Corneal Topography for Selective Suture Removal After Penetrating Keratoplasty Scott Strelow, M.D., Elisabeth J. Cohen, M.D., Kent G. Leavitt, M.D., and Peter R. Laibson, M.D.

Twenty-nine suture removals from 20 eyes (21 patients) on which penetrating keratoplasty had been performed were analyzed in a nonrandomized consecutive study to evaluate the role of computer-assisted corneal topography in selective suture removal to reduce astigmatism. Topographic guidance for suture removal resulted in a net decrease in refractive and keratometric astigmatism in 21 of the 29 cases. The net reduction in astigmatism averaged 1.4, 0.9, and 1.0 diopters when measured by refraction, keratometry, and topography, respectively. The preliminary choice of sutures to be removed on the basis of refraction, keratometry, and inspection was changed in 20 of the 29 cases when information added by the topographic map was considered. Although many variables of suture removal remain unpredictable, computer-assisted corneal topography is a powerful means of describing corneal power after penetrating keratoplasty and is useful as a guide in selective suture removal for reduction of astigmatism. CORNEAL ASTIGMATISM is often a problem after penetrating keratoplasty and can compromise results. Excessive astigmatism can be associated with poor uncorrected or best-corrected visual acuity, tear film abnormalities, difficult contact-lens fitting, and asthenopic symptoms.' Some of the factors that may contribute to astigmatism are mismatch between donor and host tissues, irregular wound healing, and variations in suture placement and tension.! Vari-

Accepted for publication Aug. 28, 1991. From the Cornea Service, Wills Eye Hospital, Philadelphia, Pennsylvania. This study was supported in part by The Lions Eye Bank of Delaware Valley, Philadelphia, Pennsylvania. Reprint requests to Elisabeth J. Cohen, MoD., Wills Eye Hospital, 9th & Walnut Sts., Philadelphia, PA 19107.

©AMERICAN JOURNAL OF OPHTHALMOLOGY

112:657-665,

ous suture techniques, including interrupted or combined running and interrupted closure, allow for the selective removal of interrupted sutures, with the goal of reducing astigmatism in the postoperative period.!" Successful visual rehabilitation therefore depends in part on accurate identification of the interrupted suture or sutures whose removal would most effectively reduce astigmatism. In practice, this involves identifying the steepest corneal hemimeridian and the tight suture responsible for inducing this steepening. The clinician has several commonly available tools for measuring corneal power and curvature, including refraction, retinoscopy, and keratometry. These tools are limited to describing one steep and one flat corneal meridian, a situation that may be particularly misleading in patients undergoing keratoplasty in whom irregular or complex astigmatism is common (Fig. 1). Keratoscopy and photokeratography are more powerful tools than refraction, retinoscopy, and keratometry for assessing corneal curvature by allowing the localization of hemimeridional steepness and flatness." Multiple steep hemimeridians or subtle contour abnormalities, however, cannot always be easily Interpreted.v" Recently there has been much interest in computer-assisted videokeratography to assess normal and pathologic corneal topography.v" The ability to map subtle corneal power changes accurately over the entire optical zone and beyond gives computer-assisted corneal topography the potential to become the standard for monitoring changes that develop after an operation.6.8.13.14 The purpose of this study was to evaluate the role of computer-assisted videokeratography in selective interrupted suture removal after penetrating keratoplasty for the reduction of graft astigmatism. We used computer-assisted corneal topography on 22 consecutive eyes after penetrating keratoplasty.

DECEMBER,

1991

657

Fig. 1 (Strelow and associates). Diagram and topographic maps from a patient before this study demonstrate the limitation of refraction and keratometry in identifying the steepest meridian. Left, Diagram shows four remaining sutures (short radial lines). The steep meridian by refraction (+4.5 diopters) and keratometry (+5.0 diopters) both indicate removal of the suture near 337 degrees (indicated by the X). This suture was removed. Middle, Topographic map before suture removal. Reliance on this map would have indicated that the steepest hemimeridian corresponds to the suture at 202 degrees. Right, Topographic map four weeks later shows a net increase of 8.9 diopters of astigmatism.

