Lens opacities after nonmechanical versus mechanical corneal ...

Lens opacities after nonmechanical versus mechanical corneal trephination for keratoplasty in keratoconus Ashley Behrens, MD, Berthold Seitz, MD, EBOD, Achim Langenbucher, PhD, Murat M. Kus, MD, Michael Ku¨chle, MD, Gottfried O.H. Naumann, MD ABSTRACT Purpose: To compare the lens opacity formation after penetrating keratoplasty (PKP) using nonmechanical excimer laser corneal trephination and mechanical motor trephination. Setting: University Eye Clinic, University of Erlangen-Nu¨rnberg, Erlangen, Germany. Methods: Ninety-six patients with keratoconus (96 eyes) and clear crystalline lenses were randomly assigned to the nonmechanical trephination (NMT) group (n ⫽ 46; 35 men; mean age 38.2 years ⫾ 10.8 [SD]) or the mechanical trephination (MT) group (n ⫽ 50; 35 men; mean age 34.4 ⫾ 9.0 years). Suturing and postoperative treatment were identical. Dilated pupil biomicroscopy and slitlamp lens photography were performed preoperatively and postoperatively at 3 month intervals. Opacities were identified as cortical, nuclear, and posterior subcapsular and graded from 1 (mild) to 3 (severe). Results: Mean follow-up in the NMT/MT group was 3.2 ⫾ 1.3 years/3.4 ⫾ 1.1 years. Overall, incident opacities appeared in 23.9%/32.0% of eyes (4.3%/6.0% cortical; 19.6%/26.0% posterior subcapsular; 0%/0% nuclear) (P ⫽ .833). All cortical opacities in both groups were grade 1; posterior subcapsular opacities were grade 1 in 66.6%/ 61.5% of eyes and grade 2 in 22.2%/30.8% of eyes. One patient in each group presented grade 3 posterior subcapsular opacities. No differences between trephination methods were seen in a 5 year Kaplan–Meier cumulative risk of lens opacity formation (P ⫽ .763 cortical, P ⫽ .530 posterior subcapsular). Conclusion: In addition to its optical advantages, nonmechanical corneal trephination appears to have no adverse impact on cataract formation after PKP for keratoconus. J Cataract Refract Surg 2000; 26:1605–1611 © 2000 ASCRS and ESCRS

P

enetrating keratoplasty (PKP) is probably the most successful transplantation procedure today. Now that we have a better understanding of the immunologic

Accepted for publication August 3, 2000. Reprint requests to Berthold Seitz, MD, University Eye Clinic, Schwabachanlage 6, D-91054 Erlangen, Germany. E-mail: [email protected]. © 2000 ASCRS and ESCRS Published by Elsevier Science Inc.

response, recognize the risk factors for graft failure, and have improved treatment for rejection reactions, the visual performance has become the focus of attention.1–7 A common optical problem after PKP is corneal astigmatism, which has been reported to range from 3.0 to 6.0 diopters (D).8 –10 Not all the mechanisms involved in its magnitude and axis are understood. Several variables related to the host, the donor, and the surgical technique have been identified.11 0886-3350/00/$–see front matter PII S0886-3350(00)00717-3

LENS OPACITIES AFTER PKP

One important factor proposed as a cause of postkeratoplasty astigmatism is the corneal trephination procedure.12–15 Contact methods using razor blades are not satisfactory since they are difficult to centrate,16 tend to create unparallel cuts (“vertical tilt”),1,17 and induce cut irregularities by the interacting radial (cornea) and axial (trephine) forces.18 Using the 193 nm excimer laser for nonmechanical trephination (NMT), more congruent cut edges, lower corneal topography irregularity, and better visual acuity of up to 2 decimal lines have been achieved.19 –21 A recent randomized prospective study reports that the NMT procedure produces better visual acuity and lower surface irregularity, especially after suture removal.22 One theoretical problem with NMT for PKP is the lens changes induced by intraoperative secondary radiation, with a potential effect on cataract formation. The purpose of this study was to determine whether lens opacity formation after PKP is influenced by the use of NMT in comparison with the standard mechanical motor trephination. This report is part of a prospective randomized controlled clinical trial initiated in October 1992 to analyze the outcomes of NMT in PKP.

