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Long-Term Changes in Corneal Surface Configuration After Penetrating Keratoplasty
Long-Term Changes in Corneal Surface Configuration After Penetrating Keratoplasty KEN HAYASHI, MD, AND HIDEYUKI HAYASHI, MD
● PURPOSE:
To examine the long-term longitudinal changes in corneal surface configuration as determined by Fourier series harmonic analysis of videokeratography data and of visual acuity and refraction after penetrating keratoplasty (PK). ● DESIGN: Interventional case series. ● METHODS: One hundred thirty eyes of 130 consecutive patients who were scheduled for PK using 16 interrupted 10-0 nylon sutures were recruited. Spherical equivalent power, regular astigmatism component, irregular astigmatism (asymmetry and higher-order irregularity) component of the central cornea as determined by Fourier analysis of videokeragraphic data, spectacle-corrected visual acuity, and spherical equivalent were examined at 1 week, and at 1, 3, 6, 9, 12, 18, and 24 months after PK. ● RESULTS: Spherical equivalent power increased considerably for up to 1 month after PK, but thereafter showed no further appreciable change up to the final follow-up at 24 months. The regular astigmatism component decreased markedly for up to 6 months after PK, while the total irregular astigmatism (sum of the asymmetry and higher-order irregularity) component decreased considerably up to approximately 3 months, and then these showed no further relevant change for up to 24 months. Spectacle-corrected visual acuity also improved markedly until approximately 3 months after PK, after which it was virtually stable. Furthermore, important correlations were found between regular and irregular astigmatism and the spectacle-corrected visual acuity. ● CONCLUSIONS: Corneal surface configuration after PK appears to be stable by approximately 6 months after PK, concurrent with postkeratoplasty stabilization of visual acuity. (Am J Ophthalmol 2006;141:241–247. © 2006 by Elsevier Inc. All rights reserved.)
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useful in the assessment of corneal surface configuration because it provides many advantages over keratometry. Corneal topographic analysis is essential for assessment of corneal configuration before many types of corneal surgery and can substantially show any changes arising from the surgery.1–5 Specifically, Fourier series harmonic analysis has been applied recently to videokeratography data and has helped to clarify even minute changes in the corneal configuration attributable to anterior segment surgeries including keratoplasty,6,7 photorefractive keratectomy,8,9 cataract surgery,10 –12 pterygium surgery,13 and trabeculectomy.14 It is known that the corneal configuration changes with time after penetrating keratoplasty (PK). Knowledge of temporal changes in the configuration of the transplanted cornea is of particular importance in making the decision of when astigmatic keratotomy should be performed, and when compression sutures should be placed. Many previous studies using videokeratography reported the topographic pattern of the transplanted cornea15,16 and the effect of suture removal on corneal shape after PK.4,6,17,18 However, only one study described short-term topographic changes of the graft after PK, and that study involved only eight patients, each of whom had keratoconus.19 The purpose of the study described herein was to examine the long-term longitudinal changes in corneal surface configuration after PK. To quantitatively evaluate even minute changes, we used Fourier analysis of videokeratography data. Additionally, temporal changes in visual acuity were examined and correlated with the corneal surface configuration.
PATIENTS AND METHODS ● PATIENTS:
Accepted for publication Aug 25, 2005. From the Hayashi Eye Hospital, Fukuoka, Japan (K.H.) and the Department of Ophthalmology, School of Medicine, Fukuoka University, Fukuoka, Japan (H.H.). Inquiries to Ken Hayashi, MD, Hayashi Eye Hospital, 4-7-13 Hakataekimae, Hakata-Ku, Fukuoka 812, Japan; e-mail: [email protected] 0002-9394/06/$32.00 doi:10.1016/j.ajo.2005.08.062
©
2006 BY
One hundred eighty-nine eyes of 189 consecutive patients scheduled for PK between October 1998 and July 2003 at Hayashi Eye Hospital were originally included in this study. When both eyes underwent PK, only the eye operated on first was included. The hospital’s Institutional Review Board approved the study protocol, and all patients provided informed consent.
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sutured in place with 16 interrupted 10-0 nylon sutures. At the conclusion of surgery, corneal astigmatism was adjusted by replacing tight or loose sutures, the presence of which was confirmed with a Maloney ring. In simultaneous PK and cataract surgery, the anterior capsulotomy was made with small scissors and toothed forceps in an attempt to make a circular capsulorrhexis. The nucleus was expressed using bimanual push and pull hooks or forceps, and the residual cortex was aspirated using the Simcoe irrigation-aspiration unit. After suturing the donor cornea with four interrupted nylon sutures, the lens capsule was inflated with hyaluronate sodium 1% (Healon; AMO, Santa Anna, California, USA). A 6.0-mm hydrophobic acrylic IOL (MA60BM or MA60AC, Alcon Surgical, Fort Worth, Texas, USA) or polymethyl-methacrylate IOL (MZ60BD, Alcon Surgical) was then implanted in the capsular bag. When posterior capsule rupture or zonular dehiscence occurred, scleral suturing of an IOL with eyelets (CZ60BD, Alcon Surgical) was performed. After constriction of the pupil with acetylcholine, 12 interrupted sutures were added.
TABLE 1. Preoperative Diagnosis of Patients Undergoing Penetrating Keratoplasty Preoperative Diagnosis
Number of Patients (%)
Bullous keratopathy Keratoconus Stromal scar* Stromal dystrophy Ulcer Trauma Total
56 (43.1%) 41 (31.5%) 24 (18.5%) 5 (3.8%) 3 (2.3%) 1 (0.8%) 130 (100%)
*Includes stromal opacity attributable to herpetic keratitis.
● SELECTIVE SUTURE REMOVAL: During follow-up, selective removal of the tight sutures was performed to decrease total astigmatism. When total astigmatism was 3 diopters or greater, tight sutures, the presence of which was confirmed by keratometry and videokeratography (Topographic Modeling System [TMS]; Tomey, Nagoya, Japan), were removed individually by the surgeon at 2 or more months after PK. When astigmatism was stable within 3 diopters, residual sutures were left in situ until they loosened.
FIGURE 1. Changes in mean (ⴞSD) spherical equivalent power of the central cornea after penetrating keratoplasty (PK) as determined by Fourier analysis. The mean spherical equivalent power increased considerably for up to 1 month after PK, but then did not change markedly for up to 24 months. When comparing each 2 time points, a P value of less than .0018 is considered to be statistically significant (asterisk).