Patients and Methods

Selection of patients-We enrolled 21 patients (22 eyes) between September 1990 and Decem-

ber 1990 who were being monitored after penetrating keratoplasty and who were candidates for selective interrupted suture removal on the basis of excessive residual astigmatism precluding successful spectacle correction. At least

Fig. 2 (Strelow and associates). Diagram and topographic maps demonstrate the utility of topographic guidance for suture removal. Left, Diagram shows 13 remaining sutures. The steep meridians by refraction (+4.3 diopters) and keratometry (+2.5 diopters) identify four possible sutures for removal. The suture removed (indicated by the X) on the basis of the topographic map was not identified by refraction or keratometry. Middle, Topographic map before suture removal demonstrates the flattest and steepest corneal powers along the same meridian. Refraction and keratometry cannot accurately describe this kind of astigmatism. Right, Topographic map three weeks later. The patient had a net reduction of 2.8 diopters of refractive astigmatism and was given spectacles.

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Corneal Topography After Penetrating Keratoplasty

four months had elapsed since the operation. Patients whose visual acuities could not be refracted to 20/400 or better and patients with poor topographic images that could not be analyzed by the computer were excluded from enrollment. Continuity of all Placido ring images within the central 4-mm optical zone (eight rings) was required for entry into the study. Method of examination-A standardized data sheet was compiled on each eye enrolled for each selective suture removal. Surgical history was recorded including indication for penetrating keratoplasty, graft/host trephination diameters, time interval from the operation to suture removal, and suture technique. Careful slitlamp examination included drawing a schematic cornea with precise localization of all remaining sutures. Manifest refraction (retinoscopy with subjective refinement) and keratometry (Haag-Streit keratometer, Leibefeld. Switzerland) were recorded by one of us (5.5.). The steep meridians as identified by refraction and keratometry, respectively, were used to guide slit-lamp identification of tight sutures, thereby localizing the steep corneal hemimeridian. Tight sutures were identified by visible stress lines in the cornea. The surgeon made a preliminary recording of the one or two sutures to be removed on the basis of clinical data alone (refraction, keratometry, and inspection of sutures). Generally, two sutures were chosen for higher degrees of astigmatism and when refraction and keratometry respectively identified differing steep meridians. At this point, computer-assisted videokeratography was used to generate a color-coded topographic map for analysis. The steep corneal hemimeridians were readily identified on the topographic map and were compared to the schematic drawing to locate the suture most closely associated with the steep hemimeridians by topography. One or two sutures were then removed on the basis of the topographic map (Fig. 2). Data were collected on the incidence in which the topographic map analysis resulted in removal of different sutures than had been preliminarily selected on the basis of refraction, keratometry, and inspection of sutures. The information collected by refraction and keratometry was known at the time of topographic analysis, but only sutures correlating with topographic steepness were removed. Patients were reexamined three to five weeks

659

after suture removal for change in uncorrected and best-corrected spectacle acuity, manifest refraction, keratometry, and corneal topography. Method of computer-assisted videokeratography-For each suture removal, computer-assisted videokeratography was performed immediately before suture removal and three to five weeks after suture removal by one of us (5.5.). The EyeSys corneal analyzer (Houston, Texas) was used to generate the color-coded topographic maps. This system consisted of the following: (1) a keratoscope that projects Placido rings onto the anterior corneal surface, (2) a real-time video monitoring system to capture the Placido image, and (3) computerdriven programs to digitize the image and analyze the keratograph using proprietary algorithms. The EyeSys corneal analyzer has been shown to be highly reliable and reproducible on healthy corneas." Topographic maps were then obtained. One drop of artificial tears was instilled onto the cornea to ensure adequate tear film and excessive tear lake was blotted. An eyelid speculum was not used. The patient was instructed to fixate on the central target light on the keratoscope and compliance was checked on the video monitor. The corneal image was properly aligned on the video screen and focused sharply using cross marks projected onto the corneal surface. Two high-quality topographic images were analyzed to ensure reproducibility. Highquality images were judged by absence of excessive tear pooling along the lower eyelid, resulting in image distortion, proper centration, and continuity of all Placido ring images within the central 4-mm optical zone. One topographic image was entered into the computer for processing and was displayed as a color-coded topographic map using the normalized scale. This scale used all 14 colors to describe the specific dioptric range of each cornea. Usually each color step represented a 0.7- to 1.0-diopter power change. The computer program allowed for direct comparison of the topographic maps on the same screen before and after suture removal, using a normalized scale that spanned the specific dioptric range of the two maps. The topographic map was photographed for comparison with the actual suture positions. Method of astigmatism calculation-We calculated the change in astigmatism caused by su-

