Excimer Laser Surface Ablation Research Articles

Safety and complications after three different surface ablation techniques with mitomycin C: a retrospective analysis of 2757 eyes.

To evaluate the safety and spectrum of complications of three excimer laser surface ablation techniques (SATs) with an intraoperative application of mitomycin C (MMC) 0.02%. A retrospective, non-comparative large case series. SATs were performed on 2757 eyes with a preoperative spherical equivalent (SE) of - 4.41 ± 2.44 and a Wavelight Allegretto 200 platform. Ablation zone diameters between 6.0 and 7.0mm were used according to mesopic pupil size. All patients were treated with an intraoperative application of MMC for 30 to 90s depending on refractive error. The mean follow-up time was > 3months (107 ± 24days). Complication range and incidence were analyzed retrospectively and safety index was calculated. Two thousand seven hundred and fifty-seven eyes met the inclusion criteria for surface ablation. Two thousand five hundred and seventy-three eyes were assigned to alcohol-assisted photorefractive keratectomy (APRK), 135 eyes to transepithelial photorefractive keratectomy (TPRK), and 49 eyes to off-flap epithelial laser in situ keratomileusis (EpiLASIK/EpiK). Overall, the safety index was 1.06 ± 0.28. Haze was graded according to the Fantes scale. Haze incidence rates were highest in the TPRK group (14.81%) and comparably low in APRK (2.95%) and EpiK (4.08%) groups. Intraoperative topical application of MMC (0.02%) results in good safety and no severe side effects. However, highest incidence of haze was observed after TPRK. The more frequent peripheral localization of haze might be attributed to large ablation zones and the wavefront optimized ablation profile especially in the PTK modus of the laser platform.

Long-Term Results of Excimer Laser Surface Ablation with Smoothing for High Myopia

Purpose: To evaluate long-term refractive, aberrometric and anatomical results of surface ablation plus corneal PTK-style smoothing for myopia greater than –7.00 D. Methods: One-hundred-and-fourteen eyes of 69 patients (mean age: 37.7 ± 8.3 years) underwent PRK with the NIDEK EC-5000 excimer laser (NIDEK Co. Ltd., Gamagori, Japan) using multiple optical zones ranging in diameter from 4.89 mm to 7.0 mm, and transition zones (TZ) that were at least 3 mm wider than the optical zones (OZ). A cross-cylinder technique was used for treating astigmatism greater than 0.50 D. All eyes underwent a phototherapeutic keratectomy (PTK) smoothing technique using masking fluid. The Student’s t-test was used to determine a statistically significant change after surgery. A p value less than 0.05 was considered statistically significant. Results: Preoperative corrected distance visual acuity (CDVA) was 0.88 ± 0.16 with –9.53 ± 1.18 D cycloplegic spherical equivalent (SE). Preoperative corneal pachymetry was 560.4 ± 30.1 µ. Three years after surgery uncorrected visual acuity (UCVA) was 0.79 ± 0.26, CDVA was 0.92 ± 0.19 with –0.56 ± 0.90 D SE. Mean corneal haze was highest 1 month after surgery (0.58 ± 0.35), then progressively decreased to 0.11 ± 0.32 by 3 months postoperatively. Following year one, refraction and corneal curvature remained stable. There were no cases of keractasia to date. There was no hyperopic induction due to PTK. Two eyes required retreatment due to undercorrection. Total wavefront error did not change significantly, while astigmatism decreased and coma increased (both with p< 0.001). Conclusion: Surface ablation for the treatment of high myopia using PTK smoothing with a masking fluid was safe and effective. Wide optical and transition zones prevented induction of spherical aberration and the incorporation of the smoothing technique created a regular corneal surface with regular healing and trace to no haze after surgery.

