الفهرس 
natomy, physiology and applied anatomy of the CorneaOnly 14 pages are availabe for public view
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Abstract
HOAs are among the important refractive and visual quality properties of the human ocular system and the decreased the level of some visual features such as contrast sensitivity have been partially attributed to these parameters. Evaluation of long-term changes of HOAs after CXL is useful in understanding the efficacy of CXL on improving optical, refractive, and visual acuity (VA). The aim of this study was to determine changes in the ocular higher-order aberrations (HOAs) after CXL in keratoconic patients and its correlation with changes in visual acuity.
This is a clinical study that enrolled 50 keratoconic patients with 30 males (60%) and 20 females (40%).Patients age ranged from 15 to 45 years and with mean age (27.72 ± 6.71). They were treated with CXL by accelerated type (AVEDRO) and followed up for 3 months.
All patients were subjected to pre and post operative assessment for : Best Corrected Visual Acuity, Anterior segment examination (cornea, iris and lens), posterior segment examination (vitreous and retina), corneal topography and high –order aberration using pentacam Occulyzer ІІ, Germany).
The results of this study could be summarized as follows:
1- Regarding keratometric readings in the present study, there was a statistically significant reduction in mean K1 reading in left eyes and k2 readings in both eyes. However, there was no statistically significant difference in k1 readings in right eyes as p value 0.09.
2- There was statistically insignificant difference regarding k max in both eyes pre and postoperative as p value >0.05.
3- Regarding coma aberrations there was statistically insignificant difference pre and postoperatively in both eyes as p value >0.05.
4- As regard of trefoil aberrations, there was no statistical significant difference pre and postoperatively as p value was >0.05.
5- There was no statistically significant difference in both eyes as p value was >0.05.
6- Corneal thickness changes throughout the study, reveals that initially there was a statistically insignificant corneal thinning with little reduction in corneal thickness postoperatively. These initial changes may be attributed to the corneal de -epithelialization that was performed during the CXL procedure, postoperative keratocyte apoptosis, and structural changes in corneal collagen fibrils and extracel-lular matrix in the anterior stroma.
7- The total HOAs were statistically significantly different pre and postoperatively as p value was <0.05. Previous reports mentioned significant improvement in total and corneal aberrations such as total coma and spherical aberration.
8- As regard of UCVA and BCVA, The present study revealed that there was a statistically insignificant difference in the UCVA and BCVA but there is an improvement postoperatively in mean readings.
Summary and Conclusion
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CONCLUSIONS
On conclusion:
1. Total HOAs, and keratometric readings significantly decreased after CXL.
2. Ocular aberrations play a key role in influencing retinal image quality. Correcting HOAs in patients with KC is likely to improve the quality of vision significantly. 3. Evaluation of long-term changes of HOAs after CXL is useful in understanding the efficacy of CXL on improving optical, refractive, and visual acuity (VA