الفهرس 
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Abstract
The aim of this essay is to show the role of contact lenses in the correction of some refractive errors such as aphakia, msopia and keratoconus. This study also gives an idea abQut the aptical principle, types, fitting, care and complications of contact lenses. Contact lenses provide a new smooth spherical surface, the astigma. ticdeformaties and irregular astigmatism of anterior corneal surface are removed. There are many types of contact lenses which can be ola¬ssified aocording to the size, material and consistenoy of the leDS. The water content of the lens plays an important in affeoting the oonsistency and accordingly the use of lens. High water content oontact lenses are us ed for extended wear especially for aphakias and myopics. Aphakics need extended wear oontaot lenses more than mY9pics because of their old age and handling diffioulties, while myopicS are more suitable far these lenses because of their healthy eyes and the thinner lenses in these oases alloW better oxygenation the cornea. In aphakia, espeoially uniocular aphakia, oontact lenses proved to have certain advantages over spec,1;acle: lenses. For the monocular aphake, a contact lens ia a necessity because it decrease magnification to about 7% so helping in fusion of 2 images by the visual cotex. In myopia, contact lens es have mainly cosmetic role. also increase the size of retinal image, provide a wider field of vision and eliminate spherical aberration pr o duced strong concave lens. In keratoconus, contact lenses help in preventing the and even in some cases, affect regression of the condition. Hard contact lenses are especially important in cases of high astigmatism. Also hard/soft lens combination be used in keratoconus. However, contact lenses have many complications, some of which are visual and others are non visual. Of the important complication are corneal oedema, corneal vascularization and corneal ulcers. Ala 0 allergies to some contact lens ,solu tiona are noticed, lens deposits constitute a major complication in contact lens practice.