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Three year results of refractive keratotomy using the Casebeer System
Three year results of refractive keratotomy using the Casebeer System Theodore P. Werblin, MD, PhD, G. Michael Stafford, BS
ABSTRACT Purpose: To analyze the results of one surgeon's first refractive keratotomy surgeries. Setting: The Werblin Center, Princeton, West Virginia. Methods: The three year results of 241 consecutive surgical procedures (128 patients) using Casebeer nomograms were examined. The average preoperative myopia was -4.07 :+:: 1.89 diopters (D). Two hundred twenty-two eyes were corrected with a goal of emmetropia. Two hundred of 241 eyes (83%) were followed for 3 years; 35 eyes (15%) were followed for fewer than 3 years after the last enhancement procedure, and 6 eyes (2%) were lost to follow-up. Results: At 3 years postoperatively (range 30 to 44 months), excluding postoperative suture and ALK procedures, mean residual manifest refractive error (spherical equivalent) was -0.04 :+:: 0.67 D (-2.25 to +3.13 D). Mean residual cycloplegic error was +0.45 :+:: 0.76 D (-1.00 to +4.13 D). Eighty-seven eyes (36%) required between one and six enhancement procedures. One hundred fifteen eyes (52%) had 20/20 or better visual acuity and 214 eyes (96%), 20/40 or better. One hundred fifty-two eyes (84%) were within :+::1.0 D and 120 eyes (66%) were within :+::0.5 D. Ten eyes (4%) lost one or more lines of best corrected acuity. Conclusion: Using the Casebeer system for refractive keratotomy, we obtained 20/40 or better uncorrected visual acuity in 96% of eyes with low to moderate levels of myopia. However, a significant number of enhancement procedures, 36% overall, were required to achieve this level of success. Hyperopic shift remains a significant concern following radial keratotomy procedures. J Cataract Refract Surg
1996; 22:1023-1029
I
n 1992, we reported the results of radial and astigmatic keratotomy procedures using the Casebeer Sys12 tem for keratorefractive surgery. ' Our initial study examined 1 year follow-up data on 125 consecutive pa-
Supported in part by a grant from Chiron Vision Corporation, Irvine, California. Neither ofthe authors has a proprietary interest in the development or marketing ofthe Casebeer System or a competing system. Reprint requests to Theodore P. Werblin, MD, PhD, P. 0. Box 5879, Princeton, West Virginia 24740.
tients. In this paper we studied the same patients for 3 years after their last refractive surgical procedure. While this report examines refractive results using the Casebeer System, 3 there are currently many refractive keratotomy systems that provide comparable results. Our experience has been with the Casebeer System only and thus our data represent this single approach. In fact, the Casebeer System has evolved since one of the authors (T.P.W.) began his refractive keratotomy career in 1990. The system used in this report is similar to, but not exactly like, the current system.
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In the original paper, we compared our results with those using an earlier system of refractive keratotomy, the Prospective Evaluation of Radial Keratotomy (PERK). We will again compare the outcomes of these two refractive keratotomy protocols. 1,4· 5
Subjects and Methods This study examined the refractive results of one author's (T.P.W.) first year's experience with refractive keratotomy. A review of the patient series indicated that 128 patients were operated on. (In the first year analysis, 1 the patient review mistakenly indicated that 125 patients were operated on. None of the errors in tabulation would have significantly influenced the data originally presented.) In 96 of the 128 patients (75%), both eyes were corrected for distance visual acuity; in 16 patients (12%), one eye was corrected for distance and one for near; in 14 (11 %), one eye was corrected for distance only; in 1 (1 %), both eyes were corrected for near and in 1, one eye was corrected for near only. In all, distance corrections were performed in 222 eyes (all intended distance corrections were equal to the preoperative myopia), near corrections in 19 eyes (all intended to leave -2.00 D of myopia), and 15 eyes were not operated on. Thirty-six eyes were initially corrected for near visual acuity; however, 17 of them were enhanced for distance correction. The average age of the 71 women and 57 men at the time of their primary surgery was 39 years (range 22 to 62 years). Preoperatively, the average spherical equivalent cycloplegic refraction was -4.07 ± 1.89 D (range +0.25 to -9.62 D; the +0.25 value was because the refraction for this eye was -1.50 + 3.5 X 80 and the
spherical equivalent was positive) and the average astigmatism, 1.04 ::!::: 1.17 D (range 0.00 to 5.00 D). The Casebeer System for keratorefractive surgery has been described.I.3 Briefly, a two-handed (one hand fixating the globe with forceps and the other making the incision) Russian cutting technique was used on all patients. The Magnum Diamond system blade (Chiron Vision Corp.) was used throughout and set at 100% of the thinnest pachymetry reading measured approximately 1.5 mm temporal to the corneal light reflex. The blade is sharp on both edges for the entire cutting depth. All radial incisions started 1.0 to 2.0 mm inside the limbus, well inside the vascular arcade. Patients were treated with topical blephamide in decreasing dosages for 10 days following surgery. Primary procedures only were performed in 153 eyes (63%); at least one enhancement procedure was required in 88 eyes (37%). In 9 eyes, sutures were placed to manage overcorrections; 3 for astigmatism, 3 for hyperopia, and 3 for hyperopia and astigmatism. One eye required automated lamellar keratoplasty (ALK) because of a primary hyperopic response. One hundred eighty-nine eyes (78%) had complete refractive examinations following their primary or last enhancement procedure at 3 months (range 1 to 6 months), 1 year (range 6 to 21 months), and 3 years (range 30 to 44 months). Their average follow-up was 36 months. The examinations were usually done late in the day, from 3 to 5 PM. Thirty-five eyes (15%) had fewer than 3 years of follow-up after their last enhancement procedure. Eleven eyes (5%) were followed for 3 years but did not have complete data at all times. Six eyes (2%) were lost to follow-up (Table 1). Refractive data obtained on eyes with fewer than 3 years or incom-
Table 1. Patients lost to follow-up. Visual Acuity Without Correction
Last Refraction
Last Cycloplegic Refraction
9/92
20/30 J1
-0.50 (15 mo) -2.25 (15 mo)
-0.25 (2 mo) -2.00 (2 mo)
7/91 7/91
8/92
20/20 20/20
0.00 (11 mo) 0.00 (11 mo)
0.00 (11 mo) 0.00 (11 mo)
2/91 4/91
11/93
20/20 20/20
-0.50 (4 mo) -0.50 (2 mo)
Eye
Preoperative Refraction
Date of Surgery
OD OS
-2.00 +1.25 X 86 -2.00 +2.00 X 107
6/91 5/91
2
OD OS
-1.75 -2.00
3
OD OS
-2.25 +1.50 X 110 -2.50 +1.25 X 80
Patient
1024
Date of Last Follow-up
J CATARACT REFRACT SURG-VOL 22, OCTOBER 1996
-0.5 -0.5
(4mo) (2 mo)
REFRACTIVE KERATOTOMY USING CASEBEER SYSTEM
Results
plete follow-up are included in the refractive analysis up to and including their last follow-up visit. Because we were examining the effects of incisional procedures on the cornea, the data on eyes that had sutures or ALK are not included with the refractive analysis but are pre. . 6 sented m a compamon paper.
