Progression of Visual Acuity after Penetrating Keratoplasty

Progression of Visual Acuity after Penetrating Keratoplasty FRANCIS W. PRICE, Jr., MD,t WILLIAM E. WHITSON, MD,t RONALD G. MARKS, PhD2

Abstract: A consecutive series of 721 eyes was followed for visual acuity changes after keratoplasty in four groups: keratoconus, Fuchs' dystrophy, pseudophakic bullous keratopathy with retained intraocular lenses, and aphakic/ pseudophakic bullous keratopathy with secondary implants during keratoplasty. Follow-up ranged from 12 to 84 months. Keratoconus eyes showed the quickest recovery of visual acuity: by 12 months, 91"10 attained a best-corrected vision of 20/40, and the mean lines of visual acuity for the group plateaued thereafter. The other three groups showed continuing improvement in vision through 24 months. From 3 months through 3 years after keratoplasty, the keratoconus and Fuchs' groups consistently showed better visual acuity levels than either the retained or the secondary implant groups (P < 0.0001). Reporting changes in visual acuity over time offers multiple advantages compared with providing best-attained or last-recorded visual acuities after keratoplasty. Ophthalmology 1991; 98: 1177-1185

The success rate for maintaining a clear penetrating keratoplasty has increased substantially over the last 30 years. I - 6 From the surgeon's standpoint, graft clarity indicates technically successful surgery, whereas from the patient's standpoint, the recovery of useful visual acuity is usually more important. Although numerous studies have provided either the final or best-attained visual acuities after penetrating keratoplasty, to our knowledge, none have described the continual change in best-corrected visual acuity for a large consecutive group of eyes. This study describes the changes in best-corrected visual acuity after keratoplasty for four common diagnoses: 7 ,8 keratoconus, Fuchs' dystrophy, pseudophakic bullous keratopathy with retained lens implants, and aphakic bullous keratopathy or pseudophakic bullous keratopathy with a secondary lens implant.

Originally received: August 27, 1990. Revision accepted: April 25, 1991. 1

2

Corneal Consultants of Indiana, Indianapolis. University of Florida, Gainesville.

Supported in part by a grant frorn the St. Vincent Hospital Foundation, Indianapolis, Indiana. Reprint requests to Francis W. Price, Jr., MD, 9002 N Meridian St, Suite 100, Indianapolis, IN 46260.

PATIENTS AND METHODS In July 1989, data were reviewed on all penetrating keratoplasties performed by Corneal Consultants of Indiana (FWP and WEW) from August 1982 to June 30, 1988. Data retrieval was conducted in a retrospective manner from patient records for all surgeries and examinations performed before December 1986, and in a prospective manner by computerizing patient visits after that time. Data are collected on an ongoing basis for preoperative, surgical, and postoperative examinations. Defined postoperative examinations in the data base are at 1, 3, 6, 9, 12, and 18 months, 2 years, and then each year thereafter. All keratoplasties were reviewed for a preoperative diagnosis of keratoconus, Fuchs' endothelial corneal dystrophy, or pseudophakic bullous keratopathy. Eyes with aphakic bullous keratopathy that received a secondary lens implant also were included in this analysis. No eye was entered into the data analysis more than once. Those eyes receiving a repeat keratoplasty after a secondary graft failure were not entered a second time. A total of 771 cases were found using the above criteria. Because visual acuity may recover slowly after a penetrating keratoplasty and take a number of months to stabilize, only eyes with greater than 1 year follow-up were included. Fifty eyes had less than 12 months offollow-up and were removed from this analysis, leaving 721 eyes. Those 50 1177

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Table 1. Associated Procedures at Time of Keratoplasty Bullous Keratopathy

Procedure

Keratoconus (84 cases)

Fuchs' Dystrophy (173 cases)

Secondary Implants (374 cases)

Retained Implants (90 cases)*

PKP only ECCE, PIC IOL Vitrectomy IOL removed Lysis PAS Trabeculectomy

72 (85.7%) 11 (13.1%) 1 (1 .2%) 0 0 0

19 (11 .0%) 148 (85.5%) 6 (3.5%) 0 0 0

0 0 353 (94.4%) 272 (72.7%) 43 (11 .5%) 2 (0.5%)

70 (77.8%) 0 14 (15.6%) 0 5 (5.6%) 0

0 0 0

0 0 0

6 (1.6%) 25 (6.7%) 343 (91.7%)

0 0 0

Secondary Implants

AIC PIC on capsule PIC sutured iris

PKP = penetrating keratoplasty; ECCE = extracapsular cataract extraction; PIC = posterior chamber lens; IOL = intraocular lens; PAS anterior synechiae; AIC = anterior chamber lens . • Includes four patients who had removal of some portion of retained cataract material.