Patients and Methods Patient Selection After the study was approved by the ethics committee at the University of Erlangen-Nu¨rnberg, 192 patients with keratoconus who required PKP were enrolled. Informed consent was obtained from each patient. Patients with preoperatively observed lens opacities, associated anterior segment disease, corneal vascularization, previous intraocular surgery, a planned combined glaucoma and PKP procedure, or diseases predisposing to cataract formation (eg, diabetes mellitus) were excluded. One patient developed cataract after an ocular trauma unrelated to the surgical procedure and was excluded. Ninety-six patients met the selection criteria; 46 (46 eyes) were assigned to the NMT group and 50 (50 eyes) to the mechanical trephination (MT) group using a random-number table. 1606

Trephination Procedure and Suturing Immediately before surgery, the pupil was constricted with a topical miotic agent (pilocarpine 2%). All patients were operated on by the same surgeon (G.O.H.N.). For NMT, a 193 nm argon–fluoride excimer laser (Aesculap Meditec MEL 60) was used, with settings at 15 to 20 mJ/ pulse, 25 nanosecond pulse duration, 25 Hz repetition rate, and a 1.5 ⫻ 1.5 mm spot size. Stainless-steel, open circular masks with diameters of 8.1 mm donor/8.0 mm recipient, weighing 0.18 g donor/0.40 g recipient, and 8 “ori entation teeth/notches” were used. The laser beam was guided along the mask rim, one half of the spot on the mask and one half over the cornea. An artificial anterior chamber filled with viscoelastic material (sodium hyaluronate [Healon威]) at a pressure of 20 mm Hg, coupled with an automated rotation device at a constant speed of 4 rotations/minute, was used for the donor button trephination. The donor mask was placed on the cornea and the laser beam directed to its external rim. In the recipient trephina tion, the laser beam was manually guided along the internal rim of the recipient mask using a joystick. The laser emission was stopped when signs of corneal perforation were evident (ie, sudden appearance of viscoelastic material or aqueous in the laser groove). The site of perforation was enlarged with a Graefe’s knife, and the rest of the trephination was completed with corneal scissors. For MT, a motor trephine (Mikrokeratron威, Geuder) with interchangeable razor steel blades was used. The procedure was performed from the epithelial side in both donor and recipient corneas. For donor trephination, the artificial anterior chamber was used. After a deep stromal trephination, the surgical procedure was identical to that in NMT after the focal perforation was achieved. The anterior chamber was reformed with viscoelastic material, a peripheral iridectomy was created at 12 hours, and the donor button was fixed with 8 cardinal sutures (10-0 nylon single interrupted sutures). After the donor button was secured, a secondary double-running, continuous, antitorque 16-bite diagonal suture (10-0 nylon) was applied as described by Hoffmann.23 The cardinal sutures were then removed and the secondary sutures adjusted based on intraoperative Placido-disk evaluation. Postoperative Treatment Patients received 250 mg of acetazolamide 3 times on the first day, gentamicin ointment 3% 3 times a day for 5 days, and topical eyedrops of scopolamine 0.25%

J CATARACT REFRACT SURG—VOL 26, NOVEMBER 2000


The demographic characteristics of the patients are summarized in Table 1. In the NMT group, the mean follow-up was 3.2 years ⫾ 1.3 (SD), with a median of

