- Email: [email protected]
Adaptation to monovision
Clinical Article
Adaptation to Monovision Michael Collins, Adrian Brute, and Briony Thompson
Many patients wha begin wearing monovision contact lenses report that it requires duys or weeks fur hem to become adjusted to the anisometropiu; however, it is not ckar if there are measurabk improvements in their vision during this period. We therefore studied both the objective and subjective characteristics of adaptation to monovision over a period of 8 weeks. Sixty presbyopie subjecrs wore high water content hydrogel knses in the study. During the 8 weeks of monovisicm wear, there were no significant changes in the subjects’ vist& acuities (distance, intermediate, or near) in high- and low-luminunce ccmditicms, near stereopsis, or interocular blur suppression characteristics. Neverhekss, the subjects &orted significant improvement in various aspects of visual performance during the same period. Forty-ei& percent of the subjects reported complete tolerante to the vision with their correction within the first week of monovision wear and a total of 78% of subjects were completely satisfied with the monovision correction at the compktion of 8 weeks wear. The improved toIerance to monovision may be related to changes in aspects of vision ether than those measured in this study or may reflect a psychological adjustment to the anisometropia. Keywords: Monovision; hydrogel contact lenses
Introduction Monovision is a widely used form of contact lens correction for presbyopia. The patient’s dominant sighting eye is normally corrected for distance vision, and the nondomi-
Address reprint requests to Michael Collins, Centre for Eye Research, School of Optometry, Queensland University of Technology, Locked Bag No. 2, Red Hill 4059, Queensland, Australia. Accepted for publication August 1994. 218
ICLC, Vol. 21, November/December
1994
nant eye, for near vision. The anisometropia induced by monovision causes a smal1 loss of binocular visual acuity, ‘-’ contrast sensitivity,8*g and stereoacuity.3’5*‘0*” Many patients who begin wearing monovision report that it requires days or weeks of monovision wear to become adjusted to this form of correction. However, it is not clear if there are measurable improvements in monovision wearers’ vision during this adaptation period. It is possible that patients may simply be reporting an adjustment or familiarity to the changes that monovision induces in various aspects of their vision. Sheedy et al. l2 measured performance with monovision correction, compared with single-vision correction, over periods of 3 and 8 weeks. Performance was measured in terms of speed and error rate on three near-point occupational-type tasks, two of which involved an element of hand-eye coordination. There was no significant change in performance using the monovision correction, compared with the single-vision correction. Schor et al. l3 studied the suppression characteristics of monovision subjects over a period of months. They found that the leve1 of interocular blur suppression did not sig nificantly alter during this time, in contrast with an earlier study, with fewer subjects, which had suggested an improvement in inte;ylar blur suppression ability following monovision wear. To establish if measurable change occurs in visual performance after commencing monovision wear, we monitored various aspects of visual performance over a period of 8 weeks in 60 new monovision wearers.
Methods Al1 potential and preliminary
subjects underwent a full eye examination contact lens consultation where they were 0 1994 Buttetworth-Heinemann
Aduptation to monovision: CoUins et al. screened for suitability for contact lens wear. Subjects were selected to fulfill the following criteria: 1. At least 6/6 visual acuity in each eye and less than 1
line differente in acuity between eyes. 2. NO active ocular pathology. 3. NO strabismus. 4. NO limit on refractive error magnitude (spherical or astigmatic component). 5. Near addition of 2 + 0.75 D. 6. NO previous monovision or bifocal contact lens wear. 7. NO previous unsuccessful contact lens wear. Sixty suitable subjects were then fitted with high water content hydrogel contact lenses. Astigmatic corrections of 0.75 D and above were incorporated in high water content, hydrogel toric lenses and the dominant sighting eye determined for distance correction. Near addition power in the nondominant eye was determined by overrefraction using an acuity chart positioned at the subject’s preferred working distance. Al1 60 subjects wore distance correction single-vision hydrogel lenses/near (half-eye) spectacles for the first 2 weeks of the study. This allowed US to minimize potential physiological adaptation effects (e.g., edema) from the measures of visual performance. A routine aftercare was conducted 1 week after commencing contact lens wear. Two weeks after delivery of the single-vision contact lenses, al1 subjects retumed for aftercare and delivery of the near correction contact lens to commence monovision wear. At this consultation, we measured visual acuities, near stereopsis, and blur suppression. Visual acuities and
Table 1. Time Course of the Experimental
near stereopsis were measured with both the single-vision contact lenses/near spectacles and with monovision. Subjects were also administered a questionnaire investigating their impressions of visual performance with the singlevision contact lenses/near spectacles compared with their previous spectacle correction (wom prior to commencing the study ) . At an aftercare visit 2 weeks after commencing monovision wear, we remeasured visual acuities, near stereopsis, and blur suppression. At this consultation, al1 subjects were delivered a new pair of monovision contact lenses and were administered a questionnaire that asked the subjects to compare visual performance with the monovision correction to performance with the single-vision contact lenses/ near spectacles. New lenses were delivered so that the subassessments” were not influenced by jects ’ “adaptation changes in lens quality (e.g., deposit buildup). Three further consultations followed, 2 weeks apart, over the next 6 weeks. At these consultations, a routine aftercare was conducted, new monovision lenses were delivered, and a questionnaire investigating subjective changes in visual performance with monovision was administered. At the final consultation, 8 weeks after commencing monovision wear, we also remeasured visual acuities, near stereopsis, and blur suppression. The time course of the experimental protocol is summarized in Ta& 1. Measurement Techniques Visual acuity was measured using Bailey-Lovie 1ogMAR high contrast charts at distances of 6 m, 67 cm, and 40 cm. Al1 visual acuity measurements were made binocularly in