= peripheral

Table 2. Suture Type Used for Keratoplasty Bullous Keratopathy Suture Type·

Keratoconus

Fuchs' Dystrophy

Secondary Implants

Retained Implants

Interrupted Running Double-running Combined

9 (10.7%) 0(0%) 0(0%) 75 (89.3%)

8 (4.6%) 29 (16.8%) 1 (0.6%) 135 (78.0%)

115 (30.8%) 27 (7.2%) 2 (0.5%) 230 (61 .5%)

31 (34.4%) 12 (13.3%) 0(0%) 47 (52.2%)

163 68 3 487

Total

84

173

374

90

721

Total

• Using chi-square analysis, there were no significant differences in types of sutures between keratoconus and Fuchs' dystrophy groups, nor between the groups of secondary and retained implants. Chi-square analysis did show a significant difference in the incidences of interrupted sutures (P < 0.0001) and combined sutures (P < 0 0. 001) when comparing the Fuchs' and keratoconus groups with the secondary and retained implant groups.

eyes had less than 12 months of follow-up for the following reasons: 25 patients died, 10 eyes had failed grafts, II patients were lost to follow-up, and 4 were not examined until after the data analysis began for this series. The cases were divided into the following groups: keratoconus (84), Fuchs' dystrophy (173), aphakic bullous keratopathy or pseudophakic bullous keratopathy with secondary insertion of an intraocular lens (374), and pseudophakic bullous keratopathy with the lens retained (90). Bilateral keratoplasties were evaluated in 73 patients in this study: keratoconus (15), Fuchs' dystrophy (40), aphakic or pseudophakic bullous keratopathy with secondary insertion of an intraocular lens (16),6 and pseudophakic bullous keratopathy with lens retained (2). The surgical technique for penetrating keratoplasty and postoperative care have been reported previously.9 Table I lists the associated surgical procedures performed at the time of keratoplasty, Table 2 shows the method of suturing, and Table 3 shows the types of explanted intraocular 1178

Table 3. Intraocular Lenses Removed from Secondary Implant Group Posterior chamber lenses Iris-plane lenses Anterior chamber lenses· Stableflex Leiske 91Z Choyce Hessburg Dubroff Kelman flexible Novaflex Pannu Surefit Rigid azar

2

37 229 82 60 21 21 17

6 4

4 2

2 2

• One each of the following intraocular lenses were removed in this series: Kelman rigid, 3M #70/77, Multiflex, S-flex, ORC 18J, Simcoe, Optiflex, and a Simcoe posterior chamber lens placed in the anterior chamber.

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lenses. Anterior chamber and iris-plane lenses were only retained when the lenses appeared to be well-fixated and showed absolutely no signs of inflammation. The retained lens group consisted of the following lenses: 11 rigid anterior chamber, 21 closed-loop anterior chamber, 56 posterior chamber, and 2 Copeland iris-fixated. Best-corrected visual acuity was taken as the best vision of the following: uncorrected, corrected with spectacle correction, or corrected with a hard contact lens. Manifest refractions were performed with phoropters. All visual acuities were distant visual acuities obtained with projected Snellen charts in standardized refraction lanes. Bestcorrected vision with a contact lens was used only when an eye did not attain a visual acuity of 20/40 or better with spectacle correction on an examination with a stable corneal wound, usually after sutures were removed. Visual acuities in eyes with failed grafts were recorded for the first examination at which a graft was recorded as failed and not after. There is not a single accepted technique used in the scientific literature for quantifying and analyzing visual acuity data. For the groups in this report, we believe it is most appropriate to treat each line on the Snellen chart by a count as follows: 20/20 = 1; 20/25 = 2; 20/30 = 3; 20/40 = 4; 20/50 = 5; 20/60 = 6; 20170 = 7; 20/80 = 8; 20/100 = 9; 20/200 = 10; 20/300 = 11; 20/400 = 12; counting fingers = 13; hand motions = 14; light perception = 15; and no light perception = 17. Improvement or loss in vision over time can then be quantified as the mean number of lines of vision, and standard parametric statistical analyses can be used to compare groups. Unless otherwise noted, lines of visual acuity were used for data analysis comparison of visual acuities between groups.