Epi-Bowman-Keratektomie: klinische Beurteilung einer neuen Variante der Surface Ablation

A new device for epithelial abrasion before excimer laser surface ablation or corneal cross-linking (CXL) has recently been introduced (Epi-Clear™, Orca Surgical, Kiryat-Shmona, Israel). We have reviewed the literature on the clinical results, potential benefits and drawbacks of this instrument, compared to other methods of epithelial removal. Literature search for "Epi-Bowman Keratectomy", "Epi-clear", and "Epikeratome" yielded 1 peer-review publication, 1 non-peer-review publication, 18 posters and presentations at international conferences (European Society of Cataract and Refractive Surgeons [ESCRS] and American Society of Cataract and Refractive Surgery [ASCRS]) on the use of the Epi-Clear™ device before surface ablation, 2 posters on the use of Epi-Clear before corneal crosslinking and 1 presentation on the experimental use of Epi-Clear for removal of a pterygium. Comparison of laser ablation after epithelial removal with the Epi-Clear device (Epi-Bowman Keratectomy™, EBK™) to other established methods of surface ablation, i.e. alcohol-assisted PRK or PRK with a metallic scraper, EBK, suggests that the results are generally similar. Pain perception, haze formation, and epithelial healing are reported to be better than with conventional surface ablation methods. Studies evaluating the use of the Epi-Clear device before CXL report that the healing time is significantly reduced and that less pain is perceived. The Epi-Clear device seems to be a promising new option for epithelial removal before refractive laser ablation, although a convincing explanation for its potential superiority is still missing. In contrast, when the Epi-Clear device is used before CXL, then the Bowman's layer remains intact; this may provide an adequate explanation for the reported benefits of this application. However, currently available studies are of low level of evidence, so that more prospective randomised trials are needed for a robust evaluation of this treatment.

Mitomycin C for prevention of postoperative haze following excimer laser surface ablation in moderate to high myopia

Reason for withdrawal from publication The protocol is out of date and does not meet the current methodological standards of Cochrane.

Long-Term Clinical Outcomes of Myopic Patients Having Thin Residual Corneal Thickness after Excimer Laser Surface Ablation

ABSTRACTPurpose: To investigate and compare the long-term safety, efficacy, and accuracy of PRK (photorefractive keratectomy) and LASEK (laser epithelial keratomileusis) in myopic corneas having residual corneal thickness less than 400 micron meters (µm). Methods: The medical reports of the patients who had undergone excimer laser surface ablation between 2007–2011 and had a residual corneal thickness less than 400 µm were retrospectively reviewed. Results: Forty-two eyes of 42 patients with a mean age of 28.79±7.76 years were enrolled into the study. Twenty-two PRK and 20 LASEK procedures were performed. The mean follow-up time was 45.00±11.80 months. At the end of follow-up, no ectasia was detected. Nineteen percent of eyes had trace haze. No eyes lost any lines in corrected distance visual acuity. Eighty-one percent of the patients had an uncorrected distance visual acuity better than 20/40. The regression rate was 16.7%. Sixty-two percent of eyes were within ±1.00 D. The safety and efficacy indexes were 1.19±0.42 and 1.00±0.40, respectively. There was not any difference between LASEK and PRK regarding achieved spherical equivalent refraction, haze ratio, visual acuity, safety, efficacy, and regression. Conclusions: Both PRK and LASEK are safe and effective in myopic corneas having thin residual thickness.

Corneal Molecular and Cellular Biology for the Refractive Surgeon: The Critical Role of the Epithelial Basement Membrane.

To provide an overview of the recent advances concerning the corneal molecular and cellular biology processes involved in the wound healing response after excimer laser surface ablation and LASIK surgery. Literature review. The corneal wound healing response is a complex cascade of events that impacts the predictability and stability of keratorefractive surgical procedures such as photorefractive keratectomy and LASIK. The generation and persistence of corneal myofibroblasts (contractile cells with reduced transparency) arise from the interaction of cytokines and growth factors such as transforming growth factor beta and interleukin 1 produced by epithelial and stromal cells in response to the corneal injury. Myofibroblasts, and the opaque extracellular matrix they secrete into the stroma, disturb the precise distribution and spacing of collagen fibers related to corneal transparency and lead to the development of vision-limiting corneal opacity (haze). The intact epithelial basement membrane has a pivotal role as a structure that regulates corneal epithelial-stromal interactions. Thus, defective regeneration of the epithelial basement membrane after surgery, trauma, or infection leads to the development of stromal haze. The apoptotic process following laser stromal ablation, which is proportional to the level of attempted correction, leads to an early decrease in anterior keratocyte density and the diminished contribution of these non-epithelial cells of components such as perlecan and nidogen-2 required for normal regeneration of the epithelial basement membrane. Haze persists until late repair of the defective epithelial basement membrane. Defective regeneration of the epithelial basement membrane has a critical role in determining whether a cornea heals with late haze after photorefractive keratectomy or with scarring at the flap edge in LASIK.