Protocol Consultation Delivery
Preliminary
1
Aftercare
1 week 0 weeks SV hydrogel lenses with half-eye spectacles
Time scale Correction Questions Protocol
Aftercare
Screening lens fitting
Routine delivery
2
2 weeks MV hydrogel lenses Initial impression of monovision SV CLs vs. Previous own specs Routine A/C visual acuities near stereopsis blur suppression
Routine A/C
Consultation Aftercare
3
Aftercare 4
Aftercare
5
Time scale Correction Questions
4 weeks New MV lenses MV vs. SV CLs
6 weeks New MV lenses Change in vision Q’s
8 weeks New MV lenses Change in vision Q’s
Protocol
Routine A/C visual acuities near stereopsis blur suppression
Routine A/C
Routine A/C
Aftercare
6
10 weeks Change in vision Q’s Routine A/C visual acuities near stereopsis blur suppression
SV = single vision; MV = monovision; A/C = aftercare; Q = questions. At aftercare 2, visual acuities and near stereopsis were measured with SV lenses/half-eye spectacles and with MV lenses. ICLC, Vol. 21, NovemberDecember
1994
219
Clinical Articles both high (40 ccUm*) and low (3 cd/m*) luminance conditions with natura1 pupils. Near stereopsis was measured with the Randot test at a distance of 40 cm in the highluminance condition (40 cd/m*). Measurement of blur suppression was based on a technique described by Schor et al. l4 This technique measures the contrast at which blur from one eye is suppressed under binocular monovision conditions for a smal1 spot stimulus. A circular, variable-intensity light stimulus subtending 3.5 minutes of arc was positioned at a distance of 5 m, surrounded by a dark background with surface luminance of 0.2 cd/m*. Adjustment of the stimulus brightness was conducted by the investigator. Subjects were first shown the blurred (unsuppressed) condition by making the spot stimulus bright. At this setting, the spot stimulus appears to be surrounded by a well-defined halo. Blur suppression was then measured by a method of limits, lowering the spot’s contrast until the blur just disappeared and then increasing the contrast until the blur just reappeared. Four settings were made and the results averaged. This measure of blur suppression was conducted binocularly with the subject’s monovision correction being wom. The subjects’ rating of their initial tolerante to the monovision correction was scored on a 1-10 scale after having them walk into the reception area for a period of about 5 minutes. During this time, the subjects were encouraged to look at some magazines and look out the windows to gain an initial impression of the quality of vision obtained with the monovision correction. The subjects’ impressions of changes in vision with the monovision correction was derived by asking a series of 11 questions at the aftercares 4, 6, and 8 weeks after dispensing the monovision lenses. Subjects were asked if they had noticed any change in their distance vision, intermediate vision, near vision, ghosting symptoms, hand-eye coordination, walking confidence, driving confidence (only if they regularly drove, n = 48), and vision in dull light. These questions were al1 scored on a 7-point Lickert scale from “much clearer/better” (score of 7) to “much less clear/ to “no warse” (score of l), a score of 4 corresponding change” in vision. Table 2. Group Mean (*SE)
A further question administered 4, 6, and 8 weeks after dispensing the monovision lenses was as follows: “Some people find that it takes time to be accustomed to the vision with monovision contact lenses. How long do you think that it took before you felt comfortable with the vision with the contact lenses (days)? or Not yet?” Ethicul Considerations Al1 subjects gave informed written consent before participating and were advised that they could withdraw from the study at any stage. Subjects were instructed not to use monovision when driving unless they felt completely confident with the vision achieved with the lenses. Each subject was also dispensed a spare distance single-vision contact lens for the nondominant eye, which could be wom when driving if required. They were also advised that they should revert to spectacles when driving or in any circumstance where they felt that vision with monovision or single-vision contact lenses was less than adequate. Statistical Analysis Change in each measure of visual performance over the 8 weeks of the study was assessed using a one-factor repeated measures analysis of variante (ANOVA). The near stereopsis data were considered nonparametric and were tested using a Friedman ANOVA. The changes in visual performance associated with changing from single-vision contact lens correction to monovision correction (both measurements were taken at aftercare 2) were analyzed using paired t-tests.
Results Measures of visual performance (distance, intermediate, and near visual acuities in high- or low-luminance conditions, or blur suppression) showed no significant change over the 8 weeks of monovision wear (al1 p > 0.05, Table 2). Similarly, near stereopsis did not change over the 8 weeks (p > 0.05, Ta& 3). Interocular blur suppression was 2.05 (SD + 0.07) when monovision commenced, 2.08 (+
Binocular Visual Acuities (1ogMAR) during Contact Lens (CL) Wear Correction Monovision CL
Single Vision CL’
Time Scale (weeks)
High luminance
Low luminance
DVA IVA NVA DVA IVA NVA
-0.14 * 0.01 0.43 f 0.01 0.27 0.15 0.67 0.53
DVA = distance visual acuity; IVA = intermediate ’ Single-vision contact lenses and near spectacles. 220
ICLC, Vol. 21, NovembedDecember
k k ++
-0.11
0.01 0.01 0.01 0.01 visual acuity; NVA
1994
+ 0.01
0.45 ? 0.01 0.32 0.20 0.70 0.57
+ 2 + k
8
2
0
0
0.02 0.01 0.02 0.02
= near visual acuity.
-0.12 0.47 0.32 0.18 0.72 0.56
f k f f k 2
0.01 0.01 0.01 0.01 0.02 0.01
-0.12 0.48 0.31 0.18 0.70 0.55
f + + -+ + +
0.01 0.01 0.01 0.01 0.02 0.01
Adapration COmonovisicm: CoUins et al. Table 3. Frequency Distribution of Near Stereopsis (Sec Arc) During Contact Lens (CL) Wear Correction Single Vision CL’
Monovision
CL
Time Scale (weeks) 0 15-30 sec arc 45-60 sec arc 75-90 sec arc 120-180 sec arc 240-360 sec arc 480-720 sec arc 3960 sec arc
0
2
8 12 18 7 20 13 15 15
20
7
3
42
18
18
8 18 8 2 2
5 23 13 12 22
8 18 15 15 22
Values are the percentage of subjects in each group. Single-vision contact lenses and near spectacles. ??
