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What is Keratoconus?
Keratoconus is a fairly common eye disease involving the cornea (clear portion of the eye in front of the iris). The central or paracentral area of the cornea undergoes a gradual thinning and then a protruding of the cornea or ectasia develops resulting in increased myopia, astigmatism and irregular astigmatism.
What Causes Keratoconus?
The exact etiology is not known. There are some studies that have shown an inheritance pattern but these studies have not been consistent. There has not been a gene found related to keratoconus at this time. Some recent observations have been that people with keratoconus rub their eyes excessively. This rubbing is not just using a finger to rub the eye but the person actually uses their knuckle to vigorously rub their eyes. This may cause damage to tissues of the cornea that support the shape and structure of the cornea. Keratoconus is usually bilateral but the level of severity may differ between the two eyes. The disease usually starts in the twenties and thirties and gradually progresses.
Other Risk Factors with Keratoconus
Sleep apnea
Floppy lid syndrome
Both of these have to do with tissue laxity.
What Happens to the Cornea with Keratoconus?
The outer structural layer called Bowman’s membrane is damaged. The stromal layers and the epithelium in the area of the keratoconus are reduced or thin. The inner structural layer called Descemet’s membrane has ridges, breaks or folds. The scarring in the cornea varies with the severity of the keratoconus. The result is a herniation, protruding, or ectasia of the cornea.
Diagnosis of Keratoconus
A complete eye exam is indicated in the work-up for keratoconus. There is usually a history of frequent eyeglass or contact lens prescription changes. In many cases, the vision cannot be corrected with glasses due to irregular astigmatism and the patient has to wear contact lenses to achieve their best vision. There may be a significant difference in refractive error between the two eyes.
The slit lamp exam (microscope used to exam the eye) will show some or all of these corneal changes depending on the severity of the disease. A Rizutti’s sign, Fleischer ring, Vogt’s striae, Munson’s sign, varying scarring of the cornea, Descemet’s folds, and in a very small number of cases acute hydrops may be found.
Tests Used to Diagnose Keratoconus
Keratometry
The keratometry (measurement of the curvature of the cornea) readings are steep and possibly irregular.
Corneal Topography
This instrument measures the overall shape or curvature of the cornea and shows a topographical type map of the cornea. This is similar to a geography map showing the mountains and valleys. This test has become so sensitive that it can detect keratoconus before it becomes clinically evident.
Pachymetry
This instrument measures the thickness of the cornea and with keratoconus the cornea is thin.
Summary
Keratoconus can now be diagnosed early in the disease process with the advent of new technology.
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