MyoRing Treatment for Cases of Myopia not eligible for Laser Vision Correction

ABSTRACT Pupose MyoRing implantation has been shown to be able to mechanically stabilize ectatic corneas like a bone-nail for broken legs do. Here I present typical cases of MyoRing treatment for Myopia which were not eligible for LASIK. Materials and methods Four eyes of four patients suffering from moderate to high myopia and showing risk factors for postoperative ectasia have been treated by MyoRing implantation. Two of them have been combined with laser vision correction (LVC). Results The refractive results are comparable to those published for LVC. The cases with combined MyoRing LASIK treatment performed slightly better postoperatively than those treated with MyoRing only. Conclusion MyoRing implantation is safe and effective in myopic cases presenting with mainfest signs of keratoconus. In myopic eyes without manifest keratoconus but risk factors for post-LASIK keratectasia the combination of MyoRing implantation with Excimer Laser Surface Ablation may be a good treatment option. How to cite this article Daxer A. MyoRing Treatment for Cases of Myopia not eligible for Laser Vision Correction. Int J Kerat Ect Cor Dis 2014;3(1):20-22.

Advances in biomechanical effects of laser corneal refractive surgery

Corneal biomechanical properties will change after laser refractive surgery, which can be evaluated by several biomechanical parameters. The biomechanical stress will decrease remarkably after LASIK, but thin flap is helpful to maintain its stress. Excimer laser surface ablation has biomechanical advantages over LASIK procedure. The femtosecond laser technology can achieve smooth and regular incision and make the angle design. Flap adhesion is stronger when completed by a femtosecond laser. Laser refractive surgery will become safer and achieve more stable outcomes with the emphasis on biomechanical effects.

Improved Corneal Wound Healing through Modulation of Gap Junction Communication Using Connexin43-Specific Antisense Oligodeoxynucleotides

Gap junctions play a major role in corneal wound healing. This study used reproducible models of corneal wound healing to evaluate the effect of a gap junction channel modulator, connexin43 (Cx43) antisense oligodeoxynucleotides (AsODN), on corneal healing dynamics. A mechanical scrape wound model was used to evaluate Cx43 AsODN penetration and initial wound reepithelialization 12 hours postsurgery. Thereafter, detailed analyses of corneal edema, inflammation, and healing were performed in an excimer laser surface ablation model. In vivo confocal microscopy determined clinical parameters (edema, haze) and cellular changes (stromal hypercellularity, reepithelialization), whereas histology and immunohistochemistry were used to quantify stromal edema, inflammation, and reepithelialization. Cx43 AsODN penetrated through the hydrophilic stroma where the epithelium had been removed and accumulated in the basal epithelium close to the wound edge. Twelve hours after scrape wounding, Cx43 AsODN-treated eyes showed a significant reduction in wound area compared with the vehicle alone (1.59±0.37 and 2.29±0.58 mm2, respectively, P<0.01). After excimer laser ablation, stromal edema and inflammation were reduced, with endothelial structures being clearly visible, and reepithelialization rates were again increased in Cx43 AsODN-treated eyes. Histologic analysis confirmed reduced edema in the central wound site and at the periphery of treated corneas (P<0.05), whereas immunohistochemistry showed lower Cx43 levels (P<0.05), reduced myofibroblast activation, and improved epithelial basal lamina deposition in antisense-treated wounds (P<0.01). Application of Cx43 AsODN to the cornea reduces stromal edema and inflammation, promoting faster wound closure and a more uniform repair of the epithelial basal lamina after laser ablation.

F 2 excimer laser (157 nm) radiation modification and surface ablation of PHEMA hydrogels and the effects on bioactivity: Surface attachment and proliferation of human corneal epithelial cells