0.07) after 2 weeks monovision wear, and 2.12 (+0.06) after 8 weeks of monovision wear. Not surprisingly, there were smal1 but highly statistically significant reductions in distance visual acuity (high luminance p = 0.0004, low luminance p = 0.0001) and near visual acuity (high luminance p = 0.0003, low luminance p = 0.02) with t h e monovision correction compared with the single-vision correction (Table 2). Visual acuity at the intermediate test distance was significantly worse with monovision correction in low luminance (p = 0.04) but not in high luminance (p = 0.2). There was a significant loss in near stereopsis with monovision correction compared with the single-vision correction, using a Spearman rank correlation (2 = 2.5, p = 0.01) (Tdbk 3). The subjects’ ratings of visual performance during the 8 weeks of the study are presented in Figure 1. For each question asked of the subjects, we compared the subjects’ group mean response with a nomina1 population mean of 4 (the score equivalent to the “no change” response) using a onegroup tetest. After 2 weeks of single-vision contact lens/ near spectacle correction, the subjects reported significantly improved visual performance compared with their previous spectacle correction for distance vision, intermediate vision, driving confidence, walking confidence, hand-eye coordination, and vision in dull light. The subjects’ ratings of near vision and ghosting symptoms were not significantly different, when comparing single-vision contact lens/near spectacle correction with their previous spectacle correction. Following 2 weeks of monovision wear, the subjects were questioned on the differences in visual performance between the monovision correction and the single-vision contact lens/near spectacles. The group mean ratings were significantly warse with monovision for distance vision, vision in dull light, and ghosting symptoms. However, the ratings were significantly higher for monovision for intermediate vision and walking confidence. Over the next three visits, subjects were asked to rate their visual performance with the monovision correction
compared with their last visit (i.e., change in monovision performance), 2 weeks previously. For distance vision, intermediate vision, near vision, walking confidence, and hand-eye coordination, the subjects’ ratings indicated significant improvement in visual performance compared with the last visit, for at least two of the three visits. Ratings for driving confidence, vision in dull light, and ghosting symp toms showed no significant changes at any of these three visits. Forty-eight percent of the subjects reported that they were “adapted” to the vision with monovision within the fust week of wear (Figure 2). In the second week, a further 8% of monovision subjects reported satisfactory adaptation, and at the end of 8 weeks of monovision wear, a total of 78% of patients were accustomed to the vision provided by monovision correction. There was a statistically significant correlation between the initial subjective rating of the quality of vision with monovision (at delivery) and the length of time before the subjects felt that they were subjectively “adapted” to monovision (Figure 3). A linear regression on these variables gave an r = 0.36 (F = 8.5, df = 59, p = 0.005).
weet* GYeauo”*
0
fJ&
2
y;g
4
$yy
6
;;y
8
$y
0 SY CL
vs.+.?c
2 MVVS. SVCL
4
6
Change inMv
8
change changs inw I”l.4”
Figure 1. Monovision subject’s ratings of aspects of visual performance during the study (scale of 1-7, ranging from “warse” to “bette?). hach subjective rating is a comparison of the vision obtained with that experienced at the previous visit. Asterisks indicate subjective ratings that were significantly different (p < 0.05) from a score of 4 (a rating of 4 indicated no change in vision). KXC,
Vol. 21, NovembedDecember
1994
221
Chical Articles
1
2
3
4
Perlod Of rnonO”l,iO”
5
6
7
8
wear (Wwks)
Figure 2. Monovision subjects’ impressions of the number weeks before they were “adapted” to monovision (n = 60).
of
Figure 3. Correlation between the subject% initial impression of monovision (at delivery) compared with the subject’s estimate of the number of days required to “adapt” to monovision. Initial impression of monovision was scored on a scale from 1 (poor) to 10 (good). Linear regression on these data gave r = 0.36 (p = 0.005).