● MAIN OUTCOME MEASURES:
All patients underwent videokeratography, visual acuity measurement, and determination of refractive status at 1 week and at 1, 3, 6, 9, 12, 18, and 24 months after surgery. The videokeratographic examination was made using the TMS. Best spectaclecorrected visual acuity was determined using decimal charts at each interval, and was converted to a logarithm of minimal angle of resolution (logMAR) scale for statistical analysis. The spherical and cylindrical refractive powers were measured using an autokerato-refractometer (KR-7100; Topcon, Tokyo, Japan). The spherical equivalent value was determined as the spherical power minus half the cylindrical power. Videokeratograhic data stored in the TMS computer were used for determination of spherical equivalent power, regular astigmatism, and irregular astigmatism of the central cornea by Fourier series harmonic analysis, which has been described previously.11,14 In brief, the dioptric powers on a mire ring i, Fi(E-), are transformed into trigonometric components as follows: Fi共兲 ⫽ a0 ⫹ c1cos共 ⫺ ␣1兲 ⫹ c2cos 2共 ⫺ ␣2兲 ⫹ c3cos 3共 ⫺ ␣3兲 ⫹ · · · ⫹ cncos n 共 ⫺ ␣n兲 where a0 is the spherical equivalent power of the ring, c1 the asymmetry component, c2 the regular astig-
● SURGICAL PROCEDURES:
All surgeries were performed by a single surgeon (K.H.) using the same surgical procedures in all cases. Surgery was performed under regional anesthesia consisting of a retrobulbar block and a seventhnerve block. For eyes scheduled for PK alone, miosis was induced with pilocarpine 3%, while full mydriasis was induced for eyes scheduled for combined PK and cataract extraction with posterior chamber intraocular lens (IOL) implantation. Donor corneas were punched out from the endothelial side with a Barron donor punch (Katena Products, Denville, New Jersey, USA) with a diameter that was the same as that of the recipient in keratoconus cases and 0.25-mm larger in the other cases. After placement of a single Flieringa ring using six 7-0 silk sutures, the recipient cornea was incised with a Hessburg-Barron vacuum trephine (Katena Products) with a 7.5- or 7.75-mm diameter. Removal of the cornea was completed with curved corneal scissors, after which the donor cornea was
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FIGURE 2. Changes in mean (ⴞSD) regular astigmatism component after penetrating keratoplasty (PK) as determined by Fourier analysis. The mean regular astigmatism component decreased significantly for up to approximately 6 months after PK, but then it showed no further relevant change for up to 24 months. When comparing each 2 time points, a P value of less than .0018 is considered to be statistically significant (asterisk), and a P value of less than .0050 is regarded as marginally significant (dagger).
FIGURE 4. Changes in mean (ⴞSD) higher-order irregularity component after penetrating keratoplasty (PK) as determined by Fourier analysis. The higher-order irregularity component decreased significantly for up to approximately 3 months after PK, but then it showed no further marked change for up to 24 months. When comparing each 2 time points, a P value of less than .0018 is considered to be statistically significant (asterisk) while a P value of less than .0050 is regarded as marginally significant (dagger).
(c3. . . n) components can be regarded as irregular astigmatism. In this study, these calculations were performed on rings 2 through 9, which correspond to the central 3.0 mm optical zone of the cornea. The average of the eight rings was calculated and considered to be the representative value of each component. All examinations were performed by ophthalmic technicians. ● STATISTICAL ANALYSIS:
FIGURE 3. Changes in mean (ⴞSD) asymmetry component after penetrating keratoplasty (PK) as determined by Fourier analysis. The mean asymmetry component decreased significantly for up to 1 month after PK, but then showed no further significant change for up to 24 months. When comparing each 2 time points, a P value of less than .0018 is considered statistically significant (asterisk).
matic component, and c3. . . n the third and higher-order irregularity components. Spherical equivalent power (a0) and the second order harmonic regular astigmatism component (c2) can theoretically be corrected by a spherocylindrical lens, while the first-order harmonic asymmetry component (c1) and third and higher-order irregularity VOL. 141, NO. 2
Temporal changes in spherical equivalent power, regular astigmatism component, asymmetry component, and higher-order irregularity component as determined by Fourier analysis, logMAR visual acuity, and manifest spherical equivalent were tested by means of the Kruskal-Wallis test. When the overall change was considerable, the difference between each 2 time points was further compared by use of the Mann-Whitney U test with the Bonferroni adjustment. The spherical equivalent power and regular and irregular astigmatism components were correlated with the logMAR visual acuity using a simple correlation analysis. Any differences showing a P value of less than .05 were considered to be statistically significant.
RESULTS OF THE 189 PATIENTS ORIGINALLY ENROLLED, 59 (31.2%)
were excluded during the follow-up. The reasons for exclusion were graft failure in 13 patients (6.9%), undergoing cataract or glaucoma surgery after PK in 21 (11.1%),
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TABLE 2. Simple Correlation Coefficients Between Regular and Irregular Astigmatism Components and Spectacle-Corrected logMAR Visual Acuity Following Penetrating Keratiplasty
Postoperative Interval
Regular astigmatism component 1 week 1 month 3 months 6 months 9 months 12 months 18 months 24 months Irregular astigmatism component‡ 1 week 1 month 3 months 6 months 9 months 12 months 18 months 24 months
FIGURE 5. Changes in mean (ⴞSD) spectacle-corrected logMAR visual acuity after penetrating keratoplasty (PK). Mean spectacle-corrected visual acuity improved considerably for up to approximately 3 months after PK, but then it showed no further significant improvement. When comparing each 2 time points, a P value of less than .0018 is considered to be statistically significant (asterisk), while a P value of less than .0050 is regarded as marginally significant (dagger).
Correlation Coefficient
P Value
0.486 0.550 0.374 0.516 0.356 0.361 0.372 0.158
⬍.0001* ⬍.0001* ⬍.0001* ⬍.0001* ⬍.0001* ⬍.0001* ⬍.0001* .0725†
0.490 0.314 0.329 0.416 0.502 0.424 0.423 0.311
⬍.0001* .0003* .0001* ⬍.0001* ⬍.0001* ⬍.0001* ⬍.0001* .0003*
*Statistically significant correlation. † No statistically significant correlation. ‡ Sum of the asymmetry and higher-order irregularity components.
