Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes

Corneal fibrosis: From in vitro models to current and upcoming drug and gene medicines

Fibrotic diseases are characterised by myofibroblast differentiation, uncontrolled pathological extracellular matrix accumulation, tissue contraction, scar formation and, ultimately tissue / organ dysfunction. The cornea, the transparent tissue located on the anterior chamber of the eye, is extremely susceptible to fibrotic diseases, which cause loss of corneal transparency and are often associated with blindness. Although topical corticosteroids and antimetabolites are extensively used in the management of corneal fibrosis, they are associated with glaucoma, cataract formation, corneoscleral melting and infection, imposing the need of far more effective therapies. Herein, we summarise and discuss shortfalls and recent advances in in vitro models (e.g. transforming growth factor-β (TGF-β) / ascorbic acid / interleukin (IL) induced) and drug (e.g. TGF-β inhibitors, epigenetic modulators) and gene (e.g. gene editing, gene silencing) therapeutic strategies in the corneal fibrosis context. Emerging therapeutical agents (e.g. neutralising antibodies, ligand traps, receptor kinase inhibitors, antisense oligonucleotides) that have shown promise in clinical setting but have not yet assessed in corneal fibrosis context are also discussed.

Management of Corneal Haze After Photorefractive Keratectomy

Photorefractive keratectomy (PRK) is a safe and popular corneal surgery performed worldwide. Nevertheless, there is potential risk of corneal haze development after surgery. Proper management of post PRK haze is important for good visual outcome. We performed a comprehensive review of the literature on the various risk factors and treatments for PRK haze, searching the PubMed, Google Scholar, SCOPUS, ScienceDirect, and Embase databases using relevant search terms. All articles in English from August 1989 through April 2023 were reviewed for this study, among which 102 articles were chosen to be included in the study. Depending on the characteristics of and examination findings on post PRK haze, different management options may be preferred. In the proposed framework, management of PRK haze should include a full workup that includes patient's subjective complaints and loss of vision as well as visual acuity, biomicroscopy, anterior segment optical coherence tomography, epithelial mapping, and Scheimpflug densitometry. Topical steroid treatment for haze should be stratified based on early- or late-onset haze. Mechanical debridement or superficial phototherapeutic keratectomy (PTK) may be used to treat superficial corneal haze. Deep PTK and/or PRK can be used to treat deep corneal haze. Mitomycin-C and topical steroids are prophylactic post-surgery agents to prevent recurrence of haze.

Blocking Mitochondrial Pyruvate Transport Alters Corneal Myofibroblast Phenotype: A New Target for Treating Fibrosis

Purpose

The purpose of this study was to critically test the hypothesis that mitochondrial pyruvate carrier (MPC) function is essential for maintenance of the corneal myofibroblast phenotype in vitro and in vivo.

Methods

Protein and mRNA for canonical profibrotic markers were assessed in cultured cat corneal myofibroblasts generated via transforming growth factor (TGF)-β1 stimulation and treated with either the thiazolidinedione (TZD) troglitazone or the MPC inhibitor alpha-cyano-beta-(1-phenylindol-3-yl) acrylate (UK-5099). RNA sequencing was used to gain insight into signaling modules related to instructive, permissive, or corollary changes in gene expression following treatment. A feline photorefractive keratectomy (PRK) model of corneal wounding was used to test the efficacy of topical troglitazone at reducing α-smooth muscle actin (SMA)-positive staining when applied 2 to 4 weeks postoperatively, during peak fibrosis.

Results

Troglitazone caused cultured myofibroblasts to adopt a fibroblast-like phenotype through a noncanonical, peroxisome proliferator-activated receptor (PPAR)-γ-independent mechanism. Direct MPC inhibition using UK-5099 recapitulated this effect, but classic inhibitors of oxidative phosphorylation (OXPHOS) did not. Gene Set Enrichment Analysis (GSEA) of RNA sequencing data converged on energy substrate utilization and the Mitochondrial Permeability Transition pore as key players in myofibroblast maintenance. Finally, troglitazone applied onto an established zone of active fibrosis post-PRK significantly reduced stromal α-SMA expression.

Conclusions

Our results provide empirical evidence that metabolic remodeling in myofibroblasts creates selective vulnerabilities beyond simply mitochondrial energy production, and that these are critical for maintenance of the myofibroblast phenotype. For the first time, we provide proof-of-concept data showing that this remodeling can be exploited to treat existing corneal fibrosis via inhibition of the MPC.

Surgical Technique to Treat Presbyopic Inlay-Associated Corneal Haze With Sequential Excimer Photoablation: A Case Series

PURPOSE

To describe an approach using sequential excimer laser ablation of the stromal surface of the corneal flap with or without subsequent excimer ablation to the stromal bed to reduce presbyopic inlay-associated corneal haze.

METHODS

Twelve patients who underwent KAMRA inlay (Acufocus) explantation due to corneal haze were included. The mean interval between explantation and the primary surgery (phototherapeutic keratotomy [PTK] to corneal flap) was 16.2 ± 29.7 months (range = 1 to 83 months). The corneal flap was lifted and laid on an evisceration spoon and an excimer laser was used to ablate the flap stroma by 30 to 40 µm depth. Subsequently, an excimer laser was used to ablate and treat the stromal bed following a second flap lift according to the manifest refraction, leaving a minimal residual stromal bed thickness of greater than 300 µm. For both procedures, mitomycin C 0.02% was applied to the stromal bed before the flap was replaced and a bandage contact lens applied.

RESULTS

Reductions in corneal haze were observed, following PTK to the corneal flap with or without photorefractive keratectomy (PRK) to the stromal bed, both clinically and on imaging. No significant changes in uncorrected distance visual acuity (P = .442) and corrected distance visual acuity (P = .565) were observed. Improvements were observed for both spherical equivalent refractive errors (P = .036) and corneal light backscatter (P = .019). There were significant improvements in spherical aberrations (P = .014) but no changes in total lower and higher order aberrations.

CONCLUSIONS

PTK to the corneal flap with or without subsequent stromal bed PRK is an effective technique in treating corneal haze following presbyopic inlay explantation. [J Refract Surg. 2023;39(9):639-646.].

Effect of Short Versus Long-Term Steroid on Corneal Haze After Photorefractive Keratectomy: A Randomized, Double-Masked Clinical Trial

PURPOSE

To compare the effect of duration of fluorometholone 0.1% treatment on corneal haze after photorefractive keratectomy (PRK) with mitomycin C (MMC) 0.02%.

DESIGN

Prospective, randomized, double-blind, clinical trial.