660

December, 1991

AMERICAN JOURNAL OF OPHTHALMOLOGY

TABLE 1 VISUAL ACUITY AND CLINICAL DATA UNCORRECTED

BEST-CORRECTED

VISION

VISION

MONTHS

CLINICAL SUTURE

AFTER

NO. OF

BEFORE

AFTER

BEFORE

AFTER

CHOICE

PATIENT

DIAGNOSIS (ORIGINAL

THE

SUTURES

SUTURE

SUTURE

SUTURE

SUTURE

CHANGED BY

NO.'

GRAFT INDICATION)

OPERATION

REMOVED

REMOVAL

REMOVAL

REMOVAL

REMOVAL

TOPOGRAPHY

30 23 11

2 1

1 2

Chandler's syndrome Keratoconus

Yes

20/80

20/200

20/30

20/60 20/100

20/60 20/70

20/30 20/20

20/15

No Yes

20/20 20/25

3

Graft failure (scar)

4A

Pseudophakic bullous keratopathy Pseudophakic bullous keratopathy

12

20/100

20/80

20/100

20/70

Yes

13

20/80

20/70

20/70

20/70

Yes

Pseudophakic bullous keratopathy Fuchs' syndrome Fuchs'syndrome

14

20/70

20/70

20/70

20/50

Yes

4B 4C 5t 6A 68 7 8A* 8B 9 10 11 12

12

1

20/200

20/200

2 2

20/300

20/40 20/70

20/50 20/50

No Yes

1

20/300 20/300 20/800

20/50 20/800

20/50 20/50

20/50 20/25

Yes No

Keratoconus Keratoconus

11 12

2 2

20/60 20/80

20/80 20/40

20/50 20/40

20/40 20/25

Yes Yes

Pseudophakic bullous keratopathy Pseudophakic bullous keratopathy Keratoconus

13

1

20/50

20/60

20/40

20/30

No

55

2

20/800

20/800

20/50

20/30

Yes

20/400 20/50 20/80 20/800

20/400 20/50 20/100

20/20

20/15 20/40 20/20 20/50

No Yes No Yes

20/70 20/30

No Yes

20/50 20/40

Yes Yes

Fuchs' syndrome Pseudophakic bullous keratopathy

13 14, R.E.

29 12 49 41

14, L.E.

Fuchs' syndrome

16

15 16

Keratoconus Fuchs' syndrome

17 18A 18B

Pseudophakic bullous keratopathy Fuchs' syndrome Fuchs' syndrome

25 31 4

18C 180

Fuchs' syndrome Fuchs' syndrome

18E 19

Fuchs' syndrome Fuchs' syndrome Graft failure (ulcer)

218*

2

25 26 51

Interstitial keratitis Keratoconus Pseudophakic bullous keratopathy

20 21A

2

Graft failure (pseudophakic bullous keratopathy) Graft failure (pseudophakic bullous keratopathy)

17 18 18 19 19 31 11 11

20/100 20/60 20/70 20/60

20/50

20/50 20/25 20/60

20/80

20/70

20/70 20/70

20/30 20/40

20/70

20/50 20/60 20/50 20/50

2 2 2 1

20/300 20/300 20/80 20/400

20/300 20/80 20/400 20/400

2 1 1 2

20/400 20/80 20/200 20/80

20/200 20/30 20/100 20/100

20/100

20/100

12

-A,B,C,D,E indicate separate suture removals in the same eye. tNot included in data analysis. *Combined running/interrupted suture technique used in Patient 8.

20/50

No

20/80 20/60 20/30 20/50 20/50

20/50 20/80 20/60 20/40 20/30 20/40 20/50

Yes Yes No Yes Yes Yes No

20/50

20/50

Yes

661

Corneal Topography After Penetrating Keratoplasty

Vol. 112, No.6

TABLE 2

ASTIGMATISM BEFORE AND AFTER SUTURE REMOVAL SUTURE INDUCED REFRACTIVE

KERATOMETRIC

TOPOGRAPHIC

TOPOGRAPHIC

ASTIGMATISM (DIOPTERS)

ASTIGMATISM (DIOPTERS)

ASTIGMATISM (DIOPTERS)

POWER (DIOPTERS)t

BEFORE

AFTER

BEFORE

AFTER

BEFORE

AFTER

BEFORE

AFTER

PATIENT

SUTURE

SUTURE

SUTURE

SUTURE

SUTURE

SUTURE

SUTURE

SUTURE

NO.'

