Development of late-onset subepithelial corneal haze after laser-assisted subepithelial keratectomy with prophylactic intraoperative mitomycin-C

Safety and efficacy of combination of suberoylamilide hydroxyamic acid and mitomycin C in reducing pro-fibrotic changes in human corneal epithelial cells

Corneal haze post refractive surgery is prevented by mitomycin c (MMC) treatment though it can lead to corneal endothelial damage, persistent epithelial defects and necrosis of cells. Suberanilohydroxamic acid (SAHA) however has been proposed to prevent corneal haze without any adverse effects. For clinical application we have investigated the short and long term outcome of cells exposed to SAHA. Human donor cornea, cultured limbal epithelial cells, corneal rims and lenticules were incubated with SAHA and MMC. The cells/tissue was then analyzed by RT-qPCR, immunofluorescence and western blot for markers of apoptosis and fibrosis. The results reveal that short term exposure of SAHA and SAHA + MMC reduced apoptosis levels and increased αSMA expression compared to those treated with MMC. Epithelial cells derived from cultured corneal rim that were incubated with the MMC, SAHA or MMC + SAHA revealed enhanced apoptosis, reduced levels of CK3/CK12, ∆NP63 and COL4A compared to other treatments. In SAHA treated lenticules TGFβ induced fibrosis was reduced. The results imply that MMC treatment for corneal haze has both short term and long term adverse effects on cells and the cellular properties. However, a combinatorial treatment of SAHA + MMC prevents expression of corneal fibrotic markers without causing any adverse effect on cellular properties.

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.

Late onset corneal haze after corneal cross-linking for progressive keratoconus

Purpose

To present the case of a patient that underwent corneal crosslinking for progressive keratoconus and 18 months later revealed clinically significant corneal stromal haze.

Observations

A 20-year-old male presented with progressive visual loss OU for the past few years. His corrected distance visual acuity (CDVA) OD was 20/30 (−2.75 -1.75 @55) and OS 20/30 (−0.50 -1.75@110). Corneal topography revealed keratoconus OU and the patient underwent corneal crosslinking according to the Dresden Protocol. The postoperative regimen included combined tobramycin and dexamethasone qid along with lubrication until epithelium healed and then fluorometholone qid with weekly tapering. At 3 months postoperatively, his topography was stable and his corrected distance visual acuity (CDVA) was 20/25 OU. On slit lamp examination, only clinically insignificant stromal haze was observed. At 18 months postoperatively, the patient reported vision deterioration. On examination his CDVA was 20/25 in right eye, and 20/40 in his left eye. Deep stromal haze was revealed in his central cornea, more dense in his left eye. Corneal topography was stable and the CDVA loss was attributed to the notable deep stromal haze. The patient was treated with dexamethasone qid with biweekly tapering. 18 months after corneal crosslinking, the patient demonstrated clinically significant stromal haze, most prominent OS. He was treated with dexamethasone qid. One month later his CDVA OS gradually improved to 20/25, and stromal haze was still noted but less dense.

Conclusions and importance

Late-onset deep corneal haze is a possible complication of corneal crosslinking in keratoconic patients.

High myopic photorefractive keratectomy outcomes with the Alcon Wavelight® EX500 excimer laser

Purpose

To present refractive outcomes from consecutive cases with the Alcon Wavelight^® EX500 excimer laser using photorefractive keratectomy (PRK) in patients with high myopia.

Methods

A retrospective chart review of consecutive cases of high myopic eyes (≥6.0 Diopters [D]) undergoing PRK with the Alcon Wavelight EX500 excimer laser (Alcon Laboratories, Fort Worth, TX, USA) was done. Moderately high myopic eyes (6.0 to <8.0 D [6 D]) were compared with high myopic eyes (8.0 D or greater [8 D]). Outcomes measured included pre- and postoperative refractive error, uncorrected distance visual acuity (UDVA), corrected distance visual acuity, spherical equivalent correction (SEQ), haze incidence, and intraocular pressure (IOP).

Results

One hundred eighteen eyes of 63 patients were evaluated, with 59 eyes having 12 months of follow-up. Thirty-one eyes of 19 patients had 8.0 D or more of myopia. Twelvemonth average LogMAR UDVA was -0.06 (20/17) for the 6 D group and -0.08 (20/16) for the 8 D group. Average 12-month SEQ was -0.18 D and preoperatively was -7.52 D for the 6 D group and -0.09 and -9.02 in the 8 D group. Sixty-five eyes (86%) and 24 eyes (96%) had an SEQ within 0.50 D of emmetropia at 3 months in the 6 and 8 D groups, respectively. One eye had visually significant haze developed at 8 months. Three eyes had IOP elevation that resolved with addition of short-term topical IOP-lowering medication.

