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Astigmatism Definition - It is a type of refractive error where in the refraction varies in the different meridian. The rays of light entering the eye can not converge to a point focus but form a focal lne. Types of astigmatism - 1. Regular astigmatism 2. Irregular astigmatism Etiology of regular astigmatism - 1. corneal astigmatism 2. lenticular astigmatism 3. retinal astigmatism Types of regular astigmatism - 1. depending upon axis and angle b/w two principal meridian- -with the rule astigmatism - against the rule astigmatism - oblique astigmatism - bi oblique astigmatism 2. depending upon their position of two focal lines- - simple astigmatism - compound astigmatism - mixed astigmatism Optics of regular astigmatism Treatment of regular astigmatism Irregular astigmatism Etiological types Symptoms of astigmatism Treatment Read less