Laser-assisted subepithelial keratectomy retreatment after laser in situ keratomileusis

ARTICLE

Laser-assisted subepithelial keratectomy retreatment after laser in situ keratomileusis Ayman Saeed, MRCOphth, FRCS(Glasgow), Maeve O’Doherty, MRCOphth, John O’Doherty, PhD, Michael O’Keefe, FRCOphth

PURPOSE: To evaluate the efficacy and safety of laser-assisted subepithelial keratectomy (LASEK) retreatment after laser in situ keratomileusis (LASIK). SETTING: Mater Private Hospital, Dublin, Ireland. METHODS: In this retrospective study, 22 eyes of 20 patients had LASEK retreatment for residual refractive errors after LASIK. All patients who had the procedure between January 2004 and May 2007 were included in the study. The main outcome measures at the final follow-up visit were efficacy, predictability, safety, and stability. RESULTS: The mean spherical equivalent (SE) was 4.50 diopters (D) G 2.88 (SD) (range 10.00 to C3.87 D) before LASIK and 1.23 G 0.95 D (range 2.50 to C2.00 D) after LASIK. The mean time between the initial LASIK procedure and LASEK enhancement was 56.2 G 24.3 months (range 6 to 84 months). The mean follow-up after retreatment was 6.68 G 6.47 months (range 3 to 24 months). At the final follow-up visit, 19 eyes (86.4%) had an uncorrected visual acuity of 20/30 or better and 17 eyes (77.3%) were within G1.00 D of the target refraction. No patient lost more than 1 line of best corrected visual acuity or developed corneal haze greater than grade 1. CONCLUSION: Results indicate that LASEK retreatment after LASIK is a safe and effective alternative when LASIK retreatment is deemed unsafe because there is not sufficient residual corneal stromal bed or when retreatment is required many years after LASIK and relifting the original flap is expected to be problematic. J Cataract Refract Surg 2008; 34:1736–1741 Q 2008 ASCRS and ESCRS

Although laser in situ keratomileusis (LASIK) has been shown to be safe and effective,1,2 between 5% and 20% of those who have the procedure require a second treatment to achieve satisfactory visual outcomes.3–6 Previous reports show that LASIK enhancement, whether by flap relifting or by cutting a new flap, successfully treats residual refractive errors after LASIK in most cases.3–8 However, the amount of the estimated residual stromal tissue after LASIK revision is a limiting factor because a residual stromal

Accepted for publication June 18, 2008. From Mater Private Hospital (Saeed, M. O’Doherty, O’Keefe) and the National University of Ireland (J. O’Doherty), Dublin, Ireland. No author has a financial or proprietary interest in any material or method mentioned. Corresponding author: Dr. Ayman Saeed, Mater Private Hospital, Eccles Street, Dublin 7, Ireland. E-mail: [email protected].

1736

Q 2008 ASCRS and ESCRS Published by Elsevier Inc.

thickness of 250 mm or less has been associated with post-LASIK corneal ectasia.9,10 Surface ablation procedures, including photorefractive keratectomy (PRK) and laser-assisted subepithelial keratectomy (LASEK), are potentially useful modalities in the treatment of residual refractive errors after LASIK when further LASIK surgery is deemed unsafe. However, PRK retreatment after LASIK has been associated with severe corneal haze and loss of the best corrected visual acuity (BCVA).11 We conducted a retrospective analysis of the visual and refractive outcomes of LASEK enhancement in 22 eyes that had LASEK to treat residual refractive errors after LASIK. PATIENTS AND METHODS This study was a retrospective analysis of the records of all patients who had LASEK retreatment after LASIK between January 2004 and February 2007. Laser-assisted subepithelial keratectomy enhancement was the technique of choice to correct residual refractive errors after LASIK when the initial 0886-3350/08/$dsee front matter doi:10.1016/j.jcrs.2008.06.020

1737

LASEK RETREATMENT AFTER LASIK

Table 1. Visual and refractive details at baseline, after LASIK, and after LASEK enhancement. Preoperative Eye