Conclusion

High myopic PRK with the Alcon Wavelight EX500 excimer laser yields excellent refractive outcomes with a low incidence of complications.

Phototherapeutic Keratectomy: Science and Art

PURPOSE

To describe, with videos, the principles of excimer laser phototherapeutic keratectomy (PTK) for the treatment of corneal scars, corneal surface irregularity, and recurrent corneal erosions.

METHODS

Depending on the pathology in a treated cornea, the epithelium is removed either by transepithelial PTK ablation with the excimer laser or thorough scraping with a scalpel blade. Stromal PTK can be performed with or without photorefractive keratectomy (PRK), depending on the refractive status of both eyes. Residual surface irregularity is treated with masking-smoothing PTK. Typically, 0.02% mitomycin C treatment is applied for 30 seconds to corneas treated with PTK for scars and surface irregularity.

RESULTS

Transepithelial PTK with masking-smoothing typically improves corrected distance visual acuity in the eye even if the entire stromal opacity cannot be removed and can be used to debulk surface irregularity to facilitate subsequent therapeutic customized wavefront-guided or optical coherence tomography-guided PTK or PRK. PTK for recurrent erosion is performed after thorough mechanical epithelial debridement of redundant epithelial basement membrane (EBM) with a scalpel and should only include a dusting of excimer laser to remove residual EBM without inducing central irregular astigmatism or damaging limbal tissues. Meta-analyses are provided for PTK treatment for corneal scars, corneal dystrophies, and recurrent corneal erosions.

CONCLUSIONS

Excimer laser PTK is a highly effective treatment for superficial corneal scars, central corneal irregular astigmatism, and recurrent corneal erosions unresponsive to medical treatment or mechanical epithelial debridement alone. [J Refract Surg. 2017;33(3):203-210.].

Corneal Complications During and After Vitrectomy for Retinal Detachment in Photorefractive Keratectomy Treated Eyes

To evaluate the occurrence of late-onset corneal haze (LOCH) after vitrectomy for rhegmatogenous retinal detachment (RRD) in photorefractive keratectomy (PRK)-treated eyes. This observational cohort study comprised 13 eyes of 13 patients who underwent vitrectomy for RRD and who had been subjected to PRK years earlier. The occurrence of LOCH was evaluated together with all the preoperative, intraoperative, and postoperative factors that could affect final corneal status. LOCH developed in 2 eyes. Both patients had undergone PRK for high myopia--one 3 years and the other 9 years prior to RRD. Both patients presented with RRD due to giant retinal tear and were subjected to scleral buckle, 20-gauge vitrectomy, and silicone oil tamponade. Three months after vitrectomy and 1 month after silicone oil removal they both developed LOCH. During vitreoretinal surgery neither of the 2 patients needed mechanical epithelial debridement. Intraoperative epithelial debridement was performed in 2 of the other patients of the series, who had undergone previous PRK for high myopia and had clear corneas at presentation; in 1 of them this manoeuvre hampered intraoperative visualization. Follow-up after retinal detachment surgery ranged from 6 to 156 months (mean, 37.5 months). Subepithelial corneal scarring may be reactivated many years after PRK. In our series this happened after vitrectomy.

Very late-onset corneal scar triggered by trauma after photorefractive keratectomy

A 54-year-old woman who had photorefractive keratectomy (PRK) more than 10 years earlier presented with a history of being hit in the eye by a tree branch and developing blurred vision a short time later. The corrected visual acuity was 20/100 with localized grade 3 stromal haze. The haze intensified despite initial response to corticosteroids and cyclosporine, and treatment with phototherapeutic keratectomy and 0.02% mitomycin-C (MMC) was effective in restoring corneal clarity and normal vision. Late-onset stromal scar can be triggered by trauma years after PRK. Phototherapeutic keratectomy with MMC can be an effective treatment for late-onset scar. Persistent haze or scar after trauma if PRK had not been performed previously is exceedingly rare.

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.

