Picture of Keratoconus
We see through the cornea, which is the clear, central part of the front surface of the eye. Normally, the cornea has a round shape, like a Ping-Pong ball. Sometimes, however, the structure of the cornea is just not strong enough to hold this round shape. The normal pressure inside the eye makes the cornea bulge outward like a cone, causing distorted vision. This condition is called keratoconus. Often the cause of keratoconus is unknown. The disease usually does not cause blindness. However, the changes to the cornea will make it impossible for the eye to focus well even with glasses or soft contact lenses. Rigid contact lenses or corneal transplantation may be necessary to provide good vision.
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Image Source: Dr. Umberto Benelli, MD, PhD/EyeAtlas
Text: MedicineNet - Keratoconus