DATA ANALYSIS Statistical analyses reported in this article use a oneway analysis of variance (ANOVA) to detect overall differences among groups unless otherwise reported. Statistically significant results are then followed by Duncan's multiple range test to detect differences between pairs of means.

RESULTS Table 4 provides the demographic data on age and follow-up. Using ANOVA and Duncan's multiple range test, there was no significant difference in the mean ages between the two groups of retained and secondary implants, but there was a significant difference between the four groups overall (P < 0.0001). The keratoconus group was youngest by far, with a mean age of 43 years, and the Fuchs' group was significantly younger than the retained lens and secondary lens implant groups. There was no significant difference noted in the mean length of followup between all groups. The mean lines of best-corrected vision preoperatively by group were: keratoconus, 9.5;

Table 4. Age and Follow-up of Study Groups Age (yrs)*

Follow-up (mas)

Diagnoses

No.

Mean

Range

Mean

Range

Keratoconus Fuchs' dystrophy Secondary implants Retained implants

84 173 374 90

42.9 71.3 74.8 74.0

15-83 42-91 34-97 54-91

30.1 32.2 29.3 28.5

12-84 12-84 12-84 12-60

* Mean age at time of penetrating keratoplasty.

Fuchs', 8.8; secondary implants, 11.4; and retained implants, 11.7. Preoperatively, 29 of 84 (34.5%) eyes with keratoconus had a preoperative vision with a hard contact lens. The eyes with aphakic and pseudophakic bullous keratopathy showed a tendency to have more preoperative visual loss. Table 5 lists the number of eyes examined at each designated time interval and the percentage available of the total possible. For a variety of reasons, patients were not always available for each designated time period, although 65.8% of the eyes in the study were available for all their possible postoperative examinations. Table 6 and Figure 1 provide the mean lines of acuity for each group over time. Keratoconus eyes had a more rapid visual recovery rate than those in the other groups. Keratoconus eyes had significantly better lines of acuity than both the retained and secondary lens groups at all time intervals through 3 years and better than Fuchs' eyes through 18 months. The Fuchs' group also had significantly better mean lines of visual acuity through 3 years compared with the two groups having cataract surgery before keratoplasty. The significant differences in the mean lines of visual acuity of the keratoconus and Fuchs' groups versus those with retained or secondary implants persisted until the 4-year interval when sample sizes were too small for statistical significance. However, the tendency, as shown graphically in Figure 1, indicates the differences between these groups may be maintained. For purposes of comparison, Figure 2 depicts the changes in visual acuity between groups when analyzed using the decimal equivalent of the Snellen visual acuity. Although looking at the mean visual acuity is important to see how the groups perform as a whole, it is also important to look at what portion of eyes obtain a successful result. A visual acuity of 20/40 or better is often chosen as a successful visual result after keratoplasty. Figure 3 shows the percentage of eyes obtaining a visual acuity of 20/40 or better for each group over time. Keratoconus eyes showed the most rapid rate of obtaining 20/40, as well as the highest percentage of eyes achieving that vision. The eyes with retained implants and those with secondary implants closely parallel each other's rate of attaining 20/ 40 or better visual acuity with the Fuchs' eyes falling between those two groups and keratoconus. A comparison was made regarding the lines of visual acuity recovery between the subgroups of retained anterior chamber lenses and the retained posterior chamber lenses. 1179

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Table 5. Patient Availability" Bullous Keratopathy