UCVA

Subjective Refraction

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

20/200 20/200 CF 20/120 CF 20/60 20/200 20/200 20/200 20/60 CF 20/200 CF CF CF CF CF CF CF 20/200 20/200 20/200

2.25 1.00  30 2.00 0.50  130 8.50 0.75  170 4.25 C0.50  160 6.75 0.75  50 C3.50 C0.75  170 0.75 3.50  150 4.25 0.75  100 4.00 0.75  60 2.50 6.75 0.75  5 8.50 C1.50  90 4.00 10.00 5.25 4.50 6.25 0.50  160 4.00 2.00  14 5.00 0.50  110 3.00 2.50 2.75

MSE (D)

BCVA

CT (mm)

UCVA

2.75 2.25 8.88 4.75 6.63 3.63 2.38 5.13 4.50 3.00 8.75 8.75 4.00 10.00 5.00 4.75 6.25 5.00 5.00 3.00 2.50 2.75

20/16 20/20 20/30 20/30 20/20 20/30 20/30 20/16 20/16 20/16 20/20 20/20 20/20 20/30 20/20 20/20 20/20 20/30 20/16 20/20 20/30 20/20

618 624 605 515 589 602 534 587 584 475 540 670 520 620 514 519 570 563 616 611 620 483

20/80 20/40 20/120 20/25 20/40 20/60 20/40 20/40 20/40 20/40 20/60 20/80 20/40 20/40 20/120 20/120 20/30 20/40 20/40 20/60 20/200 20/40

BCVA Z best corrected visual acuity; CF Z counting fingers; CH Z corneal haze score; CT Z corneal thickness; FU Z follow-up after LASEK; LASEK Z laser-assisted subepithelial keratectomy; MSE Z manifest spherical equivalent; SE Z spherical equivalent; UCVA Z uncorrected visual acuity *Residual refractive error after LASEK secondary to regression; no evidence of corneal ectasia

LASIK treatment was performed several years before the need for revision, when the corneal thickness at retreatment was 500 mm or less, or when the estimated residual stromal tissue after laser ablation was 250 mm or less. No patient in the study had an eventful initial LASIK procedure. Before both the primary LASIK procedure and LASEK enhancement, all patients had a detailed ocular examination including uncorrected visual acuity (UCVA), BCVA, refraction (cycloplegic and subjective), anterior segment examination with slitlamp biomicroscopy, intraocular pressure check with Goldmann applanation tonometry, corneal topography, pachymetry, pupillometry, Schirmer test, and dilated fundus examination. Postoperatively, patients had ophthalmic reviews at 1 day, 1 week, 3 and 6 months, and 1 year. Subsequent visits were decided on an individual basis. Both the initial and retreatment procedures were performed by the same experienced surgeon (M.O.K.). The primary LASIK procedure was performed using a standard technique. Local anesthetic drops (proxymethacaine 0.5%) were instilled into the conjunctival sac before surgery. The cornea was marked with gentian violet, and a corneal flap (160 to 180 mm) with a superior base was cut using a Hansatome microkeratome (Bausch & Lomb). The flap was then lifted and laser ablation performed using a 193 nm argon– fluoride excimer laser (217 Technolas, Bausch & Lomb). The mean optical zone of laser ablation was 6.02 mm G 0.50 (SD) (range 5.5 to 7.0 mm). After ablation, the flap was repositioned.

The LASEK procedure was performed under topical anesthesia (proxymethacaine 0.5%). An alcohol solution cone with 8.5 mm diameter was placed on the eye. Twenty percent alcohol solution was instilled inside the cone, left for 30 seconds, and then carefully washed off with a chilled balanced salt solution. The epithelial flap was gently lifted and peeled back as a single sheet toward the 12 o’clock position using a spatula. Excimer laser treatment was then performed. The mean optical zone of laser ablation was 6.64 G 0.32 mm (range 6.0 to 7.0 mm). The flap was repositioned with a spatula, and a therapeutic bandage contact lens was placed on the eye. The bandage contact lens was removed, on average 4 days after the procedure, when the epithelium was healed. Postoperative medications included chloramphenicol 4 times a day until complete healing of the corneal epithelium followed by a tapering course of dexamethasone 0.1% 4 times a day for 3 weeks followed by twice a day for 3 weeks. Intraocular pressure was monitored while patients were on topical steroids. Statistical analysis of the data was performed using the Proc Mixed procedure of SAS (SAS Institute).12 A P value less than 0.05 was considered significant. Snellen visual acuity measurements were converted to logMAR values for statistical analysis.