The refractive data for noncycloplegic, cycloplegic, and uncorrected acuity are shown in Tables 2 to 4. The effect of surgery tended to increase over time in all eyes. The cycloplegic refractions were 0.5 D more hyperopic
Table 2. Noncyclopegic refraction outcome* (D) by preoperative myopia and time after surgery.
sot
Postop Time
Preop Myopia
Number
1 month
+0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62
55 37 80
-0.40 ± 0.46 -0.31 ± 0.57 -0.29 ± 0.58
-2.00 to 0.75 -1.50 to 1.75 -1.75 to 1.25
172
-0.33 ± 0.54
-2.00 to 1.75
70 47 92
-0.26 ± 0.44 -0.33 ± 0.58 -0.36 ± 0.58
-1.62 to 1.00 -1 .50 to 1.25 -1.75 to 1.75
209
-0.32 ± 0.53
-1.75 to 1.75
66 45 87
-0.21 ± 0.49 -0.23 ± 0.51 -0.14 ± 0.59
-1.50 to 1.00 -1.50 to 1.00 -1.75 to 2.00
198
-0.18 ± 0.54
-1.75 to 2.00
64 42 77
-0.16 ± 0.52 -0.01 ± 0.64 +0.03 ± 0.78
-1.25 to 1.50 -1.00 to 3.13 -2.25 to 2.25
183
-0.04 ± 0.67
-2.25 to 3.13
3 months
1 year
3 years
+0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62 +0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62 +0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62
Mean±
Range
*Following last surgical procedure (enhancement/primary), distance corrected eyes = standard deviation
tso
Table 3. Cycloplegic refraction outcome* by preoperative myopia and time after surgery. Mean±
sot
Postop Time
Preop Myopia
Number
1 month
+0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62
55 37 79
-0.20 ± 0.43 -0.06 ± 0.53 +0.03 ± 0.64
-1.00 to 0.88 -1.25 to 1.75 -1.25 to 1.50
171
-0.06 ± 0.56
-1.25 to 1.75
70 46 92
-0.01 ± 0.54 -0.01 ± 0.59 -0.04 ± 0.66
-1.62 to 1.50 -1.25 to 1.75 -2.25 to 1.25
208
-0.02 ± 0.60
-2.25 to 1.75
66 45 87
+0.17 ± 0.62 +0.31 ± 0.65 +0.20 ± 0.65
-2.25 to 1.50 -1.00 to 2.00 -1.75 to 2.50
+0.22 ± 0.64
-2.25 to 2.50
62 43 77
+0.34 ± 0.64 +0.40 ± 0.75 +0.56 ± 0.84
-0.75 to 2.37 -0.50 to 4.13 -1.00 to 3.00
182
+0.45 ± 0.76
-1.00 to 4.13
3 months
1 year
3 years
+0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62 +0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62
+0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62
-198 --
---
Range
*Following last surgical procedure (enhancement/primary), distance corrected eyes = standard deviation
tso
J CATARACT REFRACT SURG-VOL 22, OCTOBER 1996
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REFRACTIVE KERATOTOMY USING CASEBEER SYSTEM
than the manifest refractions (Tables 2 and 3). The standard deviation was between 0.40 and 0.80 D. Uncorrected visual acuity was 20/40 in 214 eyes (96%) and 20/25 or better in 168 (76%) (Table 4). Spectacle-corrected distance acuity was 20/40 or better in 123 eyes (98%) and 20/25 or better in 100 (79%). The rate of enhancement procedures was 46% in the highest myopia group and 27% in the lowest (Table 5); the difference was statistically significant (P < .05). One patient in the lowest preoperative myopia group who never had more than 1.25 D of astigmatism had six enhancement procedures. All used T-cuts of2.5 mm at varying orientations. Uncorrected visual acuity throughout was 20/20 to 20/40; final acuity was 20/20. Cycloplegic refraction throughout was plano. The enhancement procedures gradually moved the spherical equivalent and residual astigmatism toward emmetropia. Only 50% of the eyes that had suturing procedures for extreme hyperopic shifts achieved better than 20/40 uncorrected acuity. A larger percentage of eyes that had suturing procedures for overcorrected astigmatism achieved this uncorrected acuity (Table 6).