The average age of the patients (⫾SD) was 58.7 ⫾ 20.0 years, with a range of 19 to 85 years. There were 68 men and 62 women. The preoperative diagnoses of these patients are shown in Table 1. Of the 130 patients analyzed, 19 (14.6%) did not undergo selective suture removal. Selective removal of the tight sutures were completed between 2 and 6 months after PK in 86 patients (66.2%), while the other 25 (19.2%) continued to undergo selective suture removal for up to 6 months or later. The spherical equivalent power, regular astigmatism component, asymmetry component, and higher-order irregularity component as determined by Fourier analysis, spectacle-corrected logMAR visual acuity, and manifest spherical equivalent changed remarkably during the 24month follow-up (P ⬍ .0001, Kruskal-Wallis test). Figure 1 shows changes in mean (⫾SD) spherical equivalent power of the central cornea. The spherical equivalent power increased significantly for up to 1 month after PK, but remained relatively unchanged thereafter. Additionally, no significant correlation was found between the spherical equivalent power and spectacle-corrected logMAR visual acuity for each patient throughout the 24-month follow-up period. Figure 2 shows changes in the mean (⫾SD) regular astigmatism component. The mean regular astigmatism component decreased considerably for up to approximately
FIGURE 6. Changes in mean (ⴞSD) manifest spherical equivalent after penetrating keratoplasty (PK). The mean manifest spherical equivalent changed appreciably towards myopia for up to approximately 1 month after PK, but then it showed no further significant change. When comparing each 2 time points, a P value of less than .0018 is considered to be statistically significant (asterisk).
moving out of the area in 3 (1.6%), and lost to follow-up because of a scheduling conflict in 11 (5.8%). We also excluded 11 patients (5.8%) whose visual acuity throughout the follow-up period was 2/20 or worse because of amblyopia in 4 (2.1%), glaucomatous central visual field defects in 3 (1.6%), and macular degeneration in 4 (2.1%). A total of 130 patients (68.8%) thus remained for analysis. 244
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6 months after PK, but then showed no further significant change up to the 24-month cut-off point. Changes in mean (⫾SD) asymmetry and higher-order irregularity components are shown in Figures 3 and 4, respectively. The asymmetry component decreased significantly for up to 1 month after PK, while the higher-order irregularity component decreased for up to approximately 3 months, but there was no further significant change in these parameters for up to 24 months. Additionally, the total amount of irregular astigmatism (sum of asymmetry and higher-order irregularity components) decreased significantly for up to 3 months after PK, which indicates a concurrent stabilization of spectacle-corrected visual acuity and irregular astigmatism. Figure 5 shows mean (⫾SD) spectacle-corrected logMAR visual acuity. Mean spectacle-corrected logMAR visual acuity improved significantly for up to approximately 3 months after PK, and then showed no further significant improvement. The mean manifest spherical equivalent changed significantly towards myopia for up to approximately 1 month after PK, and then showed no further significant change (Figure 6). Table 2 shows the simple correlation coefficients between regular astigmatism and irregular astigmatism components and logMAR visual acuity. For each patient, a significant correlation was found between these components and the spectacle-corrected logMAR visual acuity.
DISCUSSION OUR STUDY HAS CLARIFIED THAT THE PARAMETERS WHICH
reflect corneal surface configuration as determined by Fourier analysis including spherical equivalent power, regular astigmatism, corneal asymmetry, and higher-order irregularity components change significantly with time after PK. Spectacle-corrected visual acuity also improves gradually. However, the postoperative time points at which these changes stabilize are not the same. It is important to understand when and how the corneal surface configuration changes and stabilizes after PK to guide the timing of additional surgical manipulations that facilitate visual rehabilitation; these supplementary procedures include astigmatic keratotomy and placement of compression sutures. Spherical equivalent power increased significantly for up to 1 month after PK, and then showed no further significant change up to conclusion of the study at 24 months. Since selective suture removal in this study was begun at 2 months after PK, the spherical equivalent power stabilized before selective suture removal. This indicates that the average curvature of a transplanted cornea steepens spontaneously soon after PK. This increase in spherical equivalent power in the central cornea would lead to a myopic shift of refractive status, which was consistent with the changes in manifest spherical equivalent seen in this study. VOL. 141, NO. 2
Additionally, the time point for stabilization of the spherical equivalent power of the central cornea coincided with that of manifest spherical equivalent. The regular astigmatism component decreased significantly for up to 6 months after PK, and then stabilized. More specifically, the decrease noted from 1 to 6 months after surgery was prominent. Because most of the selective removal of sutures was performed within this 6-month period, the decrease is most likely attributable predominantly to suture removal. These results indicate that selective removal of tight sutures is effective in reducing the regular astigmatism,17,20 –22 and that stabilization of regular astigmatism coincides with completion of suture removal. The asymmetry component decreased for up to 1 month after PK, while higher-order irregularity decreased for up to approximately 3 to 6 months, and then these two components stabilized. These results indicate that corneal asymmetry decreases spontaneously before suture removal. Conversely, corneal surface irregularity persists until 3 to 6 months after PK. Consequently, total irregular astigmatism, theoretically the sum of the asymmetry and higherorder irregularity components, was reduced postoperatively and stabilized at 3 months after PK. Spectacle-corrected visual acuity improved for up to approximately 3 to 6 months after PK. Thus, stabilization of spectacle-corrected visual acuity occurs a little earlier than does that of regular astigmatism, but occurs at the same time as does irregular astigmatism. Furthermore, spectacle-corrected visual acuity was correlated significantly with both regular and irregular astigmatism. The typical degree of regular astigmatism can theoretically be corrected with spectacles. Our results, however, suggest that the excessive amount of regular astigmatism present after PK may impair even spectacle-corrected visual acuity. Conversely, since irregular astigmatism cannot be corrected with spectacles, it is reasonable to suppose that the time point of stabilization of irregular astigmatism coincides with that of spectacle-corrected visual acuity, and the amount of the irregular astigmatism is correlated well with the visual acuity. The change in postoperative corneal shape is the most important issue to be addressed after PK. Many previous studies using keratometry showed changes in corneal astigmatism both with and without suture removal.23–30 Recent studies by means of videokeratography have classified the patterns of corneal topography after PK,15,16 while other studies showed an effect on corneal configuration of removal of the running sutures,17,18 but did not describe general longitudinal changes in the transplanted cornea. Only one study, that by Khong and associates,19 examined short-term changes in the configuration of the cornea after PK and sought a correlation with visual acuity. However, Khong and associates could not quantify the changes in corneal configuration well because their sample size was small and appropriate measurements of corneal
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shape were not available at that time. Our study is thus the first to quantitatively clarify the long-term changes in corneal configuration after PK using the parameters as determined by Fourier analysis of videokeratographic data. The central cornea steepens spontaneously with the reduction of asymmetry soon after PK, probably secondary to restoration of intraocular pressure and subsequent early loosening of the sutures, while regular astigmatism decreased because of selective suture removal. Regular astigmatism undergoes little change spontaneously, and intentional manipulation may, therefore, be necessary because this type of astigmatism is caused mainly by the presence of the firm tight sutures. Corneal surface irregularity also takes 3 to 6 months to stabilize, probably because it takes more than 6 months after PK for the corneal epithelium to return to normal.31,32 Healing of the graft-donor junction after PK is also important because it has been considered as the time at which all remaining sutures can be removed. Although our study clarified the time at which stabilization of corneal configuration occurs, it appears to be different from that of healing of the graft-donor junction. Even when the corneal shape stabilizes, graft-host junction may not be completely healed. It has been reported that unpredictable change in corneal astigmatism occurred because of suture removal more than 1 year after PK.24,27 Because portions of the interrupted sutures that did not have to be removed were left in place in our study, the exact time at which healing of the graft-donor junction was complete cannot be determined from our results. We acknowledge several limitations of this study. First, our study evaluated statistically the temporal changes in corneal configuration. However, complete stabilization of the configurational parameters appears to occur a little later than statistical stabilization does. This is partly attributable to the fact that some specific cases required much more time for the changes to be complete. However, the discrepancy between complete stabilization and the statistical time point of stabilization was small and may be negligible. Second, penetrating keratoplasty cases in which interrupted sutures were placed were the only ones included. It is possible that the cases with continuous sutures show more abrupt changes because of continuous suture removal than the more gradual changes seen in the study described herein. However, changes in corneal configuration of patients with interrupted sutures are generally thought to be similar to those of patients with continuous sutures. In conclusion, configuration of the corneal surface changes after PK, both spontaneously and because of suture removal, but it is generally stable after approximately 6 months. Spectacle-corrected visual acuity also stabilizes by approximately 3 to 6 months after PK, which coincides with stabilization of the corneal configuration. More specifically, regular and irregular corneal astigmatisms are correlated significantly with visual acuity. Our 246
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study examined the changes in corneal shape only after PK. Further study is called for to examine changes that may occur after other corneal transplantation procedures, such as deep lamellar keratoplasty.