Follow-up (mas) 1 3 6 9 12 18 24 36 48 60

72

Keratoconus No·t Percent*

Fuchs' Dystrophy No·t Percent*

Secondary Implants No·t Percent*

Retained Implants No·t Percent*

Total

82 (97.6) 81 (96.4) 80 (95.2) 74 (88.1) 81 (96.4) 66 (91.7) 51 (91.1) 27 (90.0) 18 (90.0) 9 (100) 2 (100)

171 (98.8) 168 (97.1) 154 (89.0) 144 (83.2) 157 (90.7) 125 (83.3) 117 (92.9) 75 (82.4) 43 (87.7) 14 (77.8) 4 (80.0)

369 (98.4) 365 (97.6) 350 (93.6) 319 (85.3) 357 (95.2) 278 (89.4) 225 (92.6) 128 (90.8) 72 (94.7) 29 (90.6) 10 (100)

89 (98.9) 87 (96.7) 84 (93.3) 73 (81.1) 76 (84.4) 71 (88.7) 58 (90.6) 36 (94.7) 13 (92.9) 2 (66.7) 0(0)

711 701 668 610 671 540 451 266 146 54 16

" Patients were not always available for each deSignated time period, therefore, numbers vary. During the course of the study, 65.8% of eyes were available for all their possible examination periods. t Number of eyes available for visual acuity measurements at each time interval. * Percent of eyes available out of total possible for that time interval. Table 6. Mean Lines of Acuity Bullous Keratopathy Follow-up (mas)

PValue

Keratoconus

Fuchs' Dystrophy

Secondary Implants

Retained Implants

Standard Deviation"

3 6 9 12 18 24 36 48 60

0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 NS NS

4.7 3.9 3.4 3.1 3.0 2.8* 3.0* 3.3t 3.2t

5.5 4.9 4.5 4.4 4.2 3.5* 3.7* 3.3t 3.3t

8.8 7.4t 7.0t 6.2t 5.8t 5.7t 5.3t 5.3t 5.1t

8.0 6.8t 6.9t 6.0t 6.2t 5.6t 5.8t 5.2t 4.0t

3.11 3.34 3.29 3.23 3.23 3.26 3.29 3.35 2.79

NS = not significant. Groups at the same postoperative examination period with a common superscript (t. *) are not significantly different from each other. The Pvalue indicates the overall significance among the four groups using a one-way analysis of variance. Duncan's multiple range test was used to determine significance between pairs of groups. " Represents the pooled standard deviation of the four study groups.

Through 12 months, eyes with retained posterior chamber lenses showed better lines of visual acuity with significance only at the 3- and 12-month examinations. After 36 months, the eyes with retained anterior chamber lenses showed better lines of visual acuity, but there was no statistical significance. The recovery of visual acuity is influenced by a number of variables. Two important variables are suture removal and use of hard contact lenses. Table 7 lists the cumulative number of eyes with complete suture removal at each examination period. Complete suture removal occurred after sutures became loose and bad to be removed or if the wound was healed and vision could not satisfactorily 1180

be corrected by spectacles. Most eyes showed an improvement in visual acuity after suture removal. Overall, 14.5% of eyes had a best-corrected visual acuity of 20/40 or better before complete suture removal, and 3.6% actually had a major decrease in best-corrected spectacle visual acuity after suture removal, necessitating the use of a contact lens. Eyes with combined running and interrupted sutures had selective suture removal with photokeratoscopic control because of reports of more rapid visual recovery using this suturing technique. lO- I3 Because there was a significant difference between groups regarding types of sutures, the mean lines of visual acuity for each group were re-evaluated using only eyes with combined running and inter-

PRICE et al

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VISUAL ACUITY AFTER PENETRATING KERATOPLASTY

Mean Lines of Acuity

Mean Fractions of Acuity

12

K F S R

11

?:

·S
"

. " ."

"0 CI)

::::; CI)

:;;

10 9

8 7

6

5 4 3

2

S R\S

Keratoconus Fuchs' Secondary Implants Retained Implants

?: .60 "S u c( .55

..

"0 .50 c

~ ....e

-S

R-R~

K'-.....

