Mitomycin C safe and effective to prevent corneal haze following Transepithelial Photorefractive Keratectomy in Myopia
Refractive errors are the most prevalent visual problem worldwide. According to the World Health Organization, refractive errors are the primary cause of visual impairment and even vision loss globally affecting all age groups. Various types of refractive surgeries have been developed in the past years to correct vision by modifying the shape of the cornea through laser photoablation such as laser-assisted in situ keratomileusis (LASIK), laser-assisted subepithelial keratomileusis (LASEK), and photorefractive keratectomy (PRK).
PRK involves mechanical debridement of epithelium using a blade and followed by surface ablation of the stroma. This method is appropriate for patients with thin corneas who cannot undergo LASIK. Although safe, effective, and even correct high range refractive errors, the development of postoperative corneal haze is one of the serious complications of PRK due to the ongoing surgery-made aberrant wound healing process in the tissue.
Unlike the above methods, transepithelial photorefractive keratectomy (T-PRK) has advantages as it is a non-touch, gentle laser-corrective method that removes corneal epithelium along with stroma in a single step. This procedure has demonstrated minimal corneal epithelial defect to ablate stroma resulting in faster re-epithelialization and enhanced visual recovery along with proven safety and efficacy through lower pain scores and shorter healing time.
Following any in-depth laser ablation method, the corneal stromal keratocytes undergo abnormal proliferation causing subepithelial fibrosis, which leads to haze formation. Several studies have shown that this corneal haze can be effectively prevented by the application of mitomycin C (MMC) over the surface ablated stroma due to its interference with the stromal wound healing process. MMC is a known non-cell cycle-specific antineoplastic agent that actively inhibits the proliferation of highly mitotic cells by blocking their DNA synthesis and causing cell cycle arrest. MMC also mediates inhibition of keratocyte activation and differentiation into myofibroblasts and counteracts disorganized deposition of stromal extracellular matrix. Thus, the use of MMC has been found to be critical in increasing corneal transparency in high myopic patients treated with higher ablation depths. The declination of the endothelial cell density/number has become a key concern in using MMC prophylactically to prevent subepithelial scarring during the refractive correction.
In this study, Al-Mohaimeed investigated the MMC-induced changes in corneal endothelium when used as prophylaxis to inhibit corneal haze formation following T-PRK-based refractive correction of low, moderate, and high myopia. The MMC treatment has been given according to the surface ablation depths of T-PRK. This is the first clinical study that addresses the effect of MMC on corneal endothelium post-T-PRK from low- to high-order myopia.
A total of 120 eyes of 60 patients with low, moderate, and high myopia were subjected to T-PRK with intraoperative application of MMC (0.02%) for 30–50s.
Patients' files were categorized into three groups according to ablation depths (if ≥100 µm) during T-PRK as follows: (1) Group A – low myopia without MMC, (2) Group B – low myopia with MMC, and (3) Group C – moderate/high myopia with MMC.
Preoperative/surgical parameters and refractive outcomes were documented.
Overall, 119 out of 120 eyes showed significant prevention of corneal haze. Groups A and C showed no significant changes in endothelial CD and NUM. Group B showed a non-significant reduction in CD. However, all three groups showed significant variations in HEX/6A, CCT, AVG, and SD.
This is the first clinical study that addresses the effect of MMC on corneal endothelium post-T-PRK from low- to high-order myopia. In this study, the MMC treatment was selectively given based on the ablation depth required during T-PRK to correct myopia. This has been an important criterion to limit the unnecessary exposure of MMC. Although the ablations were deeper for the moderate/high myopic group using T-PRK (131.75 ± 17.23 µm) in this study, the duration of MMC exposure has been limited to 30–50 s to prevent any consequences. Author used the standard dose of 0.02% MMC as this concentration has been found to be safe and effective in minimizing corneal haze and accelerating visual outcome in PRK.
Generally, the incidence of corneal haze is common among high order refractive corrections due to deeper ablations. However, the T-PRK procedure itself reduces haze formation as it is gentle and aberration-free. Furthermore, the combined effect of MMC has resulted in significant prevention of corneal haze in 119 out of 120 eyes including the high order myopic subjects used in the study.
The current study demonstrates the safety and efficacy of MMC application in reducing corneal haze after T-PRK in low- to high-order myopia. The MMC does not affect the corneal endothelial number or density, especially in moderate and high myopic T-PRK. There were slight differences noted in certain parameters relating to endothelial changes, which were of less clinical significance. Despite the contradictions in results and certain limitations in the study, it can be deduced that this study allows further investigation on long-term effects of MMC on endothelium after T-PRK with the severity of myopia.
Source: Al-Mohaimeed; Clinical Ophthalmology 2022:16