REFERENCES 1. McDonnell PJ, Garbus J. Corneal topographic changes after radial keratotomy. Ophthalmology 1989;96:45– 49. 2. Bogan SJ, Maloney RK, Drews CD, Waring GO III. Computer-assisted videokeratography of corneal topography after radial keratotomy. Arch Ophthalmol 1991;109:834 – 841. 3. Frangieh GT, Kwitko S, McDonnell PJ. Prospective corneal topographic analysis in surgery for postkeratoplasty astigmatism. Arch Ophthalmol 1991;109:506 –510. 4. Lin DTC, Wilson SE, Reidy JJ, et al. Topographic changes that occur with 10-0 running suture removal following penetrating keratoplasty. Refract Corneal Surg 1990;6:21–25. 5. Hayashi K, Hayashi H, Nakao F, Hayashi F. The correlation between incision size and corneal shape changes in sutureless cataract surgery. Ophthalmology 1995;102:550 –556. 6. Kagaya F, Tomidokoro A, Tanaka S, Amano S, Oshika T. Fourier series harmonic analysis of corneal topography following suture removal after penetrating keratoplasty. Cornea 2002;21:256 –259. 7. Miyai S, Miyata K, Nejima R, et al. Visual acuity measurement using Fourier series harmonic analysis of videokeratography data in eyes after penetrating keratoplasty. Ophthalmology 2005;112:420 – 424. 8. Keller PR, McGhee CN, Weed KH. Fourier analysis of corneal topography data after photorefractive keratectomy. J Cataract Refract Surg 1998;24:1447–1455. 9. Tomidokoro A, Soya K, Miyata K, et al. Corneal irregular astigmatism and contrast sensitivity after photorefractive keratectomy. Ophthalmology 2001;108:2209 –2212. 10. Olsen T, Dam-Johansen M, Bek T, Hjortdal JØ. Corneal versus scleral tunnel incision in cataract surgery: a randomized study. J Cataract Refract Surg 1997;23:337–341. 11. Hayashi K, Hayashi H, Oshika T, Hayashi F. Fourier analysis of irregular astigmatism after implantation of 3 types of intraocular lenses. J Cataract Refract Surg 2000;26:1510 – 1516. 12. Oshika T, Sugita G, Tanabe T, Tomidokoro A, Amano S. Regular and irregular astigmatism after superior versus temporal scleral incision cataract surgery. Ophthalmology 2000; 107:2049 –2053. 13. Tomidokoro A, Oshika T, Amano S, Eguchi K, Eguchi S. Quantitative analysis of regular and irregular astigmatism induced by pterygium. Cornea 1999;18:412– 415. 14. Hayashi K, Hayashi H, Oshika T, Hayashi F. Fourier analysis of irregular astigmatism after trabeculectomy. Ophthalmic Surg Lasers 2000;31:94 –99. 15. Ibrahim O, Bogan S, Waring GO III. Patterns of corneal topography after penetrating keratoplasty. Eur J Ophthalmol 1996;6:1–5. 16. Karabatsas CH, Cook SD, Sparrow JM. Proposed classification for topographic patterns seen after penetrating keratoplasty. Br J Ophthalmol 1999;83:403– 409. OF
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17. Strelow S, Cohen EJ, Leavitt KG, Laibson PR. Corneal topography for selective suture removal after penetrating keratoplasty. Am J Ophthalmol 1991;112:657– 665. 18. Shimazaki J, Tsubota K. Analysis of videokeratography after penetrating keratoplasty: topographic characteristics and effects of removing running sutures. Ophthalmology 1997;104: 2077–2084. 19. Khong AM, Mannis MJ, Plotnik RD, Johnson CA. Computerized topographic analysis of the healing graft after penetrating keratoplasty. Am J Ophthalmol 1993;115:209 –215. 20. Binder PS. Selective suture removal can reduce postkeratoplasty astigmatism. Ophthalmology 1985;92:1412–1416. 21. Feldman ST, Brown SI. Reduction of astigmatism after keratoplasty. Am J Ophthalmol 1987;103:477– 478. 22. Binder PS. The effect of suture removal on postkeratoplasty astigmatism. Am J Ophthalmol 1988;105:637– 645. 23. Musch DC, Meyer RF, Sugar A, Soong HK. Corneal astigmatism after penetrating keratoplasty: The role of suture technique. Ophthalmology 1989;96:698 –703. 24. Musch DC, Meyer RF, Sugar A. The effect of removing running sutures on astigmatism after penetrating keratoplasty. Arch Ophthalmol 1988;106:488 – 492. 25. Van Meter WS, Gussler JR, Solomon KD, Wood TO. Postkeratoplasty astigmatism control: Single continuous suture adjustment versus selective interrupted suture removal. Ophthalmology 1991;98:177–183.
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26. Filatov V, Steinert RF, Talamo JH. Postkeratoplasty astigmatism with single running suture or interrupted sutures. Am J Ophthalmol 1993;115:715–721. 27. Mader TH, Yuan R, Lynn M, Stulting RD, Wilson LA, Waring GO III. Changes in keratometric astigmatism after suture removal more than one year after penetrating keratoplasty. Ophthalmology 1993;100:119 –126; Discussion 127. 28. Limberg MB, Dingeldein SA, Green MT, Klyce SD, Insler MS, Kaufman HE. Corneal compression sutures for the reduction of astigmatism after penetrating keratoplasty. Am J Ophthalmol 1989;108:36 – 42. 29. Levery GW, Lindstorom RL, Hofter LA, Doughman DJ. The surgical management of corneal astigmatism after penetrating keratoplasty. Ophthalmic Surg 1985;16:165–169. 30. Mandel MR, Shapiro MB, Krachmer JH. Relaxing incisions with augmentation sutures for the correction of postkeratoplasty astigmatism. Am J Ophthalmol 1987;103:441– 447. 31. Tsubota K, Mashima Y, Murata H, Yamada M, Sato N. Corneal epithelium following penetrating keratoplasty. Br J Ophthalmol 1995;79:257–260. 32. Shimazaki J, Shimmura S, Mochizuki K, Tsubota K. Morphology and barrier function of the corneal epithelium after penetrating keratoplasty: association with original diseases, tear function, and suture removal. Cornea 1999;18:559 –564.