.75 .70 .65

. ~

S;><~

c

F" R ~~s F R-"""""" K"""",- - F - F _ F S K-K ----F-F ___ -K-K K-KF=KF ----K-

K/

.40 .30 .25 .20

K"""'---

F

F_F

K/

.45 .35

K_K/ "---K><:F /F-F"""'--K

F

./. / F -

F"""""--

R--::::;::SR~~7 /S_S

AS

R----- / '

-s

/ R _ _ RS

R/

/' /S/

K = Keratoconus F = Fuchs' S = Secondary Implants R = Retained Implants

S

.15

o ~---------------------------------3

6

9

12

18

24

36

48

9

6

60

Months Postop

Fig 1. Comparison over time of the mean lines of visual acuity among the four study groups.

rupted sutures (Fig 4). Both the relative differences and the statistical differences between groups persisted through 36 months, except the retained implant group was not statistically different from the Fuchs' group at the 6-month examination period. Manifest refractions or uncorrected visions accounted for the majority of "best-corrected" visual acuities in this study. Only a small percentage of the acuities obtained used contact lenses. Table 8 lists the study population's percentage of best-corrected visual acuities using contact lenses. The increasing use of contact lenses through 24 to 36 months corresponds with increased stability of corneal wounds and complete removal of sutures, but the increasing use was not enough to explain the continued increase in visual acuity through 2 years. Eliminating contact lens visual acuities caused minor changes in the mean lines of visual acuity within groups and no changes in relative rates of visual recovery or statistical differences between groups. During the course of the study, 81 eyes had relaxing incisions using a titrated technique. 14 Eyes per group with relaxing incisions were: secondary lens implant group (39), Fuchs' dystrophy (20), retained lenses (14), and keratoconus (17). Three eyes had wedge resections.

DISCUSSION Before this report, there has been no description of the changes in visual acuity over time for a large group of eyes after penetrating keratoplasty. Most previous studies on visual acuity after keratoplasty have reported best-obtained or last-recorded visual acuity. Reporting the lastobtained visual acuity for a series of eyes with varying lengths of follow-up can significantly skew the data on the degree of visual recovery. For instance, based on our results, if a group of eyes were reported with variable lengths offollow-up in the secondary intraocular lens implant group, eyes with less than 1 year offollow-up would

12

18

24

36

48

60

Months Postop

Fig 2. Comparison over time of the mean decimal equivalent of the Snellen acuity among the four study groups.

Percentage of Eyes with Visual Acuity of 20/40 Over Time

.'"

~ ~ If

100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10

K = Keratoconus

F = Fuchs' S = Secondary Implants R = Retained Implants

5 0 12

18

24

36

48

60

Montha Po.top

Fig 3. Comparison over time of the percentage of eyes in each group attaining a best-corrected visual acuity of 20/40 or better.

shift the mean best-corrected visual acuity to an overall poorer mean visual result. Likewise, reporting only the best-attained visual acuity in the same group of eyes could minimize decreased vision over time that may occur because of recurrent cystoid macular edema, retinal degeneration, glaucoma, or irregular astigmatism. Just as life table analysis provides for more accurate descriptions of graft survival over time,4,5,15-18 plotting visual changes over time, as shown in Figures 1 to 4, minimizes variation and biases introduced by varying lengths of follow-up. It also highlights potential positive or negative changes in vision over time. High-lighting negative influences on vision over time may be important in the future for identifying particular procedures or groups of eyes more prone to eventual visual loss from any number of causes. Cohen et al 19 and Kornmehl et al 20 each reported improved visual acuities between eyes followed for more than 2 years compared with those followed for 12 months after keratoplasty for pseudophakic bullous keratopathy. Koe1181

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Table 7. Cumulative Incidence of Complete Suture Removal Bullous Keratopathy

NA

=

Months

Keratoconus

Fuchs' Dystrophy

Secondary Implants

Retained Implants

3 6 9 12 18 24 36 48 60 72

2/81 (2.5%) 20/80 (25.0%) 25/74 (33.8%) 30/81 (37.0%) 36/66 (54.5%) 28/51 (54.9%) 18/27 (66.7%) 13/18 (72.2%) 6/9 (66.7%) 2/2 (100%)

