Purpose
To evaluate the visual and refractive results and the incidence of complications after laser subepithelial keratectomy (LASEK) enhancement using mitomycin C (MMC) after a previous LASEK procedure with MMC.
Design
Retrospective, noncomparative, interventional case series.
Methods
Setting was Vissum Santa Hortensia, Madrid, Spain. We performed a retrospective study of LASEK-treated eyes that received intraoperative MMC for 30 seconds and that needed an enhancement procedure. LASEK retreatment with MMC 0.02%, applied for 60 seconds, was performed 3 to 6 months after the initial surgery. We measured the visual and refractive results 3 months after the enhancement and the incidence of complications.
Results
Eighty-two eyes were included in the study. The preoperative data were best spectacle-corrected visual acuity (BSCVA) 1.08 ± 0.19, sphere −4.68 ± 2.8 diopters (D), and cylinder −1.30 ± 1.20 D. Three to 6 months postoperatively, before enhancement, the uncorrected VA (UCVA) was 0.59 ± 0.2; the BSCVA, 0.976 ± 0.2; the residual sphere, +0.17 ± 0.7 D, and the cylinder, −0.39 ± 0.5 D. Three months after retreatment, the UCVA was 0.93 ± 0.1; the BSCVA, 0.977 ± 0.1; the residual sphere, 0.09 ± 0.3 D; and the residual cylinder, −0.2 ± 0.3 D. The safety index after retreatment was 1.01 ± 0.1, and the efficacy index was 0.96 ± 0.1. No haze, no delay in epithelial healing, and no case of endothelial decompensation were detected.
Conclusion
Surface ablation retreatment using MMC seems to be effective to correct residual refractive errors after an initial surgery with MMC.
Mitomycin C (MMC) has played a deciding role in the current revival of excimer laser surface ablation techniques. MMC is an alkylating agent with cytotoxic and antiproliferative effects that reduces the myofibroblast repopulation after laser surface ablation and, therefore, reduces the risk of postoperative corneal haze. It is used prophylactically to avoid haze after primary surface ablation and therapeutically to treat pre-existing haze.
When performing a retreatment over a previous surface ablation, there is no consensus on the need for MMC. Some authors have performed surface ablation enhancements without MMC and found no significant incidence of postoperative haze when treating low residual myopia. Nevertheless, because of the presence of activated keratocytes at the site of ablation, haze may be more likely to appear and may cause a decrease in best spectacle-corrected visual acuity (BSCVA). Therefore, it has been suggested that MMC would be useful in surface ablation enhancements. We had observed a greater tendency to develop haze after surface ablation enhancements in which no MMC was applied even if it had been applied during the initial surgery, especially when a hyperopic error was retreated. Retreatment with MMC of clinically significant haze after a previous surface ablation is a well established indication, and we had detected no complications when using this drug to treat haze developed after a previous surgery in which MMC had already been used. Therefore, we started using MMC in surface ablation enhancements in eyes with no clinically significant haze to avoid its development after the retreatment. However, there are no studies regarding the safety of reapplying the drug. That is the reason why we decided to evaluate the visual and refractive results and the incidence of complications after surface ablation enhancements using intraoperative MMC after an initial surface ablation procedure in which the MMC was already applied.
Patients and Methods
We performed a retrospective study of consecutive eyes that underwent laser-assisted subepithelial keratectomy (LASEK) to correct a myopic error (with or without astigmatism) between January 1, 2006, and December 31, 2007, and that received intraoperative MMC prophylactically because of an ablation depth greater than 50 μm. Among these patients, those that needed enhancement because of residual refraction 3 to 6 months postoperatively and in which LASEK retreatment was performed with a second application of MMC 0.02% were included in the study. The use of MMC in this setting is considered “off-label,” both during the primary treatment and during the retreatment.
When evaluated for surgery, we excluded patients with unstable refraction and keratoconus suspects. The decision to perform LASEK instead of laser in situ keratomileusis (LASIK) had been based either on the calculated residual stromal thickness being too thin to perform LASIK or on the patient preferences after being fully informed about the advantages and disadvantages of this procedure.
All study patients underwent a full ophthalmologic examination before surgery that included the measurement of uncorrected visual acuity (UCVA), the BSCVA (using a Snellen chart [Nidek auto chart projector CP 670; Nidek Co, Ltd, Gamagori, Japan] and including manifest and cycloplegic refractions), slit-lamp biomicroscopy, tonometry (CT-80; Topcon, Tokyo, Japan), corneal pachymetry (DGH 5100 contact pachymeter; DGH Technology, Inc, Exton, Pennsylvania, USA), keratometry and corneal topography (CSO; Compagnia Strumenti Oftalmici, Firenze, Italy), mesopic pupil measurement (Colvard pupillometer; Oasis, Glendora, California, USA), and funduscopy.
Surgical Technique
All procedures were performed by 2 surgeons (M.A.T., L.B.L.), using the same Esiris Schwind excimer laser (Schwind Eye Tech Solutions, Kleinostheim, Germany) using a PRK nomogram and a conventional treatment. Both surgeons had experience with both techniques before starting this study, thus avoiding the possible effect of the learning curve on the visual results.
