Evaluation of endothelial function after using high concentration and prolonged exposure of mitomycin C following photorefractive keratectomy for high myopia and astigmatism

Purpose: To evaluate endothelial function after using high concentration and prolonged exposure of mitomycin C following PRK for high myopia and astigmatism.
Participants: Twenty-two eyes of highly myopic patients with or without astigmatism seeking refractive correction.
Methods: Twenty-two (22) eyes of fourteen(14) patients with high myopia (more than 6 diopters myopia together with astigmatism) seeking for refractive correction at the research institute of ophthalmology-Egypt, were subjected to Photorefractive keratectomy (PRK) using the ALLEGRETTO WAVE EYE-Q 1010 with application of high concentration of mitomycin C 0.027%  for more than two minutes after excimer laser ablation.  Postoperatively, patients were given topical moxifloxacin eye drops, steroid eye drops, NSAIDs eye drops in addition to oral analgesics. A contact lens was applied to counteract pain and is removed once the epithelium was healed. Patients will be examined 1,6,7 days, 2 weeks and 1,2 months after surgery. Specular microscopy was performed before surgery and again1-2 months after PRK to detect any possible reduction of endothelial function. Final corneal haze as well as BCVA were reported at 1- 2 months after stabilization of refractive error. Collected data were subjected to statistical analysis including determination of mean value, standard deviation of each studied item in addition to minimum and maximum values. Comparison tests (t-test) as well as correlation tests were performed. Results: The age ranged from 18-39 years (mean 28.10±6.24).The corrected sphere (D) ranged from -3.0 to -10.0 (mean -6.82±2.08), cylinder (D) ranged from -1.0 to -4.5 (mean -2.56±1.13) and the total sphero-cylindrical correction (D) ranged from -6.25 to -11.25 (mean -8.78±1.52). No significant corneal haze developed in any of the cases included in the study. Regarding specular microscopy, the  endothelial cell density(CD)/ mm² changed from a mean value of 2667.05±218.35 preoperatively to a mean value of 2697.32± 245.97 at 1-2 months postoperatively
with a non-significant difference (p>0.05). The average endothelial cell area (Avg) (µm2) changed from a mean value 
of 377.41±31.38 preoperatively to a mean value of 373.77±36.51at 1-2 months postoperatively with a non-
significant difference (p>0.05). The average coefficient of variation in cell size (CV) i.e; polymegathism changed from a mean value of 28.22±6.98 preoperatively to a mean value of 26.09±4.39at1-2 months postoperatively with a non-significant difference (p>0.05). The average hexagonal cells percentage (Hex%) i.e; pleomorphism, changed from a mean value of 68.18±8.35 preoperatively to a mean value of 69.95±6.47 at 1-2 months postoperatively with a non-significant difference (p>0.05). A non-significant correlation (P>0.05) existed between length of mitomycin C exposure and post-PRK changes in the cell density (CD) (r=0.14), average cell area change (r=-0.18) as well as coefficient of variation in cell size (CV) (r=0.02) but there was a statistically significant correlation between the length of mitomycin C exposure and post-PRK changes in the hexagonal cells percentage (p < 0.05, r=0.37).
Conclusion: Photorefractive keratectomy using higher concentration of mitomycin C (0.027%) for exposure time of (2.20-3minutes) provided excellent refractive and visual results for high myopia and astigmatism without significant negative effects on the corneal endothelium.