METHODS

Single-center clinical trial of 252 myopic PRK candidates (252 eyes) aged 21 to 40 years with a mean spherical equivalent (SE) of ≤ 6 diopters (D). Participants were randomized to receive one of the three corticosteroid regimens after PRK: Group A = 1 month followed by 2-month placebo; Group B = 2 months followed by 1-month placebo; and Group C = 3 months. The main outcome measures were corneal haze incidence, subjective SE, uncorrected distance visual acuity (UDVA), and corneal densitometry.

RESULTS

The corneal haze incidence (Grade ≥ 1) at 12 months was 1.35% (1/74 eyes) in Group A and 0% in the other two groups. The mean anterior corneal densitometry (grayscale unit) was 21.19 ± 2.07, 21.09 ± 2.19, and 21.31 ± 2.21 in Groups A, B and C, respectively. The mean SE was 0 ± 0.09, 0 ± 0.11, and 0 ± 0.10, and UDVA (decimal) was 1 ± 0, 1 ± 0.01, and 1 ± 0 in Groups A, B and C, respectively. During 1-year follow-up, no statistically significant difference was observed in mean SE (P = .158), UDVA (P = .343), and anterior corneal densitometry (P = .109) at any stage between the study groups.

CONCLUSIONS

Long-term topical corticosteroids are unnecessary following PRK with MMC for moderate myopia.

Twelve-Month Outcomes of the Wavefront-Optimized Photorefractive Keratectomy for High Myopic Correction Compared with Low-to-Moderate Myopia

Purpose

To evaluate the 12-months outcomes of photorefractive keratectomy (PRK) in patients with high myopia (≥ 6.0 diopters, D) compared with low-to-moderate myopia (< 6.0 D).

Patients and Methods

Records of 46 patients (69 eyes) who underwent PRK for myopic and astigmatic correction between October 2015 and December 2018 were reviewed. High myopic eyes (29 eyes) were compared with low-to-moderate myopic eyes (40 eyes). All surgeries were adjunct with 0.02% mitomycin C intraoperatively. Measured outcomes included postoperative uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction spherical equivalent, corneal haze rate, and any complications.

Results

At 12 months post-PRK, 26 eyes (89.7%) in the high myopia and 39 eyes (97.5%) in the low-to-moderate myopia group had UDVA ≥ 20/20, (p=0.30). Average postoperative logMAR UDVA at 12 months was −0.04 (20/18) and −0.11 (20/15) for the high myopia and low-to-moderate myopia groups, respectively. No eyes in either group had residual refractive errors >1 D. No eyes in both groups developed significant corneal haze at month 12. No eyes had a loss of greater than two Snellen lines of CDVA at 12 months post-surgery. The efficacy and safety indices at 12 months post-surgery were not significantly different between groups (1.06±0.26 vs.1.14±0.27, p =0.25 and 1.14±0.27 vs 1.17±0.26, p=0.60 for low-to-moderate myopia vs high myopia groups, respectively).

Conclusion

PRK with high myopic correction provides excellent refractive outcomes and is safe, compared to those of low-to-moderate myopic correction.

Corneal haze post photorefractive keratectomy

Corneal haze represents subepithelial corneal fibrosis, a manifestation of a pathological healing process. It occurs as a result of an epithelial-stromal lesion involving a break in the epithelial barrier. It is an inflammatory response that involves the migration, multiplication and differentiation of keratocytes into mature myofibroblasts, causing loss of corneal transparency. Although it is a transient phenomenon, this complication is feared following refractive photokeratectomy (PRK), because it can cause alterations in the quality of vision, refractive regression and decreased visual acuity. The severity of these symptoms is correlated with the severity of the corneal haze, which can be assessed clinically or by objective means such as corneal densitometry measurement. The frequency and severity of corneal haze increase with the depth of photoablation in PRK and are therefore increased during the treatment of severe ametropia. Considering that no consensus exists, the application of mitomycin C (MMC) intraoperatively and topical corticosteroids postoperatively are conventionally used to inhibit collagen synthesis, sometimes in combination with various protocols depending on the center or surgeon. This review of the literature reports the current knowledge on corneal haze, in order to better understand it and optimise its prevention in the context of a decreased MMC supply, which has occurred in the past and could recur in the future.

The Effectiveness and Safety of Dextenza 0.4 mg for the Treatment of Postoperative Inflammation and Pain in Patients After Photorefractive Keratectomy: The RESTORE Trial

PURPOSE

To determine patient preference and treatment outcomes with an intracanalicular dexamethasone 0.4 mg insert compared to a standard steroid drop regimen in the contralateral eye following bilateral photorefractive keratectomy (PRK).

METHODS

In this randomized, prospective, self-controlled, open-label interventional study, one eye received the dexamethasone insert and the second eye received prednisolone acetate 1% taper following bilateral PRK surgery. Postoperative evaluations were performed on day 3, day 4, month 1, and month 3. Phone call surveys were performed on week 2. The Comparison of Ophthalmic Medications for Tolerability questionnaire was used to determine patient preference between postoperative regimens and postoperative pain. Corneal endpoints included time to epithelialization, presence of corneal haze, sodium fluorescein staining, and modified Standardized Patient Evaluation of Eye Dryness (SPEED) scores. Both corrected distance visual acuity (CDVA) and uncorrected distance visual acuity (UDVA) were assessed.

RESULTS

Twenty patients participated in the study. At month 3, 70% of patients preferred the dexamethasone insert, 20% preferred prednisolone acetate, and 10% expressed no preference. Patient surveys did not show a difference in postoperative pain between the study group and control group. No statistical difference was shown in time to epithelialization, 90-day CDVA or UDVA, postoperative corneal haze, corneal staining, or modified SPEED scores.

CONCLUSIONS

In patients undergoing PRK, there was preference toward a dexamethasone insert in place of topical prednisolone acetate for the postoperative steroid treatment. There were no statistically or clinically significant differences between the two cohorts in regard to healing time or visual outcomes. [J Refract Surg. 2021;37(9):590-594.].

Mitomycin C for the prevention of corneal haze in photorefractive keratectomy: a meta-analysis and trial sequential analysis

PURPOSE

To evaluate the anti-haze effect and visual outcome after intraoperative mitomycin C (MMC) use during photorefractive keratectomy (PRK) in myopia or myopic astigmatism patients.

METHODS

We searched in PubMed, EMBASE, Cochrane Library and Google Scholar comprehensively to obtain studies comparing the clinical effects after PRK with and without MMC published until February 2020. Meta-analysis of primary outcome (corneal haze rate) and secondary outcomes [predictability, efficacy, safety and corneal endothelial cell density (ECD)] were conducted. We used trial sequential analysis (TSA) in an effort to collect firm evidence supporting our conclusion.

