Cornea is a transparent area which makes one-sixth of the outer circumference of the eye. At the periphery is a transition zone 1– 1.5 mm, limbus where corneal stroma is bonded to the sclera. The adult cornea is 10.5 mm vertically and 11.5 mm horizontally. The anterior and posterior surfaces are parallel to each other in the central 4 mm spherical-shaped “optical zone” where the cornea averages 0.52 mm in thickness. The peripheral cornea is slightly flattened, anterior and posterior surfaces are no longer parallel and corneal thickness increases to 0.65 mm. Even though central cornea is responsible for the formation of sharp retinal image as it lies in the visual axis, studies have proven that peripheral cornea also has significant role in affecting the optical quality of the image formed.