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Biosketch Hideyuki Hayashi, MD, DMSc, is an Professor of Ophthalmology at Fukuoka University, Fukuoka Japan. He graduated Fukuoka University at 1978, and trained in Fukuoka University Hospital, Beth Israel Hospital at Boston and Wilmer Eye Institute. His main interests are vitreo-retinal surgery, diagnostic ocular imaging, pediatric retinal diseases and ocular angiogenesis. He has published more than 60 international peer-reviewed articles.
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Biosketch Ken Hayashi, MD, is the director of the Hayashi Eye Hospital in Fukuoka, Japan. He graduated in medicine from Kyushu University in 1982 and completed postgraduate training in 1989. His main research interests are anterior segment diseases, particularly as they relate to cataract surgery, keratoplasty, and glaucoma surgery. He has published more than 60 peer-reviewed articles in internationally acclaimed journals. He currently serves as editor of the Japanese Journal of Cataract and Refractive Surgery.
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● PURPOSE:
To examine the long-term longitudinal changes in corneal surface configuration as determined by Fourier series harmonic analysis of videokeratography data and of visual acuity and refraction after penetrating keratoplasty (PK). ● DESIGN: Interventional case series. ● METHODS: One hundred thirty eyes of 130 consecutive patients who were scheduled for PK using 16 interrupted 10-0 nylon sutures were recruited. Spherical equivalent power, regular astigmatism component, irregular astigmatism (asymmetry and higher-order irregularity) component of the central cornea as determined by Fourier analysis of videokeragraphic data, spectacle-corrected visual acuity, and spherical equivalent were examined at 1 week, and at 1, 3, 6, 9, 12, 18, and 24 months after PK. ● RESULTS: Spherical equivalent power increased considerably for up to 1 month after PK, but thereafter showed no further appreciable change up to the final follow-up at 24 months. The regular astigmatism component decreased markedly for up to 6 months after PK, while the total irregular astigmatism (sum of the asymmetry and higher-order irregularity) component decreased considerably up to approximately 3 months, and then these showed no further relevant change for up to 24 months. Spectacle-corrected visual acuity also improved markedly until approximately 3 months after PK, after which it was virtually stable. Furthermore, important correlations were found between regular and irregular astigmatism and the spectacle-corrected visual acuity. ● CONCLUSIONS: Corneal surface configuration after PK appears to be stable by approximately 6 months after PK, concurrent with postkeratoplasty stabilization of visual acuity. (Am J Ophthalmol 2006;141:241–247. © 2006 by Elsevier Inc. All rights reserved.)
C
OMPUTER-ASSISTED VIDEOKERATOGRAPHY IS MOST
useful in the assessment of corneal surface configuration because it provides many advantages over keratometry. Corneal topographic analysis is essential for assessment of corneal configuration before many types of corneal surgery and can substantially show any changes arising from the surgery.1–5 Specifically, Fourier series harmonic analysis has been applied recently to videokeratography data and has helped to clarify even minute changes in the corneal configuration attributable to anterior segment surgeries including keratoplasty,6,7 photorefractive keratectomy,8,9 cataract surgery,10 –12 pterygium surgery,13 and trabeculectomy.14 It is known that the corneal configuration changes with time after penetrating keratoplasty (PK). Knowledge of temporal changes in the configuration of the transplanted cornea is of particular importance in making the decision of when astigmatic keratotomy should be performed, and when compression sutures should be placed. Many previous studies using videokeratography reported the topographic pattern of the transplanted cornea15,16 and the effect of suture removal on corneal shape after PK.4,6,17,18 However, only one study described short-term topographic changes of the graft after PK, and that study involved only eight patients, each of whom had keratoconus.19 The purpose of the study described herein was to examine the long-term longitudinal changes in corneal surface configuration after PK. To quantitatively evaluate even minute changes, we used Fourier analysis of videokeratography data. Additionally, temporal changes in visual acuity were examined and correlated with the corneal surface configuration.
PATIENTS AND METHODS ● PATIENTS:
Accepted for publication Aug 25, 2005. From the Hayashi Eye Hospital, Fukuoka, Japan (K.H.) and the Department of Ophthalmology, School of Medicine, Fukuoka University, Fukuoka, Japan (H.H.). Inquiries to Ken Hayashi, MD, Hayashi Eye Hospital, 4-7-13 Hakataekimae, Hakata-Ku, Fukuoka 812, Japan; e-mail: [email protected] 0002-9394/06/$32.00 doi:10.1016/j.ajo.2005.08.062
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2006 BY
One hundred eighty-nine eyes of 189 consecutive patients scheduled for PK between October 1998 and July 2003 at Hayashi Eye Hospital were originally included in this study. When both eyes underwent PK, only the eye operated on first was included. The hospital’s Institutional Review Board approved the study protocol, and all patients provided informed consent.
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sutured in place with 16 interrupted 10-0 nylon sutures. At the conclusion of surgery, corneal astigmatism was adjusted by replacing tight or loose sutures, the presence of which was confirmed with a Maloney ring. In simultaneous PK and cataract surgery, the anterior capsulotomy was made with small scissors and toothed forceps in an attempt to make a circular capsulorrhexis. The nucleus was expressed using bimanual push and pull hooks or forceps, and the residual cortex was aspirated using the Simcoe irrigation-aspiration unit. After suturing the donor cornea with four interrupted nylon sutures, the lens capsule was inflated with hyaluronate sodium 1% (Healon; AMO, Santa Anna, California, USA). A 6.0-mm hydrophobic acrylic IOL (MA60BM or MA60AC, Alcon Surgical, Fort Worth, Texas, USA) or polymethyl-methacrylate IOL (MZ60BD, Alcon Surgical) was then implanted in the capsular bag. When posterior capsule rupture or zonular dehiscence occurred, scleral suturing of an IOL with eyelets (CZ60BD, Alcon Surgical) was performed. After constriction of the pupil with acetylcholine, 12 interrupted sutures were added.