Prior to surgery, all eyes had better than 20/40 best corrected visual acuity. Postoperatively, all had 20/40 or better. At the end of the 3 year follow-up, 12 eyes (5%) had less than 20/25 best corrected acuity; 8 (3%) had 20/30 and 4 (2%) 20/40. Four of the eyes were overcorrected and had either ALK or suture procedures (Table 6). Two eyes (1 %) lost three lines of visual acuity from the preoperative level, five (2%) lost two lines, and three (1 %) lost one line. Two eyes did not change. No significant surgical complications occurred during the study. However, approximately 5% of eyes had a microperforation, usually on the last or next-to-last temporal incision and at the end of the incision (near the clear central zone mark). When no leakage was noted at the end of surgery, the event was not recorded. No macroperforations and no intrusions into the central dear zone occurred. We achieved 98% follow-up in this review of patients. The three (6 eyes) lost to follow-up had little or no residual refractive error on their last examination (Table 1). Various health- and time-related reasons, not dissatisfaction, kept them from returning. Two of the three were able to answer our questionnaire by phone
Table 4. Uncorrected visual acuity in distance corrected eyes. Last Visit Uncorrected Acuity ~20/20 ~20/25 ~20/30 ~20/40
<20/40 Preoperative refraction +0.25 to -3.12 D ~20/20 ~20/25 ~20/30
~20/40
<20/40 Preoperative refraction -3.25 to -4.37 D ~20/20
~20/25 ~20/30
~20/40
<20/40 Preoperative refraction -4.50 to -9.62 D ~20/20 ~20/25 ~20/30 ~20/40
<20/40
1026
Number of Eyes
3 Year Visit Percentage
Number of Eyes
Percentage
115 168 199 214 8
52 76 90 96 4
100 139 167 175 6
55 77 92 97 3
43 58 70 74 2
57 76 92 97 3
38 49 59 62
60 78 94 98 2
30 41 46 49 0
61 84 94 100 0
27 35 40 42 0
64 83 95 100 0
42 69 83 91 6
43 71 86 94 6
35 55 68 71 5
46 72 89 93 7
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and indicated that they were very satisfied with their surgery and would have it again if given the choice.
Discussion Most surgeons use nomograms that attempt to achieve a slight undercorrection. However, most patients who are accustomed to 20/20 or better corrected visual acuity prior to surgery are not satisfied with less than 20/25 or 20/30 uncorrected visual acuity postop-
eratively. Some are even dissatisfied with 20/20 acuity, especially if the fellow eye is 20/15. Therefore, a delicate balance between the amount of undercorrection that is surgically advisable (vis-a-vis hyperopic shift) and that which is tolerable and functional for the patient has to be achieved. In this study, the overall outcome at 3 years was similar to that seen at 1 year with 96% of eyes having 20/40 or better uncorrected acuity. In our earlier study,
Table 5. Enhancements after refractive keratotomy by preoperative myopia (3 year data). Preoperative Myopia (D)
Number of Eyes
Number of Enhancements
153 54 17 9 5 2
0 2 3 4 5 6
-3.25 to -4.37 (n =51)
+0.25 to -3.12 (n = 89)
-4.50 to -9.12 (n = 101)
n
%
n
%
n
%
65 16 5 0 2 (1) 0 1+
73 18 6 0 2 0
33 11 [1]* 3 3 0 1 0
65 22 6 6 0 2 0 33
55 27 (3)t 9 (2) 6 (1) 3 1 (1) 0
55 27 9 6 3 1 0 46
Overall % enhancement~
27
*ALK enhancement in brackets tsuture enhancement in parentheses +Patient discussed in the text ~Percentage of eyes with enhancement procedures
Table 6. Suture and ALK procedures after refractive keratotomy.
Patient
2 3
Eye
Preop Refraction
OD -7.75 +2.00 X 120 OS -9.75 +1.75 X 94 OD -8.75 +1.50 X 116
Astigmatism and hyperopia 4 OS -5.25 +2.25 X 57 5 5 Hyperopia 6 7 8
Preop Acuity with Correction
Pre Suture Enhancement Procedure
20/20 20/30 20/20
+1.50 +1.50 X 40 -1.25 +3.50 X 15 -2.25 +2.25 X 25
20/20
+0.25 +0.75 +2.25 +0.25 +2.75
+3.25 +2.00 +1.00 + 1.50 +1.00
Postop Acuity Suture Postop Refraction Without With Correction Correction Technique Cycloplegic
Plano -0.50- _t -1.00 +1.00 X 20*
150 -1.75 + 0.75 X 10* 100 +2.5- _t X 75 +1.5 X 105t X 35 X 115 X X
OD -7.50 +2.75 X 1 OS -7.25 +2.75 X 178
20/20 20/30
OS -7.50 +1.00 X 150 OD -2.5 OS -7.00 +0.50 X 92
20/20 20/20 20/20
+2.50 +0.50 X 120 +0.75 +0.5 x 95t +1.50 +0.75 X 77 -2.75 +1.00 X 60t Plano* +2.50
20/20
+3.50 +1.25 X 30
ALK procedure OS -3.50 9
- +1.00 X 105*
20/25 20/30 20/30
20/25 20/30 20/25
Interrupted Interrupted Interrupted
20/60
20/20
20/60 20/70
20/30 20/40+
Interrupted/ pursestring Interrupted Interrupted
20/25 20/200 20/25
20/20 20/25 20/25
Pursestring Interrupted Pursestring
20/40
ND
*Cycloplegic tManifest *Irregular astigmatism
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Table 7. Eyes with significant postoperative hyperopic shift. Postoperative Refraction (Spherical Equivalent) At 3 years (n = 182) +1.00 to +1.49 +1.50 to +1.99 +2.00 to +2.49 +2.50 to +2.99 +3.00 to +3.49 +3.50 to +3.99 +4.00 to +4.49 Between 3 months and 3 years (n +1.00 to +1.49 +1.50 to +1.99 +2.00 to +2.49 +2.50 to +2.99
Number of Eyes
Preoperative Refraction Percentage
+0.25 to -3.12
-3.25 to -4.37
-4.50 to -9.12
13.7 3.8 1.6 1.6 0.5 0.0 0.5
6 3
5
14 3 2 3 1 0 0
25 7 3 3 0 =
11.3 3.1 3.6 1.5
22 6 7 3
Table 8. Postoperative refraction. Manifest
Cycloplegic
Preoperative Myopia
n
%
n
%
Between + 1.0 and -1.0 (inclusive) +0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62 All eyes
60 40 69 169
94 95 90 92
55 38 59 152
89 88
1028
0 0 0 0
195)