1/168 (0.6%) 4/154 (2.6%) 12/144 (8.3%) 22/157 (14.0%) 24/125 (19.2%) 29/117 (24.8%) 31/75 (41.3%) 20/43 (46.5%) 9/14 (64.3%) 3/4 (75.0%)

1/365 (0.3%) 19/350 (5.4%) 34/319 (10.0%) 63/357 (17.6%) 78/278 (28.1%) 79/225 (35.1%) 74/128 (57.8%) 41 f72 (56.9%) 21/29 (72.4%) 10/10 (100%)

0/87 (0%) 5/84 (6.0%) 8/73 (11.0%) 9/76 (11.8%) 19/71 (26.8%) 22/58 (37.9%) 16/36 (44.4%) 8/13 (61.5%) 1/2 (50.0%) NA

not applicable.

nig et atzl reported an interesting observation describing a series of eyes with 75% of eyes attaining 20/40 visual acuity after keratoplasty for pseudophakic bullous keratopathy. However, their patients had visual measurements using both a gas permeable hard contact lens and a pinhole; and with refractions, only 35% attained visual acuity of 20/40. Although those authors stated their measured acuity "may not represent functional vision," their study demonstrated many eyes previously believed to have poor visual acuity after keratoplasty may actually have had decreased vision from irregularities in corneal topography and not particularly a loss of vision because of retinal changes. These findings are particularly relevant when evaluating visual acuity results in reported series with short follow-up such as open-loop anterior chamber lenses placed at keratoplasty for pseudophakic bullous keratopathy.22 With longer follow-up, visual acuities may improve. One series with sutured posterior chamber lenses has shown improved visual recovery with longer followUp.23,24 The recovery of visual acuity after keratoplasty is affected by a complex interrelationship of many factors, including healing of the cornea and gradual diminishing of irregular astigmatism. This occurs at varying rates in different individuals and certainly appears to be influenced by the age of the recipient, as younger individuals heal more quickly. This may explain why the group of keratoconus eyes had the most rapid rate of visual recovery. Although suture removal does not completely explain the gradual recovery of vision after keratoplasty, it certainly provides a dramatic and sudden improvement in vision for a number of eyes. Table 7 shows the cumulative incidence of complete suture removal. However, it is difficult to directly correlate complete suture removal with rates of visual recovery between groups. The two groups with the most rapid and best levels of visual recovery, keratoconus and Fuchs', had the fastest and slowest rates of suture removal, respectively. Likewise, the type of suturing technique used can affect the rate of visual recovery.25 1182

12

Eyes With Combined Suture Technique

11

10

K=Keratoconus

F=Fuchs' S=Secondary Implants R=Retained Implants

12

18

24

36

48

Months Postop

Fig 4. Comparison over time of the mean lines of visual acuity among the four study groups when compared eyes were restricted to ones with combined interrupted and running 10-0 nylon sutures.

The secondary and retained implant groups had significantly more eyes with interrupted sutures than the keratoconus and Fuchs' groups. However, when the mean lines of visual acuity between the four groups were compared using only eyes with combined 10-0 nylon running and interrupted sutures, there were only minimal changes compared with the overall results with all suture techniques combined (Figs 1,4). Fitting a contact lens provides for dramatic visual improvement in some cases. In our series, contact lenses were used only after suture removal in eyes not satisfactorily corrected with spectacles. Our incidence of using contact lenses appears low (Table 8) and certainly is much less than reported in keratoconus by Smiddy et al 26 (60%) and Lass et at2 7 (56%). We believe the visual acuities in our report are functional acuities achieved by our patients after keratoplasty. Hard contact lenses were worn for variable amounts of time, depending on the patient, their

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Table 8. Incidence of Using Hard Contact Lenses for Best-corrected Visual Acuity Bullous Keratopathy Months

Keratoconus HCL */No. t /Percentt

Fuchs' Dystrophy HCL * /No.t /Percentt

Secondary Implants HCL */No. t /Percentt

Retained Implants HCL */No.t/Percentt

3 6 9 12 18 24 36 48 60

0/81 (0%) 0/80 (0%) 2/74 (2.7%) 5/81 (6.2%) 7/66 (10.6%) 6/51 (11.8%) 6/27 (22.2%) 2/18 (11.1%) 1/9 (11.1%)