TABLE 1. Preoperative Diagnosis of Patients Undergoing Penetrating Keratoplasty Preoperative Diagnosis
Number of Patients (%)
Bullous keratopathy Keratoconus Stromal scar* Stromal dystrophy Ulcer Trauma Total
56 (43.1%) 41 (31.5%) 24 (18.5%) 5 (3.8%) 3 (2.3%) 1 (0.8%) 130 (100%)
*Includes stromal opacity attributable to herpetic keratitis.
● SELECTIVE SUTURE REMOVAL: During follow-up, selective removal of the tight sutures was performed to decrease total astigmatism. When total astigmatism was 3 diopters or greater, tight sutures, the presence of which was confirmed by keratometry and videokeratography (Topographic Modeling System [TMS]; Tomey, Nagoya, Japan), were removed individually by the surgeon at 2 or more months after PK. When astigmatism was stable within 3 diopters, residual sutures were left in situ until they loosened.
FIGURE 1. Changes in mean (ⴞSD) spherical equivalent power of the central cornea after penetrating keratoplasty (PK) as determined by Fourier analysis. The mean spherical equivalent power increased considerably for up to 1 month after PK, but then did not change markedly for up to 24 months. When comparing each 2 time points, a P value of less than .0018 is considered to be statistically significant (asterisk).
● MAIN OUTCOME MEASURES:
All patients underwent videokeratography, visual acuity measurement, and determination of refractive status at 1 week and at 1, 3, 6, 9, 12, 18, and 24 months after surgery. The videokeratographic examination was made using the TMS. Best spectaclecorrected visual acuity was determined using decimal charts at each interval, and was converted to a logarithm of minimal angle of resolution (logMAR) scale for statistical analysis. The spherical and cylindrical refractive powers were measured using an autokerato-refractometer (KR-7100; Topcon, Tokyo, Japan). The spherical equivalent value was determined as the spherical power minus half the cylindrical power. Videokeratograhic data stored in the TMS computer were used for determination of spherical equivalent power, regular astigmatism, and irregular astigmatism of the central cornea by Fourier series harmonic analysis, which has been described previously.11,14 In brief, the dioptric powers on a mire ring i, Fi(E-), are transformed into trigonometric components as follows: Fi共兲 ⫽ a0 ⫹ c1cos共 ⫺ ␣1兲 ⫹ c2cos 2共 ⫺ ␣2兲 ⫹ c3cos 3共 ⫺ ␣3兲 ⫹ · · · ⫹ cncos n 共 ⫺ ␣n兲 where a0 is the spherical equivalent power of the ring, c1 the asymmetry component, c2 the regular astig-
● SURGICAL PROCEDURES:
All surgeries were performed by a single surgeon (K.H.) using the same surgical procedures in all cases. Surgery was performed under regional anesthesia consisting of a retrobulbar block and a seventhnerve block. For eyes scheduled for PK alone, miosis was induced with pilocarpine 3%, while full mydriasis was induced for eyes scheduled for combined PK and cataract extraction with posterior chamber intraocular lens (IOL) implantation. Donor corneas were punched out from the endothelial side with a Barron donor punch (Katena Products, Denville, New Jersey, USA) with a diameter that was the same as that of the recipient in keratoconus cases and 0.25-mm larger in the other cases. After placement of a single Flieringa ring using six 7-0 silk sutures, the recipient cornea was incised with a Hessburg-Barron vacuum trephine (Katena Products) with a 7.5- or 7.75-mm diameter. Removal of the cornea was completed with curved corneal scissors, after which the donor cornea was
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FIGURE 2. Changes in mean (ⴞSD) regular astigmatism component after penetrating keratoplasty (PK) as determined by Fourier analysis. The mean regular astigmatism component decreased significantly for up to approximately 6 months after PK, but then it showed no further relevant change for up to 24 months. When comparing each 2 time points, a P value of less than .0018 is considered to be statistically significant (asterisk), and a P value of less than .0050 is regarded as marginally significant (dagger).
FIGURE 4. Changes in mean (ⴞSD) higher-order irregularity component after penetrating keratoplasty (PK) as determined by Fourier analysis. The higher-order irregularity component decreased significantly for up to approximately 3 months after PK, but then it showed no further marked change for up to 24 months. When comparing each 2 time points, a P value of less than .0018 is considered to be statistically significant (asterisk) while a P value of less than .0050 is regarded as marginally significant (dagger).
(c3. . . n) components can be regarded as irregular astigmatism. In this study, these calculations were performed on rings 2 through 9, which correspond to the central 3.0 mm optical zone of the cornea. The average of the eight rings was calculated and considered to be the representative value of each component. All examinations were performed by ophthalmic technicians. ● STATISTICAL ANALYSIS:
FIGURE 3. Changes in mean (ⴞSD) asymmetry component after penetrating keratoplasty (PK) as determined by Fourier analysis. The mean asymmetry component decreased significantly for up to 1 month after PK, but then showed no further significant change for up to 24 months. When comparing each 2 time points, a P value of less than .0018 is considered statistically significant (asterisk).
matic component, and c3. . . n the third and higher-order irregularity components. Spherical equivalent power (a0) and the second order harmonic regular astigmatism component (c2) can theoretically be corrected by a spherocylindrical lens, while the first-order harmonic asymmetry component (c1) and third and higher-order irregularity VOL. 141, NO. 2
Temporal changes in spherical equivalent power, regular astigmatism component, asymmetry component, and higher-order irregularity component as determined by Fourier analysis, logMAR visual acuity, and manifest spherical equivalent were tested by means of the Kruskal-Wallis test. When the overall change was considerable, the difference between each 2 time points was further compared by use of the Mann-Whitney U test with the Bonferroni adjustment. The spherical equivalent power and regular and irregular astigmatism components were correlated with the logMAR visual acuity using a simple correlation analysis. Any differences showing a P value of less than .05 were considered to be statistically significant.
RESULTS OF THE 189 PATIENTS ORIGINALLY ENROLLED, 59 (31.2%)
were excluded during the follow-up. The reasons for exclusion were graft failure in 13 patients (6.9%), undergoing cataract or glaucoma surgery after PK in 21 (11.1%),
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TABLE 2. Simple Correlation Coefficients Between Regular and Irregular Astigmatism Components and Spectacle-Corrected logMAR Visual Acuity Following Penetrating Keratiplasty
Postoperative Interval
Regular astigmatism component 1 week 1 month 3 months 6 months 9 months 12 months 18 months 24 months Irregular astigmatism component‡ 1 week 1 month 3 months 6 months 9 months 12 months 18 months 24 months
FIGURE 5. Changes in mean (ⴞSD) spectacle-corrected logMAR visual acuity after penetrating keratoplasty (PK). Mean spectacle-corrected visual acuity improved considerably for up to approximately 3 months after PK, but then it showed no further significant improvement. When comparing each 2 time points, a P value of less than .0018 is considered to be statistically significant (asterisk), while a P value of less than .0050 is regarded as marginally significant (dagger).
