Most refractive techniques aim to correct ametropia by modifying the curvature of the cornea,the most powerful refractive element of the eye. Convential ways to analyze the surgical outcome traditionally compare the preoperative and final refractions as a measure of predictability of a specific technique However,other factors,such as glare , decreased contrast sensitivity and the presence of ghost images , may have a negative impact on the patient quality of vision without measurably affecting refraction