3.3 years and a range of 0.7 to 5.6 years. In the MT group, the mean follow-up was 3.4 ⫾ 1.1 years, with a median of 3.5 years and a range of 0.7 to 5.2 years. The mean time until removal of the first suture was 1.3 ⫾ 0.4 years in the NMT group and 1.2 ⫾ 0.3 years in the MT group. The second suture was removed after a mean interval of 1.7 ⫾ 0.4 years and 1.8 ⫾ 0.5 years, respectively. Three (6.5%) immunologic graft reactions occurred in the NMT group and 3 (6.1%) in the MT group (P ⫽ .895). All cases resolved with medical therapy. One patient in each group developed posterior subcapsular opacities. No cases of primary graft failure were seen. One patient (2.2%) in the NMT group had cataract surgery after PKP, and 1 patient (2.0%) in the MT group required surgery for significant lens opacification. This was not significant (P ⫽ .954). Overall, 11 patients (23.9%) in the NMT group and 16 patients (32.0%) in the MT group presented some form of opacity during the study period. However, the between-group difference was not significant (P ⫽ .833). With both trephination methods, the posterior subcapsular was the most frequent type of cataract (P ⫽ .003). No cases of nuclear cataract were seen. The incidence of cataract by location of the opacities is summarized in Table 2. No correlation was found between cataract formation and sex in the cortical(P ⫽ .244) or posterior subcapsular (P ⫽ .353) group or between laterality and appearance of cortical (P ⫽ .494) or posterior subcapsular opacities (P ⫽ .776). No correlation between laser exposition time and cataract formation was found (P ⫽ .884). Similar risks of cataract formation were observed in the Kaplan–Meier survival curves for both groups in the cortical (Figure 1) and posterior subcapsular (Figure 2) zones. The log-rank test showed that the differences between trephination techniques were not statistically sig-

Table 1. Demographic attributes of the study groups.

Table 2. Incidence of opacities in 2 trephination methods.

2 times a day and prednisolone acetate 1% 5 times a day for 6 weeks starting on the fifth postoperative day. Steroid dosage was tapered progressively for 6 months: 4 times a day for 6 weeks, 3 times a day for 4 weeks, 2 times a day for 4 weeks, and once a day for 4 weeks. Postoperative Follow-Up A 3 month follow-up was made to assess the presence of newly acquired lens opacities. Biomicroscopy and retroillumination evaluation with dilated pupil of the lens status preoperatively and after each postoperative visit were obtained in a masked fashion. A slitlamp photograph of the crystalline lens was also recorded at all visits. The location of the lens opacity was recorded in 3 sectors: cortical, nuclear, and posterior subcapsular. Opacity intensity was graded semiquantitatively on a scale from 1 (mild) to 3 (severe). Statistical Analysis For statistical analysis, SPSS/PC 6.1.3 (Windows) was used. Variables were recalled from a common relational database system (Microsoft Access 2.0). Comparisons between groups or variables were performed using nonparametric tests (Mann–Whitney U and Wilcoxon). Formulating the risk of developing cataracts as a target criterion, Kaplan–Meier survival graphs were displayed. A log-rank test was used to compare the cataract formation in both groups of patients. The laser trephination time and cataract formation were analyzed with the Pearson correlation coefficient. A P value ⱕ .05 was considered statistically significant.

Results

Characteristic

NMT Group

MT Group

Mean years ⫾ SD

38.2 ⫾ 10.8

34.4 ⫾ 9.0

Range (years)

16.8 to 69.8

15.3 to 53.3

Sex, male/female

35/11

35/15

Laterality, right/left eyes

25/21

22/28

NMT ⫽ nonmechanical trephination; MT ⫽ mechanical trephination; SD ⫽ standard deviation

Number of Cases (%) Cortical Cataract

Posterior Subcapsular Cataract

NMT group*

2 (4.3)

9 (19.6)

MT group*

3 (6.0)

13 (26.0)

Trephination Method

NMT ⫽ nonmechanical trephination; MT ⫽ mechanical trephination *No nuclear cataracts were observed.


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Figure 1. (Behrens) Kaplan–Meier survival curve for thee risk of cortical opacity formation after PIP using the 2 trephination techniques. The log-rank test showed no significant difference (P ⫽ .911).

nificant in a 5 year estimation. The cumulative probability of cataract formation was also similar in both groups, as noted in Table 3. In 77.8% (7 eyes) of the patients presenting posterior subcapsular cataracts in the NMT group and in 69.2% (9 eyes) in the MT group, the opacities developed in the fourth and fifth decades of life. The remainder of the posterior subcapsular cataracts occurred in patients younger than 40 years. Cortical opacities were observed only after the fourth decade of life. The cataract intensity in all patients in both groups presenting cortical cataracts was grade 1. In the NMT group, 66.6% (6 eyes) of the posterior subcapsular opacities were classified as grade 1, 22.2% (2 eyes) as grade 2, and 11.1% (1 eye) as grade 3. In the MT group, 61.5% (8 eyes) were classified as grade 1, 30.8% (4 eyes) as grade 2, and 7.7% (1 eye) as grade 3. None of the patients with grade 1 or 2 opacities had changes in best corrected visual acuity or visual com-

Table 3. Kaplan–Meier survival analysis of the risk of lens opacity formation at 1, 3, and 5 years after PKP using NMT and MT.

