الفهرس 
Correction of refractive errorsOnly 14 pages are availabe for public view
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Abstract
The refractive state of the eye is governed by the contribution of four different components: corneal curvature, anterior chamber depth, lens curvature, and axial length. The interrelationship of these variables that determined an individual’s refraction, which may be emmetropic or ammetropic (myopic, hyperopic, or astigmatic).
Correction of refractive errors may be non surgical (glasses or contact lenses) or surgical, which may be corneal (PRK, LASIK, Intacs, and AK) or lens surgery (CLE and phakic IOL).
LASIK, has emerged as one of the most common refractive surgical procedures being utilized today. It combines lamellar dissection with the microkeratome (flap creation) and a refractive ablation in the bed with excimer laser.
LASIK may be considered for the correction of 0.5 to 10 D of myopia or 0.5 to 6 D of hyperopia. Up to 6 D of astigmatism may also be corrected. These ranges are not absolute indications for the procedure.
Despite excellent results of LASIK, there are many complications which may affect the visual outcome.
These is complications may be intraoperative (interface debris, incomplete flap, buttonhole, flap striae, decentration or corneal perforation) or postoperative,(infectious keratitis, DLK, epithelial ingrowth, central islands, corneal ectasia, regression or over and undercorrection).
Re-treatment (LASIK enhancement) is sometimes necessary because of undercorrection, overcorrection, central island and or regression. The flap can be done by lifting or recutting methods, while ablation can be done by standard (simple) ablation or customized ablation techniques.
Optical customized corneal ablation may be topography guided or wavefront guided, the later can eliminate all ocular aberrations by using wavefront sensing devices.
In cases of no enough residual corneal thickness or keratectasia, we can’t do enhancement and in this instance we can use Intacs. The goal of implanting Intacs for keratectasia after LASIK is to reduce the corneal steepening in eyes associated with iatrogenic keratectasia and to correct the amount of regression, resulting in a favorable visual outcome and eliminating or delaying the need for keratoplasty.
In high refractive errors, bioptic treatment (combination of 2 refractive procedures e.g.: LASIK and phakic IOL) appears to be safe, predictable, and stable with absence of major complications.
Keratoplasty either lamellar or penetrating usually becomes necessary in cases of progressive keratectasia.
The art of refractive surgery is to determine which modality will serve the individual patient best.