Discussion There appears to be little objective change in visual acuity, near stereopsis, or interocular blur suppression ability during the first 8 weeks of monovision contact lens wear. However, the subjects’ impressions of visual performance were not always consistent with the objective data. Any improvement in visual performance during adaptation to monovision would be likely to occur as a result of improvement in the subjects’ ability to suppress the blurred eye (interocular blur suppression). Visual acuities were measured in both high- and low-luminance conditions, since in monovision it appears that interocular blur suppression is more difficult for high contrast targets in lowluminance conditions. l4 Yet, there was no significant improvement in low-luminance visual acuities or interocular blur suppression ability during the study period. This is confirmed to some extent by the subject’s ratings of vision in dull light and ghosting symptoms, which showed no significant improvement after monovision wear commenced. However, the subjects did show the expected loss of performance in dull light and ghosting symptoms when monovision was compared with single-vision correction. The subjects reported significant improvements in their 222
ICLC, Vol. 21, NovembedDecember
1994
distance, intermediate, and near vision at various stages during monovision wear that were not apparent in the measurements of visual acuity taken at similar times. If these subjective ratings are valid, then the improvement must relate to some objective change in visual performance (outside of the measures employed in this study) such as contrast sensitivity or could be related to a psychological adaptation or familiarity with monovision (possibly similar to “adaptation” to progressive addition spectacle lenses). In terms of task-related performance, the subject’s ratings of driving confidence were significantly higher for singlevision contact lenses/near spectacles than for their previous spectacle correction, presumably related to factors such as field of view and off-axis aberrations. Monovision correction caused a substantial drop in the performance rating for driving confidence, but this result was not statistically significant (p = 0.1) and subjective performance remained relatively unchanged for the remainder of monovision wear. Walking confidence showed the greatest subjective improvements in performance. Subjects reported that singlevision contact lenses were significantly better than were their previous spectacles for walking confidence and this improvement continued when they changed to monovision. We presume that this improvement relates to factors such as blur in downgaze associated with multifocal or halfeye spectacles. Hand-eye coordination was reported to improve with single-vision contact lenses/near spectacles compared with the subject’s previous spectacle correction and further improvements in performance were noted following commencement of monovision wear. This subjective impression is seemingly contradicted by the objective measures of near stereopsis, which show no significant changes during monovision wear. However, the process of hand-eye coordination is more complex than simply near stereopsis demands. About half of the monovision subject group felt that they were adapted to the monovision correction within the first week of wear. However, there remained 22% of subjects who did not fee1 completely adapted to the correction at the end of 8 weeks of wear. This finding is in broad agreement with the success rate reported by Koetting” of 82% after 2 months monovision wear. The initial impression of the quality of vision with monovision at the delivery visit proved to be a predictor of the length of time subsequently required to “adapt” to monovision (albeit a relatively weak predictor). This finding is of clinical interest, in that a patient’s initial impressions of vision at the trial fitting of monovision correction gives an indication of the likely time course of adaptation and satisfaction with the correction. For example, a patient who finds the vision with monovision correction to be poor at the initial fitting consultation is less likely to be satisfied with the vision after weeks or months of lenswear. Monovision wearers subjectively notice an improvement in some aspects of visual performance during the initial
Adapration to monouision: Colh months of contact lens wear. However, in terms of clinical measures of visual performance, they appear to show no significant improvement in visual acuities (at far, intermediate, or near distances in high- or low-luminance conditions), near stereopsis, or blur suppression ability during this same period. Therefore, if monovision wearers are adapting to the correction (anisometropia), the changes in visual performance may be occurring in aspects of vision other than those measured in this study or are related to some psychological adjustment to the monovision correction.
4.
5.
6.
7. 8.
Acknowledgments 9.
This work was funded through a grant from the National Health and Medical Research Council (Australia). We thank Vicki Shuley, Alan Tait, and Andrew Goode for their assistance during the study.
10.
ll.
References 12.
Brown B, Bowman KJ, Collins MJ: Visual performance with multifocal contact lenses and spectacles. Report to Aviation Medicine Branch, Department of Transport and Communications, Queensland Institute of Technology, 1987. Back AP, Woods R, Holden BA: The comparative visual performance of monovision and various concentric Trans BCLA Conf 1987;4:4&47. McGill E, Erickson P: Stereopsis in presbyopes
bifocals. wearing
13.
14.
et al.
monovision and simultaneous vision bifocal contact lenses. Am ] Optorn Physiol Opt 1988;65:619-626. Robboy MW, Cox IG, Erickson P: Effects of sighting and sensory dominante on monovision high and low contrast visual acuity. CLAO _J 1990;16:299-301. Erickson P, McGill E: R o 1e o f vlsua 1 acuity, stereoacuity, and ocular dominante in monovision patient success. Optorn Vis Sci 1992;69:761-764. Harris MG, Sheedy JE, Gan CM: Vision and task performance with monovision and diffractive bifocal contact lenses. Optorn Vis Sci 1992;69:609-614. Collins MJ, Goode A, Brown B: Distance visual acuity and monovision. Optorn Vis Sci 1993;70:723-728. Loshin DS, Loshin MS, Corner G: Binocular summation with monovision contact lens correction for presbyopia. ZCLC 1982;9:161-165. Collins MJ, Brown B, Bowman KJ: Contrast sensitivity with contact lens corrections for presbyopia. Ophthal Physiol Opt 1989;9:133-138. Koetting RA: Stereopsis in presbyopes fitted with single vision contact lenses. Am j Optorn Arch Am Acad Optorn 1970; 47557-561. Kast1 PR: Stereopsis in anisometropically fit presbyopie contact lens wearers. CLAO J 1983;9:322-323. Sheedy JE, Harris MG, Gan CM: Does the presbyopie visual system adapt to contact lenses? Optorn Vis Sci 1993;70:482486. Schor C, Carson M, Peterson G, Suzuki J, Erickson P: Effects of interocular blur suppression ability on monovision task performance. J Am Opt Assoc 1989;60:188-192. Schor C, Landsman L, Erickson P: Ocular dominante and the interocular suppression of blur in monovision. Am J Optorn Physiol Opt 1987;64:723-730.
ICLC, Vol. 21, NovembedDecember
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Clinical Articles Michael Collins, DipAppSc (Optorn), MAppSc, FAAO, is a graduate of the Queensland University of Technology (QUT). He worked in private practice before joining the faculty of the School of Optometry at QUT in 1981, where he is now a senior lecturer. He is currently responsible for contact lens teaching and is involved in various aspects of contact lens and vision research.
Adrian Brute graduated in optometry in 1984 from The University of Melbourne. He gained a PhD degree in 1990, under the supervision of Noel Brennan, on the topic of “Diagnostic assessment of comeal function during extended wear of hydrogel contact lenses.” Since 1991, Dr. Brute has been a postdoctoral research fellow at the QUT, Centre for Eye Research.
Dr. Briony Thompson is senior lecturer in organizational psychology in the School of Applied Psychology at Griffith University, Queensland. Her research areas include organizational psychology and interpersonal skills. Briony has taught in these areas for 15 years and is committed to improving effective communication at work. She has provided training in interpersonal skills for a wide range of health professionals and is currently investigating client perceptions of health professional’s interpersonal skills as a determinant of choice of health care.