All surgeries were performed using topical anesthesia (lidocaine 2%). A 20% alcohol solution (diluted in balanced salt solution [BSS]) was instilled inside an 8-mm corneal marker centered on the pupil and left for 40 seconds. During the primary surgery, the ablation depth was deeper than 50 μm, and therefore a 7-mm round cellulose sponge soaked in MMC 0.02% was applied for 30 seconds over the ablated stroma, carefully avoiding leakage of the drug to the epithelial flap and the limbus. Because no study has demonstrated yet the exact ablation depth below which there is no risk of haze, we arbitrarily set the cut-off for using prophylactic MMC at 50 μm of ablation depth, as previously reported. The programmed ablation was 10% less than the intended correction to avoid overcorrection. The stroma then was rinsed copiously with BSS, and the epithelial flap was repositioned using the same cannula. A therapeutic soft contact lens (Acuvue Oasys; Johnson & Johnson Vision Care, Inc, Jacksonville, Florida, USA) was placed carefully on the eye and antibiotic drops (ciprofloxacin 3 mg/mL) and nonsteroidal anti-inflammatory drops (ketorolac trometamol 5 mg/mL) were applied.
The enhancement procedure was performed exactly as described for primary treatments, using MMC 0.02% during 60 seconds over the ablated stroma in all cases.
Postoperative Follow-Up
The medications consisted of topical antibiotic (ciprofloxacin 3 mg/mL) and steroid (dexamethasone alcohol 1 mg/mL) drops 4 times daily during the first week postoperatively. The drops were then tapered and stopped 1 month after the surgery. The therapeutic contact lens was removed 1 week after surgery if re-epithelialization was complete. Otherwise, the contact lens was put back in place and the patient reviewed after 24 hours, following the same protocol.
Examinations were scheduled at 1 day, 1 week, and 1 and 3 months postoperatively. Two optometrists did the refractions at each postoperative visit. All patients were refracted in the same room with the same light adjusted to mesopic conditions. Just before writing this manuscript (1.5 to 3.5 years after the initial surgery), patients were contacted by telephone to check whether any complication had appeared in the meantime.
Statistical Analysis
The Statview+Graphics program (Abacus Concept Inc, Cupertino, California, USA) was used for data analysis. Statistical comparisons were done with the unpaired 2-tailed Student t test. P ≤ .05 was considered statistically significant. Visual acuity was converted to the logarithm of minimal angle of resolution (logMAR) from the decimal notation for statistical analysis, using a visual acuity conversion chart. Continuous data are expressed as the mean ± standard deviation.
Results
Eighty-two consecutive eyes were analyzed. The mean patient age was 31.9 ± 6.8 years (range, 19 to 63 years). The mean preoperative spherical refraction values were −4.68 ± 2.8 diopters (D) (range, −0.50 to −13.00 D). The mean preoperative cylinder values were −1.3 ± 1.2 D (range, 0 to −6.00 D). BSCVA was 1.08 ± 0.19 (range, 0.4 to 1.25).
Table 1 shows the postoperative data 3 to 6 months after the initial surgery and before retreatment, compared to data 3 months after enhancement. The UCVA significantly improved after enhancement, whereas the BSCVA did not show any significant change after enhancement compared to before retreatment or before the initial surgery. The Figure shows the change in lines of BSCVA 3 months after the enhancement compared to the initial BSCVA.
| Before Enhancement | 3 Months After Enhancement | P Value | |
|---|---|---|---|
| Sphere (D) | +0.17 ± 0.7 | −0.09 ± 0.3 | .04 |
| (range) | (+4.50 to −3.00) | (+1.00 to −1.50) | |
| Cylinder (D) | −0.39 ± 0.5 | −0.2 ± 0.3 | .0001 |
| (range) | (0 to −3.50) | (0 to −1.25) | |
| BSCVA a | 0.976 ± 0.2 | 0.977 ± 0.1 | .8 |
| (range) | (0.4 to 1.2) | (0.5 to 1.25) | |
| UCVA a | 0.59 ± 0.2 | 0.93 ± 0.1 | .0001 |
| (range) | (0.1 to 0.95) | (0.45 to 1.25) |
Table 2 shows the safety and efficacy indices before and after enhancement. Efficacy index improved after enhancement, with no decrease in the safety index.
| Before enhancement | ||
| Safety index | Before Enhancement BSCVA/Preop BSCVA | 1.004 ± 0.1 |
| Efficacy index | Before enhancement UCVA/preop BSCVA | 0.61 ± 0.2 |
| 3 months after enhancement | ||
| Safety index | After enhancement BSCVA/preop BSCVA | 1.01 ± 0.19 |
| Efficacy index | After enhancement UCVA/preop BSCVA | 0.96 ± 0.1 |
| Safety index | After enhancement BSCVA/before enhancement BSCVA | 1.01 ± 0.1 |
| Efficacy index | After enhancement UCVA/before enhancement BSCVA | 0.96 ± 0.1 |
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