Photorefractive keratectomy after radial keratotomy

Photorefractive keratectomy after radial keratotomy

a r t -c I I es Photorefractive keratectomy after radial keratotomy Jenny Meza, M.D., Juan J. Perez-Santonja, M.D., Eva Moreno, M.D., Miguel A. Za...

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Photorefractive keratectomy after radial keratotomy Jenny Meza, M.D., Juan J. Perez-Santonja, M.D., Eva Moreno, M.D., Miguel A. Zato, M.D.

ABSTRACT We report the results of a prospective study that evaluated the efficacy, predictability, and safety of excimer laser photorefractive keratectomy (PRK) to correct residual myopia after radial keratotomy (RK). Using a 193 nm excimer laser, we performed PRK on ten undercorrected myopic eyes that had previous RK surgery. The mean interval between the RK and PRK was 1.5 years. Mean follow-up was seven months. Mean preoperative refraction was -4.08 ± 1.35 diopters (D) and after PRK was +1.61 ± 1.18 D at three months, +1.05 ± 0.75 D at six months, and +0.79 ± 0.83 D at 12 months. An uncorrected visual acuity of 20/40 or better was achieved in eight eyes at three months, seven eyes at six months, and three eyes at 12 months. One eye had a transient loss of two Snellen lines of best spectacle corrected visual acuity because of increased haze. No other significant complication was noted. Our study shows that PRK is a predictable, effective, stable, and safe technique to correct residual myopia after RK. The results were similar to those of PRK without prior surgery, although we noted a slightly greater hyperopic deviation. We believe that eyes undercorrected by RK may benefit from subsequent PRK. Key Words: excimer laser, keratotomy

myopia,

In radial keratotomy (RK), radial incisions approximately 90% to 95% deep are made in the cornea with a calibrated crystal knife. The incisions weaken the peripheral cornea, which moves anteriorly under the influence of intraocular pressure (lOP), causing a compensatory posterior movement and flattening of the central cornea.' Undercorrection and overcorrection are common. In one study, five years after surgery, 19% of operated eyes remained myopic by more than 1.00 diopter (0). 2 Three basic techniques can be used to reduce myopia further: deepening, adding, or lengthening incisions. 1•2 However, the nonlinear characteristics of corneal biomechanics often limit the amount of central flattening that can be achieved. 3 Therefore, some patients (4. 5% to 23.0% )4 •5 have a residual myopic refractive error.

photorefractive

keratectomy,

radial

Photorefractive keratectomy (PRK) is a relatively new procedure that reduces central corneal curvature by direct photoablation of the central cornea. 6 Recent studies have found that excimer laser PRK offers better predictability, efficacy, and safety than RK. 7- 10 Patients undercorrected after RK might benefit from an additional flattening induced by a different procedure, such as PRK. However, few studies have been published on PRK after RK. 11 - 13 We present the results of excimer laser PRK on ten eyes of seven patients undercorrected by previous RK surgery.

MATERIALS AND METHODS Between March 1992 and March 1993, we performed one-step PRK with the ExciMed UV200 193 nm ex-

From the Department of Ophthalmology, Jimenez-Diaz Foundation, Autonomous University ofMadrid School ofMedicine, Madrid, Spain. Reprint requests to Miguel A. Zato, M.D., Department of Ophthalmology, Fundacion Jimenez-Diaz, Avenida Reyes Cat6licos 2, 28040-Madrid, Spain. J CATARACT REFRACT SURG-VOL 20, SEPTEMBER 1994

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Table 1. Manifest refraction (spherical equivalent in diopters) after excimer laser PRK in eyes with residual myopia after RK. RefracUncorrected Refraction; Uncorrected VA; Corrected VA After PRK Sex/ tion Be- VA; Corrected 3 Months 12 Months 1 Month 6 Months Eye Age fore PRK VA Before PRK 1 F/36 3.00 20/400;20/20 +0. 75;20/28;20/20 +2.00;20/22;20/20 + 1.50;20/20;20/20 + 1.50;20/22;20/20 -3.75 2 F/38 20/400;20/22 + 1.00;20/20;20/20 + 1.00;20/25;20/20 + 1.00;20/20;20/20 -4.50 3 F/38 20/600;20/28 + 1.75;20/32;20/28 +0 .25 ;20/28 ;20/25 -0.25;20/28;20/25 4 M/34 -4.87 20/800;20/28 + 2.88 ;20150;20/20 +0.38;20/32;20/20 +0.13;20/32;20/22 -0.12;20/28;20/22 5 M/36 -2.12 20/100;20/20 +2.25;20/28;20/25 + 2.25;20/20;20/20 + 1. 75;20/20;20/20 -5.00 20/800;20/50 +2.00;20/60;20/50 + 1.00;20/60;20/50 + 1.50;20/60;20/40 6 F/21 -4.50 7 F/21 20/600;20/60 + 3.25;20/ 100;20/60 + 2.00;20/60;20/60 8 M/29 -5.75 20/800;20/20 +4. 75;20/20;20/20 + 3. 75;20/22;20 /20 + 1.75;20/40;20/32 + 1.00;20/25;20/20 20/800;20/28 + 2.50;20/32;20/28 + 3.00;20/28 ;20/25 + 1.00;20/25;20/25 9 M/26 -5.50 10 M/36 -1.87 20/60;20/20 +0. 75;20/20;20/20 +0.50;20/20;20/20 Note: Eyes 2 and 3, 6 and 7, and 5 and 10 are the right and left eyes of one patient.