RESULTS Of the 20 patients (22 eyes) who had LASEK retreatment, 14 (70.0%) were women and 6 (30.0%) were

J CATARACT REFRACT SURG - VOL 34, OCTOBER 2008

1738

LASEK RETREATMENT AFTER LASIK

Table 1. (Cont.) Before LASEK Retreatment Subjective Refraction 1.50 1.50 2.50 1.00 1.00 C2.00 C0.75 1.25 1.00 1.00 1.00 1.75 1.25 1.00 1.75 1.75 C0.25 1.00 0.75 0.75 1.50 1.00

0.75  15 0.50  140 0.50  85 0.50  50 1.00  140 0.25  170 0.50  180 0.50  170 0.50  50 1.25  180 0.50  60 1.00  130 0.50  180 0.25  25 1.00  80 0.25  90 0.25  10 0.75  5 0.50  10

Final Visit (After LASEK Retreatment)

SE (D)

BCVA

CT (mm)

UCVA

Subjective Refraction

1.88 1.75 2.50 1.25 1.25 C2.00 0.25 1.38 1.25 1.25 1.25 2.38 1.50 1.50 2.00 1.88 0.25 1.13 0.88 1.13 1.75 1.00

20/20 20/20 20/20 20/16 20/20 20/30 20/20 20/20 20/20 20/20 20/20 20/20 20/20 20/20 20/20 20/20 20/16 20/16 20/16 20/20 20/20 20/20

570 603 436 441 436 594 534 485 483 509 472 590 511 436 429 426 435 500 438 541 577 467

20/30 20/40 20/20 20/16 20/25 20/40 20/30 20/16 20/16 20/16 20/25 20/30 20/30 20/160 20/20 20/16 20/16 20/25 20/16 20/20 20/25 20/20

C1.25 1.25  175 C0.25 0.75  170 0.75 0.25  80 C0.50 0.50  80 0.75 0.75  130 C2.00 1.25  70 C0.50 0.50  110 C0.25 0.25  150 0.50 0.25  180 0.25 0.25 0.50  30 C0.50 0.50  180 1.25 0.50  120 4.00 2.00  170 0.5 0.25 C0.25 C0.25  120 C0.50 0.25  110 C0.50 C0.50  140 0.00 1.00  150 0.75 0.75  140 C0.50 0.50  180

men. The mean age of patients was 33 G 14 years (range 19 to 57 years). Twenty-one eyes (95.4%) had LASIK to treat myopia. Of those, 7 (33.3%) had 3.0 diopters (D) or less of myopia, 8 (38.1%) had between 3.0 D and 6.0 D, and 6 (28.6%) had more than 6.0 D. The mean time between the initial LASIK surgery and the LASEK enhancement was 56 G 24.3 months (range 6 to 84 months). The mean follow-up after retreatment was 6.68 G 6.47 months (range 3 to 24 months). The visual and refractive data at baseline, after LASIK, and after LASEK enhancement are shown in Table 1. Changes in the mean spherical equivalent (SE), mean UCVA, and mean BCVA are shown in Table 2. The clinical outcome measures in terms of efficacy, predictability, and safety are shown in Table 3. There was no statistically significant difference in the mean SE 1 week after LASEK or at the final visit (P Z .40). DISCUSSION Post-LASIK enhancement is usually done by relifting the original flap followed by laser ablation of the underlying stromal bed (LASIK revision). Potential complications of LASIK revision include flap-related problems

SE (D)

BCVA

FU (Mo)

CH

0.13 0.25 1.25 0.25 1.13 1.38 0.25 0.63 0.13 0.25 0.50 0.25 1.50 5.00* 0.25 0.50 0.00 0.38 0.75 0.50 0.63 0.25

20/20 20/20 20/16 20/16 20/20 20/30 20/20 20/16 20/16 20/16 20/20 20/20 20/30 20/25 20/16 20/16 20/16 20/20 20/16 20/20 20/25 20/20