0/168 (0%) 0/154 (0%) 2/144 (1.4%) 2/157 (1.3%) 4/125 (3.2%) 6/117 (5.1%) 4/75 (11.6%) 5/43 (11.6%) 0/14 (0%)

0/365 (0%) 7/350 (2.0%) 16/319 (5.0%) 34/357 (9.5%) 29/278 (10.4%) 29/225 (12'.9%) 22/128 (17.2%) 8/72 (11.1%) 4/29 (13.8%)

2/87 (2.3%) 1/84 (1.2%) 3/73 (4.1%) 4/76 (5.3%) 5/71 (7.0%) 5/58 (8.6%) 6/36 (16.7%) 2/13 (15.4%) 0/2 (0%)

* Number of eyes with visual acuity using hard contact lens at each time interval. t Total number of eyes available with visual acuity measurement at each time interval. t Percentage of eyes using hard contact lens acuity of the number examined for that time period.

needs and abilities. Usually, if patients were unable to have satisfactory visual recovery with either spectacle correction or contact lenses, a relaxing incision or wedge resection was performed. Five eyes in this study were regrafted for astigmatism when either high regular or irregular astigmatism prevented useful vision and the patients were unable to either successfully wear contact lenses or have corrective surgery such as relaxing incisions or wedge resections. "Graft failure" from astigmatism has been reported 15 and has the same indications for grafting as keratoconus. Eyes with cystoid macular edema can take a long time to recover useful vision or show resolution of edema. 28.29 This would especially delay visual recovery in the secondary lens implant group. Price and Whitson 29 have reported a case taking 48 months to recover visual acuity of 20/40 after lens exchange and penetrating keratoplasty for cystoid macular edema with pseudophakic bullous keratopathy. In that particular case of persistent cystoid macular edema, contact lens visions were checked and remained less than 20/40 at both 2 and 3 years after surgery. There was a significant difference between the mean ages in the keratoconus group (42.9 years) and the secondary lens implant group (74.8 years). This difference in mean ages probably helps explain the marked difference in visual recovery between these two groups. Price and Whitson 9 reported the causes of decreased vision in patients with suture-fixated posterior chamber lenses; those problems are seldom encountered in the younger age group undergoing surgery for keratoconus. However, the difference in age may not completely explain the significant difference in visual recovery between the Fuchs' dystrophy group and those with either secondary lenses or the retained lenses. Clinically, there appears to be more that comes into play. Intraoperative inflammation associated with intraocular lens exchange or the continued breakdown of the blood-aqueous barrier after surgery,

with either retained lenses or secondary lenses, may be additional factors affecting visual recovery differences. The analysis of visual acuity results over time may prove Table 9. Hypothetical Visual Changes in a Group of Five Eyes Over Three Measurement Periods* Time Period

III

Snellen Acuity

Decimal Fraction

20/20 20/25 20/30 20/400 CF

1 0.8 0.67 0.05 0.03

20/20 20/40 20/60 20/400 CF

1 0.5 0.33 0.05 0.03

20/20 20/40 20/60 NLP NLP

1 0.5 0.33 0 0

Mean of Group

0.51

0.38

0.37

Lines of Visual Acuity

1 2 3 12 13 1 4 6 12 13 1 4 6 17 17

Mean Lines of Group

6.2

7.2

9.0

CF = counting fingers; NLP = no light perception. * Five hypothetical eyes had visual acuity measurements over three time periods. These visual acuity measurements are converted to the decimal equivalent of a Snellen fraction and to the lines of visual acuity as used in this article. The difference between periods I and II shows two eyes having a loss of two Snellen lines of visual acuity. With two lines of visual acuity loss on the Snellen acuity chart, one goes from 20/25 to 20/40 and one goes from 20/30 to 20/60. There is a dramatic change in the fraction of the Snellen acuity between those measurements. Between periods two and three, two eyes go from 20/400 and counting fingers, respectively, to no light perception. The change in the mean decimal equivalent of the Snellen fraction for the group is minimal (0.01). However, the mean lines of visual acuity shows a pronounced change.