99% had 20/40 acuity or better; the lower rate in the current study is largely due to the hyperopic changes seen in these patients (Table 7). In the earlier study, two of the three patients (1 %) with less than 20/40 or better uncorrected acuity were overcorrected by 1.0 D or more. In the current study, six of the eight patients (4%) with less than 20/40 or better uncorrected acuity were overcorrected by 1.0 D or more. This still compares favorably with the 3 year PERK data 5 which show 75% of eyes with acuity of 20/40 or better, but these patients were without the benefit of surgical enhancement. When the PERK study included enhanced eyes, 7 ' 8 its result of 85% with 20/40 or better comes closer to our results. The ability to control the spherical equivalent refraction at the end of surgery is critical in preventing large numbers of hyperopic results. 9 In this study, at
Between +0.5 and -0.5 (inclusive) +0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62 All eyes
0 0 0 0
50 33 49 132
78 79 64 72
42 34 44 120
6
5
0
0
3 months the mean cycloplegic refraction was close to plano (Table 2). At 3 years, 22% of eyes were+ 1.0 D or more (Tables 7 and 8). Had the 3 month mean refraction been closer to -1.0 D, only about 4% of eyes would have been + 1.0 or more at 3 years. Slight myopia is desirable, particularly in the immediate postoperative period. This can be accomplished by revising the nomograms used for primary procedures, by being more conservative with enhancement operations, or both. In general, reoperations did not cause a decrease in best corrected acuity. Only 10 eyes (4%) had a significant decrease in best corrected acuity from their preoperative 20/20 to 20/25 acuities. Four of these eyes had only one enhancement, two had no enhancement, three had suturing procedures, and one had an ALK procedure. Therefore, patients with more reoperations did not lose significant amounts of best corrected acuity. Suture procedures can, however, cause loss of best corrected acuity, at least on a temporary basis, because of induced irregular astigmatism. Three of eight sutured eyes with normal preoperative visual acuity had less than 20/25 best corrected acuity (two were 20/30 and one was 20/40).
Conclusion
77 84 68 79 57 66
11 4 5 3
The goal of refractive surgeons will not be met until 95 to 99% of patients achieve 20/20 uncorrected acuity with long-term stability. 10 None of the currently available refractive keratotomy procedures are sufficiently effective to generate this degree of accuracy or stability.
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REFRACTIVE KERATOTOMY USING CASEBEER SYSTEM
This is true despite the significant evolution of refractive keratotomy procedures and technology since the early 1980s. We believe it is improbable that any corneal refractive procedure will achieve this goal. It is also true, however, that a large percentage of patients, perhaps up to 97%, will be satisfied with the uncorrected acuity
6.
7.
achieved after refractive keratotomy procedures as they are now performed. A conservative approach to refractive keratotomy with careful concern and consideration of hyperopic changes should still allow reasonably safe and accurate surgical results. Further refinements of surgical technique
11 12 '
8.
and perhaps greater integration of
results from topographical analysis may provide a more accurate corneal, or perhaps noncorneal, refractive sur-
9.
gical procedure. 10.
References 1. Werblin TP, Stafford GM. The Casebeer System for predictable keratorefractive surgery; one-year evaluation of 205 consecutive eyes. Ophthalmology 1993; 100:10951102 2. Friedlander MH, Nordan LT, Maxwell WA, et al. Radial keratotomy predictability (letters to the editor). Ophthalmology 1994; 101:411-416 3. Casebeer JC. Casebeer Incisional Keratotomy. Thorofare, NJ, Slack Inc, 1994 4. Waring GO III, Moffitt SO, 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 5. Waring GO III, Lynn MJ, Culbertson W, et al. Three-
11.
12.
year results of the Prospective Evaluation of Radial Keratotomy (PERK) study. Ophthalmology 1987; 94: 1339-1354 Werblin TP, Stafford GM. Hyperopic shift after refractive keratotomy using the Casebeer System. J Cataract Refract Surg 1996; 22:1030-1036 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: 1164-1176 Waring GO III, LynnMJ, McDonnell PJ, and the PERK Study Group. Results of the Prospective Evaluation of Radial Keratotomy (PERK) study 10 years after surgery. Arch Ophthalmol1994; 112:1298-1308 Deitz MR, Sanders DR, Raanan MG. A consecutive series (1982-1985) of radial keratotomies performed with the diamond blade. Am J Ophthalmol1987; 103:417422 Werblin TP. Should we consider clear lens extraction for routine refractive surgery? Refract Corneal Surg 1992; 8:480-481 Assil KK, KassoffJ, Schanzlin OJ, Quantock A]. A combined incision technique of radial keratotomy; a comparison to centripetal and centrifugal incision techniques in human donor eyes. Ophthalmology 1994; 101:746-754 Lindstrom RL. Minimally invasive radial keratotomy: mini-RK. J Cataract Refract Surg 1995; 21:27-34
Mike Lynn, MS, PERKstatistician, Emory University, provided unpublished PERK data used in this paper. Dan Krider, PhD, chairman of the mathematics department, Concord College, and David Musch, PhD, Kellogg Eye Center, University ofMichigan, provided statistical assistance.