Effectiveness of scraping and mitomycin C to treat haze after myopic photorefractive keratectomy

To report the possibility of post myopic photorefractive keratectomy (PRK) haze treatment in a patient with expressed reluctance for any additional laser therapy. Seven months after bilateral PRK with subsequent development of corneal haze and refractive regression in both eyes, a 37-old-year male patient presented a best-spectacle corrected visual acuity (BSCVA) of 20/30 in the right eye and of 20/22 in the left eye. Both eyes were sequentially treated by scraping the stromal surface and application of mitomycin C (MMC) for 2 minutes. Both eyes had significant improvement in corneal transparency. Eighteen months after this treatment BSCVA had improved to 20/20 in each eye. No toxic effects were observed during either re-epithelialization or follow-up periods. In conclusion scraping and application of MMC could be considered a good tool in the treatment of selected cases of haze after myopic PRK, especially with patients that are reluctant to undergo a secondary laser procedure.

Keratocyte density after laser-assisted subepithelial keratectomy with mitomycin C

PURPOSE

To study the effects of laser-assisted subepithelial keratectomy (LASEK) with mitomycin C (MMC) on the keratocyte population.

DESIGN

Prospective, nonrandomized, interventional, comparative case series.

METHODS

Fifty-six eyes treated at Vissum Santa Hortensia, Madrid, Spain, were included in the study. We compared 28 eyes treated with LASEK with intraoperative 0.02% MMC versus 28 non-treated eyes. Keratocyte density was measured 3 months after the surgery in the anterior, mid, and posterior stroma and was compared with the corresponding layers in the control eyes. The anterior layer in the LASEK group was compared with 2 layers in the control group: the most anterior stromal layer and the 80 μm-deep layer, because that was the mean ablation depth performed in eyes that underwent LASEK.

RESULTS

We found a statistically significantly lower keratocyte population in the most anterior stromal layer after LASEK with MMC compared with both the most anterior stromal layer and the 80 μm-deep layer in controls. On the contrary, the treated group showed a significantly higher keratocyte density in both the mid stroma and the deep stroma. The comparison between the average densities through the entire cornea showed a significantly higher keratocyte population in the LASEK with MMC group.

CONCLUSIONS

LASEK with MMC seems to cause a decrease in the anterior stromal cells 3 months after the surgery compared with nonoperated corneas. There seems to be a compensating proliferation of keratocytes in the deeper corneal layers, suggesting that the ability of keratocytes to repopulate the cornea is maintained after the surgical procedure.

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 0.2mg/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.

Corneal molecular and cellular biology update for the refractive surgeon

PURPOSE

To review clinically relevant progress in understanding cellular and molecular interactions in the cornea that relate to refractive surgical outcomes in patients.

METHODS

Recent published literature focused on femtosecond LASIK and surface ablation procedures, such as photorefractive keratectomy, was reviewed and correlated with clinical results of surgery.

RESULTS

The femtosecond laser has a direct necrotic effect on stromal keratocytes, resulting in the release of cellular components that are chemotactic to bone marrow-derived inflammatory cells. Developments of the femtosecond laser led to lower energy delivery to the stroma and altered laser ablation profiles that decrease epithelial damage during the side-cut, and have markedly improved femtosecond LASIK to the point that the overall early postoperative healing response is indistinguishable from microkeratome LASIK. New studies have directly demonstrated the importance of surface irregularity and resulting structural and functional defects in the epithelial basement membrane, in the generation and persistence of anterior stromal myofibroblasts and haze following surface ablation procedures. These defects augment penetration of epithelium-derived TGF-beta, which is a critical modulator of myofibroblast development in the stroma. Studies on the mechanism of action of mitomycin C treatment to prevent haze have confirmed that the most powerful effect is on stromal cell proliferation and, therefore, decreased population of the anterior stroma with myofibroblast progenitor cells. An undesirable long-term effect of mitomycin C is diminished anterior stromal keratocyte density due to diminished keratocyte re-population. This raises concerns regarding future corneal anomalies in treated corneas.

CONCLUSIONS

Basic research studies of refractive procedures provide important insights into the effects of wound healing on surgical outcomes.

Comparison of standard (0.02%) and low dose (0.002%) mitomycin C in the prevention of corneal haze following surface ablation for myopia

PURPOSE

To retrospectively compare the safety and efficacy of lower dose mitomycin C (MMC) (0.002%) to that of the standard dose (0.02%) in eyes treated with photorefractive keratectomy (PRK) for myopia.