REMOVAL

REMOVAL

REMOVAL

REMOVAL

REMOVAL

REMOVAL

REMOVAL

REMOVAL

3.3 5.8 3.5 2.5 3.0 3.8 7.5 7.0 6.0 5.0 3.5 1.5 5.0 5.0 3.8 5.0 6.5 7.5 4.0 2.8 5.8 1.5 4.0 3.8 2.5 6.0 4.8 3.5 4.3 7.5 2.0

4.0 4.0 1.3 3.0 3.8 1.5 6.3 6.0 0.0 2.5 1.5 2.5

0.5 13.5 4.5 2.5 5.0 1.0 8.5 6.0 15.5 3.0 7.0 5.0 7.5 4.0 5.5 8.0 5.5 9.0 4.5 2.0 6.5 6.0 7.5 5.0 1.0 10.0 6.0 2.5 2.5 5.5 3.0

3.0 11.0 1.5 5.0 1.0 3.5 NA 15.5 13.0 3.0 5.0 1.0 4.0 9.0 3.5 2.5 4.5 3.5 1.5 1.3 8.0 3.0 5.0 1.0 10.0 6.0 5.0 1.0 1.5 3.0 NA

4.5 9.6 5.0 10.0 6.5 5.8 9.7 6.6 9.9 7.0 3.8 6.9 8.6 6.3 6.3 9.1 5.0 7.9 5.3 3.4 12.3 7.6 7.8 7.5 8.3 10.9 8.2 4.7 3.8 9.4 9.0

4.6 12.3 1.8 6.5 5.8 4.1 NA 9.9 13.1 3.1 6.9 2.2 5.8 5.3 3.5 5.5

49.7

50.5

46.4 48.9

46.0 42.7

46.9

NA

51.8

47.3

46.7

46.4

46.6 49.6

46.2 44.6 46.9

1 2 3 4A 48 4C 5* 6A 68 7

8A' 88 9 10

11 12 13 14, R.E. 14, L.E. 15 16 17

18A 188

18C 180

18E 19 20

21A

218*

1.8

9.5 3.0 0.3 4.5

1.8

1.0 0.0 7.5 1.5 3.8 2.5 6.0 4.8 4.0 1.5 1.5 2.0 5.0

4.4

7.8 3.6 2.2 7.8 4.6 7.5 8.3 10.9 8.2 7.1 4.1 2.2 9.0 NA

46.7 47.9 43.2 48.1 44.8 50.1

47.7 40.4 46.6 42.7 47.7

50.7

47.3

46.8 45.7

45.4 45.4

52.0

NA

'A,8,C,D,E indicates separate suture removals in the same eye. tPower at the 3-mm optic zone of the steep hemimeridian corresponding to the tight suture removed. *Not included in data analysis. 'Combined running/interrupted suture technique used in Patient 8. NA indicates data not attainable because of poor epithelial surface.

ture removal in terms of refractive astigmatism, keratometric astigmatism, and topographic astigmatism. The goal of selective suture removal is to move from a more irregular astigmatic contour toward a more regular spherical contour. Therefore, net astigmatic change was

calculated for refractive and keratometric astigmatism using simple subtraction of dioptric astigmatism before and after suture removal without regard to axis shift. The change in astigmatism was expressed as a positive (+) value if astigmatism increased and a negative

662

AMERICAN JOURNAL OF OPHTHALMOLOGY

December, 1991

Fig. 3 (Strelow and associates). Topographic maps of the right eye demonstrate that there is less refractive cylinder and better uncorrected visual acuity than might be predicted on the basis of the topographic map. Left, Topographic map before suture removal. The patient had 20/800 uncorrected visual acuity and 7.5 diopters of refractive cylinder. A suture was removed at the 165-degree hemimeridian. Right, Topographic map three weeks later. Uncorrected visual acuity has improved to 20/50 with a net decrease of 5.7 diopters of refractive astigmatism. By topographic measurement, 7.8 diopters of astigmatism remains, but the pattern of residual astigmatism demonstrated by topography apparently does not adversely affect the visual axis.