cimerlaser(Summit Technology, Waltham, MA) on ten myopic eyes (seven patients) that were undercorrected after RK surgery. We used an energy fluence of 180 mJ/cm 2, repetition rate of 10Hz, and cut rate of 0.25 )lm per pulse. Ablation zone diameter was 5.00 mm; no more than 6.00 D of myopia was corrected. Patient age ranged from 21 years to 38 years (mean 31.43 years; SD 6.26 years). Five eyes were in male patients and five in female (Table l ). The time between RK and PRK was from one year to three years (mean l. 5 years). Seven eyes had eight-incision RK, one eye had 16-incision RK, and two had combined eight radial and two T-incisions. Preoperative and postoperative examination included uncorrected and corrected visual acuit~, manifest and cycloplegic refractions, slitlamp mtcrosc~py, manual and automated keratometry, and applanatiOn tonometry. Surgery was performed under topical anesthesia with 0.5% proparacaine. Before treatment, miosis was induced with pilocarpine 2% drops. Manual abrasion of the central corneal epithelium was done with a hockey knife within the central6 mm of the cornea, followed by cleaning with a microsponge. After the patient fixated on the target light, we fired the excimer laser with the pupil centered with the helium-neon beams. Postoperatively, tobramycin 0.3% ointment was instilled four times daily and the eye patched for three to four days until re-epithelialization was complete. After re-epithelialization, 0.10% topical fluorometholone was used five times a day for one month, then tapered for two more months. Postoperative evaluations were conducted at three days; one and two weeks· one three six ' ' ' ' and 12 months; and as necessary. Corneal haze was graded from 0 to 4 (Table 2). All patients gave informed consent after receiving a detailed description of PRK and a thorough review of the procedure's known risks. The paired Student's t-test was used for statistical analysis. 486

RESULTS Re-epithelialization was complete within three to four days in all patients, and slitlamp microscopy of the central portion of the radial incisions included within the ablation zone showed no morphologic changes. No infection or recurrent erosions were noted. Preoperative uncorrected visual acuity ranged from 20/800 to 20/60 and best spectacle corrected visual acuity, from 20/60 to 20/20 (Table 1). Eight eyes had an uncorrected visual acuity of 20/40 or better at three months after surgery, seven eyes at six months, and three eyes at 12 months. Statistical analysis showed that at one, three, six, and 12 months, uncorrected visual acuity improved significantly from preoperative acuity (P < .000 1). Best spectacle corrected visual acuity was equal to or better than the preoperative level in nine eyes at one month, ten eyes at three months, seven eyes at six months, and three eyes at 12 months. No statistically significant change in best spectacle corrected visual acuity was found from the preoperative to any postoperative examination (Table 1). Two eyes (#6 and #7) of the Same patient had a preoperative best spectacle corrected visual acuity equal to or worse than 20/50 because of irregular Table 2. Classification of subepithelial corneal haze after PRK. Grade 0

Description Clear cornea T~ace ofh~ze, perc~pti~le

m1croscop1c exammatwn 2 3 4

only by careful slitlamp

Mild haze, easily detectable by slitlamp microscopic examination Moderate opacity that partially impairs the view of the anterior chamber and iris details Marked opacity