Cataract Type

Trephination Procedure

Cumulative Probability Percentage (SE) 3 Years

5 Years

0

4.5 (3.1)

4.5 (3.1)

MT

4.0 (2.8)

4.0 (2.8)

7.0 (4.0)

NMT

5.4 (3.0)

21.1 (6.9)

28.3 (9.3)

MT

10.1 (4.3)

27.2 (6.5)

27.2 (6.5)

NMT

1 Year

Cortical Posterior subcapsular

SE ⫽ standard error; NMT ⫽ nonmechanical trephination; MT ⫽ mechanical trephination

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plaints. However, patients with grade 3 opacities required cataract surgery because of significant visual impairment.

Discussion Excimer laser NMT has been developed and refined by Naumann and others since 1989.1,16 –22,24 –29 The technique has been performed in more than 850 patients, and it has become the standard method of trephination for avascular corneal processes having PKP in our department. The technique allows different shapes of trephination and cut angles, such as elliptical trephination with divergent or convergent angles, by changing the open-mask configuration or the laser beam incidence.24 –26 Since this is a noncontact procedure, cutting the cornea in perforated and predescemetal corneal ulcers is facilitated.27 A straightforward corneal donor button fitting and orientation in its recipient bed by means of orientation teeth and notches at the trephination margins are additional benefits of this method.28 These structures prevent the “horizontal torsion” induced by asymmetric placement of the sutures or loss of radiality using interrupted suturing, since they anchor the donor button in the correspondent bed like a key in a keyhole. Donor cornea mismatching is avoided, and correct positioning of the 8 cardinal sutures is more easily achieved. Additionally, a topography-guided “harmonization” of the donor– host becomes feasible by creating a greater tooth/notch as a marker.29



Figure 2. (Behrens) Kaplan–Meier survival curve for the risk of posterior subcapsular opacity formation after PIP using the 2 trephination techniques. The log-rank test showed no significant difference (P ⫽ .857).

The incidence of cataract after PKP ranges from 1% to 60% in various studies.30 –35 Several variables are involved, and some such as age, sex, surgical manipulation, postoperative corticosteroid therapy, and underlying pathology may intervene simultaneously.31 Cataract formation after PKP for keratoconus appears low when compared with other entities.34 This postulate was considered when selecting the cohort for the study, as this could facilitate assessment of the effect of the trephination technique on the cataract developing process. With similar preoperative, intraoperative, and postoperative conditions in 2 cohorts, the effect of different trephination procedures on cataractogenesis should be more clearly assessed in a group with a low cataract incidence. The absence of standard quantitative methods of evaluating cataract intensity limits adequate comparison of cataract formation studies after PKP. In addition, reports in the literature are usually retrospective, which accounts for more variable and subjective lens evaluation criteria. In our experience, slitlamp evaluation including retroillumination in an eye with a maximally dilated pupil was considerably more sensitive in detecting subtle, newly acquired lens opacities, especially at the posterior subcapsular region, than the photographic record. Since some of these changes were overlooked with the second method, the direct examination criterion prevailed over the clinical photography evaluation. According to Costagliola et al.,36 deleterious excimer laser radiation effects reflected in lens alterations might be expected in the short term. Moreover, an increased incidence of cataracts relative to the laser expo-

