الفهرس 
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Abstract
Keratoconus (KC) is a progressive, non-inflammatory corneal degenerative disease. It is a pathology characterized by a progressive thinning and protrusion of the cornea that ends in a cone‐shaped cornea. This results in progressive myopia and irregular astigmatism with associated progressive loss of vision and thus reduced quality of life. There is no significant gender difference. Keratoconus is considered a disease of the adolescent from the age of 20 to 30, the clinical onset is at puberty and progresses until 3rd to 4th decay. Corneal collagen cross-linking (CXL) is the only procedure that potentially can slow down or block the progression of keratoconus. It is based on a photo-oxidative reaction, catalyzed by riboflavin(B2 vitamin) and UVA. That induces the release of free radicals which promote cross-linking between corneal collagen fibers and thus increase corneal stiffness. This blocks the progression of the disease. One of the concerns about CXL is its safety. So in the current study, we judge the endothelial cell changes after accelerated corneal collagen cross-linking using specular microscopy. Other secondary outcomes are maximum keratometry, pachymetry at the thinnest location, UDVA, CDVA, and RSE. The study includes 30 eyes (of 18 subjects) of progressive keratoconus. They underwent Pulsed-light Accelerated CXL using the KXL system (avedro, Inc., Waltham, MA, USA). Corneal soak time was 10 minutes with Vibex Rapid® (Riboflavin 0.1% in HPMC). Then 30 mW/ cm2 UVA at 365 nm wavelength was applied to the corneas for 8 minutes pulsed mode (1sec on, 1 sec off). The total +was almost stable on a 6-month follow-up (slightly higher). Meanwhile, Minimum cell size increased significantly and maximum cell size decreased insignificantly from baseline through 6 months of follow-up. Regarding other outcomes of the study; Kmax showed stabilization in its values 6 months after CXL. There weren’t any significant changes in pachymetry at the thinnest location, UDVA, CDVA, and RSE. In conclusion, according to our study high fluency pulsed accelerated CXL is considered a safe and effective procedure in keratoconic patients. It showed no significant changes in corneal endothelium using specular microscopy as regards ECD, CV, and hexagonality. Also, pulsed accelerated CXL showed efficacy in halting keratoconus in 93.3% of cases as measured by Kmax. In addition, there was stabilization in mean pachymetry at the thinnest location, UDVA, CDVA, and RSE. Further studies are needed to confirm the safety of pulsed A-CXL on corneal endothelium focusing on soaking time, irradiance level, and timing of UVA on/off period. Also, we may need to study the correlation between different parameters of A-CXL and the safety of corneal endothelium in thin corneas or corneas with previous unhealthy endothelium.