الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
The Refractive Surgery is a technique used in ophthalmology which modify the refractive state of the eye. Since the cornea is the main responsible for the refraction of the eye, its refractive properties are used to change the optical system of the eye. Photorefractive keratectomy (PRK) and small incision lenticule extraction (SMILE) are two flapless procedures for the correction of myopia and astigmatism. PRK is a surface ablation procedure in which excimer laser is used for ablation a planned pretreatment stromal thickness whereas in SMILE, the femtosecond laser is used to create an intrastromal corneal lenticule. The removal of the stromal lenticule is through a small arcuate incision. SMILE allows for good stability because most of Bowman’s layer remains intact. In addition, the time to return to normal life (visual recovery) is short.
In this study we compared the refractive outcomes after PRK and SMILE in moderate myopia with or without astigmatism.
There was a statistically significant improvement of the mean UCDVA and BCDVA compared with the preoperative data in both groups with no significant difference between both groups. There was a significant decrease in the mean MRSE postoperatively in both groups compared with the preoperative data with no significant difference between both .
We found that efficacy and safety were high and comparable in both groups while the predictability in SMILE group was higher than PRK group ( 95% , 90% respectively) .
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Regarding the pentacam findings:
We observed that there was a significant decrease in mean keratometric (Km) power at anterior corneal surface postoperatively and a significant decrease in central corneal thickness in both groups postoperatively as compared to preoperative data with no significant differences between both groups. There was no significant difference between PRK and SMILE in postoperative PCE whereas there was a slight increase in ΔPCE in SMILE group than PRK but it is also not statistically significant.
Conclusion:
PRK and SMILE procedures have an excellent and high Safety, Efficacy and Predictability in moderate myopia.
There were changes detected in the posterior corneal surface postoperatively in both procedures. It was almost within normal range but need follow up to detect any progression for early detection of ectatic changes.
Recommendations:
• Corneal biomechanics, corneal aberrations and contrast sensitivity should be in concern and added to the comparison items in further studies.
• It is better to assess the astigmatism in separate component.
• Further studies with long term follow up to these post operative data to detect either changes occurs or not (early detection of changes especially on posterior corneal surface is of a great importance for early detection of ectasia).