RESULTS

Of the included 11 randomized controlled trials, five cohort and one case-control studies, 3536 eyes (2232 and 1304 in the MMC and control groups, respectively) were enrolled for meta-analysis. The TSA disclosed strong evidence of decline in corneal haze rate in the MMC group compared with that of the control group. In the subgroup analysis of duration, MMC seemed to reduce corneal haze rate in early-onset and late-onset haze. Predictability of refraction and visual acuity were greater in the MMC groups, not significantly though. The proportion of patients losing at least two lines of best corrected visual acuity postoperatively in the MMC groups was lower than that in the control groups. The corneal postoperative ECD showed no significant difference between the MMC and control groups.

CONCLUSION

Our meta-analysis revealed that MMC is an important anti-haze agent in PRK for reducing both early- and late-onset haze and can also help improving predictability of refraction and subjective postoperative visual acuity.

Clinical Applications of In Vivo Confocal Microscopy in Keratorefractive Surgery

PURPOSE

To review the contribution of in vivo confocal microscopy (IVCM) to the understanding of corneal wound healing following refractive surgery, and its role in the diagnosis and management of complications arising from keratorefractive procedures.

METHODS

Review of the basic science and clinical literature relating to the study of keratorefractive surgical procedures using IVCM.

RESULTS

Extensive research using IVCM has generated a comprehensive understanding of tissue responses after corneal refractive surgery. Epithelial thickness and stromal keratocyte density can be quantified postoperatively and studied longitudinally. Corneal nerve loss and subsequent reinnervation has been characterized and differs significantly between laser refractive techniques. IVCM has also been used to study complications arising from postoperative inflammation (diffuse lamellar keratitis, central toxic keratopathy, ring keratitis, and ectasia), infection (microbial keratitis), and neuropathy (dry eye and neuralgia). This imaging technique can have a critical role in the diagnosis of these complications and subsequent monitoring of treatment response. Manual processing of IVCM images is time-consuming and there may be significant interobserver and intraobserver variability with poor repeatability. However, increasing automation and the use of artificial intelligence is improving the speed and accuracy of image analysis.

CONCLUSIONS

IVCM has historically been confined to a research setting because image capture and subsequent processing was extremely labor intensive. However, advances in both hardware and software capabilities promise to allow the use of IVCM in routine clinical practice. Real-time evaluation of the cornea at a cellular level will be particularly useful in patients with inflammatory, infectious, or neuropathic complications of keratorefractive surgery. [J Refract Surg. 2021;37(7):493-503.].

Quality of Vision Following LASIK and PRK-MMC for Treatment of Myopia

INTRODUCTION

Femtosecond-assisted thin flap, laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy with mitomycin-C (PRK-MMC) are the two most common refractive surgical procedures used to enhance visual capability in the U.S military. The purposes of the study were to examine effects on quality of vision following LASIK and PRK-MMC using a novel computer-based quick contrast sensitivity function (qCSF) test.

MATERIALS AND METHODS

This prospective clinical study included 58 active duty U.S. military service members who elected LASIK (n = 29) or PRK-MMC (n = 29) refractive surgery for myopia (nearsightedness) treatment. Monocular photopic and mesopic quality of vision of the right eyes in spectacle correction preoperatively and unaided right eyes at four postoperative follow-up visits (1 week, 2 weeks, 1 month, and 3 months) were examined using the qCSF device. Two qCSF parameters, area under a log CSF (AULCSF) between 1.5 and 18 cycles per degree, and CSF cutoff acuity (CSF Acuity), were collected using a 50-trial setting at a 4-m testing distance. General linear model (GLM) Repeated-measures Analysis of Covariance was used to examine effects on quality of vision following LASIK and PRK-MMC. Post hoc testing with Bonferroni correction was used for pairwise comparisons, and preoperative cylinder refraction was used as a covariate. Two-tailed independent t-test was used to compare preoperative and postoperative parameters between LASIK and PRK-MMC. Pearson's correlation, Bland-Altman plots, and multiple linear regression were used to examine the relationship among the qCSF and other vision tests.

RESULTS

Quality of vision, AULCSF, and CSF Acuity returned to the preoperative baseline at postoperative 2 weeks under mesopic condition and at postoperative 1 month under photopic condition after PRK-MMC. In comparison, photopic and mesopic quality of vision were not significantly different from the baseline at any of the four postoperative visits following LASIK. Changes of CSF Acuity from the baseline after LASIK were significantly better under photopic than mesopic condition by 0.067 ± 0.014 logarithm of the minimum angle of resolution (logMAR); P < .001). Quality of vision was not significantly different between the LASIK and PRK-MMC groups at postoperative 1 and 3 months. When predicting photopic AULCSF (overall model fit R2 = 0.47), 5% contrast acuity (beta = -0.43), visual acuity in 100% contrast (beta = -0.18), and residual refraction in spherical equivalent (beta = 0.20) were significant predictors (P ≤ .001), while high-order aberrations (beta = -0.07, P = .22) were not significant predictors. Visual acuity (beta = -0.12, P = .07) and high-order aberrations (beta = -0.04, P = .58) were not significant predictors of mesopic AULCSF. Bland-Altman plots show that photopic CSF Acuity and visual acuity had a mean difference of 0.19 ± 0.01 logMAR with limits of agreement (LOAs) at -0.01 and 0.39 logMAR. Photopic CSF Acuity and 5% contrast acuity had a mean difference of -0.06 ± 0.01 logMAR with LOAs at -0.33 and 0.21 logMAR.

CONCLUSION

Quality of vision recovers at postoperative 1 week after LASIK and at postoperative 1 month after PRK-MMC. The standard black-on-white high-contrast, chart-based visual acuity test is weak in predicting quality of vision. The qCSF detects mild-to-moderate visual changes and is suitable for quality of vision assessment following refractive eye surgery.

Biological effects of mitomycin C on late corneal haze stromal fibrosis following PRK

This review details the current understanding of the mechanism of action and corneal effects of mitomycin C (MMC) for prophylactic prevention of stromal fibrosis after photorefractive keratectomy (PRK), and includes discussion of available information on dosage and exposure time recommended for MMC during PRK. MMC is an alkylating agent, with DNA-crosslinking activity, that inhibits DNA replication and cellular proliferation. It acts as a pro-drug and requires reduction in the tissue to be converted to an active agent capable of DNA alkylation. Although MMC augments the early keratocyte apoptosis wave in the anterior corneal stroma, its most important effect responsible for inhibition of fibrosis in surface ablation procedures such as PRK is via the inhibition of mitosis of myofibroblast precursor cells during the first few weeks after PRK. MMC use is especially useful when treating eyes with higher levels of myopia (≥approximately 6 D), which have shown higher risk of developing fibrosis (also clinically termed late haze). Studies have supported the use of MMC at a concentration of 0.02%, rather than lower doses (such as 0.01% or 0.002%), for optimal reduction of fibrosis after PRK. Exposure times for 0.02% MMC longer than 40 s may be beneficial for moderate to high myopia (≥6D), but shorter exposures times appear to be equally effective for lower levels of myopia. Although MMC treatment may also be beneficial in preventing fibrosis after PRK treatments for hyperopia and astigmatism, more studies are needed. Thus, despite the clinical use of MMC after PRK for nearly twenty years-with limited evidence of harmful effects in the cornea-many decades of experience will be needed to exclude late long-term effects that could be noted after MMC treatment.

