 1991;98:1164-76. 5. Holladay JT, Lynn MJ, Waring GO III, et al. The relationship of visual acuity, refractive error, and pupil size after radial keratotomy. Arch Ophthalmol 1991;109:70-6. 6. Santos VR, Waring GO III, Lynn MJ, et al. Morning-toevening change in refraction, corneal curvature, and visual acuity 2 to 4 years after radial keratotomy in the PERK Study. Ophthalmology 1988;95:1487-93 .
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