3 6 12 4 3 24 24 3 3 6 3 4 7 16 3 4 3 3 3 4 3 6

1 0 1 1 0 1 0 0 0 0 0 1 1 1 1 1 0 0 0 0 1 0

(eg, difficulty relifting the flap), epithelial ingrowth at the flap interface, and post-LASIK corneal ectasia (particularly when the residual stromal thickness after the second procedure is estimated to be %250 mm).3–6 Surface ablation procedures (PRK and LASEK) preserve corneal stromal tissue and are not associated with flap-related complications. Photorefractive keratectomy enhancement after myopic LASIK was previously evaluated by Carones et al.11; however, they reported poor visual results. In their study, the attempted mean SE correction at PRK was 2.48 G 0.74 D (range 1.50 to 3.75 D). Fourteen (82.3%) of the 17 eyes that had PRK enhancement developed grade 3 or 4 corneal haze, and all had significant loss of BCVA. As a result, Carones et al. advise against the use of PRK to treat residual refractive errors after myopic LASIK. Laser-assisted subepithelial keratectomy is a surface ablation procedure that was introduced in 1999 by Massimo Camelin (M. Cimberle, ‘‘LASEK May Offer the Advantages of Both LASIK and PRK,’’ Ocular Surgery News, International Edition, March 1999, page 28). The preserved epithelial layer in LASEK is the main feature that distinguishes it from PRK. However, there is no consensus in the literature on whether

J CATARACT REFRACT SURG - VOL 34, OCTOBER 2008

1739

LASEK RETREATMENT AFTER LASIK

Table 2. Mean SE, mean UCVA, and mean BCVA before and after LASEK enhancement. Parameter

Preoperative

Mean SE (D) SD Range Mean logMAR UCVA (Snellen) SD Range

4.50 2.80 10.00 to C3.87 1.3 (20/400)

Mean logMAR BCVA (Snellen) SD Range

1 Wk After LASIK 0.19 0.69 1.50 to C1.25 0.1 (20/25)

At Retreatment 1.20 0.95 2.50 to C2.00 0.4 (20/50)

1 Wk After LASEK 0.30 0.73 2.37 to C0.75 0.2 (20/32)

At Final Visit 0.30 1.25 5.00 to C1.37 0.1 (20/25)

0.52 (5 lines) 2.0 to 0.5 (CF to 20/63) 0.02 (20/20)

0.13 (1.3 lines) 0.3 to 0.1 (20/40 to 20/16) 0.01 (20/20)

0.23 (2.3 lines) 1.0 to 0.1 (20/200 to 20/25) 0.02 (20/20)

0.21 (2.1 lines) 0.8 to 0.1 (20/120 to 20/16) 0.01 (20/20)

0.24 (2.4 lines) 1.0 to 0.1 (20/200 to 20/16) 0.02 (20/20)

0.11 (1.1 lines) 0.2 to 0.1 (20/32 to 20/16)

0.06 (0.6 line) 0.18 to 0.1 (20/32 to 20/16)

0.08 (0.8 line) 0.18 to 0.1 (20/32 to 20/16)

0.07 (0.7 line) 0.3 to 0.1 (20/40 to 20/16)

0.09 (0.9 line) 0.18 to 0.1 (20/32 to 20/16)

BCVA Z best corrected visual acuity; LASEK Z laser-assisted subepithelial keratectomy; LASIK Z laser in situ keratomileusis; SE Z spherical equivalent; UCVA Z uncorrected visual acuity

LASEK is superior to PRK. Lee et al.13 found that LASEK was associated with less severe ocular pain and less dense corneal haze than PRK. In contrast, Pirouzian et al.14–16 observed no difference between the 2 techniques in postoperative pain or achieved UCVA. Laboratory studies,17,18 however, show that the preserved epithelial layer in LASEK may act as a natural contact lens barrier against inflammatory mediators, thus decreasing keratocyte activation and subsequent corneal haze formation. At the final follow-up visit, 95% of our patients achieved a UCVA of 20/40 or better and 77% had a mean SE within G1.00 D of the target refraction.

