الفهرس 
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Abstract
Photorefractive keratectomy (PRK) was described for the first time by Munnerlyn et al., (103) in their paper published in 1988. The original technique depends on mechanical removal of the corneal epithelium, and later alcohol use was tried (A-PRK). Transepithelial PRK (T-PRK) was described in the late 1990s by Clinch et al., (104) as an alternative to the conventional mechanical or alcohol assisted removal of the epithelium.
The advantages of T-PRK include; no instrumental direct contact with the eye, reduced procedure time and the potential to minimize the epithelial raw area needed for the correcting ablation. Avoiding using alcohol is alleged to avoid the potential toxicity to the limbal stem cells, decrease the postoperative pain and corneal haze with rapid healing time and a faster visual recovery. Thus, this study aimed to compare the effect of trans-epithelial versus alcohol assisted PRK in cases of myopia and myopic astigmatism correction regarding efficacy and safety. This was a prospective cohort study included 38 patients with myopia with or without astigmatism undergoing PRK. Patients were divided into two groups of patients who are eligible for PRK surgery:
Group1: 19 patients (38 eyes) with Trans-Epithelial PRK.
group 2: 19 patients (38 eyes) with Alcohol-Assisted PRK.
Patients were selected according to the inclusion and exclusion criteria as follows:
Inclusion Criteria: Patients with myopia with age between 21 and 49 years, minimum corneal thickness of 500 μm, mean keratometry between 40 and 47 Diopters, normal corneal pentacam examination, refraction between -1 to -10 and astigmatism between -0.5 to -5.0 D and Exclusion Criteria: Patients with abnormal corneal topography, pachymetry lower than 500 micro, flat cornea with k1 less than 40D, cases with previous refractive surgery and other ocular pathologies and systemic (e.g., history of herpes keratitis, diagnosed autoimmune disease, systemic connective tissue disease, glaucoma, cataract, diabetic retinopathy, and age-related macular degeneration).
The current findings can be summarized as follows:
Spherical equivalent did not show any significant differences between T-PRK and A-PRK groups pre- and post-operation (P>0.05).
Spherical equivalent was significantly gradually decreased among patients in both T-PRK and A-PRK groups post-operation than pre-operation (P<0.001).
Sphere (spherical error of refraction) did not show any significant differences between the two groups post-operation (P>0.05).
Sphere was significantly gradually decreased among patients in both T-PRK and A-PRK groups post-operation than pre-operation (P<0.001).
Cylinder did not show any significant differences between T-PRK and A-PRK groups pre and after operation (P<0.05).
Cylinder was significantly gradually decreased among patients in both T-PRK and A-PRK groups post-operation than pre-operation (P<0.001).
UCVA, did not show any significant differences between T-PRK and A-PRK groups pre and after operation (P<0.05).
The UCVA value was significantly gradually increased among patients in both T-PRK and A-PRK groups post-operation than pre-operation (P<0.001).
There were no significant differences between T-PRK and A-PRK groups regarding BCVA, CCT and K max value (P>0.05).
Epithelial healing time was significantly shorter among T-PRK group (2.26±0.45) than A-PRK group (2.79±0.54) with (P=0.002); While pain score and haze didn’t show any significant difference between the two groups (P>0.05).
Haze was significantly correlated with (cylinder and K max) pre-operation. Also, with cylinder at 3 days post operation. And with cylinder and UCVA at 1 month post operation. Additionally with cylinder at 3 months post operation (P<0.05).
Epithelial healing time showed significant correlation with K max pre-operation (P<0.05).
Pain score didn’t show any significant correlation with all parameters pre or post operation (P>0.05).