Duration of topical steroid application after photorefractive keratectomy with mitomycin C

Contradictory results of postoperative steroid application in photorefractive keratectomy (PRK) led to a meta-analysis of the existing data to achieve a definite conclusion on the optimum dosage and duration of corticosteroid therapy after PRK. The overall pooled unstandardized mean difference (PUMD) of the corneal haze score was -0.20 (95% CI, -0.29 to -0.12). In subgroup analysis, the PUMD of the corneal haze score was statistically significant in 2 subgroups, -0.57 (-0.85 to -0.30) for 3 to 6 months postoperatively and -0.13 (-0.23 to -0.04) for ≤ 3 months postoperatively. Analysis of the PUMD of postoperative spherical equivalent in participants with low to moderate myopia (≥-6.00 D) and high myopia (<-6.00 D) showed positive effects of steroids on prevention of myopia regression. In conclusion, long-term topical steroid application after PRK seems unnecessary in low and moderate myopia. New randomized clinical trials using current technologies are recommended for postoperative treatments.

Impact of topical anti-fibrotics on corneal nerve regeneration in vivo

Recent work in vitro has shown that fibroblasts and myofibroblasts have opposing effects on neurite outgrowth by peripheral sensory neurons. Here, we tested a prediction from this work that dampening the fibrotic response in the early phases of corneal wound healing in vivo could enhance reinnervation after a large, deep corneal injury such as that induced by photorefractive keratectomy (PRK). Since topical steroids and Mitomycin C (MMC) are often used clinically for mitigating corneal inflammation and scarring after PRK, they were ideal to test this prediction. Twenty adult cats underwent bilateral, myopic PRK over a 6 mm optical zone followed by either: (1) intraoperative MMC (n = 12 eyes), (2) intraoperative prednisolone acetate (PA) followed by twice daily topical application for 14 days (n = 12 eyes), or (3) no post-operative treatment (n = 16 eyes). Anti-fibrotic effects of MMC and PA were verified optically and histologically. First, optical coherence tomography (OCT) performed pre-operatively and 2, 4 and 12 weeks post-PRK was used to assess changes in corneal backscatter reflectivity. Post-mortem immunohistochemistry was then performed at 2, 4 and 12 weeks post-PRK, using antibodies against α-smooth muscle actin (α-SMA). Finally, immunohistochemistry with antibodies against βIII-tubulin (Tuj-1) was performed in the same corneas to quantify changes in nerve distribution relative to unoperated, control cat corneas. Two weeks after PRK, untreated corneas exhibited the greatest amount of staining for α-SMA, followed by PA-treated and MMC-treated eyes. This was matched by higher OCT-based stromal reflectivity values in untreated, than PA- and MMC-treated eyes. PA treatment appeared to slow epithelial healing and although normal epithelial thickness was restored by 12 weeks-post-PRK, intra-epithelial nerve length only reached ∼1/6 normal values in PA-treated eyes. Even peripheral cornea (outside the ablation zone) exhibited depressed intra-epithelial nerve densities after PA treatment. Stromal nerves were abundant under the α-SMA zone, but appeared to largely avoid it, creating an area of sub-epithelial stroma devoid of nerve trunks. In turn, this may have led to the lack of sub-basal and intra-epithelial nerves in the ablation zone of PA-treated eyes 4 weeks after PRK, and their continuing paucity 12 weeks after PRK. Intra-operative MMC, which sharply decreased α-SMA staining, was followed by rapid restoration of nerve densities in all corneal layers post-PRK compared to untreated corneas. Curiously, stromal nerves appeared unaffected by the development of large, stromal, acellular zones in MMC-treated corneas. Overall, it appears that post-PRK treatments that were most effective at reducing α-SMA-positive cells in the early post-operative period benefited nerve regeneration the most, resulting in more rapid restoration of nerve densities in all corneal layers of the ablation zone and of the corneal periphery.

Effect of age on visual and refractive results after laser-assisted subepithelial keratomileusis (LASEK) with adjuvant use of mitomycin C

PURPOSE

To evaluate the influence of age on visual and refractive results after laser-assisted subepithelial keratomileusis (LASEK) with the adjuvant use of mitomycin C (MMC) for the correction of myopia.

METHODS

Retrospective, nonrandomized, cohort study. A total of 1374 eyes treated with LASEK+MMC were included in the study (we compared 1163 eyes of patients aged 18 to 40 years versus 211 eyes of patients over 40 years). Visual and refractive results were evaluated at the 6-month postoperative visit.

RESULTS

Six months postoperatively, both the uncorrected distance visual acuity and the corrected distance visual acuity were significantly better in the group of young patients (P=0.0001). We found a slight tendency to overcorrection in the group of young patients compared to a slight tendency to undercorrection in the group of patients over 40 years (P=0.002). The efficacy index was significantly better in the group of younger patients (0.91±0.2) than in the older patients (0.86±0.2) (P=0.0001). No significant difference was found in the safety index between groups. 81.5% of eyes in the group of patients aged 18 to 40 years compared to 75.3% of eyes in the group of patients aged >40 years were within±0.5D of emmetropia (P=0.001).

CONCLUSIONS

A tendency toward undercorrection and less predictability was found with aging after myopic LASEK with MMC for the correction of myopia.

A Critical Overview of the Biological Effects of Mitomycin C Application on the Cornea Following Refractive Surgery

During the last 2 decades, modifying the shape of the cornea by means of laser photoablation has emerged as a successful and popular treatment option for refractive errors. Corneal surface ablation techniques such as photorefractive keratectomy (PRK) and laser-assisted subepithelial keratomileusis (LASEK) offer good refractive results while having a minimal impact on corneal biomechanical stability. Past limitations of these techniques included the long-term regression of refractive outcome and a vigorous healing response that reduced corneal clarity in some patients (giving rise to what is clinically described as “haze”). Mitomycin C (MMC) was introduced as a healing modulator and applied on the corneal surface after refractive surgery to address these drawbacks. This article critically reviews the available evidence on the biological effects, safety, and clinical benefits of the off-label use of MMC in corneal refractive surgery.

Early Refractive and Clinical Outcomes of High-Myopic Photorefractive Keratectomy as an Alternative to LASIK Surgery in Eyes with High Preoperative Percentage of Tissue Altered

Objective

To analyze the safety and efficacy of high-myopic PRK as an alternative to LASIK surgery in patients with a high preoperative percentage tissue altered (PTA).

Design

Retrospective interventional case series.