224
ICLC, Vol. 21, NovembedDecember 1994
Adaptation to Monovision Michael Collins, Adrian Brute, and Briony Thompson
Many patients wha begin wearing monovision contact lenses report that it requires duys or weeks fur hem to become adjusted to the anisometropiu; however, it is not ckar if there are measurabk improvements in their vision during this period. We therefore studied both the objective and subjective characteristics of adaptation to monovision over a period of 8 weeks. Sixty presbyopie subjecrs wore high water content hydrogel knses in the study. During the 8 weeks of monovisicm wear, there were no significant changes in the subjects’ vist& acuities (distance, intermediate, or near) in high- and low-luminunce ccmditicms, near stereopsis, or interocular blur suppression characteristics. Neverhekss, the subjects &orted significant improvement in various aspects of visual performance during the same period. Forty-ei& percent of the subjects reported complete tolerante to the vision with their correction within the first week of monovision wear and a total of 78% of subjects were completely satisfied with the monovision correction at the compktion of 8 weeks wear. The improved toIerance to monovision may be related to changes in aspects of vision ether than those measured in this study or may reflect a psychological adjustment to the anisometropia. Keywords: Monovision; hydrogel contact lenses
Introduction Monovision is a widely used form of contact lens correction for presbyopia. The patient’s dominant sighting eye is normally corrected for distance vision, and the nondomi-
Address reprint requests to Michael Collins, Centre for Eye Research, School of Optometry, Queensland University of Technology, Locked Bag No. 2, Red Hill 4059, Queensland, Australia. Accepted for publication August 1994. 218
ICLC, Vol. 21, November/December
1994
nant eye, for near vision. The anisometropia induced by monovision causes a smal1 loss of binocular visual acuity, ‘-’ contrast sensitivity,8*g and stereoacuity.3’5*‘0*” Many patients who begin wearing monovision report that it requires days or weeks of monovision wear to become adjusted to this form of correction. However, it is not clear if there are measurable improvements in monovision wearers’ vision during this adaptation period. It is possible that patients may simply be reporting an adjustment or familiarity to the changes that monovision induces in various aspects of their vision. Sheedy et al. l2 measured performance with monovision correction, compared with single-vision correction, over periods of 3 and 8 weeks. Performance was measured in terms of speed and error rate on three near-point occupational-type tasks, two of which involved an element of hand-eye coordination. There was no significant change in performance using the monovision correction, compared with the single-vision correction. Schor et al. l3 studied the suppression characteristics of monovision subjects over a period of months. They found that the leve1 of interocular blur suppression did not sig nificantly alter during this time, in contrast with an earlier study, with fewer subjects, which had suggested an improvement in inte;ylar blur suppression ability following monovision wear. To establish if measurable change occurs in visual performance after commencing monovision wear, we monitored various aspects of visual performance over a period of 8 weeks in 60 new monovision wearers.
Methods Al1 potential and preliminary
subjects underwent a full eye examination contact lens consultation where they were 0 1994 Buttetworth-Heinemann
Aduptation to monovision: CoUins et al. screened for suitability for contact lens wear. Subjects were selected to fulfill the following criteria: 1. At least 6/6 visual acuity in each eye and less than 1
line differente in acuity between eyes. 2. NO active ocular pathology. 3. NO strabismus. 4. NO limit on refractive error magnitude (spherical or astigmatic component). 5. Near addition of 2 + 0.75 D. 6. NO previous monovision or bifocal contact lens wear. 7. NO previous unsuccessful contact lens wear. Sixty suitable subjects were then fitted with high water content hydrogel contact lenses. Astigmatic corrections of 0.75 D and above were incorporated in high water content, hydrogel toric lenses and the dominant sighting eye determined for distance correction. Near addition power in the nondominant eye was determined by overrefraction using an acuity chart positioned at the subject’s preferred working distance. Al1 60 subjects wore distance correction single-vision hydrogel lenses/near (half-eye) spectacles for the first 2 weeks of the study. This allowed US to minimize potential physiological adaptation effects (e.g., edema) from the measures of visual performance. A routine aftercare was conducted 1 week after commencing contact lens wear. Two weeks after delivery of the single-vision contact lenses, al1 subjects retumed for aftercare and delivery of the near correction contact lens to commence monovision wear. At this consultation, we measured visual acuities, near stereopsis, and blur suppression. Visual acuities and
Table 1. Time Course of the Experimental
near stereopsis were measured with both the single-vision contact lenses/near spectacles and with monovision. Subjects were also administered a questionnaire investigating their impressions of visual performance with the singlevision contact lenses/near spectacles compared with their previous spectacle correction (wom prior to commencing the study ) . At an aftercare visit 2 weeks after commencing monovision wear, we remeasured visual acuities, near stereopsis, and blur suppression. At this consultation, al1 subjects were delivered a new pair of monovision contact lenses and were administered a questionnaire that asked the subjects to compare visual performance with the monovision correction to performance with the single-vision contact lenses/ near spectacles. New lenses were delivered so that the subassessments” were not influenced by jects ’ “adaptation changes in lens quality (e.g., deposit buildup). Three further consultations followed, 2 weeks apart, over the next 6 weeks. At these consultations, a routine aftercare was conducted, new monovision lenses were delivered, and a questionnaire investigating subjective changes in visual performance with monovision was administered. At the final consultation, 8 weeks after commencing monovision wear, we also remeasured visual acuities, near stereopsis, and blur suppression. The time course of the experimental protocol is summarized in Ta& 1. Measurement Techniques Visual acuity was measured using Bailey-Lovie 1ogMAR high contrast charts at distances of 6 m, 67 cm, and 40 cm. Al1 visual acuity measurements were made binocularly in