Correlation Coefficient
P Value
0.486 0.550 0.374 0.516 0.356 0.361 0.372 0.158
⬍.0001* ⬍.0001* ⬍.0001* ⬍.0001* ⬍.0001* ⬍.0001* ⬍.0001* .0725†
0.490 0.314 0.329 0.416 0.502 0.424 0.423 0.311
⬍.0001* .0003* .0001* ⬍.0001* ⬍.0001* ⬍.0001* ⬍.0001* .0003*
*Statistically significant correlation. † No statistically significant correlation. ‡ Sum of the asymmetry and higher-order irregularity components.
The average age of the patients (⫾SD) was 58.7 ⫾ 20.0 years, with a range of 19 to 85 years. There were 68 men and 62 women. The preoperative diagnoses of these patients are shown in Table 1. Of the 130 patients analyzed, 19 (14.6%) did not undergo selective suture removal. Selective removal of the tight sutures were completed between 2 and 6 months after PK in 86 patients (66.2%), while the other 25 (19.2%) continued to undergo selective suture removal for up to 6 months or later. The spherical equivalent power, regular astigmatism component, asymmetry component, and higher-order irregularity component as determined by Fourier analysis, spectacle-corrected logMAR visual acuity, and manifest spherical equivalent changed remarkably during the 24month follow-up (P ⬍ .0001, Kruskal-Wallis test). Figure 1 shows changes in mean (⫾SD) spherical equivalent power of the central cornea. The spherical equivalent power increased significantly for up to 1 month after PK, but remained relatively unchanged thereafter. Additionally, no significant correlation was found between the spherical equivalent power and spectacle-corrected logMAR visual acuity for each patient throughout the 24-month follow-up period. Figure 2 shows changes in the mean (⫾SD) regular astigmatism component. The mean regular astigmatism component decreased considerably for up to approximately
FIGURE 6. Changes in mean (ⴞSD) manifest spherical equivalent after penetrating keratoplasty (PK). The mean manifest spherical equivalent changed appreciably towards myopia for up to approximately 1 month after PK, but then it showed no further significant change. When comparing each 2 time points, a P value of less than .0018 is considered to be statistically significant (asterisk).
moving out of the area in 3 (1.6%), and lost to follow-up because of a scheduling conflict in 11 (5.8%). We also excluded 11 patients (5.8%) whose visual acuity throughout the follow-up period was 2/20 or worse because of amblyopia in 4 (2.1%), glaucomatous central visual field defects in 3 (1.6%), and macular degeneration in 4 (2.1%). A total of 130 patients (68.8%) thus remained for analysis. 244
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6 months after PK, but then showed no further significant change up to the 24-month cut-off point. Changes in mean (⫾SD) asymmetry and higher-order irregularity components are shown in Figures 3 and 4, respectively. The asymmetry component decreased significantly for up to 1 month after PK, while the higher-order irregularity component decreased for up to approximately 3 months, but there was no further significant change in these parameters for up to 24 months. Additionally, the total amount of irregular astigmatism (sum of asymmetry and higher-order irregularity components) decreased significantly for up to 3 months after PK, which indicates a concurrent stabilization of spectacle-corrected visual acuity and irregular astigmatism. Figure 5 shows mean (⫾SD) spectacle-corrected logMAR visual acuity. Mean spectacle-corrected logMAR visual acuity improved significantly for up to approximately 3 months after PK, and then showed no further significant improvement. The mean manifest spherical equivalent changed significantly towards myopia for up to approximately 1 month after PK, and then showed no further significant change (Figure 6). Table 2 shows the simple correlation coefficients between regular astigmatism and irregular astigmatism components and logMAR visual acuity. For each patient, a significant correlation was found between these components and the spectacle-corrected logMAR visual acuity.
DISCUSSION OUR STUDY HAS CLARIFIED THAT THE PARAMETERS WHICH
reflect corneal surface configuration as determined by Fourier analysis including spherical equivalent power, regular astigmatism, corneal asymmetry, and higher-order irregularity components change significantly with time after PK. Spectacle-corrected visual acuity also improves gradually. However, the postoperative time points at which these changes stabilize are not the same. It is important to understand when and how the corneal surface configuration changes and stabilizes after PK to guide the timing of additional surgical manipulations that facilitate visual rehabilitation; these supplementary procedures include astigmatic keratotomy and placement of compression sutures. Spherical equivalent power increased significantly for up to 1 month after PK, and then showed no further significant change up to conclusion of the study at 24 months. Since selective suture removal in this study was begun at 2 months after PK, the spherical equivalent power stabilized before selective suture removal. This indicates that the average curvature of a transplanted cornea steepens spontaneously soon after PK. This increase in spherical equivalent power in the central cornea would lead to a myopic shift of refractive status, which was consistent with the changes in manifest spherical equivalent seen in this study. VOL. 141, NO. 2
Additionally, the time point for stabilization of the spherical equivalent power of the central cornea coincided with that of manifest spherical equivalent. The regular astigmatism component decreased significantly for up to 6 months after PK, and then stabilized. More specifically, the decrease noted from 1 to 6 months after surgery was prominent. Because most of the selective removal of sutures was performed within this 6-month period, the decrease is most likely attributable predominantly to suture removal. These results indicate that selective removal of tight sutures is effective in reducing the regular astigmatism,17,20 –22 and that stabilization of regular astigmatism coincides with completion of suture removal. The asymmetry component decreased for up to 1 month after PK, while higher-order irregularity decreased for up to approximately 3 to 6 months, and then these two components stabilized. These results indicate that corneal asymmetry decreases spontaneously before suture removal. Conversely, corneal surface irregularity persists until 3 to 6 months after PK. Consequently, total irregular astigmatism, theoretically the sum of the asymmetry and higherorder irregularity components, was reduced postoperatively and stabilized at 3 months after PK. Spectacle-corrected visual acuity improved for up to approximately 3 to 6 months after PK. Thus, stabilization of spectacle-corrected visual acuity occurs a little earlier than does that of regular astigmatism, but occurs at the same time as does irregular astigmatism. Furthermore, spectacle-corrected visual acuity was correlated significantly with both regular and irregular astigmatism. The typical degree of regular astigmatism can theoretically be corrected with spectacles. Our results, however, suggest that the excessive amount of regular astigmatism present after PK may impair even spectacle-corrected visual acuity. Conversely, since irregular astigmatism cannot be corrected with spectacles, it is reasonable to suppose that the time point of stabilization of irregular astigmatism coincides with that of spectacle-corrected visual acuity, and the amount of the irregular astigmatism is correlated well with the visual acuity. The change in postoperative corneal shape is the most important issue to be addressed after PK. Many previous studies using keratometry showed changes in corneal astigmatism both with and without suture removal.23–30 Recent studies by means of videokeratography have classified the patterns of corneal topography after PK,15,16 while other studies showed an effect on corneal configuration of removal of the running sutures,17,18 but did not describe general longitudinal changes in the transplanted cornea. Only one study, that by Khong and associates,19 examined short-term changes in the configuration of the cornea after PK and sought a correlation with visual acuity. However, Khong and associates could not quantify the changes in corneal configuration well because their sample size was small and appropriate measurements of corneal
