Keratoconus is an eye (ocular) disorder characterized by progressive thinning and changes in the shape of the cornea. The cornea is the thin, clear outer layer of the eye and is normally dome-shaped. Slowly progressive thinning of the cornea causes a cone-shaped bulge to develop towards the center of the cornea in the areas of greatest thinning. Affected individuals develop blurry or distorted vision, sensitivity to light (photophobia), and additional vision problems. Keratoconus often begins at puberty and most often is seen in teenagers or young adults. The specific underlying cause is not fully understood and most likely the condition results from the interaction of multiple factors including genetic and environmental ones. One factor known to contribute to progression of keratoconus is eye rubbing. In some cases, keratoconus may occur as part of a larger disorder. Keratoconus is treated with glasses or contact lenses early in the condition. A small number of individuals may require surgery.
Signs & Symptoms
The corneas in both eyes are usually affected (bilateral), although the progression and severity of the condition in each eye may differ (asymmetric development), which means one eye may be notably worse than the other. Symptoms usually become apparent during adolescence or young adulthood (i.e. late teens through early 20s). Keratoconus may become progressively worse for 10 to 20 years before slowing. Older adults typically do not have worsening of keratoconus. Because of the progressive nature of the disorder, affected individuals may have to change glasses frequently.
The cornea’s primary function is acting as the eye’s most powerful lens, bending incoming light onto the lower-powered internal lens, where the light is then directed to the retina (a membranous layer of light-sensing cells in the back of the eye). The retina converts light to specific nerve signals, which are then transmitted to the brain to form images. The cornea must remain clear (transparent) and the proper shape in order to be able to transmit and focus incoming light.
The abnormal cone-shape that characterizes keratoconus leads to changes in the ability of the cornea to help focus light appropriately on the retina (i.e., refractive abnormalities). Keratoconus may initially cause slight blurring of vision, abnormally increased sensitivity to glare or bright light, and difficulty seeing at night (poor night vision). Some individuals may experience double vision (diplopia) or see a partial, incomplete image around what they are looking at (‘ghost’ images). In some cases, there may be a loss of clarity of vision (visual acuity). With progressive corneal changes, affected individuals experience increased difficulty in seeing far away (nearsightedness or myopia) and further decreased clarity of vision. Overall vision changes can vary from one person to another and the severity can range from mild vision loss to more severe vision loss that causes a decreased ability to see clearly even with corrective lenses. Some affected individuals may develop an irregular astigmatism, in which there is an irregular curvature of the eye.
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