Protocol Consultation Delivery
Preliminary
1
Aftercare
1 week 0 weeks SV hydrogel lenses with half-eye spectacles
Time scale Correction Questions Protocol
Aftercare
Screening lens fitting
Routine delivery
2
2 weeks MV hydrogel lenses Initial impression of monovision SV CLs vs. Previous own specs Routine A/C visual acuities near stereopsis blur suppression
Routine A/C
Consultation Aftercare
3
Aftercare 4
Aftercare
5
Time scale Correction Questions
4 weeks New MV lenses MV vs. SV CLs
6 weeks New MV lenses Change in vision Q’s
8 weeks New MV lenses Change in vision Q’s
Protocol
Routine A/C visual acuities near stereopsis blur suppression
Routine A/C
Routine A/C
Aftercare
6
10 weeks Change in vision Q’s Routine A/C visual acuities near stereopsis blur suppression
SV = single vision; MV = monovision; A/C = aftercare; Q = questions. At aftercare 2, visual acuities and near stereopsis were measured with SV lenses/half-eye spectacles and with MV lenses. ICLC, Vol. 21, NovemberDecember
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Clinical Articles both high (40 ccUm*) and low (3 cd/m*) luminance conditions with natura1 pupils. Near stereopsis was measured with the Randot test at a distance of 40 cm in the highluminance condition (40 cd/m*). Measurement of blur suppression was based on a technique described by Schor et al. l4 This technique measures the contrast at which blur from one eye is suppressed under binocular monovision conditions for a smal1 spot stimulus. A circular, variable-intensity light stimulus subtending 3.5 minutes of arc was positioned at a distance of 5 m, surrounded by a dark background with surface luminance of 0.2 cd/m*. Adjustment of the stimulus brightness was conducted by the investigator. Subjects were first shown the blurred (unsuppressed) condition by making the spot stimulus bright. At this setting, the spot stimulus appears to be surrounded by a well-defined halo. Blur suppression was then measured by a method of limits, lowering the spot’s contrast until the blur just disappeared and then increasing the contrast until the blur just reappeared. Four settings were made and the results averaged. This measure of blur suppression was conducted binocularly with the subject’s monovision correction being wom. The subjects’ rating of their initial tolerante to the monovision correction was scored on a 1-10 scale after having them walk into the reception area for a period of about 5 minutes. During this time, the subjects were encouraged to look at some magazines and look out the windows to gain an initial impression of the quality of vision obtained with the monovision correction. The subjects’ impressions of changes in vision with the monovision correction was derived by asking a series of 11 questions at the aftercares 4, 6, and 8 weeks after dispensing the monovision lenses. Subjects were asked if they had noticed any change in their distance vision, intermediate vision, near vision, ghosting symptoms, hand-eye coordination, walking confidence, driving confidence (only if they regularly drove, n = 48), and vision in dull light. These questions were al1 scored on a 7-point Lickert scale from “much clearer/better” (score of 7) to “much less clear/ to “no warse” (score of l), a score of 4 corresponding change” in vision. Table 2. Group Mean (*SE)
A further question administered 4, 6, and 8 weeks after dispensing the monovision lenses was as follows: “Some people find that it takes time to be accustomed to the vision with monovision contact lenses. How long do you think that it took before you felt comfortable with the vision with the contact lenses (days)? or Not yet?” Ethicul Considerations Al1 subjects gave informed written consent before participating and were advised that they could withdraw from the study at any stage. Subjects were instructed not to use monovision when driving unless they felt completely confident with the vision achieved with the lenses. Each subject was also dispensed a spare distance single-vision contact lens for the nondominant eye, which could be wom when driving if required. They were also advised that they should revert to spectacles when driving or in any circumstance where they felt that vision with monovision or single-vision contact lenses was less than adequate. Statistical Analysis Change in each measure of visual performance over the 8 weeks of the study was assessed using a one-factor repeated measures analysis of variante (ANOVA). The near stereopsis data were considered nonparametric and were tested using a Friedman ANOVA. The changes in visual performance associated with changing from single-vision contact lens correction to monovision correction (both measurements were taken at aftercare 2) were analyzed using paired t-tests.
Results Measures of visual performance (distance, intermediate, and near visual acuities in high- or low-luminance conditions, or blur suppression) showed no significant change over the 8 weeks of monovision wear (al1 p > 0.05, Table 2). Similarly, near stereopsis did not change over the 8 weeks (p > 0.05, Ta& 3). Interocular blur suppression was 2.05 (SD + 0.07) when monovision commenced, 2.08 (+
Binocular Visual Acuities (1ogMAR) during Contact Lens (CL) Wear Correction Monovision CL
Single Vision CL’
Time Scale (weeks)
High luminance
Low luminance
DVA IVA NVA DVA IVA NVA
-0.14 * 0.01 0.43 f 0.01 0.27 0.15 0.67 0.53
DVA = distance visual acuity; IVA = intermediate ’ Single-vision contact lenses and near spectacles. 220
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-0.11
0.01 0.01 0.01 0.01 visual acuity; NVA
1994
+ 0.01
0.45 ? 0.01 0.32 0.20 0.70 0.57
+ 2 + k
8
2
0
0
0.02 0.01 0.02 0.02
= near visual acuity.