Participants

Charts of 256 consecutive eyes that underwent PRK with application of mitomycin-C 0.02% for high myopia were retrospectively reviewed.

Methods

Refractive (refraction and refractive accuracy) and visual outcomes (uncorrected and corrected visual acuities), as well as occurrence of haze in the eyes with preoperative PTA expected to be higher than 40% with a 110-micron flap if undergoing LASIK surgery, were analyzed.

Results

Mean follow-up was 7.3 ± 4.8 months. A total of 187 of 256 eyes (73.0%) were included in the analysis because they were expected to have a PTA greater than 40%, should they have undergone LASIK surgery. The actual mean PTA of those eyes following PRK was 31.8 ± 2.2%, and none had a PTA ≥ 40%. UDVA of 20/16, 20/20, and 20/25 or better was achieved in 1.2% (2 eyes), 65.5% (112 eyes), and 85.4% (146 eyes), respectively. The percentage of eyes with postoperative SE within ±0.5 D and ±1.0 D of planned SE was 71% and 93%, respectively. None of the eyes lost 2 or more lines of CDVA. The rate of stromal haze, managed successfully with topical steroids only, was 4.8%.

Conclusion

High-myopic PRK with application of mitomycin-C in the eyes at risk of developing ectasia because of high preoperative PTA was demonstrated to be a safe and effective alternative to the LASIK procedure.

Ascorbic acid versus placebo in postoperative lid edema postphotorefractive keratectomy: A double-masked, randomized, prospective study

INTRODUCTION

Photorefractive keratectomy (PRK) is a proper type of refractive surgery used to remodel corneal stroma to compensate refractive errors. Corneal haze was reported as one of the side effects in several studies. This study was conducted for investigation of the effect of preventive effect of Vitamin C on eyelid edema, corneal haze, corneal epithelial healing, mitigation of pain, and epiphora.

MATERIALS AND METHODS

This study has been performed as a double-blind clinical trial on 51 patients who underwent PRK surgery. The patients were randomly divided into two groups as follows: case group who received oral ascorbic acid 250 mg once daily for 7 days and control group that took placebo 3 days before and 4 days after the surgical operation. The patients underwent a surgical operation on day 0. Then, the following factors were evaluated as the main outcome: postoperative lid edema, pain, corneal haze, and corneal reepithelialization.

RESULTS

The mean age of the patients was 28.52 ± 8.05 years. There was no statistically significant difference in the primary outcome of the subjective pain scores along with corneal haze and corneal reepithelialization between the treatment and placebo groups at any point during the postoperative period; however, there was a statistically significant difference and trend for lower lid edema in the ascorbic acids group on postoperative day 1 (P < 0.05).

CONCLUSION

This study demonstrates that ascorbic acid may provide an alternative or add-on option for lid edema relief after PRK.

Corneal myofibroblasts inhibit regenerating nerves during wound healing

Abnormal nerve regeneration often follows corneal injury, predisposing patients to pain, dry eye and vision loss. Yet, we lack a mechanistic understanding of this process. A key event in corneal wounds is the differentiation of keratocytes into fibroblasts and scar-forming myofibroblasts. Here, we show for the first time that regenerating nerves avoid corneal regions populated by myofibroblasts in vivo. Recreating this interaction in vitro, we find neurite outgrowth delayed when myofibroblasts but not fibroblasts, are co-cultured with sensory neurons. After neurites elongated sufficiently, contact inhibition was observed with myofibroblasts, but not fibroblasts. Reduced neurite outgrowth in vitro appeared mediated by transforming growth factor beta 1 (TGF-β1) secreted by myofibroblasts, which increased phosphorylation of collapsin response mediating protein 2 (CRMP2) in neurons. The significance of this mechanism was further tested by applying Mitomycin C after photorefractive keratectomy to decrease myofibroblast differentiation. This generated earlier repopulation of the ablation zone by intra-epithelial and sub-basal nerves. Our findings suggest that attaining proper, rapid corneal nerve regeneration after injury may require blocking myofibroblast differentiation and/or TGF-β during wound healing. They also highlight hitherto undefined myofibroblast-neuron signaling processes capable of restricting neurite outgrowth in the cornea and other tissues where scars and nerves co-exist.

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

BACKGROUND

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.

METHODS

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 7.0 mm were used according to mesopic pupil size. All patients were treated with an intraoperative application of MMC for 30 to 90 s depending on refractive error. The mean follow-up time was > 3 months (107 ± 24 days). Complication range and incidence were analyzed retrospectively and safety index was calculated.

RESULTS

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.

CONCLUSIONS

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.

Two-year follow-up of corneal cross-linking and refractive surface ablation in patients with asymmetric corneal topography

Aims

To evaluate the safety and efficacy of corneal cross-linking (CXL) followed by photorefractive keratectomy (PRK) for refractive correction in patients with bilateral asymmetric topography.

Methods

Forty-four patients (88 eyes) were enrolled in this prospective randomised clinical trial. CXL with subsequent PRK after 6 months was performed in one eye (study group), and PRK alone was performed in contralateral eyes (control group). Patients were followed for 24 months after PRK. Outcome measures investigated included visual acuity (VA), refraction, aberrometry, topography, pachymetry and endothelial cell count. Groups were compared with linear mixed regression and repeated measures logistic regression. Multiple comparison adjustment with the Holm procedure was performed.

Results

At baseline, the logMAR VA (best spectacle corrected) in study and control groups was 0.12±0.13 (mean±SD) and 0.08D±0.14, respectively, and axial inferior–superior index (IS) (topographic IS) in study and control groups were 0.59D±0.31D and 0.58D±0.32D, respectively. After 24 months, a mean under correction of −0.50D was observed in both groups. Change from baseline in logMAR VA in study and control groups was 0.00D±0.08D and −0.02D±0.10D, respectively. Frequency of haze at 30 months in study and control group eyes was, respectively, 18.2% and 4.6% (p=0.05). There was no statistical difference between groups in spherical aberration and coma after adjustment for multiple comparisons.

Conclusions

Non-simultaneous CXL followed by PRK may be performed safely, and refractive results over a 2-year follow-up are highly similar in virgin and previously cross-linked corneas. Despite using mitomycin C, corneal haze can be significantly higher in the first year after PRK in eyes pretreated with CXL.

EpiLASIK with Mitomycin C

Purpose

Mitomycin C after photorefractive keratectomy (PRK) is used to reduce the development of haze and regression in higher intended corrections. The aim of this study was to investigate the safety, stability, and efficacy of EpiLASIK with mitomycin C.

Methods

Fifty eyes of 29 patients underwent EpiLASIK with the Gebauer EpiLift microkeratome. The mean preoperative spherical equivalent was −6.89 D (SD ±0.63, range −6.0 to −8.0 D). After the laser ablation, mitomycin C 0.02% was applied for 30 seconds on a sterile filter paper. Preoperatively and 1, 3, 6, and 12 months after surgery, a full ophthalmic examination was performed.