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astigmatism, probably as a result of the previous RK (Table 1). The PRK did not improve best spectacle corrected visual acuity significantly. The preoperative mean refractive error of -4.08 ± 1.35 D changed to +2.18 ± 1.25 D at one month after surgery, + 1.61 ± 1.18 D at three months, + 1.05 ± 0.75 D at six months, and +0.79 ± 0.83 D at 12 months (Figure 1). All eyes showed a postoperative hyperopia, which tended to approach emmetropia in subsequent months (Figure 1). Three months and six months postoperatively, five and four eyes, respectively, were within ± 1.00 D of attempted correction, as were two eyes at 12 months. Preoperative keratometric readings were 7.88 ± 0.34 mm; they reached their maximum value (8.92 ± 0.65 mm) at one month after surgery (P < .0001 ). The values gradually decreased up to 12 months (8.37 ± 0.26 mm) (one versus six months; P < .01) (Figure 2). However, the readings did not achieve preoperative keratometric values. Corneal haze was pronounced one and three months after surgery but gradually decreased (Figures 3 and 4). One eye (#8) showed grade 3 corneal haze six months after surgery and uncorrected visual acuity in that eye dropped to 20/40; reinstatement of fluorometholone treatment substantially decreased haze and improved visual acuity. Transient lOP elevation in one eye (22 mm Hg) at three months was controlled by stopping corticosteroid drops and administering beta-blockers. The most common subjective complaints were blurring or decreased vision and glare or halos at night (Table 3).

Keratometric

r-----------------

readings (mm)

10 ............ . . . .............. . ... ..... . . . ...................... .

9 ......... . ...................................... .

8 ........................ . .......

······ ... ·········

7 ···· · · ... . ..... . .... . . .... . ...... . ........ .. ..... · · ······· · · · · ···.

6~----------------~

Pre-PRK

3

(Months)

6

12

Fig. 2.

(Meza) Keratometric readings (mean± SO) in eyes that received PRK for residual myopia after RK.

Fig. 3.

(Meza) Slitlamp photograph three months after PRK showing a grade 2 haze.

DISCUSSION In refractive surgery, anterior corneal curvature is often changed to correct myopia. Radial keratotomy is the most widely used technique. 1 Studies have shown that RK is a relatively safe, effective procedure to treat low to moderate myopia. 2 • 14 Yet, the procedure has ManHest refraction (D)

5..-----------------------, 4

3

2 o,_----~---~--~--~---­

-1

-2 -3 -4

-5 -6~--~-------------~

Pre-PRK

3

6

12

(Months)

Fig. 1.

(Meza) Evolution of manifest refraction (spherical equivalent) during the 12 months after PRK in eyes with previous RK surgery. The solid line represents mean values.

limited acceptance because it often produces inaccurate incisions, resulting in corneal complications, limited predictability, refractive fluctuation, and continued progressive effect. 2 •15 Excimer laser PRK is a relatively new technique to treat low to moderate myopia. Clinical results indicate that PRK offers good predictability, efficacy, and safety. ?-to Our study investigated whether the safety, predictability, and effectiveness after PRK in eyes that had previous RK surgery were different from that in eyes that had PRK only. It also looked at potential postoperative complications. Predictability of intended refractive change was demonstrated by mean refraction at six and 12 months postoperatively. Mean refraction at six months (±SD) was + 1.05 ± 0.75 D and at 12 months was +0.79 ± 0.83 D. However, the mean postoperative hyperopia in our series was greater than that of PRK alone at any time of

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(%)

.I

100

HAZE EVOLUTION

I

70

80

66

0 Grade 0 Grade 1 .Grade 2 .Grade 3

1 Month

3 Months

6 Months

12 Months

(Time)

Fig. 4.

(Meza) Percentage of eyes with a defined haze grade at each follow-up.

Table 3. Complications. Number of Eyes (N = 10)

Complication Increased lOP, corticosteroid induced Haze (grade 2 or more) Decrease in best spectacle corrected visual acuity (transient) Blurred or decreased night vision (at six months) Glare or halos at night (at six months)

RK.7,9,10,12,13

5 5

follow-up (at one month: +2.18 D versus +1.76 0, 9 + 1.66 0,1° and + 1.11 0 16 ; at three months: + 1.61 D versus +0.49 0 9 and +0.43 D; 10 at six months: + 1.05 D versus +0.21 0 10 and -0.06 0;9 and at 12 months: +0. 79 D versus -0.04 D 10 and -0.52 0 9), although there was no difference in standard deviations. 9 •10 Because of the greater hyperopic shift in our study, only foureyes(50%) and two eyes(66%)at six and 12 months after surgery, respectively, were within ± 1.00 D of attempted correction, compared with 78% 9 and from 71% 9 to 86% 10 of eyes at six and 12 months, respectively, after PRK alone. Mean postoperative refraction at six and 12 months postoperatively may indicate the stability of the refractive results. Some studies on PRK have reported that stabilization of mean refraction was observed between six and 12 months after surgery. 7• 10 But the sample at 12 months after surgery was too small to lead us to conclude that the stability suggested by the mean refractions at six and 12 months predicts future refractive stability. Uncorrected visual acuity is the main criterion used to assess the effectiveness of a refractive procedure. 17 In this series, seven eyes and three eyes had an uncorrected visual acuity of 20/40 or better at six months and at 12 months after surgery, respectively. These results were similar to the PRK-alone series. 7•9 • 10 488