sure time through a full-depth ablation procedure may be presumed. However, results of the Kaplan–Meier analysis of our series suggest that the risk of having lens changes during the first year of follow-up are even lower in the NMT group than in the standard MT procedure. Furthermore, a correlation between laser exposure time and cataract formation was not demonstrated. Posterior subcapsular cataracts have been reported as common opacities after PKP for keratoconus,31,35 and this observation is consistent with our results. This type of cataract has been related predominantly to the use of postoperative corticosteroids, and its incidence seems to vary from 1% to 32%.30,31,34,35,37 Urban and Cotlier38 postulate that this form of acquired cataract rarely produces visual impairment, an observation that we corroborated in our series. Patients presenting grade 1 or 2 opacities at the lens examination had no changes in BCVA or subjective visual complaints at the time the opacities were detected. A grade 3 opacity did cause enough visual disturbance to require surgery. One patient from each group had a grade 3 opacity and therefore surgery was performed. The intense steroid regimen used to prevent immunologic rejection may elucidate the apparently high ratio of posterior subcapsular cataracts observed in our series. The long-term, high-dosage prednisolone therapy, in some cases for up to 1 year, may have played an important role in our results. However, a comparable incidence of posterior subcapsular cataracts in middle-aged patients was observed in both trephination groups. This finding adds to the presumption of a secondary origin of the opacities, probably not related to the trephination


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technique itself but to the postoperative therapy, since in this age group cataract formation is otherwise infrequent. Seitz et al.39 demonstrate an analogous risk (around 7%) of immunologic graft reactions between the NMT procedure and conventional trephination methods. Ku¨chle et al.40 demonstrate the advantages of NMT over MT in reducing disruption of the blood–aqueous barrier and therefore the inflammatory reaction in the anterior chamber in the first days after PKP.40 Assuming that early blood–aqueous breakdown has an adverse impact on the risk of later graft reactions,41 a significant reduction in postoperative topical steroids may be justified after NMT. Steroid dosage tapering using the laser flare– cell meter changes as a quantitative guide has been used during the past 4 years in our department as a more objective criterion. This may reduce the incidence of posterior subcapsular cataracts in these patients, as reported with low steroid dosage protocols.34 Results of this prospective study are beyond the scope of the present study. Considering the important benefits of the laser in NMT for PKP, the 2.94 ␮m erbium:YAG laser is currently under investigation as a more practical laser emission alternative. Advantages are reduced equipment size, lower acquisition and maintenance costs, and solid-state laser safety. Preliminary in vitro results have shown the feasibility of the procedure.27,42– 45 Currently, the animal research phase is underway to establish the effect of using this midinfrared laser as an emission device for NMT. The results obtained with our analysis suggest that excimer laser NMT in patients with keratoconus produces no additional inadvertent effects clinically on the lens status than standard MT. Considering the important optical advantages obtained with NMT, our results represent supplementary evidence supporting this procedure as the method of choice for corneal trephination in PKP.

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3. Vail A, Gore SM, Bradley BA, et al. Clinical and surgical factors influencing corneal graft survival, visual acuity, and astigmatism. Ophthalmology 1996; 103:41– 49 4. Palay DA, Kangas TA, Stulting RD, et al. The effects of donor age on the outcome of penetrating keratoplasty in adults. Ophthalmology 1997; 104:1576 –1579 5. Scho¨nherr U, Martus P, Ha¨ndel A, Naumann GOH. Transplantatreaktion nach Keratoplastik wegen Keratokonus; Ha¨ufigkeit und Risikofaktoren. Ophthalmologe 1996; 93:227–231 6. Borderie VM, Scheer S, Touzeau O, et al. Donor organ cultured corneal tissue selection before penetrating keratoplasty. Br J Ophthalmol 1998; 82:382–388 7. Zhao J-C, Jin X-Y. Local therapy of corneal allograft rejection with cyclosporine. Am J Ophthalmol 1995; 119:189 –194 8. Perlman EM. An analysis and interpretation of refractive errors after penetrating keratoplasty. Ophthalmology 1981; 88:39 – 45 9. Gross RH, Poulsen EJ, Davitt S, et al. Comparison of astigmatism after penetrating keratoplasty by experienced cornea surgeons and cornea fellows. Am J Ophthalmol 1997; 123:636 – 643 10. Belmont SC, Zimm JL, Storch RL, et al. Astigmatism after penetrating keratoplasty using the Krumeich guided trephine system. Refract Corneal Surg 1993; 9:250 –254 11. Reing CS, Speaker MG. Postkeratoplasty astigmatism. In: Krachmer JH, Mannis MJ, Holland EJ, eds, Cornea. Vol 3: Surgery of the Cornea and Conjunctiva. St Louis, MO, Mosby, 1997; 1675–1685 12. van Rij G, Waring GO III. Configuration of corneal trephine opening using five different trephines in human donor eyes. Arch Ophthalmol 1988; 106:1228 –1233 13. Perlman EM. Unusual refractive errors induced by interchanging trephines during penetrating keratoplasty. Refract Corneal Surg 1989; 5:271–273 14. Wilbanks GA, Cohen S, Chipman M, Rootman DS. Clinical outcomes following penetrating keratoplasty using the Barron-Hessburg and Hanna corneal trephination systems. Cornea 1996; 15:589 –598 15. Krumeich J, Binder PS, Knulle A. The theoretical effect of trephine tilt on postkeratoplasty astigmatism. CLAO J 1988; 14:213–219 16. Langenbucher A, Seitz B, Kus MM, et al. Graft decentration in penetrating keratoplasty: nonmechanical trephination with the excimer laser (193 nm) versus the motor trephine. Ophthalmic Surg Lasers 1998; 29:106 – 113 17. Lang GK, Schroeder E, Koch JW, et al. Excimer laser keratoplasty. Part 1: basic concepts. Ophthalmic Surg 1989; 20:262–267 18. Seitz B, Langenbucher A, Fischer S, et al. The regularity of laser keratectomy depth in nonmechanical trephina-