Physical and chemical changes at the surface of poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels modified by ablation with an F 2 excimer laser were investigated experimentally. An important observation was that only the outer exposed surface layers of the hydrogel were affected by the exposure to 157 nm radiation. The effect of the surface changes on the tendency of cells to adhere to the PHEMA was also investigated. A 0.5 cm 2 area of the hydrogel surfaces was exposed to laser irradiation at 157 nm to fluences of 0.8 and 4 J cm −2. The changes in surface topography were analysed by light microscopy and atomic force microscopy, while the surface chemistry was characterized by attenuated total reflection infrared and X-ray photoelectron spectroscopies. Cell-interfacial interactions were examined based on the proliferation of human corneal limbal epithelial (HLE) cells cultured on the laser-modified hydrogels, and on the unexposed hydrogels and tissue culture plastic for comparison. It was observed that the surface topography of laser-exposed hydrogels showed rippled patterns with a surface roughness increasing at the higher exposure dose. The changes in surface chemistry were affected not only by an indirect effect of hydrogen and hydroxyl radicals, formed by water photolysis, on the PHEMA, but also by the direct action of laser radiation on PHEMA if the surface layers of the gel become depleted of water. The laser treatment led to a change in the surface characteristics, with a lower concentration of ester side-chains and the formation of new oxygenated species at the surface. The surface also became more hydrophobic. Most importantly, the surface chemistry and the newly created surface topographical features were able to improve the attachment, spreading and growth of HLE cells.

Isolated Bowman layer transplantation to manage persistent subepithelial haze after excimer laser surface ablation

In a 21-year-old patient with persistent dense subepithelial haze after photorefractive keratectomy, unresponsive to retreatment, a stromal flap, 9.0 mm in diameter and approximately 60 microm in thickness, was excised and an unsutured 9.0 mm donor Bowman layer was transplanted onto the stromal bed. The corrected distance visual acuity improved from 20/40 (0.5) before surgery to 20/18 (1.2) with a scleral-supported contact lens 2 months after transplantation. With optical coherence tomography, the transplanted Bowman layer was seen as a fine white line bordering the anterior host stroma. No recurrence of stromal haze was seen throughout the 6-month follow-up. Isolated Bowman layer transplantation may be a new technique for the management of anterior stromal opacities or complicated epithelial wound healing such as persistent corneal haze after excimer laser surface ablation.

Excimer laser surface ablation – a review

Corneal surface laser ablation procedures for the correction of refractive error have enjoyed a resurgence of interest, especially in patients with a possible increased risk of complications after lamellar surgery. Improvements in the understanding of corneal biomechanical changes, the modulation of wound healing, laser technology including ablation profiles and different methods for epithelial removal have widened the scope for surface ablation. This article discusses photorefractive keratectomy, trans-epithelial photorefractive keratectomy, laser-assisted sub-epithelial keratomileusis and epithelial-laser-assisted in situ keratomileusis.

Ten-year Follow-up of Excimer Laser Surface Ablation for Myopia in Thin Corneas

Ten-year Follow-up of Excimer Laser Surface Ablation for Myopia in Thin Corneas

Mitomycin C in Corneal Refractive Surgery

Mitomycin C has played a deciding role in the current revival of excimer laser surface ablation techniques. We review the literature regarding mechanism of action of mitomycin C, histological effects on the cornea, and indications, dose, exposure time, and toxicity of mitomycin C in corneal refractive surgery. Mitomycin C 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. There is no definite evidence that establishes an exact diopter limit or ablation depth at which to apply prophylactic mitomycin C. It is usually applied at a concentration of 0.2 mg/ml (0.02%) for 12 to 120 seconds over the ablated stroma, although some studies suggest that lower concentrations (0.01%, 0.002%) could also be effective in preventing haze when treating low to moderate myopia. This dose of mitomycin C has not been associated with any clinically relevant epithelial corneal toxicity. Its effect on the endothelium is more controversial: two studies report a decrease in endothelial cell density, but the majority of reports suggest that the endothelium is not altered. Regarding mitomycin C's effect on keratocyte population, although animal studies report keratocyte depletion after its use, longer follow-up suggested that the initial keratocyte depletion does not persist over time.