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useful in evaluating surgical procedures and treatment methods. Theoretically, any group of eyes that have undergone keratoplasty should show a peaking of best-corrected visual acuity, a possible plateau, and then a gradual decline. Age-related macular degeneration, glaucoma, recurrent cystoid macular edema, difficulties with the graft, or systemic diseases such as strokes and diabetes, would all cause the gradual decline in vision over time. Evaluating trends in visual acuity could help determine which techniques of implanting lenses are better. By following visual acuity over time, it may be determined if vision recovers at varying rates, as well as if vision begins to deteriorate sooner for different techniques. Analysis of visual acuity data presents a number of difficulties. While Snellen acuities are numerical measurements, analysis of these measurements may not provide meaningful data in all cases, and each different method of presenting this data has limitations. For instance, converting Snellen acuities to a fraction is the simplest and most straightforward means of analysis. Numerically, these measurements can be easily compared. This technique is essentially based on a scale from 1 to 0 with 1 being 20/20 and 0 being no light perception. However, half of the change in the range between 1 and 0 occurs from 20/20 to 20/40. Visual losses after 20/400 become rather meaningless as the equivalent for 20/400 is 0.05. Therefore, this technique will minimize changes that occur in a population having visions of 20/400 deteriorating to lesser acuities of finger counting, hand motions, or loss of vision. However, it is extremely sensitive to changes occurring in acuities between 20/20 and 20/60. Table 9 demonstrates this. Another alternative to analyzing visual acuity changes is to assign "a line of visual acuity to different levels of recorded vision." Using this technique, one chooses numerical lines to correspond to different visual acuities, such as 20/20, 20/25, 20/400, finger counting, or no light perception. In this manner, the numerical designation of the lines of vision can be weighed to show a more significant change in the mean lines of visual acuity for losses of visual acuity from 20/400 to light perception (Table 9). This latter technique is more appropriate in analyzing visual results for procedures where there is a higher proportion of individuals with visual acuity of 20/40 or less, and particularly in groups where there may be a profound visual loss with a number of individuals potentially losing all useful vision, such as going from finger counting to light perception or no light perception. Figure 4 shows that in this study population, there is a sizable number of eyes with visual acuities less than 20/40, especially in the two groups with previous cataract surgery. Corneal transplant patients and those undergoing complicated glaucoma surgeries would probably be best analyzed using the technique with lines of visual acuity. However, groups of patients with relatively good vision, such as those undergoing uncomplicated cataract extraction, would probably be best analyzed using the decimal conversion of the Snellen fraction. Westheimer30 has reported another 1184

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technique of analyzing visual acuity where measurements are scaled to the minimum angle of resolution.

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22. Waring GO III, Kenyon KR, Gemmill MC. Results of anterior segment reconstruction for aphakic and pseudophakic corneal edema. Ophthalmology 1988; 95:836-41. 23. Soong HK, Meyer RF, Sugar A. Posterior chamber IOL implantation during keratoplasty for aphakic or pseudophakic corneal edema. Cornea 1987; 6:306-12. 24. Soong HK, Musch DC, Kowal V, et aI. Implantation of posterior chamber intraocular lenses in the absence of lens capsule during penetrating keratoplasty. Arch Ophthalmol1989; 107:660-5. 25. Olson RJ. Modulation of postkeratoplasty astigmatism by surgical and suturing techniques.lnt Ophthalmol Clin 1983; 23(4):137-51.

26. Smiddy WE, Hamburg TR, Kracher GP, Stark WJ. Keratoconus: contact lens or keratoplasty? Ophthalmology 1988; 95:487-92. 27. Lass JH, Lembach RG, Park S8, et al. Clinical management of keratoconus: a multicenter analysis. Ophthalmology 1990; 97:433-45. 28. Stark WJ, Maumenee AE, Fagadau W, et al. Cystoid macular edema in pseudophakia. Surv Ophthalmol1984; 28(Suppl):442-51. 29. Price FW Jr, Whitson WE. Natural history of cystoid macular edema in pseudophakic bullous keratopathy. J Cataract Refract Surg 1990; 16:163-9. 30. Westheimer G. Scaling of visual acuity measurements. Arch Ophthalmol 1979; 97:327-30.

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