Table 3. Efficacy, predictability, and safety of LASEK retreatment measured by the clinical outcomes at the final visit. Parameter Efficacy UCVA R6/7.5 UCVA R6/9 UCVA R6/12 Predictability Mean SE G0.50 D Mean SE G1.00 D Safety BCVA, lost 1 line BCVA, lost O1 line BCVA, gained R1 line Corneal haze, grade 1 Corneal haze, Ograde 1 Corneal ectasia

Number (%)

15 (68.2) 19 (86.4) 21 (95.4) 12 (55.4) 17 (77.3) 2 (9.1) 0 7 (31.8) 10 (45.4) 0 0

BCVA Z best corrected visual acuity; SE Z spherical equivalent; UCVA Z uncorrected visual acuity

These findings are comparable to those reported after LASIK revision by Saeed et al.3 and Netto and Wilson,4 who recorded a UCVA of 20/40 or better in 95% of cases and 92% of cases, respectively. The mean baseline SE in these 2 studies ( 4.85 G 2.57 D and 5.90 G 2.50 D, respectively) was comparable to that in our patients. Three recently published studies19–21 evaluated the efficacy and safety of LASEK enhancement after LASIK; none used mitomycin-C (MMC) as an adjuvant to LASEK. Cagıl et al.19 recorded a post-LASEK UCVA of 20/25 or better and 20/40 or better in 62.5% and 87.5% of eyes, respectively. These results compare favorably with ours; 68% and 95% of the retreated eyes achieved a UCVA of 20/25 or better and 20/40 or better, respectively, at the final visit. However, in terms of safety, Cagıl et al. report significant corneal haze in 5 eyes after LASEK. In 4 of the eyes, corneal haze regressed after intensive steroid treatment; however, in 1 eye (4%), the haze persisted despite treatment. In all eyes that developed significant haze, the SE of the attempted correction at LASEK was 2.00 D or more. In contrast, none of our patients lost lines of BCVA or developed greater than grade 1 corneal haze over the study period. A possible explanation for less corneal haze in our study is that the attempted mean SE correction at LASEK was less than that attempted in Cagıl et al.’s study ( 1.23 G 0.95 D, range 2.50 to C 2.00 D). Similarly, Li et al.,20 in an earlier report, recorded an improvement in UCVA after LASEK enhancement, with no patient developing greater than grade 1 corneal haze. In their study, the attempted SE correction at LASEK ranged from 1.00 to 3.25 D. Attempted corrections of higher degrees of myopia are associated with deeper laser

J CATARACT REFRACT SURG - VOL 34, OCTOBER 2008

1740

LASEK RETREATMENT AFTER LASIK

ablations. A possible correlation between ablation depth and the density of post-LASEK corneal haze was found by Lin et al.22 Beerthuizen and Siebelt21 evaluated the safety of surface ablation (LASEK and PRK) retreatment after LASIK and concluded that surface ablation is safe and effective in the treatment of small amounts of residual myopia after LASIK. However, their results did not distinguish retreatment outcomes of PRK from those of LASEK. Also, they used wavefrontguided retreatments in all patients, whereas none of our patients had wavefront-guided retreatment. Therefore, it would be difficult to draw direct comparisons between our results and their results because of the differences in methodology. In our study, the mean time before LASEK retreatment was 56 G 24 months (range 6 to 84 months). Attempting to relift flaps so many years after the initial LASIK is difficult and may result in complications (flap tears or buttonholes).23,24 Our results suggest that LASEK enhancement in these circumstances would be a safer alternative. The use of MMC has been advocated as a prophylactic measure against the development of corneal haze after PRK. Carones et al.25 report lower haze rates, better visual results, and more accurate refractive outcomes after PRK when a single dose of diluted MMC 0.02% was used intraoperatively. Srinivasan et al.26 also report less corneal haze when MMC was used with PRK to treat residual refractive errors after LASIK. The safety of using MMC 0.02% in refractive surgery has been investigated. Although Nassiri et al.27 and Morales et al.28 report a statistically significant drop in the endothelial cell count after MMC-supplemented PRK, other reports29–31 indicate that MMC has no deleterious effects on the corneal endothelium. Therefore, our current practice is to reserve the use of MMC 0.02% to treat cases of significant corneal haze rather than as a prophylactic measure. Residual stromal bed (RSB) thickness has been identified as a significant risk factor for the development of corneal ectasia after laser ablation.9,10 Reliable measurements of RSB thickness have been obtained using new techniques including in vivo confocal microscopy,32 very-high-frequency ultrasound,33 and highspeed optical coherence tomography of the cornea and anterior segment.34 Accurate preoperative measurement of the RSB would help the surgeon identify patients at risk for corneal ectasia in whom LASEK retreatment would be a safer option than LASIK revision. The limitations of our study are its retrospective nature, the small number of treated eyes, and the relatively short follow-up after LASEK retreatment.