Refractive technique safety is documented by two variables: loss of best spectacle corrected visual acuity and vision-threatening complications. 18 Only one eye in our series lost two Snellen lines (at six months postoperatively because of increased haze); resuming steroid therapy improved visual acuity. The incidence of haze was similar to that of PRK alone 7 •9 and only affected best spectacle corrected visual acuity in one eye. A corticosteroid-induced transient lOP increase developed in one eye (I 0% ). The subjective symptoms reported in our study were not different from those in cases in which only PRK was performed. 7 McDonnell and coauthors 11 reported good refractive results in two eyes three months after PRK with previous RK. Seiler and Jean 12 presented five eyes undercorrected by RK that were treated with PRK with a follow-up of six months to one year. The predictability, efficacy, stability, and safety in their study were similar to that of a series of PRK without previous RK. Hahn and coauthors 13 performed PRK on ten undercorrected eyes after RK; follow-up was nine months. Their results were also similar to those obtained with PRK without previous surgery. Nevertheless, our results show a greater hyperopic shift than PRK with or without previous In conclusion, our study shows that PRK is a predictable, effective, stable, and safe technique to correct residual myopia after RK. Our results are similar to those of eyes that had PRK but no previous surgery, although there was a slightly greater hyperopic deviation in our study. A decrease in steroid therapy might lessen this difference. 10 Although the number of cases and length offollow-up in our study were too small to produce definitive results, we believe that eyes undercorrected by RK may benefit from subsequent PRK. REFERENCES I. Waring GO III. Radial keratotomy. Ophthalmol Clin NA 1992; 5:695-707 2. Waring GO III, Lynn MJ, Nizam A, et al. Results of the Prospective Evaluation of Radial Keratotomy (PERK) Study five years after surgery. Ophthalmology 1991; 98: 1164-1176 3. Hanna KD, Jouve FE, Waring GO III. Preliminary computer simulation of the effects of radial keratotomy. Arch Ophthalmol 1989; 107:911-918 4. Franks S. Radial keratotomy undercorrections: a new approach. J Refract Surg 1986; 2:171-173 5. Hofmann R. Reoperation after radial and astigmatic keratotomy. J Refract Surg 1987; 3:119-128 6. Thompson K. Photorefractive keratectomy. Ophthalmol Clin NA 1992; 5:745-751 7. Kim JH, Hahn TW, Lee YC, et al. Photorefractive keratectomy in 202 myopic eyes: one year results. Refract Corneal Surg 1993; 9(suppi):SII-SI6 8. Seiler T, Wollensak J. Myopic photorefractive keratectomy with the excimer laser. One year follow-up. Ophthalmology 1991; 98: 1156-1163 9. Brancato R, Tavola A, Carones F, et al. Excimer laser

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photorefractive keratectomy for myopia: results in 1165 eyes. Refract Corneal Surg 1993; 9:95-104 Tengroth B, Epstein D, Fagerholm P, eta!. Excimer laser photorefractive keratectomy for myopia. Clinical results in sighted eyes. Ophthalmology 1993; 100:739-745 McDonnell PJ, Garbus JJ, Salz JJ. Excimer laser myopic photorefractive keratectomy after undercorrected radial keratotomy. Refract Corneal Surg 1991; 7:146-150 Seiler T, Jean B. Photorefractive keratectomy as a second attempt to correct myopia after radial keratotomy. Refract Corneal Surg 1992; 8:211-214 Hahn TW, Kim JH, Lee YC. Excimer laser photorefractive keratectomy to correct residual myopia after radial keratotomy. Refract Corneal Surg 1993; 9(suppl):S25S29

14. Deitz MR, Sanders DR, Raanan MG. A consecutive series (1982-1985) of radial keratotomies performed with the diamond blade. Am J Ophthalmol 1987; 103:417-422 15. Rashid ER, Waring GO III. Complications from radial keratotomy. Surv Ophthalmol1989; 34:73-106 16. Moreno E, Meza J, Gasco J, Zato MA. Resultados preliminares tras Ia correcci6n de la miopia mediante lliser excimer. Arch Soc Esp Oftalmol 1993; 64:3-10 17. Lynn MJ, Waring GO III, Carter JT. Combining refractive error and uncorrected visual acuity to assess the effectiveness of refractive corneal surgery. Refract Corneal Surg 1990; 6:103-109 18. Waring GO III. Standardized data collection and reporting for refractive surgery. Refract Corneal Surg 1992; 8(suppl): 1-42

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