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ABSTRACT Purpose: To analyze the results of one surgeon's first refractive keratotomy surgeries. Setting: The Werblin Center, Princeton, West Virginia. Methods: The three year results of 241 consecutive surgical procedures (128 patients) using Casebeer nomograms were examined. The average preoperative myopia was -4.07 :+:: 1.89 diopters (D). Two hundred twenty-two eyes were corrected with a goal of emmetropia. Two hundred of 241 eyes (83%) were followed for 3 years; 35 eyes (15%) were followed for fewer than 3 years after the last enhancement procedure, and 6 eyes (2%) were lost to follow-up. Results: At 3 years postoperatively (range 30 to 44 months), excluding postoperative suture and ALK procedures, mean residual manifest refractive error (spherical equivalent) was -0.04 :+:: 0.67 D (-2.25 to +3.13 D). Mean residual cycloplegic error was +0.45 :+:: 0.76 D (-1.00 to +4.13 D). Eighty-seven eyes (36%) required between one and six enhancement procedures. One hundred fifteen eyes (52%) had 20/20 or better visual acuity and 214 eyes (96%), 20/40 or better. One hundred fifty-two eyes (84%) were within :+::1.0 D and 120 eyes (66%) were within :+::0.5 D. Ten eyes (4%) lost one or more lines of best corrected acuity. Conclusion: Using the Casebeer system for refractive keratotomy, we obtained 20/40 or better uncorrected visual acuity in 96% of eyes with low to moderate levels of myopia. However, a significant number of enhancement procedures, 36% overall, were required to achieve this level of success. Hyperopic shift remains a significant concern following radial keratotomy procedures. J Cataract Refract Surg
1996; 22:1023-1029
I
n 1992, we reported the results of radial and astigmatic keratotomy procedures using the Casebeer Sys12 tem for keratorefractive surgery. ' Our initial study examined 1 year follow-up data on 125 consecutive pa-
Supported in part by a grant from Chiron Vision Corporation, Irvine, California. Neither ofthe authors has a proprietary interest in the development or marketing ofthe Casebeer System or a competing system. Reprint requests to Theodore P. Werblin, MD, PhD, P. 0. Box 5879, Princeton, West Virginia 24740.
tients. In this paper we studied the same patients for 3 years after their last refractive surgical procedure. While this report examines refractive results using the Casebeer System, 3 there are currently many refractive keratotomy systems that provide comparable results. Our experience has been with the Casebeer System only and thus our data represent this single approach. In fact, the Casebeer System has evolved since one of the authors (T.P.W.) began his refractive keratotomy career in 1990. The system used in this report is similar to, but not exactly like, the current system.
J CATARACT REFRACT SURG-VOL 22, OCTOBER 1996
1023
REFRACTIVE KERATOTOMY USING CASEBEER SYSTEM
In the original paper, we compared our results with those using an earlier system of refractive keratotomy, the Prospective Evaluation of Radial Keratotomy (PERK). We will again compare the outcomes of these two refractive keratotomy protocols. 1,4· 5
Subjects and Methods This study examined the refractive results of one author's (T.P.W.) first year's experience with refractive keratotomy. A review of the patient series indicated that 128 patients were operated on. (In the first year analysis, 1 the patient review mistakenly indicated that 125 patients were operated on. None of the errors in tabulation would have significantly influenced the data originally presented.) In 96 of the 128 patients (75%), both eyes were corrected for distance visual acuity; in 16 patients (12%), one eye was corrected for distance and one for near; in 14 (11 %), one eye was corrected for distance only; in 1 (1 %), both eyes were corrected for near and in 1, one eye was corrected for near only. In all, distance corrections were performed in 222 eyes (all intended distance corrections were equal to the preoperative myopia), near corrections in 19 eyes (all intended to leave -2.00 D of myopia), and 15 eyes were not operated on. Thirty-six eyes were initially corrected for near visual acuity; however, 17 of them were enhanced for distance correction. The average age of the 71 women and 57 men at the time of their primary surgery was 39 years (range 22 to 62 years). Preoperatively, the average spherical equivalent cycloplegic refraction was -4.07 ± 1.89 D (range +0.25 to -9.62 D; the +0.25 value was because the refraction for this eye was -1.50 + 3.5 X 80 and the
spherical equivalent was positive) and the average astigmatism, 1.04 ::!::: 1.17 D (range 0.00 to 5.00 D). The Casebeer System for keratorefractive surgery has been described.I.3 Briefly, a two-handed (one hand fixating the globe with forceps and the other making the incision) Russian cutting technique was used on all patients. The Magnum Diamond system blade (Chiron Vision Corp.) was used throughout and set at 100% of the thinnest pachymetry reading measured approximately 1.5 mm temporal to the corneal light reflex. The blade is sharp on both edges for the entire cutting depth. All radial incisions started 1.0 to 2.0 mm inside the limbus, well inside the vascular arcade. Patients were treated with topical blephamide in decreasing dosages for 10 days following surgery. Primary procedures only were performed in 153 eyes (63%); at least one enhancement procedure was required in 88 eyes (37%). In 9 eyes, sutures were placed to manage overcorrections; 3 for astigmatism, 3 for hyperopia, and 3 for hyperopia and astigmatism. One eye required automated lamellar keratoplasty (ALK) because of a primary hyperopic response. One hundred eighty-nine eyes (78%) had complete refractive examinations following their primary or last enhancement procedure at 3 months (range 1 to 6 months), 1 year (range 6 to 21 months), and 3 years (range 30 to 44 months). Their average follow-up was 36 months. The examinations were usually done late in the day, from 3 to 5 PM. Thirty-five eyes (15%) had fewer than 3 years of follow-up after their last enhancement procedure. Eleven eyes (5%) were followed for 3 years but did not have complete data at all times. Six eyes (2%) were lost to follow-up (Table 1). Refractive data obtained on eyes with fewer than 3 years or incom-
Table 1. Patients lost to follow-up. Visual Acuity Without Correction
Last Refraction
Last Cycloplegic Refraction
9/92
20/30 J1
-0.50 (15 mo) -2.25 (15 mo)
-0.25 (2 mo) -2.00 (2 mo)
7/91 7/91
8/92
20/20 20/20
0.00 (11 mo) 0.00 (11 mo)
0.00 (11 mo) 0.00 (11 mo)
2/91 4/91
11/93
20/20 20/20
-0.50 (4 mo) -0.50 (2 mo)
Eye
Preoperative Refraction
Date of Surgery
OD OS
-2.00 +1.25 X 86 -2.00 +2.00 X 107
6/91 5/91
2
OD OS
-1.75 -2.00
3
OD OS
-2.25 +1.50 X 110 -2.50 +1.25 X 80
Patient
1024
Date of Last Follow-up
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-0.5 -0.5
(4mo) (2 mo)
REFRACTIVE KERATOTOMY USING CASEBEER SYSTEM
Results
plete follow-up are included in the refractive analysis up to and including their last follow-up visit. Because we were examining the effects of incisional procedures on the cornea, the data on eyes that had sutures or ALK are not included with the refractive analysis but are pre. . 6 sented m a compamon paper.