Results

In 42 of 50 eyes, the bandage contact lens was removed at day 3. Twelve months after surgery, 96% of all eyes were within ±1.0 D and 82% were within ±0.5 D of intended correction. Five percent of all patients lost 1 line of best-corrected Snellen visual acuity, 42% were stable, and 56% gained 1 or more lines. In most patients, the cornea was clear during the whole follow-up, and in 10% only trace haze was visible. The uncorrected visual acuity was at least 1.0 in 86% of all patients, and all patients reached 0.5.

Conclusions

EpiLASIK with mitomycin C with higher intended corrections seems to be an effective and safe procedure. With the application of mitomycin C, only minimal haze appears.

Clinical Study of Mitomycin C in Reducing Haze Formation After Ultraviolet A/Riboflavin Crosslinking for Keratoconus

OBJECTIVES

To evaluate the safety and efficacy of mitomycin C (MMC) in haze formation after ultraviolet A/riboflavin corneal crosslinking (CXL) for progressive keratoconus.

METHODS

A total of 60 keratoconic eyes of 48 patients were enrolled in this prospective comparative study after obtaining informed consent. In the CXL group, standard corneal CXL was performed, whereas in the CXL+MMC group, 0.02% MMC was used for 30 s soon after CXL. Comprehensive ophthalmologic examinations were performed on all patients before surgery and at 1, 3, 6, and 12 months after surgery.

RESULTS

The epithelium recovered within 3 to 4 days after CXL, and the healing time was comparable in the two groups. There was no significant endothelial cell density loss after CXL in both groups. Eyes in both groups showed improvement of uncorrected distance visual acuity (Snellen) and best-corrected visual acuity (Snellen; P<0.05), and there was a decrease in K-max, cylinder degree, and central corneal thickness (CCT) (P<0.05). There was no significant statistical difference between the groups regarding postoperative K-max reduction, refraction, and CCT (P>0.05). Corneal haze scores were significantly higher in the CXL group at 1 and 3 months after CXL (P=0.012 and P=0.028, respectively), but were similar to the MMC group at 6 and 12 months after surgery (P=0.329 and P=0.543, respectively).

CONCLUSIONS

Prophylactic intraoperative use of 0.02% MMC can significantly reduce CXL-associated haze formation, especially in the early postoperative period, and no signs of weakening CXL efficacy were observed.

Endothelial cell changes after photorefractive keratectomy with graded usage of mitomycin C

PURPOSE

To compare differences in the endothelial cells before and after photorefractive keratectomy (PRK) for myopia with refractive error graded mitomycin C (MMC) application.

METHODS

In a prospective randomized clinical trial, forty-eight myopic patients referred to Khatam-al-Anbia Eye Hospital, Mashhad, Iran, for PRK. Patients were treated with PRK by a Bausch and Lomb Technolas 217z excimer laser (Bausch and Lomb, Rochester, NY). MMC was applied after PRK 5 s for each diopter of spherical equivalent myopic refractive error corrected. The manifest refraction, visual acuity, MMC treatment length, corneal pachymetry and specular microscopy were evaluated preoperatively and at 1 and 6 months postoperatively.

RESULTS

A total of 48 cases (96 eyes, 68.75% female) were treated, with a mean age of 26.70 ± 4.89 years (range, 18-34 years). Postoperative cell density, cell size and polymegathism did not significantly change. On the other hand, standard deviation (SD) of cell size (P = 0.008), pleomorphism (P = 0.003) and coefficient of variation (CV) (P = 0.016) were significantly increased. None of these parameters was related to the length of MMC application. Corneal thickness decreased significantly after the operation but it increased 6 months postoperatively compared with the first month (P < 0.001).

CONCLUSION

MMC application for PRK in myopia can affect the endothelial cells, but in early follow-ups, it does not affect the cell density or size. Cell size was changed but it was obvious not in mean cell size, but in SD and CV. MMC time below the 30 s was not significant on endothelial cell changes.

Adjunctive Therapies for Bacterial Keratitis

Bacterial keratitis is the most common type among all types of infectious keratitis. Currently, antibiotics are the main-stay of treatment. The objective of this systematic review is to review published clinical studies which discuss the adjunctive treatment of bacterial keratitis to guide clinical decision-making. We reviewed the role of a variety of medications and surgeries which can help in managing bacterial keratitis complications, which include as thinning, perforation, and impaired wound healing. We have included appropriate animal and laboratory studies, case reports and case series, and randomized clinical trials regarding each therapy.

Effect of Mitomycin C on Myopic versus Astigmatic Photorefractive Keratectomy

Purpose. Long-term mitomycin C (MMC) effects on photorefractive keratectomy (PRK) were compared in simple myopic and astigmatic patients. Methods. In this observational cohort study, subjects were selected based on preoperative and postoperative data collected from medical records; they were divided into simple myopia with/without MMC and myopic astigmatism with/without MMC groups. Haze, uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), subjective refraction, and K-reading were evaluated at 1-, 3-, 6-, and 12-month follow-ups. Results. One hundred fifty-nine eyes of 80 subjects (34 women and 46 men; mean age, 26.81 ± 7.74 years; range, 18-53 years; spherical powers, -0.50 to -8.00 DS; and cylindrical powers, -0.25 to -5.00 DC) were enrolled. One year postoperatively, the simple myopia with/without MMC groups showed no difference in UCVA (P = 0.187), BCVA (P = 0.163), or spherical equivalent (P = 0.163) and a significant difference (P = 0.0495) in K-reading; the haze formation difference was nonsignificant (P = 0.056). Astigmatic groups with/without MMC showed a significant difference in K-reading (P < 0.0001). MMC groups had less haze formation (P < 0.0001). Conclusion. PRK with intraoperative MMC application showed excellent visual outcomes. MMC's effect on astigmatic patients was significantly better with acceptable safety and minimal side effects.

Mitomycin-C in corneal surface excimer laser ablation techniques: a report by the American Academy of Ophthalmology

OBJECTIVE

To review the published literature assessing the efficacy and safety of mitomycin-C (MMC) as an adjunctive treatment in corneal surface excimer laser ablation procedures.

METHODS

Literature searches of the PubMed and Cochrane Library databases were last conducted on August 19, 2014, without language or date limitations. The searches retrieved a total of 239 references. Of these, members of the Ophthalmic Technology Assessment Committee Refractive Management/Intervention Panel selected 26 articles that were considered to be of high or medium clinical relevance, and the panel methodologist rated each article according to the strength of evidence. Ten studies were rated as level I evidence, 5 studies were rated as level II evidence, and the remaining 11 studies were rated as level III evidence.