Narrow angle light scatter in rabbit corneas after excimer laser surface ablation

Corneal haze following excimer laser ablation is an adverse after-effect of photorefractive keratectomy (PRK) and is associated with the development of subepithelial opacities. The present work pertains to the measurement of light scattering in rabbit corneas following excimer laser treatment; to the microscopic analysis of the light-scattering corneal structures; and to the development of a mathematical model of light propagation through the post-laser treatment cornea. Photorefractive keratectomy (PRK-6D, 6 mm optical zone) followed by standard postoperative pharmaceutical treatment was performed on rabbit eyes. Animals were examined clinically on a weekly basis and sacrificed after the tenth postoperative week. Confocal microscope image sequences were acquired immediately before animal sacrifice. After the scatter measurement, the corneas were prepared for histopathological evaluation. The subepithelial structures observed using the confocal microscope correspond to refractive index (and therefore optical path difference (OPD) variation. This OPD distribution can be approximated with a fractal surface, band-pass filtered in the Fourier domain. The angular distribution of scattered light is characterised by a narrow forward peak of the order of 0.5 degrees full-width at half maximum (FWHM) in accordance with the sizes of the subepithelial structures (5-150 microm).The intensity of scattered light is correlated with the thickness of the subepithelial scar-tissue layer.

Ten-year Follow-up of Excimer Laser Surface Ablation for Myopia in Thin Corneas

To evaluate the long-term outcomes of excimer laser surface ablation performed on thin corneas. Retrospective study. We included in the study 75 eyes (49 patients) with a preoperative central corneal thickness (CCT) thinner than 500 mum that had undergone surface ablation to correct their myopia and that had at least 10 years of follow-up. We evaluated the stability of visual acuity (VA) and refraction, the predictability, corneal keratometry, safety, efficacy, and postoperative complications at the examinations 3 months and 1, 2, 5, and 10 years after surgery. Preoperative CCT was 481.54 +/- 15.7 microm (range, 438 to 499 microm). Preoperative spherical equivalent was -6.12 +/- 2.67 diopters (D) (range, -2 to -14 D). The best spectacle-corrected VA significantly improved (P < .01) during the follow-up. The uncorrected VA showed significant improvement in all visits when compared with the 3-month postoperative visit. Both the sphere and cylinder showed a slight but significant regression (P < .01) only in the comparison between 3 months and 10 years after the surgery. Ten years after the surgery, 30 eyes (40%) were within 0.50 D and 43 eyes (57.33%) were within 1.00 D of emmetropia. The safety index improved over the 10 year period and was always higher than 0.9. The efficacy index remained stable around 0.8. The topography did not show signs of corneal ectasia and the keratometry showed no increase in corneal power. Thirty eyes (40%) needed enhancement. Surface ablation seems to be safe and effective to correct myopia in corneas thinner than 500 microm, with stable visual and refractive outcomes in a 10-year follow-up.

Detection of Corneal Fibrosis by Imaging Second Harmonic–Generated Signals in Rabbit Corneas Treated with Mitomycin C after Excimer Laser Surface Ablation

Recent studies have shown that confocal imaging of second harmonic-generated (SHG) signals can detect corneal collagen organization. The purpose of this study was to assess whether SHG signals can detect differences in corneal fibrosis after excimer laser surface ablation (photorefractive keratectomy [PRK]). Rabbits received 9-D PRK in one eye followed by treatment with either mitomycin C (MMC) or vehicle. Corneal haze was measured by in vivo confocal microscopy before and 2, 4, 8, and 12 weeks after surgery. Animals were then killed and corneas were evaluated by visible and nonlinear confocal microscopy. PRK induced significant haze in vehicle-treated corneas that peaked at 2 weeks and remained elevated at 12 weeks after surgery. MMC treatment significantly (P < 0.05) reduced corneal haze at 2 weeks and was essentially normal by 12 weeks. Imaging of SHG signals in vehicle-treated eyes showed an anterior layer of collagen forming a honeycomb network blending into a dense mat of irregularly arranged collagen fibers that overlaid normal orthogonally arranged collagen lamellae. MMC treatment showed normal collagen organization at the surface. Fibrotic tissue was associated with a high cell density and alignment of intracellular actin filaments with collagen fiber bundles. In MMC-treated eyes, an anterior acellular zone overlaid a sparsely populated stroma containing isolated and enlarged keratocytes. Imaging of SHG signals provides a sensitive means for detection of corneal fibrosis after surface ablation and can be used to assess the effects of antifibrotic therapy on corneal healing after refractive surgery.