The refractive data for noncycloplegic, cycloplegic, and uncorrected acuity are shown in Tables 2 to 4. The effect of surgery tended to increase over time in all eyes. The cycloplegic refractions were 0.5 D more hyperopic
Table 2. Noncyclopegic refraction outcome* (D) by preoperative myopia and time after surgery.
sot
Postop Time
Preop Myopia
Number
1 month
+0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62
55 37 80
-0.40 ± 0.46 -0.31 ± 0.57 -0.29 ± 0.58
-2.00 to 0.75 -1.50 to 1.75 -1.75 to 1.25
172
-0.33 ± 0.54
-2.00 to 1.75
70 47 92
-0.26 ± 0.44 -0.33 ± 0.58 -0.36 ± 0.58
-1.62 to 1.00 -1 .50 to 1.25 -1.75 to 1.75
209
-0.32 ± 0.53
-1.75 to 1.75
66 45 87
-0.21 ± 0.49 -0.23 ± 0.51 -0.14 ± 0.59
-1.50 to 1.00 -1.50 to 1.00 -1.75 to 2.00
198
-0.18 ± 0.54
-1.75 to 2.00
64 42 77
-0.16 ± 0.52 -0.01 ± 0.64 +0.03 ± 0.78
-1.25 to 1.50 -1.00 to 3.13 -2.25 to 2.25
183
-0.04 ± 0.67
-2.25 to 3.13
3 months
1 year
3 years
+0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62 +0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62 +0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62
Mean±
Range
*Following last surgical procedure (enhancement/primary), distance corrected eyes = standard deviation
tso
Table 3. Cycloplegic refraction outcome* by preoperative myopia and time after surgery. Mean±
sot
Postop Time
Preop Myopia
Number
1 month
+0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62
55 37 79
-0.20 ± 0.43 -0.06 ± 0.53 +0.03 ± 0.64
-1.00 to 0.88 -1.25 to 1.75 -1.25 to 1.50
171
-0.06 ± 0.56
-1.25 to 1.75
70 46 92
-0.01 ± 0.54 -0.01 ± 0.59 -0.04 ± 0.66
-1.62 to 1.50 -1.25 to 1.75 -2.25 to 1.25
208
-0.02 ± 0.60
-2.25 to 1.75
66 45 87
+0.17 ± 0.62 +0.31 ± 0.65 +0.20 ± 0.65
-2.25 to 1.50 -1.00 to 2.00 -1.75 to 2.50
+0.22 ± 0.64
-2.25 to 2.50
62 43 77
+0.34 ± 0.64 +0.40 ± 0.75 +0.56 ± 0.84
-0.75 to 2.37 -0.50 to 4.13 -1.00 to 3.00
182
+0.45 ± 0.76
-1.00 to 4.13
3 months
1 year
3 years
+0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62 +0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62
+0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62
-198 --
---
Range
*Following last surgical procedure (enhancement/primary), distance corrected eyes = standard deviation
tso
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REFRACTIVE KERATOTOMY USING CASEBEER SYSTEM
than the manifest refractions (Tables 2 and 3). The standard deviation was between 0.40 and 0.80 D. Uncorrected visual acuity was 20/40 in 214 eyes (96%) and 20/25 or better in 168 (76%) (Table 4). Spectacle-corrected distance acuity was 20/40 or better in 123 eyes (98%) and 20/25 or better in 100 (79%). The rate of enhancement procedures was 46% in the highest myopia group and 27% in the lowest (Table 5); the difference was statistically significant (P < .05). One patient in the lowest preoperative myopia group who never had more than 1.25 D of astigmatism had six enhancement procedures. All used T-cuts of2.5 mm at varying orientations. Uncorrected visual acuity throughout was 20/20 to 20/40; final acuity was 20/20. Cycloplegic refraction throughout was plano. The enhancement procedures gradually moved the spherical equivalent and residual astigmatism toward emmetropia. Only 50% of the eyes that had suturing procedures for extreme hyperopic shifts achieved better than 20/40 uncorrected acuity. A larger percentage of eyes that had suturing procedures for overcorrected astigmatism achieved this uncorrected acuity (Table 6).