In conclusion, our study confirms the safety of LASEK as a retreatment option after LASIK when LASIK revision is deemed unsafe because there is not sufficient RSB or when retreatment is required many years after LASIK and relifting the original flap is expected to be problematic. REFERENCES 1. Gimbel HV, Anderson Penno EE, van Westenbrugge JA, Ferensowicz M, Furlong MT. Incidence and management of intraoperative and early postoperative complications in 1000 consecutive laser in situ keratomileusis cases. Ophthalmology 1998; 105:1839–1847; discussion by TE Clinch, 1847– 1848 2. O’Doherty M, O’Keefe M, Kelleher C. Five year follow up of laser in situ keratomileusis for all levels of myopia. Br J Ophthalmol 2006; 90:20–23 3. Saeed A, O’Doherty M, O’Doherty J, O’Keefe M. Analysis of the visual and refractive outcome following laser in situ keratomileusis (LASIK) retreatment over a four-year follow-up period. Int Ophthalmol 2007; 27:23–29 4. Netto MWV, Wilson SE. Flap lift for LASIK retreatment in eyes with myopia. Ophthalmology 2004; 111:1362–1367 5. Brahma A, McGhee CNJ, Craig JP, Brown AD, Weed KH, McGhee J, Brown R. Safety and predictability of laser in situ keratomileusis enhancement by flap reelevation in high myopia. J Cataract Refract Surg 2001; 27:593–603 6. Lyle WA, Jin GJC. Retreatment after initial laser in situ keratomileusis. J Cataract Refract Surg 2000; 26:650–659 7. Rubinfeld RS, Hardten DR, Donnenfeld ED, Stein RM, Koch DD, Speaker MG, Frucht-Pery J, Kameen AJ, Negvesky GJ. To lift or recut: changing trends in LASIK enhancement. J Cataract Refract Surg 2003; 29:2306–2317 8. Davis EA, Hardten DR, Lindstrom M, Samuelson TW, Lindstrom RL. LASIK enhancements; a comparison of lifting to recutting the flap. Ophthalmology 2002; 109:2308–2313; discussion by RS Rubinfeld, 2313–2314 9. Condon PI. Will keratectasia be a major complication for LASIK in the long term? 2005 ESCRS Ridley Medal Lecture. J Cataract Refract Surg 2006; 32:2124–2132 10. Randleman JB, Russell B, Ward MA, Thompson KP, Stulting RD. Risk factors and prognosis for corneal ectasia after LASIK. Ophthalmology 2003; 110:267–275 11. Carones F, Vigo L, Carones AV, Brancato R. Evaluation of photorefractive keratectomy retreatments after regressed myopic laser in situ keratomileusis. Ophthalmology 2001; 108:1732–1737 12. Littel RC, Milliken GA, Stroup WW, Wolfinger RD. SASÒ Systems for Mixed Models. Gary, NC, SAS Institute, 1996 13. Lee JB, Seong GJ, Lee JH, Seo KY, Lee YG, Kim EK. Comparison of laser epithelial keratomileusis and photorefractive keratectomy for low to moderate myopia. J Cataract Refract Surg 2001; 27:565–570 14. Pirouzian A, Thornton J, Ngo S. One-year outcomes of a bilateral randomized prospective clinical trial comparing laser subepithelial keratomileusis and photorefractive keratectomy. J Refract Surg 2006; 22:575–579 15. Pirouzian A, Ngo S, Thornton J. LASEK versus PRK [letter]. Ophthalmology 2006; 113:1883 16. Pirouzian A, Thornton JA, Ngo S. A randomized prospective clinical trial comparing laser subepithelial keratomileusis and photorefractive keratectomy. Arch Ophthalmol 2004; 122:11–16 17. Esquenazi S, He J, Bazan NG, Bazan HEP. Comparison of corneal wound-healing response in photorefractive keratectomy