METHODS

The clinical efficacy of 95 eyes receiving myopic PRK with a standard concentration of MMC (0.02%) is sequentially compared to 126 eyes receiving low dose MMC (0.002%). The topical exposure times for MMC varied between 30 seconds and 2 minutes in both groups, and direct contralateral eye comparison of these two exposure times was analyzed in a prospective subset of 39 patients from among the low dose group. Patients were examined preoperatively and postoperatively at 1, 3, 6-9, and 9-12 months. Haze, visual acuity, and efficacy ratio outcomes were analyzed.

RESULTS

The preoperative findings were overall statistically similar, except for higher spherical equivalent refractive error (P = .007) and best spectacle-corrected visual acuity (P = .007) in the standard MMC group. Postoperatively, haze levels ranged from 0 to 4+. With multivariable analysis, significantly less haze was noted among the standard dose MMC eyes for high myopia and higher ablation depth at all postoperative time points. In contrast, the haze levels were statistically similar for moderate myopia and lower ablation depths at the latter postoperative time points. The subset of contralateral eyes randomly receiving low dose MMC (0.002%) at either 30 seconds or 2 minutes exposure showed no significant difference in haze between these exposure times.

CONCLUSIONS

The standard concentration of topical MMC (0.02%) is more effective than low dose MMC (0.002%) in preventing postoperative haze following surface ablation for myopia > or = -6.00 D and deeper ablation depth > or = 75 microm. However, for moderate myopia and shallow depth, low dosing appears to be equally effective. The duration of MMC exposure appears to be less important than its concentration.

Complications of sub-Bowman's keratomileusis with a femtosecond laser in 3009 eyes

PURPOSE

To assess the safety and complication rate of sub-Bowman's keratomileusis (SBK) in 3009 eyes.

METHODS

The flaps were created using the IntraLase femtosecond laser, and excimer ablation was performed with the Bausch & Lomb H.Eye.Tech laser system. The complications of SBK were evaluated retrospectively. The types of complications were grouped into intra- and postoperative flap related.

RESULTS

In 3009 SBK procedures, the total complication rate was 0.63%. Intra- and postoperative flap-related complication rates were 0.33% and 0.30%, respectively. Only 1 (0.033%) eye lost one line of best spectacle-corrected visual acuity from diffuse lamellar keratitis (DLK). Intraoperative complications included flap tear, free cap, bubble escape, and flap folds. Postoperative complications included DLK and epithelial ingrowth. Other flap-related complications such as uneven bed, buttonhole, short flap, flap striae, or wrinkles did not occur in this series. All intraoperative complications were managed within the same day.

CONCLUSIONS

The complication rate of SBK is low. Vision loss is also rare.

Low-dose mitomycin C as a prophylaxis for corneal haze in myopic surface ablation

PURPOSE

To evaluate the efficacy of low-dose (0.002%) mitomycin C (MMC) vs no prophylactic MMC (control) in reducing corneal haze after surface laser ablation.

DESIGN

Two-year retrospective follow-up study performed in Jaipur, India.

METHODS

Ninety-two eyes with no MMC application and 83 eyes with 0.002% MMC application during laser epithelial keratomileusis (LASEK) were analyzed in a retrospective chart review with one month, two months, three months, six months, one year, and two years of postoperative follow-up. Postoperative haze, visual acuity, and efficacy ratio (EFFR) then were analyzed statistically.

RESULTS

The no-dose MMC and low-dose MMC groups were statistically similar except for a thinner corneal pachymetry (P < .001), higher spherical equivalent error (P = .006), and smaller ablation zone (P = .009) in eyes not treated with MMC when subjected to univariate analysis. Multivariate analysis was used to overcome the preoperative statistical differences among the two groups. Eyes treated with low-dose MMC (0.002%) demonstrated statistically less haze at all postoperative time points and in each myopic subgroup (P < .001). The postoperative uncorrected visual acuity (UCVA) and EFFR, however, showed no difference between the groups, except for better EFFR with MMC at one month (P < .001) and two months (P = .034).

CONCLUSIONS

Low-dose MMC (0.002%) in eyes after LASEK results in less corneal haze than in eyes not receiving this agent. Concerns regarding the potential toxicity of MMC make a 10-fold less concentration more desirable in refractive surgery. Further comparative study of low- vs higher-dose MMC is recommended to characterize its clinical benefit fully.