Effect of mitomycin-C on the corneal endothelium during excimer laser surface ablation

Effect of mitomycin-C on the corneal endothelium during excimer laser surface ablation

Surface ablation after laser in situ keratomileusis: Retreatment on the flap

To evaluate the safety and efficacy of superficial laser ablation on the flap as a treatment for residual ametropia after laser in situ keratomileusis (LASIK). Private practice refractive surgery center, Utrecht, The Netherlands. This retrospective study comprised 18 eyes of 15 patients who had alcohol-assisted photorefractive keratectomy (PRK) or laser-assisted subepithelial keratectomy (LASEK) retreatment for residual ametropia after LASIK. All patients who had retreatment on the flap between June 2004 and June 2005 were included in the study. Retreatments were performed by wavefront-guided excimer laser surface ablation using the Visx Star S4 laser. Outcome measures included uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), subjective refraction, and biomicroscopy at the 3-, 6-, and 12-month postoperative visits. The preoperative spherical equivalent (SE) refraction was -0.63 diopter (D) +/- 0.87 (SD) (range -2.00 to +1.38 D). The mean amount of ablated cornea was 21.3 +/- 7.4 microm. At 3 months, the mean UCVA was 0.83 +/- 1.5 lines (range 0.40 to 1.25), yielding an efficacy index of 0.87. At 6 months, the mean UCVA increased to 0.98 +/- 0.8 line (range 0.63 to 1.25) and the efficacy index, to 1.03. At 12 months, 6 eyes were lost to follow-up. The mean UCVA was 0.83 +/- 2.2 lines (range 0.20 to 1.25), with an efficacy index of 0.87. The mean BSCVA was 0.98 +/- 0.9 line (range 0.80 to 1.25) at 3 months and 1.05 +/- 0.6 line (range 0.80 to 1.25) at 6 months, yielding a safety index of 1.03 and 1.11, respectively. At 12 months, the mean BSCVA was 0.95 +/- 1.0 line (range 0.63 to 1.25), with a safety index of 1.0. At 6 months, no eye had lost lines of BSCVA, 11 eyes had no change, and 7 eyes gained 1 line. At 12 months, 2 eyes lost 1 line of BSCVA, 8 eyes had no change, and 2 eyes gained 1 line. The mean SE refraction was +0.10 +/- 0.27 D (range -0.25 to +0.63 D) at 3 months, +0.06 +/- 0.37 D (range -0.50 to +1.13 D) at 6 months, and +0.15 +/- 0.39 D (range -0.50 to +0.88 D) at 12 months. On biomicroscopic examination, 1 eye had prolonged grade 1 haze that disappeared before 6 months. Two eyes of 1 patient who had hyperopic retreatment developed late-onset haze 8 months postoperatively. Eyes with microstriae in the flap before retreatment showed significant improvement after retreatment. There were no sight-threatening complications. Wavefront-guided LASEK or alcohol-assisted PRK retreatment on the surface of a LASIK flap was safe and effective in correcting small amounts of residual myopia.

Effect of mitomycin-C on the corneal endothelium during excimer laser surface ablation

To study the effects of mitomycin-C (MMC) on the corneal endothelium after surface ablation. This prospective observer-masked study comprised 40 consecutive patients (80 eyes) scheduled to have laser-assisted subepithelial keratectomy (LASEK) to correct myopia. The patients were divided into 2 groups. Group 1 included 32 eyes in which the ablation depth was 50 mum or less and that received no MMC. Group 2 included 48 eyes in which the ablation depth exceeded 50 mum and were treated with intraoperative MMC 0.02% for 30 seconds over the ablated zone. Preoperatively and 3 months postoperatively, 3 photographs of the central cornea of each eye were obtained using specular microscopy. A masked observer evaluated the endothelial cell density and compared the results between groups and the preoperative versus the postoperative results within the same group. The mean patient age was 31.5 years +/- 4.6 (SD) in Group 1 and 33.2 +/- 7.9 years in Group 2 (P = .3). Within-group comparison between the preoperative and postoperative endothelial cell density values showed a statistically significant increase in both groups. The mean values in Group 1 were 2462.5 +/- 226.8 cells/mm(2) preoperatively and 2562.5 +/- 258.7 cells/mm(2) postoperatively (P = .0001). The means in Group 2 were 2466.6 +/- 294.1 cells/mm(2) and 2525 +/- 312.5 cells/mm(2), respectively (P = .0008). The differences in endothelial cell counts between Group 1 and Group 2 preoperatively and postoperatively were not statistically significant (P = .9 and P =.5, respectively). A single intraoperative application of MMC 0.02% for 30 seconds after laser surface ablation did not seem to cause a substantial change in corneal endothelial cell density.