Prior to surgery, all eyes had better than 20/40 best corrected visual acuity. Postoperatively, all had 20/40 or better. At the end of the 3 year follow-up, 12 eyes (5%) had less than 20/25 best corrected acuity; 8 (3%) had 20/30 and 4 (2%) 20/40. Four of the eyes were overcorrected and had either ALK or suture procedures (Table 6). Two eyes (1 %) lost three lines of visual acuity from the preoperative level, five (2%) lost two lines, and three (1 %) lost one line. Two eyes did not change. No significant surgical complications occurred during the study. However, approximately 5% of eyes had a microperforation, usually on the last or next-to-last temporal incision and at the end of the incision (near the clear central zone mark). When no leakage was noted at the end of surgery, the event was not recorded. No macroperforations and no intrusions into the central dear zone occurred. We achieved 98% follow-up in this review of patients. The three (6 eyes) lost to follow-up had little or no residual refractive error on their last examination (Table 1). Various health- and time-related reasons, not dissatisfaction, kept them from returning. Two of the three were able to answer our questionnaire by phone
Table 4. Uncorrected visual acuity in distance corrected eyes. Last Visit Uncorrected Acuity ~20/20 ~20/25 ~20/30 ~20/40
<20/40 Preoperative refraction +0.25 to -3.12 D ~20/20 ~20/25 ~20/30
~20/40
<20/40 Preoperative refraction -3.25 to -4.37 D ~20/20
~20/25 ~20/30
~20/40
<20/40 Preoperative refraction -4.50 to -9.62 D ~20/20 ~20/25 ~20/30 ~20/40
<20/40
1026
Number of Eyes
3 Year Visit Percentage
Number of Eyes
Percentage
115 168 199 214 8
52 76 90 96 4
100 139 167 175 6
55 77 92 97 3
43 58 70 74 2
57 76 92 97 3
38 49 59 62
60 78 94 98 2
30 41 46 49 0
61 84 94 100 0
27 35 40 42 0
64 83 95 100 0
42 69 83 91 6
43 71 86 94 6
35 55 68 71 5
46 72 89 93 7
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and indicated that they were very satisfied with their surgery and would have it again if given the choice.
Discussion Most surgeons use nomograms that attempt to achieve a slight undercorrection. However, most patients who are accustomed to 20/20 or better corrected visual acuity prior to surgery are not satisfied with less than 20/25 or 20/30 uncorrected visual acuity postop-
eratively. Some are even dissatisfied with 20/20 acuity, especially if the fellow eye is 20/15. Therefore, a delicate balance between the amount of undercorrection that is surgically advisable (vis-a-vis hyperopic shift) and that which is tolerable and functional for the patient has to be achieved. In this study, the overall outcome at 3 years was similar to that seen at 1 year with 96% of eyes having 20/40 or better uncorrected acuity. In our earlier study,
Table 5. Enhancements after refractive keratotomy by preoperative myopia (3 year data). Preoperative Myopia (D)
Number of Eyes
Number of Enhancements
153 54 17 9 5 2
0 2 3 4 5 6
-3.25 to -4.37 (n =51)
+0.25 to -3.12 (n = 89)
-4.50 to -9.12 (n = 101)
n
%
n
%
n
%
65 16 5 0 2 (1) 0 1+
73 18 6 0 2 0
33 11 [1]* 3 3 0 1 0
65 22 6 6 0 2 0 33
55 27 (3)t 9 (2) 6 (1) 3 1 (1) 0
55 27 9 6 3 1 0 46
Overall % enhancement~
27
*ALK enhancement in brackets tsuture enhancement in parentheses +Patient discussed in the text ~Percentage of eyes with enhancement procedures
Table 6. Suture and ALK procedures after refractive keratotomy.
Patient
2 3
Eye
Preop Refraction
OD -7.75 +2.00 X 120 OS -9.75 +1.75 X 94 OD -8.75 +1.50 X 116
Astigmatism and hyperopia 4 OS -5.25 +2.25 X 57 5 5 Hyperopia 6 7 8
Preop Acuity with Correction
Pre Suture Enhancement Procedure
20/20 20/30 20/20
+1.50 +1.50 X 40 -1.25 +3.50 X 15 -2.25 +2.25 X 25
20/20
+0.25 +0.75 +2.25 +0.25 +2.75
+3.25 +2.00 +1.00 + 1.50 +1.00
Postop Acuity Suture Postop Refraction Without With Correction Correction Technique Cycloplegic
Plano -0.50- _t -1.00 +1.00 X 20*
150 -1.75 + 0.75 X 10* 100 +2.5- _t X 75 +1.5 X 105t X 35 X 115 X X
OD -7.50 +2.75 X 1 OS -7.25 +2.75 X 178
20/20 20/30
OS -7.50 +1.00 X 150 OD -2.5 OS -7.00 +0.50 X 92
20/20 20/20 20/20
+2.50 +0.50 X 120 +0.75 +0.5 x 95t +1.50 +0.75 X 77 -2.75 +1.00 X 60t Plano* +2.50
20/20
+3.50 +1.25 X 30
ALK procedure OS -3.50 9
- +1.00 X 105*
20/25 20/30 20/30
20/25 20/30 20/25
Interrupted Interrupted Interrupted
20/60
20/20
20/60 20/70
20/30 20/40+
Interrupted/ pursestring Interrupted Interrupted
20/25 20/200 20/25
20/20 20/25 20/25
Pursestring Interrupted Pursestring
20/40
ND
*Cycloplegic tManifest *Irregular astigmatism
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Table 7. Eyes with significant postoperative hyperopic shift. Postoperative Refraction (Spherical Equivalent) At 3 years (n = 182) +1.00 to +1.49 +1.50 to +1.99 +2.00 to +2.49 +2.50 to +2.99 +3.00 to +3.49 +3.50 to +3.99 +4.00 to +4.49 Between 3 months and 3 years (n +1.00 to +1.49 +1.50 to +1.99 +2.00 to +2.49 +2.50 to +2.99
Number of Eyes
Preoperative Refraction Percentage
+0.25 to -3.12
-3.25 to -4.37
-4.50 to -9.12
13.7 3.8 1.6 1.6 0.5 0.0 0.5
6 3
5
14 3 2 3 1 0 0
25 7 3 3 0 =
11.3 3.1 3.6 1.5
22 6 7 3
Table 8. Postoperative refraction. Manifest
Cycloplegic
Preoperative Myopia
n
%
n
%
Between + 1.0 and -1.0 (inclusive) +0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62 All eyes
60 40 69 169
94 95 90 92
55 38 59 152
89 88
1028
0 0 0 0
195)