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shape were not available at that time. Our study is thus the first to quantitatively clarify the long-term changes in corneal configuration after PK using the parameters as determined by Fourier analysis of videokeratographic data. The central cornea steepens spontaneously with the reduction of asymmetry soon after PK, probably secondary to restoration of intraocular pressure and subsequent early loosening of the sutures, while regular astigmatism decreased because of selective suture removal. Regular astigmatism undergoes little change spontaneously, and intentional manipulation may, therefore, be necessary because this type of astigmatism is caused mainly by the presence of the firm tight sutures. Corneal surface irregularity also takes 3 to 6 months to stabilize, probably because it takes more than 6 months after PK for the corneal epithelium to return to normal.31,32 Healing of the graft-donor junction after PK is also important because it has been considered as the time at which all remaining sutures can be removed. Although our study clarified the time at which stabilization of corneal configuration occurs, it appears to be different from that of healing of the graft-donor junction. Even when the corneal shape stabilizes, graft-host junction may not be completely healed. It has been reported that unpredictable change in corneal astigmatism occurred because of suture removal more than 1 year after PK.24,27 Because portions of the interrupted sutures that did not have to be removed were left in place in our study, the exact time at which healing of the graft-donor junction was complete cannot be determined from our results. We acknowledge several limitations of this study. First, our study evaluated statistically the temporal changes in corneal configuration. However, complete stabilization of the configurational parameters appears to occur a little later than statistical stabilization does. This is partly attributable to the fact that some specific cases required much more time for the changes to be complete. However, the discrepancy between complete stabilization and the statistical time point of stabilization was small and may be negligible. Second, penetrating keratoplasty cases in which interrupted sutures were placed were the only ones included. It is possible that the cases with continuous sutures show more abrupt changes because of continuous suture removal than the more gradual changes seen in the study described herein. However, changes in corneal configuration of patients with interrupted sutures are generally thought to be similar to those of patients with continuous sutures. In conclusion, configuration of the corneal surface changes after PK, both spontaneously and because of suture removal, but it is generally stable after approximately 6 months. Spectacle-corrected visual acuity also stabilizes by approximately 3 to 6 months after PK, which coincides with stabilization of the corneal configuration. More specifically, regular and irregular corneal astigmatisms are correlated significantly with visual acuity. Our 246
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study examined the changes in corneal shape only after PK. Further study is called for to examine changes that may occur after other corneal transplantation procedures, such as deep lamellar keratoplasty.
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17. Strelow S, Cohen EJ, Leavitt KG, Laibson PR. Corneal topography for selective suture removal after penetrating keratoplasty. Am J Ophthalmol 1991;112:657– 665. 18. Shimazaki J, Tsubota K. Analysis of videokeratography after penetrating keratoplasty: topographic characteristics and effects of removing running sutures. Ophthalmology 1997;104: 2077–2084. 19. Khong AM, Mannis MJ, Plotnik RD, Johnson CA. Computerized topographic analysis of the healing graft after penetrating keratoplasty. Am J Ophthalmol 1993;115:209 –215. 20. Binder PS. Selective suture removal can reduce postkeratoplasty astigmatism. Ophthalmology 1985;92:1412–1416. 21. Feldman ST, Brown SI. Reduction of astigmatism after keratoplasty. Am J Ophthalmol 1987;103:477– 478. 22. Binder PS. The effect of suture removal on postkeratoplasty astigmatism. Am J Ophthalmol 1988;105:637– 645. 23. Musch DC, Meyer RF, Sugar A, Soong HK. Corneal astigmatism after penetrating keratoplasty: The role of suture technique. Ophthalmology 1989;96:698 –703. 24. Musch DC, Meyer RF, Sugar A. The effect of removing running sutures on astigmatism after penetrating keratoplasty. Arch Ophthalmol 1988;106:488 – 492. 25. Van Meter WS, Gussler JR, Solomon KD, Wood TO. Postkeratoplasty astigmatism control: Single continuous suture adjustment versus selective interrupted suture removal. Ophthalmology 1991;98:177–183.
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26. Filatov V, Steinert RF, Talamo JH. Postkeratoplasty astigmatism with single running suture or interrupted sutures. Am J Ophthalmol 1993;115:715–721. 27. Mader TH, Yuan R, Lynn M, Stulting RD, Wilson LA, Waring GO III. Changes in keratometric astigmatism after suture removal more than one year after penetrating keratoplasty. Ophthalmology 1993;100:119 –126; Discussion 127. 28. Limberg MB, Dingeldein SA, Green MT, Klyce SD, Insler MS, Kaufman HE. Corneal compression sutures for the reduction of astigmatism after penetrating keratoplasty. Am J Ophthalmol 1989;108:36 – 42. 29. Levery GW, Lindstorom RL, Hofter LA, Doughman DJ. The surgical management of corneal astigmatism after penetrating keratoplasty. Ophthalmic Surg 1985;16:165–169. 30. Mandel MR, Shapiro MB, Krachmer JH. Relaxing incisions with augmentation sutures for the correction of postkeratoplasty astigmatism. Am J Ophthalmol 1987;103:441– 447. 31. Tsubota K, Mashima Y, Murata H, Yamada M, Sato N. Corneal epithelium following penetrating keratoplasty. Br J Ophthalmol 1995;79:257–260. 32. Shimazaki J, Shimmura S, Mochizuki K, Tsubota K. Morphology and barrier function of the corneal epithelium after penetrating keratoplasty: association with original diseases, tear function, and suture removal. Cornea 1999;18:559 –564.
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Biosketch Hideyuki Hayashi, MD, DMSc, is an Professor of Ophthalmology at Fukuoka University, Fukuoka Japan. He graduated Fukuoka University at 1978, and trained in Fukuoka University Hospital, Beth Israel Hospital at Boston and Wilmer Eye Institute. His main interests are vitreo-retinal surgery, diagnostic ocular imaging, pediatric retinal diseases and ocular angiogenesis. He has published more than 60 international peer-reviewed articles.
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Biosketch Ken Hayashi, MD, is the director of the Hayashi Eye Hospital in Fukuoka, Japan. He graduated in medicine from Kyushu University in 1982 and completed postgraduate training in 1989. His main research interests are anterior segment diseases, particularly as they relate to cataract surgery, keratoplasty, and glaucoma surgery. He has published more than 60 peer-reviewed articles in internationally acclaimed journals. He currently serves as editor of the Japanese Journal of Cataract and Refractive Surgery.
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