J CATARACT REFRACT SURG - VOL 34, OCTOBER 2008

1741

LASEK RETREATMENT AFTER LASIK

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

and laser-assisted subepithelial keratectomy. J Cataract Refract Surg 2005; 31:1632–1639 Laube T, Wissing S, Theiss C, Brockmann C, Steuhl K-P, Meller D. Decreased keratocyte death after laser-assisted subepithelial keratectomy and photorefractive keratectomy in rabbits. J Cataract Refract Surg 2004; 30:1998–2004 Cagıl N, Aydin B, Ozturk S. Hasıripi. Effectiveness of laser-assisted subepithelial keratectomy to treat residual refractive errors after laser in situ keratomileusis. J Cataract Refract Surg 2007; 33:642–647 Li Y, Li JH, Zhou F. [LASEK for the correction of residual myopia and astigmatism after LASIK]. [Chinese] Zhonghua Yan Ke Za Zhi 2005; 41:981–985 Beerthuizen JJG, Siebelt E. Surface ablation after laser in situ keratomileusis: retreatment on the flap. J Cataract Refract Surg 2007; 33:1376–1380 Lin N, Yee SB, Mitra S. Chuang AZ Yee RW. Prediction of corneal haze using an ablation depth/corneal thickness ratio after laser epithelial keratomileusis. J Refract Surg 2004; 20:797– 802 Maldonado MJ, Juberı´as JR, Pin˜ero DP, Alvarez-Vidal A, Rutzen AR. Flap tearing during lift-flap laser in situ keratomileusis retreatment. J Cataract Refract Surg 2005; 31:2016–2018 Gressel MG, Belsole VL. Laser in situ keratomileusis flap tear during lifting for enhancement in the presence of post-photorefractive keratectomy corneal haze. J Cataract Refract Surg 2004; 30:706–708 Carones F, Vigo L, Scandola E, Vacchini L. Evaluation of the prophylactic use of mitomycin-C to inhibit haze formation after photorefractive keratectomy. J Cataract Refract Surg 2002; 28:2088– 2095 Srinivasan S, Drake A, Herzig S. Photorefractive keratectomy with 0.02% mitomycin C for treatment of residual refractive errors after LASIK. J Refract Surg 2008; 24:S64–S67 Nassiri N, Farahangiz S, Rahnavardi M, Rahmani L, Nassiri N. Corneal endothelial cell injury induced by mitomycin-C in photorefractive keratectomy: nonrandomized controlled trial. J Cataract Refract Surg 2008; 34:902–908

28. Morales AJ, Zadok D, Mora-Retana R, Martı´nez-Gama E, Robledo NE, Chayet AS. Intraoperative mitomycin and corneal endothelium after photorefractive keratectomy. Am J Ophthalmol 2006; 142:400–404 29. Diakonis VF, Pallikaris A, Kymionis GD, Markomanolakis MM. Alterations in endothelial cell density after photorefractive keratectomy with adjuvant mitomycin. Am J Ophthalmol 2007; 144:99–103 30. Goldsberry DH, Epstein RJ, Majmudar PA, Epstein RH, Dennis RF, Holley G, Edelhauser HF. Effect of mitomycin C on the corneal endothelium when used for corneal subepithelial haze prophylaxis following photorefractive keratectomy. J Refract Surg 2007; 23:724–727 31. De Benito-Llopis L, Teus MA, Ortega M. Effect of mitomycin-C on the corneal endothelium during excimer laser surface ablation. J Cataract Refract Surg 2007; 33:1009–1013 32. Pisella PJ, Auzerie O, Bokobza Y, Debbasch C, Baudouin C. Evaluation of corneal stromal changes in vivo after laser in situ keratomileusis with confocal microscopy. Ophthalmology 2001; 108:1744–1750 33. Reinstein DZ, Couch DG, Archer T. Direct residual stromal thickness measurement for assessing suitability for LASIK enhancement by Artemis 3D very high-frequency digital ultrasound arc scanning. J Cataract Refract Surg 2006; 32:1884– 1888 34. Li Y, Netto MV, Shekhar R, Krueger RR, Huang D. A longitudinal study of LASIK flap and stromal thickness with high-speed optical coherence tomography. Ophthalmology 2007; 114:1124– 1132

J CATARACT REFRACT SURG - VOL 34, OCTOBER 2008

First author: Ayman Saeed, MRCOphth, FRCS(Glasgow) Mater Private Hospital, Dublin, Ireland