(-) value if astigmatism decreased. For refractive astigmatism, the difference in plus cylinder was used. For keratometric astigmatism, the dioptric difference between the steep and flat meridians were compared before and after suture removal. Topographic astigmatism was measured at specific points on the digitized color map to allow a truly hemimeridional assessment of power. Current computer-driven algorithms calculate and diagram the steep and flat meridians in graphic form. These meridians represent the average steepest and average flattest meridians and are not useful for choosing the steepest hemimeridian that corresponds to a specific suture. We chose the dioptric power represented by the data point closest to the 3-mm optical zone at the steepest and flattest hemimeridians. The dioptric difference between these two points represents the topographic astigmatism at the 3-mm optical zone. This method allows for more accurate description of the extremes of corneal power change than do averaging techniques across an entire meridian. This is especially true in irregular astigmatism in which the steep and the flat hemimeridians may line up in the same meridian. The change in topographic astigmatism after suture removal was expressed in diopters as positive (+) if astigmatism in-

creased and negative (-) if astigmatism decreased. For patients in whom a single suture was removed in the steep hemimeridian, the amount of astigmatism in-duced by that suture can be directly measured by topography. In this measurement the steep hemimeridian influenced by the tight suture is measured at the 3-mm optical zone before suture removal. The measurement is repeated after suture removal at the same point on the topographic map and simple subtraction will yield the astigmatism induced by the suture. Method of visual acuity measurement-Standard projected Snellen visual acuity was meaTABLE 3 POSTSURGICAL INTERVAL TO SELECTIVE SUTURE REMOVAL TIME (MONTHS)

NO. OF EYES

4-6 7-12 13-24 25-36 37-48

1 6 4 6 1 3

~49

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Corneal Topography After Penetrating Keratoplasty

TABLE 4 EFFECT OF SELECTIVE SUTURE REMOVAL ON ASTIGMATISM (N

Topographic astigmatism Keratometric astigmatism Refractive astigmatism

663

= 29)

NO. OF EYES

NO. OF EYES

NO. OF EYES

WITH IMPROVED

WITH UNCHANGED

WITH WORSE

ASTIGMATISM (%)

ASTIGMATISM (%)

ASTIGMATISM (%)

22 (76%)

0(0%)

7(24%)

21 (72%)

1 (3%)

7(24%)

21 (72%)

1 (3%)

7(24%)

sured for both uncorrected and best-corrected visual acuity.

Results

Twenty-two eyes from 21 patients encompassing 31 suture removals were entered into the study (Tables 1 and 2). Two patients could not be included for data analysis because of poor keratographic and keratometric mires after suture removal. In both patients, this was caused by epitheliopathy. Best-corrected visual acuity was unchanged in one patient and worse by one line in the other patient three weeks after suture removal. Therefore, data analysis included 21 eyes from 20 patients and 29 suture removals. One patient who underwent suture removal in both eyes was entered into the study. Four patients had more than one suture removal entered. The predominant surgical technique used was 16 interrupted 10-0 nylon suture closures in 20 eyes. The remaining eye was closed with a continuous 16-bite 10-0 nylon combined with eight interrupted 10-0 nylon sutures. The grafts were oversized 0.2 mm or 0.5 mm in all cases. Indications for penetrating keratoplasty were determined (Table 1). Time intervals between the operation and selective suture removal were also determined (Table 3). Selective suture removal using topographic guidance resulted in a net decrease in astigmatism in over 70% of cases (22 of 29 cases; Table 4). The net reduction in astigmatism averaged 1.0 ± 2.4, 0.9 ± 3.8, and 1.4 ± 2.5 diopters when measured by topography, keratome try, and refraction, respectively (Table 5). Topographically measured suture-induced astigmatism in the steep hemimeridian decreased an

average of 2.1 diopters (range, +0.8 to -7.4 diopters) when a single suture was removed in that hemimeridian. Topographic guidance for selective suture removal resulted in improvement of either uncorrected or best-corrected visual acuity in 25 of 29 patients (86%). Two of the four remaining patients maintained their same best-corrected visual acuity but with less refractive astigmatism (net decrease of 2.8 and 5.6 diopters, respectively). The two remaining patients (7%) had a net increase (+1.8 and +3.5 diopters) in refractive astigmatism, losing one and three lines of best-corrected visual acuity, respectively, with increased irregular astigmatism. The preliminary clinical impression (determined on the basis of keratometry, refraction, and inspection) of sutures to be removed was changed in 20 of 29 cases (69%) when the topographic map was considered. No suture was removed without topographic evidence for a corresponding steep hemimeridian. In some cases (nine of 29), topography merely confirmed the clinical choice made by keratometry, refraction, and inspection. In the other cases, TABLE 5