RESULTS

The majority of the articles surveyed in this report support the role of MMC as an adjunctive treatment in surface ablation procedures. When MMC is applied in the appropriate concentration and confined to the central cornea, the incidence of post-surface ablation haze is decreased. Although a minority of studies that evaluated endothelial cell density (ECD) reported an MMC-related decrease in ECD, no clinical adverse outcomes were reported.

CONCLUSIONS

Over the past 15 years, the use of MMC during surgery in surface ablation has become widespread. There is good evidence of the effectiveness of MMC when used intraoperatively as prophylaxis against haze in higher myopic ablations. Although there are reports of decreased endothelial counts after the administration of MMC during surgery, the clinical significance of this finding remains uncertain, because no adverse outcomes were reported with as much as 5 years of follow-up. Optimal dosage, effectiveness as prophylaxis in lower myopic and hyperopic ablations, and long-term safety, particularly in eyes with reduced corneal endothelial cell counts from prior intraocular surgery, have yet to be established.

Long term followup of photorefractive keratectomy with adjuvant use of mitomycin C

Purpose. To study the long term refractive and visual outcomes of photorefractive keratectomy (PRK) with intraoperative application of mitomycin C (MMC). Methods. This study included 37 eyes who received myopic PRK; after photoablation, a sponge soaked in 0.02% MMC solution was applied in all corneas for 2 minutes. Efficacy, safety, predictability, and stability of PRK MMC were evaluated. Endothelial cell density was evaluated at the last postoperative interval. Results. Mean preoperative spherical equivalent (SEQ) was −6.03 ± 1.87 D (diopters) and reduced to −0.09 ± 0.53 D at the last postoperative examination. Mean followup was 44.73 ± 18.24 months. All the eyes were in the ±1.00 D of attempted versus achieved SEQ at the one-year follow-up interval. Furthermore, 95% of the eyes did not lose lines or gained 1 to 2 lines of CDVA, while 5% lost 1 line. At the third postoperative month, 89% of the eyes either were clear or had trace haze, while 4 eyes had mild haze; by the 12-month postoperative interval, none of the eyes demonstrated haze. Mean endothelial cell density (ECD) at the last postoperative interval was 2658 ± 153 cells/mm². Conclusions. PRK, with intraoperative use of MMC, demonstrates stable refractive and visual outcomes up to 44 months after surgery.

Triple combination of siRNAs targeting TGFβ1, TGFβR2, and CTGF enhances reduction of collagen I and smooth muscle actin in corneal fibroblasts

PURPOSE

Transforming growth factor β1 (TGFβ1), TGFβ receptor (TGFβR2), and connective tissue growth factor (CTGF) are key regulators of fibrosis in the cornea and in other tissues, including liver, skin, and kidney. We developed an antifibrotic treatment targeting these three critical scarring genes by using a combination of small interfering RNAs (siRNAs) and assessed its effect on downstream scarring genes, collagen I, and α smooth muscle actin (SMA).

METHODS

Up to six individual siRNAs for each of the three target gene mRNAs were transfected into cultures of rabbit corneal fibroblasts at concentrations from 15 to 90 nM. The knockdown of target gene proteins was measured by ELISA, and the two most effective siRNAs were tested in dual combinations. Knockdown percentages of both individual and dual siRNA combinations were analyzed for synergy by using combination index to predict "effective" and "ineffective" triple siRNA combinations. Effects of both triple siRNA combinations on target and downstream mRNAs were measured by using quantitative RT-PCR, and levels of SMA protein were assessed by immunohistochemistry.

RESULTS

Single and dual siRNA combinations produced a wide range of protein knockdown of target genes (5%-80%). The effective triple siRNA combination significantly reduced mRNA levels of target genes (>80%) and downstream scarring genes (>85%), and of SMA protein (>95%), and significantly reduced cell migration without reducing cell viability.

CONCLUSIONS

Simultaneous targeting of TGFβ1, TGFβR2, and CTGF genes by effective triple siRNA combination produced high knockdown of target and downstream scarring genes without cell toxicity, which may have clinical applications in reducing corneal fibrosis and scarring in other tissues.

Hevin plays a pivotal role in corneal wound healing

Background

Hevin is a matricellular protein involved in tissue repair and remodeling via interaction with the surrounding extracellular matrix (ECM) proteins. In this study, we examined the functional role of hevin using a corneal stromal wound healing model achieved by an excimer laser-induced irregular phototherapeutic keratectomy (IrrPTK) in hevin-null (hevin^-/-) mice. We also investigated the effects of exogenous supplementation of recombinant human hevin (rhHevin) to rescue the stromal cellular components damaged by the excimer laser.

Methodology/Principal Findings

Wild type (WT) and hevin^-/- mice were divided into three groups at 4 time points- 1, 2, 3 and 4 weeks. Group I served as naïve without any treatment. Group II received epithelial debridement and underwent IrrPTK using excimer laser. Group III received topical application of rhHevin after IrrPTK surgery for 3 days. Eyes were analyzed for corneal haze and matrix remodeling components using slit lamp biomicroscopy, in vivo confocal microscopy, light microscopy (LM), transmission electron microscopy (TEM), immunohistochemistry (IHC) and western blotting (WB). IHC showed upregulation of hevin in IrrPTK-injured WT mice. Hevin^-/- mice developed corneal haze as early as 1-2 weeks post IrrPTK-treatment compared to the WT group, which peaked at 3-4 weeks. They also exhibited accumulation of inflammatory cells, fibrotic components of ECM proteins and vascularized corneas as seen by IHC and WB. LM and TEM showed activated keratocytes (myofibroblasts), inflammatory debris and vascular tissues in the stroma. Exogenous application of rhHevin for 3 days reinstated inflammatory index of the corneal stroma similar to WT mice.

Conclusions/Significance

Hevin is transiently expressed in the IrrPTK-injured corneas and loss of hevin predisposes them to aberrant wound healing. Hevin^-/- mice develop early corneal haze characterized by severe chronic inflammation and stromal fibrosis that can be rescued with exogenous administration of rhHevin. Thus, hevin plays a pivotal role in the corneal wound healing.