99% had 20/40 acuity or better; the lower rate in the current study is largely due to the hyperopic changes seen in these patients (Table 7). In the earlier study, two of the three patients (1 %) with less than 20/40 or better uncorrected acuity were overcorrected by 1.0 D or more. In the current study, six of the eight patients (4%) with less than 20/40 or better uncorrected acuity were overcorrected by 1.0 D or more. This still compares favorably with the 3 year PERK data 5 which show 75% of eyes with acuity of 20/40 or better, but these patients were without the benefit of surgical enhancement. When the PERK study included enhanced eyes, 7 ' 8 its result of 85% with 20/40 or better comes closer to our results. The ability to control the spherical equivalent refraction at the end of surgery is critical in preventing large numbers of hyperopic results. 9 In this study, at
Between +0.5 and -0.5 (inclusive) +0.25 to -3.12 -3.25 to -4.37 -4.50 to -9.62 All eyes
0 0 0 0
50 33 49 132
78 79 64 72
42 34 44 120
6
5
0
0
3 months the mean cycloplegic refraction was close to plano (Table 2). At 3 years, 22% of eyes were+ 1.0 D or more (Tables 7 and 8). Had the 3 month mean refraction been closer to -1.0 D, only about 4% of eyes would have been + 1.0 or more at 3 years. Slight myopia is desirable, particularly in the immediate postoperative period. This can be accomplished by revising the nomograms used for primary procedures, by being more conservative with enhancement operations, or both. In general, reoperations did not cause a decrease in best corrected acuity. Only 10 eyes (4%) had a significant decrease in best corrected acuity from their preoperative 20/20 to 20/25 acuities. Four of these eyes had only one enhancement, two had no enhancement, three had suturing procedures, and one had an ALK procedure. Therefore, patients with more reoperations did not lose significant amounts of best corrected acuity. Suture procedures can, however, cause loss of best corrected acuity, at least on a temporary basis, because of induced irregular astigmatism. Three of eight sutured eyes with normal preoperative visual acuity had less than 20/25 best corrected acuity (two were 20/30 and one was 20/40).
Conclusion
77 84 68 79 57 66
11 4 5 3
The goal of refractive surgeons will not be met until 95 to 99% of patients achieve 20/20 uncorrected acuity with long-term stability. 10 None of the currently available refractive keratotomy procedures are sufficiently effective to generate this degree of accuracy or stability.
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This is true despite the significant evolution of refractive keratotomy procedures and technology since the early 1980s. We believe it is improbable that any corneal refractive procedure will achieve this goal. It is also true, however, that a large percentage of patients, perhaps up to 97%, will be satisfied with the uncorrected acuity
6.
7.
achieved after refractive keratotomy procedures as they are now performed. A conservative approach to refractive keratotomy with careful concern and consideration of hyperopic changes should still allow reasonably safe and accurate surgical results. Further refinements of surgical technique
11 12 '
8.
and perhaps greater integration of
results from topographical analysis may provide a more accurate corneal, or perhaps noncorneal, refractive sur-
9.
gical procedure. 10.
References 1. Werblin TP, Stafford GM. The Casebeer System for predictable keratorefractive surgery; one-year evaluation of 205 consecutive eyes. Ophthalmology 1993; 100:10951102 2. Friedlander MH, Nordan LT, Maxwell WA, et al. Radial keratotomy predictability (letters to the editor). Ophthalmology 1994; 101:411-416 3. Casebeer JC. Casebeer Incisional Keratotomy. Thorofare, NJ, Slack Inc, 1994 4. Waring GO III, Moffitt SO, 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 5. Waring GO III, Lynn MJ, Culbertson W, et al. Three-
11.
12.
year results of the Prospective Evaluation of Radial Keratotomy (PERK) study. Ophthalmology 1987; 94: 1339-1354 Werblin TP, Stafford GM. Hyperopic shift after refractive keratotomy using the Casebeer System. J Cataract Refract Surg 1996; 22:1030-1036 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: 1164-1176 Waring GO III, LynnMJ, McDonnell PJ, and the PERK Study Group. Results of the Prospective Evaluation of Radial Keratotomy (PERK) study 10 years after surgery. Arch Ophthalmol1994; 112:1298-1308 Deitz MR, Sanders DR, Raanan MG. A consecutive series (1982-1985) of radial keratotomies performed with the diamond blade. Am J Ophthalmol1987; 103:417422 Werblin TP. Should we consider clear lens extraction for routine refractive surgery? Refract Corneal Surg 1992; 8:480-481 Assil KK, KassoffJ, Schanzlin OJ, Quantock A]. A combined incision technique of radial keratotomy; a comparison to centripetal and centrifugal incision techniques in human donor eyes. Ophthalmology 1994; 101:746-754 Lindstrom RL. Minimally invasive radial keratotomy: mini-RK. J Cataract Refract Surg 1995; 21:27-34
Mike Lynn, MS, PERKstatistician, Emory University, provided unpublished PERK data used in this paper. Dan Krider, PhD, chairman of the mathematics department, Concord College, and David Musch, PhD, Kellogg Eye Center, University ofMichigan, provided statistical assistance.
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