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33. Pineros O, Cohen EJ, Rapuano CJ, Laibson PR. Longterm results after penetrating keratoplasty for Fuchs’ endothelial dystrophy. Arch Ophthalmol 1996; 114:15– 18 34. Martin TP, Reed JW, Legault C, et al. Cataract formation and cataract extraction after penetrating keratoplasty. Ophthalmology 1994; 101:113–119 35. Donshik PC, Cavanaugh HD, Boruchoff SA, Dohlman CH. Posterior subcapsular cataracts induced by topical corticosteroids following keratoplasty for keratoconus. Ann Ophthalmol 1981; 13:29 –32 36. Costagliola C, Balestrieri P, Fioretti F, et al. ArF 193 nm excimer laser corneal surgery as a possible risk factor in cataractogenesis. Exp Eye Res 1994; 58:453– 457 37. Koralewska-Maka´r A, Flore´n I, Stenevi U. The results of penetrating keratoplasty for keratoconus. Acta Ophthalmol Scand 1996; 74:187–190 38. Urban RC Jr, Cotlier E. Corticosteroid-induced cataracts. Surv Ophthalmol 1986; 31:102–110 39. Seitz B, Langenbucher A, Kus MM, et al. Immunologische Transplantatreaktionen nach nichtmechanischer Hornhauttrepanation mit dem Excimerlaser. Ophthalmologe 1998; 95:607– 618 40. Ku¨chle M, Nguyen NX, Seitz B, et al. Blood-aqueous barrier after mechanical or nonmechanical excimer laser trephination in penetrating keratoplasty. Am J Ophthalmol 1998; 125:177–181 41. Hoffmann F, Pahlitzsch T. Predisposing factors in corneal graft rejection. Cornea 1989; 8:215–219 42. Ku¨chle M, Behrens A, Seitz B, et al. Free-running erbium:YAG laser for nonmechanical trephination in penetrating keratoplasty: first results of experimental trephination of human donor corneas. Graefes Arch Clin Exp Ophthalmol 1999; 237:875– 877 43. Langenbucher A, Ku¨chle M, Seitz B, et al. Thermal load of laser aperture masks in nonmechanical trephination for penetrating keratoplasty with the Er:YAG laser: comparison between stainless steel and ceramic masks. Graefes Arch Clin Exp Ophthalmol 2000; 238:339 – 345 44. Behrens A, Ku¨chle M, Seitz B, et al. Stromal thermal effects induced by nonmechanical (2.94-␮m) erbium YAG laser corneal trephination. Arch Ophthalmol 1998; 116:1342–1348 From the Department of Ophthalmology, University of Erlangen-Nu¨rnberg, Erlangen, Germany. Presented in part at the annual meeting of the American Academy of Ophthalmology, New Orleans, Louisiana, USA, November 1998. Supported by DAAD (German Academic Exchange Service, Bonn, Germany) grant no. 331 4 04 001 (Dr. Behrens). None of the authors has a financial interest in any product mentioned.


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