Topical rosiglitazone is an effective anti-scarring agent in the cornea

Corneal scarring remains a major cause of blindness world-wide, with limited treatment options, all of which have side-effects. Here, we tested the hypothesis that topical application of Rosiglitazone, a Thiazolidinedione and ligand of peroxisome proliferator activated receptor gamma (PPARγ), can effectively block scar formation in a cat model of corneal damage. Adult cats underwent bilateral epithelial debridement followed by excimer laser ablation of the central corneal stroma to a depth of ~160 µm as a means of experimentally inducing a reproducible wound. Eyes were then left untreated, or received 50 µl of either 10 µM Rosiglitazone in DMSO/Celluvisc, DMSO/Celluvisc vehicle or Celluvisc vehicle twice daily for 2 weeks. Cellular aspects of corneal wound healing were evaluated with in vivo confocal imaging and post-mortem immunohistochemistry for alpha smooth muscle actin (αSMA). Impacts of the wound and treatments on optical quality were assessed using wavefront sensing and optical coherence tomography at 2, 4, 8 and 12 weeks post-operatively. In parallel, cat corneal fibroblasts were cultured to assess the effects of Rosiglitazone on TGFβ-induced αSMA expression. Topical application of Rosiglitazone to cat eyes after injury decreased αSMA expression and haze, as well as the induction of lower-order and residual, higher-order wavefront aberrations compared to vehicle-treated eyes. Rosiglitazone also inhibited TGFβ-induced αSMA expression in cultured corneal fibroblasts. In conclusion, Rosiglitazone effectively controlled corneal fibrosis in vivo and in vitro, while restoring corneal thickness and optics. Its topical application may represent an effective, new avenue for the prevention of corneal scarring with distinct advantages for pathologically thin corneas.

Comparison of TGF-β1 in tears and corneal haze following Epi-LASIK with and without mitomycin C

AIM

To compare transforming growth factor-β1 (TGF-β1) levels in tears and the degree of corneal haze formation following epithelial laser in situ keratomileusis (Epi-LASIK) with and without the use of mitomycin C (MMC) and to investigate the effect of MMC on corneal wound healing.

METHODS

Thirty-two patients (64 eyes) with high myopia underwent Epi-LASIK surgery, and MMC was randomly used in one eye in each patient. The epithelialization process was observed, and the TGF-β1 level in tears was measured at 1 day, 3, and 7 days postoperatively for comparison with baseline. Corneal haze was graded at 1 month, 3, and 6 months after surgery.

RESULTS

Mean preoperative spherical equivalent refraction was -8.24±2.18D (range -6.00 to -10.50D) in the MMC group and -7.82±1.55D (range -6.00 to -9.75D) in the non-MMC group. There was no significant difference between the two groups (P=0.38). Mean epithelialization time was (5.02±0.68) days in the MMC group and (4.86±0.57) days in the non-MMC group (P=0.31). Tear fluid TGF-β1 levels were similar before surgery (P=0.34), but were significantly higher in the non-MMC group at 1 day, 3, and 7 days postoperatively (P=0.004, 0.008, and 0.012, respectively). Corneal haze scores 1 month after surgery were significantly higher in the non-MMC group (P=0.03), and similar at 3 and 6 months after surgery (P=0.28 and 0.62, respectively).

CONCLUSION

MMC did not delay epithelialization. In early postoperative period, lower TGF-β1 levels in tears and a lower grade of corneal haze were observed in the MMC group. Our findings suggest that the ability of MMC to inhibit Epi-LASIK-induced haze might be mediated through TGF-β1 suppression.

Mitomycin C: biological effects and use in refractive surgery

PURPOSE

To provide an overview of the safety and efficacy of mitomycin C (MMC) as adjuvant therapy after refractive surgery procedures.

METHODS

Literature review.

RESULTS

Over the past 10 years, MMC has been used by refractive surgeons to prophylactically decrease haze after surface ablation procedures and therapeutically in the treatment of preexisting haze. Development of MMC treatments has had a significant role in the revival of surface ablation techniques. We reviewed the literature regarding mechanism of action of MMC, its role in modulating wound healing after refractive surgery, and its safety and efficacy as adjuvant therapy applied after primary photorefractive keratectomy surgery or after photorefractive keratectomy re-treatment after laser in situ keratomileusis and other corneal surgeries and disorders. The drug is a potent mitotic inhibitor that effectively blocks keratocyte activation, proliferation, and myofibroblast differentiation. Many studies have suggested that MMC is safe and effective in doses used by anterior surface surgeons, although there continue to be concerns regarding long-term safety. After initial depletion of anterior keratocytes, keratocyte density seems to return to normal 6 to 12 months after the use of MMC when corneas are examined with the confocal microscope. Most clinical studies found no difference between preoperative and postoperative corneal endothelial cell densities when MMC 0.02% was applied during refractive surgery, with exposure time of 2 minutes or less.

CONCLUSIONS

After more than 10 years of use, MMC has been found to be effective when used for prevention and treatment of corneal haze. Questions remain regarding optimal treatment parameters and long-term safety.

Keratocyte density 3 months, 15 months, and 3 years after corneal surface ablation with mitomycin C

PURPOSE

To study the effects of surface ablation with mitomycin C (MMC) on keratocyte population.

DESIGN

Prospective, nonrandomized, interventional, comparative case series.

METHODS

Thirty two eyes treated with surface ablation with 0.02% MMC were compared with nontreated eyes at Vissum Santa Hortensia, Madrid, Spain. Keratocyte density was measured with the Heidelberg Retina Tomograph II (Rostock Cornea Module) 3, 15, and 36 to 42 months after the surgery in the anterior, mid, and posterior stroma, and compared with control eyes.

RESULTS

Three months postoperatively, we found a lower stromal bed density compared to controls (16 993 ± 8001 vs 29 660 ± 5904 cells/mm(3), P = .0001), while there was a significantly higher cell density in the mid (30 783 ± 9300 vs 18 505 ± 1996 cells/mm(3), P = .0001) and deep stroma (30 268 ± 8321 vs 18 438 ± 2139 cells/mm(3), P = .0001). Three years after the surgery, the cellularity in the stromal bed had not significantly changed from the 3-month follow-up, but the density in the mid (18 889 ± 3474 cells/mm(3)) and posterior stroma (18 992 ± 3402 cells/mm(3)) had decreased to show no difference from controls. The mean cell density between the anterior, mid, and posterior stroma was not significantly different from controls 15 months and 3 years after the surgery.

CONCLUSION

Our study suggests that there is a reorganization of the stromal cell population soon after surface ablation with MMC, with a decrease in the stromal bed compensated initially with an increase in the mid and posterior stroma. Corneal cellularity tends to normalize over time, and 3 years postoperatively the mean cell density throughout the cornea seems to maintain normal values.

Management of corneal scarring secondary to explosion with excimer laser treatment

BACKGROUND

Improper use of pyrotechnics can result in ocular injuries producing severe vision loss.

CASE

A 20-year-old man had a pyrotechnics device explode in his face, hospitalizing him for 4 days. He was told he needed a corneal transplant and that his vision would be impaired permanently. As an alternative, phototherapeutic keratectomy was performed on each eye to remove as much scar tissue as possible. Photorefractive keratectomy was then used to treat the residual hyperopia and remove more of the scarring.

CONCLUSIONS

The combination of phototherapeutic keratectomy/photorefractive keratectomy proved to be a safe and effective method to treat corneal scarring secondary to explosive trauma and to restore normal vision.