EFFECT OF SELECTIVE SUTURE REMOVAL ON ASTIGMATISM (N = 29) NET REDUCTION IN

Topographic astigmatism Keratometric astigmatism Refractive astigmatism

ASTIGMATISM

STANDARD

RANGE

(DIOPTERS)

DEVIATION

(DIOPTERS)

- 1.0

± 2.4

+ 3.4 to - 4.8

- 0.9

± 3.8

+ 9.5 to - 5.5

- 1.4

± 2.5

+ 4.5 to - 6.0

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December, 1991

AMERICAN JOURNAL OF OPHTHALMOLOGY

TABLE 6 TOPOGRAPHIC SELECTION OF A SINGLE SUTURE FOR REMOVAL MEAN DECREASE IN ASTIGMATISM IN DIOPTERS (S.D.) CLINICAL CHOICE

CLINICAL CHOICE

OF SUTURE

OF SUTURE

METHOD OF

CONFIRMED BY

CHANGED BY TOPOGRAPHY

ASTIGMATISM

TOPOGRAPHY

MEASUREMENT

IN 7 EYES

IN 9 EYES

Topography

- 1.7 (2.2)

- 2.1 (1.6)

Keratometry

- 2.3 (1.4)

- 1.9 (2.8)

Refraction

- 2.1 (0.9)

- 1.7 (2.6)

however, the topographic map added information that changed the meridian, the hemimeridian, or the number of sutures removed. The effect of topography in changing the clinical choice of which suture to remove may be most directly evaluated in the cases of single suture removal. Reduction of astigmatism when the clinically chosen suture was confirmed by topography was not different as compared to when the clinically chosen suture was changed on the basis of topography. Topographically removed sutures were efficacious in decreasing astigmatism even when keratometry, refraction, and inspection would indicate a different suture (Table 6).

Discussion

Topography has become an integral part of our method of selective suture removal for reduction of astigmatism after penetrating keratoplasty. This study demonstrated the efficacy of using topography to reduce astigmatism by guiding suture removal. Many variables of suture removal still remain unpredictable with a considerable range in the amount of astigmatic change. We were surprised at the number of times a clinical decision to remove a suture based on refraction, keratometry, and inspection of sutures led us to a different suture choice than did topography. This study was not designed to show that topography is better or worse than refraction, keratometry, and inspection in choosing a suture to be removed. Rather, this study was conducted to indicate whether topography could fulfill its theoretical promise to be a standard guide in selective suture removal. Despite our use of topography, refraction remains essential as the' overall indicator of

visual acuity function. After keratoplasty, the cornea may be a truly multifocal surface. This can be demonstrated by topography and explains the various refractions often found after penetrating keratoplasty. A multifocal surface can also explain better uncorrected visual acuity or less refractive cylinder than would have been predicted on the basis of the topographic map (Fig. 3). We do not routinely remove sutures in patients with a crisp low cylinder refraction that provides good visual acuity. Our end point is good visual acuity regardless of how astigmatic or irregular the topographic map may appear. In analyzing our data, it was evident that single suture removal was more efficacious and predictable at decreasing astigmatism than was the removal of multiple sutures at one time. We were unable to make this conclusion, however, because of our inability to separate the confounding variable of preexisting irregular astigmatism. Irregular astigmatism exists when there is variation in corneal curvature along a given meridian or when the intersection of the steep and flat meridians is other than 90 degrees. In this analysis, patients with high degrees of irregular astigmatism were identified when the steep meridional measurements by refraction and keratometry did not correlate with the steep hemimeridians of the topographic map. Patients who had two sutures removed at one time were 2.5 times more likely to have high degrees of preexisting irregular astigmatism than were patients who had only a single suture removed. It may be the degree of preexisting astigmatic irregularity, rather than the dioptric amount of astigmatism or the number of sutures removed, that is more important in the predictability of suture removal to reduce astigmatism. This study demonstrated that corneal topography using the EyeSys corneal analyzer is a