-0.12 0.47 0.32 0.18 0.72 0.56
f k f f k 2
0.01 0.01 0.01 0.01 0.02 0.01
-0.12 0.48 0.31 0.18 0.70 0.55
f + + -+ + +
0.01 0.01 0.01 0.01 0.02 0.01
Adapration COmonovisicm: CoUins et al. Table 3. Frequency Distribution of Near Stereopsis (Sec Arc) During Contact Lens (CL) Wear Correction Single Vision CL’
Monovision
CL
Time Scale (weeks) 0 15-30 sec arc 45-60 sec arc 75-90 sec arc 120-180 sec arc 240-360 sec arc 480-720 sec arc 3960 sec arc
0
2
8 12 18 7 20 13 15 15
20
7
3
42
18
18
8 18 8 2 2
5 23 13 12 22
8 18 15 15 22
Values are the percentage of subjects in each group. Single-vision contact lenses and near spectacles. ??
0.07) after 2 weeks monovision wear, and 2.12 (+0.06) after 8 weeks of monovision wear. Not surprisingly, there were smal1 but highly statistically significant reductions in distance visual acuity (high luminance p = 0.0004, low luminance p = 0.0001) and near visual acuity (high luminance p = 0.0003, low luminance p = 0.02) with t h e monovision correction compared with the single-vision correction (Table 2). Visual acuity at the intermediate test distance was significantly worse with monovision correction in low luminance (p = 0.04) but not in high luminance (p = 0.2). There was a significant loss in near stereopsis with monovision correction compared with the single-vision correction, using a Spearman rank correlation (2 = 2.5, p = 0.01) (Tdbk 3). The subjects’ ratings of visual performance during the 8 weeks of the study are presented in Figure 1. For each question asked of the subjects, we compared the subjects’ group mean response with a nomina1 population mean of 4 (the score equivalent to the “no change” response) using a onegroup tetest. After 2 weeks of single-vision contact lens/ near spectacle correction, the subjects reported significantly improved visual performance compared with their previous spectacle correction for distance vision, intermediate vision, driving confidence, walking confidence, hand-eye coordination, and vision in dull light. The subjects’ ratings of near vision and ghosting symptoms were not significantly different, when comparing single-vision contact lens/near spectacle correction with their previous spectacle correction. Following 2 weeks of monovision wear, the subjects were questioned on the differences in visual performance between the monovision correction and the single-vision contact lens/near spectacles. The group mean ratings were significantly warse with monovision for distance vision, vision in dull light, and ghosting symptoms. However, the ratings were significantly higher for monovision for intermediate vision and walking confidence. Over the next three visits, subjects were asked to rate their visual performance with the monovision correction
compared with their last visit (i.e., change in monovision performance), 2 weeks previously. For distance vision, intermediate vision, near vision, walking confidence, and hand-eye coordination, the subjects’ ratings indicated significant improvement in visual performance compared with the last visit, for at least two of the three visits. Ratings for driving confidence, vision in dull light, and ghosting symp toms showed no significant changes at any of these three visits. Forty-eight percent of the subjects reported that they were “adapted” to the vision with monovision within the fust week of wear (Figure 2). In the second week, a further 8% of monovision subjects reported satisfactory adaptation, and at the end of 8 weeks of monovision wear, a total of 78% of patients were accustomed to the vision provided by monovision correction. There was a statistically significant correlation between the initial subjective rating of the quality of vision with monovision (at delivery) and the length of time before the subjects felt that they were subjectively “adapted” to monovision (Figure 3). A linear regression on these variables gave an r = 0.36 (F = 8.5, df = 59, p = 0.005).
weet* GYeauo”*
0
fJ&
2
y;g
4
$yy
6
;;y
8
$y
0 SY CL
vs.+.?c
2 MVVS. SVCL
4
6
Change inMv
8
change changs inw I”l.4”
Figure 1. Monovision subject’s ratings of aspects of visual performance during the study (scale of 1-7, ranging from “warse” to “bette?). hach subjective rating is a comparison of the vision obtained with that experienced at the previous visit. Asterisks indicate subjective ratings that were significantly different (p < 0.05) from a score of 4 (a rating of 4 indicated no change in vision). KXC,
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Chical Articles
1
2
3
4
Perlod Of rnonO”l,iO”
5
6
7
8
wear (Wwks)
Figure 2. Monovision subjects’ impressions of the number weeks before they were “adapted” to monovision (n = 60).
of
Figure 3. Correlation between the subject% initial impression of monovision (at delivery) compared with the subject’s estimate of the number of days required to “adapt” to monovision. Initial impression of monovision was scored on a scale from 1 (poor) to 10 (good). Linear regression on these data gave r = 0.36 (p = 0.005).
