الفهرس 
Corneal anatomyOnly 14 pages are availabe for public view
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Abstract
The cornea is a viscoelastic structure with quantifiable biomechanical properties. Laser-assisted in situ keratomileusis (LASIK) and Photorefractive keratectomy (PRK) are a commonly employed procedures for the correction of myopia. Myopia is an independent risk factor for glaucoma progression. In addition, corneal refractive laser ablation in virgin eyes weakens the cornea mechanically due to tissue removal, leading to deterioration in corneal biomechanical strength. IOP measurements following LASIK and PRK are known to be inaccurate. With the IOP being the only modifiable risk factor, obtaining accurate IOP readings is essential in diagnosing and managing glaucoma. The main source of error for measuring IOP after LASIK and PRK is the change in CCT.
Goldmann Applanation Tonometer is the standard method of measuring IOP.
The main objective of this study is to compare the changes of IOP after LASIK versus PRK in myopic eyes.
Fifty patients diagnosed clinically to have myopia were selected. Their ages ranged from 18 to 48 years. 50 eyes operated using Lasik group[1] and 50 eyes operated using PRK group[2]. Patients were subjected to corneal topography by pentacam and IOP measurement by goldmann applanation tonometer , preoperatively and postoperatively at the end of the first week, the first month and the third month.
Overall, measured IOP is underestimated after Laser correction.
In the decrease of IOP, there is no significant difference between LASIK and PRK except for the decrease of IOP caused by the lamellar flap in LASIK.
Any LASIK correction will lower IOP by approximately 1 mmHg because of the effect of the lamellar flap.
Preoperative IOP is the single strongest predictor of postoperative IOP change, with eyes with a higher preoperative IOP having a greater IOP decrease.
For patients undergoing highly myopic corrections, the IOP decrease can be dramatic. For instance, LASIK to treat 10 D of myopia can reduce measured IOP by as much as 9 mmHg.
This is important when evaluating suspicious optic nerves and visual field losses in potential glaucoma suspects who have undergone refractive surgery.
There are reports that dynamic contour tonometry is relatively unaffected by corneal biomechanics and remains unchanged after refractive surgery.
However, until there is widespread use of a tonometry device that is independent of corneal biomechanics, refractive surgical history and preoperative IOP should be recorded and included in the evaluation of a patient’s postoperative IOP.