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Corneal Topography After Penetrating Keratoplasty

reliable method of analyzing corneal power after penetrating keratoplasty to guide in selective suture removal. The importance of information provided by computerized corneal topography in facilitating visual acuity rehabilitation of patients undergoing penetrating keratoplasty remains to be decided and the superiority of topography over keratography or hand-held keratoscopy is still uncertain. The role of predictably and simultaneously removing multiple sutures and the role of decreasing the time interval between suture removals in speeding rehabilitation also remain uncertain. Some topographic patterns may also predict an unstable wound or increased unpredictability with multiple suture removal. Many questions remain to be addressed in future studies if this new technology is to realize its potential and justify its expense.

References 1. Binder, P. 5.: The effect of suture removal on postkeratoplasty astigmatism. Am. J. Ophthalmol. 105:637,1988. 2. Harris, D. J., Waring, G. O. III, and Burk, L. L.: Keratography as a guide to selective suture removal for the reduction of astigmatism after penetrating keratoplasty. Ophthalmology 96:1597, 1989. 3. Feldman, S. T., and Brown, S. I.: Reduction of astigmatism after keratoplasty. Am. J. Ophthalmol. 103:477,1987. 4. Burk, L. L., Radjee, B., Waring, G. O. III, and Stulting, R. D.: The effect of selective suture removal on astigmatism following penetrating keratoplasty. Ophthalmic Surg. 19:849, 1988. 5. Klyce, S. D.: Computer-assisted corneal topography. High-resolution graphic presentation and

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analysis of keratoscopy. Invest. Ophthalmol. Vis. Sci. 25:1426,1984. 6. Wilson, S. E., and Klyce, S. D.: Advances in the analysis of corneal topography. Surv. Ophthalmol. 35:269,1991. 7. Bogan, S. J., Waring, G. O. III, Ibrahim, 0., Drews, C.; and Curtis, L.: Classification on normal corneal topography based on computer-assisted videokeratography. Arch. Ophthalmol. 108:945, 1990. 8. Hannush, S. B., Crawford, S. L., Waring, G. O. III, Gemmill, M. c.. Lynn, M. J., and Nizam, A.: Reproducibility of normal corneal power measurements with a keratometer, photokeratoscope, and video imaging system. Arch. Ophthalmol. 108:539, 1990. 9. McDonnell, P. J., Carbus, J., and Lopez, P. F.: Topographic analysis and visual acuity after radial keratotomy. Am. J. Ophthalmol. 106:692, 1988. 10. Wilson, S. E., Lin, D. T. c.. Klyce, S. D., Reidy, J. J., and lnsler, M.S.: Topographic changes in contact lens-induced corneal warpage. Ophthalmology 97:734, 1990. 11. Lin, D. T. c.. Wilson, S. E., Klyce, S. D., and Insler, M.S.: Topographic changes that occur with 10-0 nylon suture removal following penetrating keratoplasty. Refract. Corneal Surg. 6:21, 1990. 12. Lin, D. T. c.. Wilson, S. E., Reidy, J. J., Klyce, S. D., McDonald, M. B., Kaufman, H. E., and McNeill, J. I.: An adjustable single running suture technique to reduce post keratoplasty astigmatism. A preliminary report. Ophthalmology 97:934, 1990. 13. Hannush, S. B., Crawford, S. L., Waring, G. O. III, Gemmill, M. c.. Lynn, M. J., and Nizam, A.: Accuracy and precision of keratome try, photokeratoscopy, and corneal modeling on calibrated steel balls. Arch. Ophthalmol. 107:1235, 1989. 14. Williams, C. H., Hannush, S. B., Reynolds, D. R., and Menduke, H.: Reproducibrlity of normal corneal power measurements with a keratometer and a videokeratoscope. ARVO abstracts. Supplement to Invest. Ophthalmol. Vis. Sci. Philadelphia, J. B. Lippincott, 1991, p. 999.

Corneal topography for selective suture removal after penetrating keratoplasty.

Twenty-nine suture removals from 20 eyes (21 patients) on which penetrating keratoplasty had been performed were analyzed in a nonrandomized consecuti...
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