Discussion There appears to be little objective change in visual acuity, near stereopsis, or interocular blur suppression ability during the first 8 weeks of monovision contact lens wear. However, the subjects’ impressions of visual performance were not always consistent with the objective data. Any improvement in visual performance during adaptation to monovision would be likely to occur as a result of improvement in the subjects’ ability to suppress the blurred eye (interocular blur suppression). Visual acuities were measured in both high- and low-luminance conditions, since in monovision it appears that interocular blur suppression is more difficult for high contrast targets in lowluminance conditions. l4 Yet, there was no significant improvement in low-luminance visual acuities or interocular blur suppression ability during the study period. This is confirmed to some extent by the subject’s ratings of vision in dull light and ghosting symptoms, which showed no significant improvement after monovision wear commenced. However, the subjects did show the expected loss of performance in dull light and ghosting symptoms when monovision was compared with single-vision correction. The subjects reported significant improvements in their 222
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distance, intermediate, and near vision at various stages during monovision wear that were not apparent in the measurements of visual acuity taken at similar times. If these subjective ratings are valid, then the improvement must relate to some objective change in visual performance (outside of the measures employed in this study) such as contrast sensitivity or could be related to a psychological adaptation or familiarity with monovision (possibly similar to “adaptation” to progressive addition spectacle lenses). In terms of task-related performance, the subject’s ratings of driving confidence were significantly higher for singlevision contact lenses/near spectacles than for their previous spectacle correction, presumably related to factors such as field of view and off-axis aberrations. Monovision correction caused a substantial drop in the performance rating for driving confidence, but this result was not statistically significant (p = 0.1) and subjective performance remained relatively unchanged for the remainder of monovision wear. Walking confidence showed the greatest subjective improvements in performance. Subjects reported that singlevision contact lenses were significantly better than were their previous spectacles for walking confidence and this improvement continued when they changed to monovision. We presume that this improvement relates to factors such as blur in downgaze associated with multifocal or halfeye spectacles. Hand-eye coordination was reported to improve with single-vision contact lenses/near spectacles compared with the subject’s previous spectacle correction and further improvements in performance were noted following commencement of monovision wear. This subjective impression is seemingly contradicted by the objective measures of near stereopsis, which show no significant changes during monovision wear. However, the process of hand-eye coordination is more complex than simply near stereopsis demands. About half of the monovision subject group felt that they were adapted to the monovision correction within the first week of wear. However, there remained 22% of subjects who did not fee1 completely adapted to the correction at the end of 8 weeks of wear. This finding is in broad agreement with the success rate reported by Koetting” of 82% after 2 months monovision wear. The initial impression of the quality of vision with monovision at the delivery visit proved to be a predictor of the length of time subsequently required to “adapt” to monovision (albeit a relatively weak predictor). This finding is of clinical interest, in that a patient’s initial impressions of vision at the trial fitting of monovision correction gives an indication of the likely time course of adaptation and satisfaction with the correction. For example, a patient who finds the vision with monovision correction to be poor at the initial fitting consultation is less likely to be satisfied with the vision after weeks or months of lenswear. Monovision wearers subjectively notice an improvement in some aspects of visual performance during the initial
Adapration to monouision: Colh months of contact lens wear. However, in terms of clinical measures of visual performance, they appear to show no significant improvement in visual acuities (at far, intermediate, or near distances in high- or low-luminance conditions), near stereopsis, or blur suppression ability during this same period. Therefore, if monovision wearers are adapting to the correction (anisometropia), the changes in visual performance may be occurring in aspects of vision other than those measured in this study or are related to some psychological adjustment to the monovision correction.
4.
5.
6.
7. 8.
Acknowledgments 9.
This work was funded through a grant from the National Health and Medical Research Council (Australia). We thank Vicki Shuley, Alan Tait, and Andrew Goode for their assistance during the study.
10.
ll.
References 12.
Brown B, Bowman KJ, Collins MJ: Visual performance with multifocal contact lenses and spectacles. Report to Aviation Medicine Branch, Department of Transport and Communications, Queensland Institute of Technology, 1987. Back AP, Woods R, Holden BA: The comparative visual performance of monovision and various concentric Trans BCLA Conf 1987;4:4&47. McGill E, Erickson P: Stereopsis in presbyopes
bifocals. wearing
13.
14.
et al.
monovision and simultaneous vision bifocal contact lenses. Am ] Optorn Physiol Opt 1988;65:619-626. Robboy MW, Cox IG, Erickson P: Effects of sighting and sensory dominante on monovision high and low contrast visual acuity. CLAO _J 1990;16:299-301. Erickson P, McGill E: R o 1e o f vlsua 1 acuity, stereoacuity, and ocular dominante in monovision patient success. Optorn Vis Sci 1992;69:761-764. Harris MG, Sheedy JE, Gan CM: Vision and task performance with monovision and diffractive bifocal contact lenses. Optorn Vis Sci 1992;69:609-614. Collins MJ, Goode A, Brown B: Distance visual acuity and monovision. Optorn Vis Sci 1993;70:723-728. Loshin DS, Loshin MS, Corner G: Binocular summation with monovision contact lens correction for presbyopia. ZCLC 1982;9:161-165. Collins MJ, Brown B, Bowman KJ: Contrast sensitivity with contact lens corrections for presbyopia. Ophthal Physiol Opt 1989;9:133-138. Koetting RA: Stereopsis in presbyopes fitted with single vision contact lenses. Am j Optorn Arch Am Acad Optorn 1970; 47557-561. Kast1 PR: Stereopsis in anisometropically fit presbyopie contact lens wearers. CLAO J 1983;9:322-323. Sheedy JE, Harris MG, Gan CM: Does the presbyopie visual system adapt to contact lenses? Optorn Vis Sci 1993;70:482486. Schor C, Carson M, Peterson G, Suzuki J, Erickson P: Effects of interocular blur suppression ability on monovision task performance. J Am Opt Assoc 1989;60:188-192. Schor C, Landsman L, Erickson P: Ocular dominante and the interocular suppression of blur in monovision. Am J Optorn Physiol Opt 1987;64:723-730.
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Clinical Articles Michael Collins, DipAppSc (Optorn), MAppSc, FAAO, is a graduate of the Queensland University of Technology (QUT). He worked in private practice before joining the faculty of the School of Optometry at QUT in 1981, where he is now a senior lecturer. He is currently responsible for contact lens teaching and is involved in various aspects of contact lens and vision research.
Adrian Brute graduated in optometry in 1984 from The University of Melbourne. He gained a PhD degree in 1990, under the supervision of Noel Brennan, on the topic of “Diagnostic assessment of comeal function during extended wear of hydrogel contact lenses.” Since 1991, Dr. Brute has been a postdoctoral research fellow at the QUT, Centre for Eye Research.
Dr. Briony Thompson is senior lecturer in organizational psychology in the School of Applied Psychology at Griffith University, Queensland. Her research areas include organizational psychology and interpersonal skills. Briony has taught in these areas for 15 years and is committed to improving effective communication at work. She has provided training in interpersonal skills for a wide range of health professionals and is currently investigating client perceptions of health professional’s interpersonal skills as a determinant of choice of health care.
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