|In keratoconus, the cornea progressively thins, causing vision distortion.
Keratoconus (kehr-a-toh-KOH-nus) is a non-inflammatory condition in which the center of the cornea progressively thins and develops a cone-shaped bulge that blurs and distorts vision. A normal cornea is round, with even curvature like that of a sphere. But with keratoconus, the curvature is irregular and too steep, like the narrow end of an egg. Any change in the shape of the cornea changes the way light passes through the eye, and results in a change in vision. When the cornea is too steep, light converges in front of the retina, causing nearsightedness.
Keratoconus, which comes from the Greek words karato meaning "cornea" and konos meaning "cone," usually begins during the late teen years or early 20s and can progress over a 10- to 20-year span. Each eye can be affected differently, but as the cornea bulges more, distortion and
nearsightedness increases. Rarely, keratoconus causes sudden swelling in the cornea that leads to rapid changes in vision.
A definitive cause of keratoconus is unknown, but several theories exist. Some eyecare specialists and researchers believe the condition is hereditary, since it appears to run in families. Others believe it is degenerative. Another theory is that it may be related to the endocrine system, since keratoconus develops after puberty, while other research suggests that it may be related to other conditions, since it seems to occur in conjunction with diseases such as Marfan's syndrome, Down syndrome, mitral valve prolapse and retinitus pigmentosa.
One theory vigorously being investigated is that keratoconus may be the result of frequent eye-rubbing. Some research indicates that at least two in three keratocones have reported a history of vigorously rubbing their eyes with their knuckles. But itchiness can be caused by the changes in the corneal tissue, so it is unclear whether the eye rubbing is a cause or effect of the condition. Whether a cause or effect, eye-rubbing is known to worsen the condition and patients with keratoconus are advised to avoid rubbing their eyes.
The most noticeable symptom is blurred vision – especially at distances – or distorted images like that of
astigmatism. Other symptoms you may notice include:
- Sensitivity to light or glare
- Excessive tearing
- Seeing halos around streetlights or other objects, especially at night
- "Double" vision or seeing multiple images of a single object
- Increased squinting to see images clearly
- A frequent change in corrective lens prescription (i.e. at every annual eye exam)
Since the exact cause of keratoconus is unknown, definitive ways to prevent the condition cannot be recommended. However, it is generally recognized that eye rubbing exasperates the condition in those with it.
Keratoconus is diagnosed with special instruments and microscopes that enable eyecare providers to detect evidence of cornea thinning. One indication is Fleischer's ring, a brownish circular deposit at the base of the abnormal zone of the cornea. Others include Vogt's striae, which are fine, white lines deep within the middle layer of the cornea, and swelling, cracks or scars on the cornea. To help diagnose and track the progress of keratoconus, the exact shape of the cornea can be mapped over time using keratometry
or computerized corneal topography.
Once diagnosed, there are several treatment options:
- Corrective lenses. Eyeglasses or soft contact lenses are typically used to correct the mild nearsightedness and astigmatism that is caused in the early stages of keratoconus. As the disorder progresses and the cornea continues to thin and change shape, rigid gas permeable (RGP) are usually prescribed to more adequately correct vision. When wearing RPG lenses, tears under the lenses smooth out the cornea’s irregular shape. However, proper fit is essential, so you may require frequent checkups and lens changes to maintain good vision. Poor fitting lenses may aggravate keratoconus, rendering the lenses uncomfortable and even scarring the cornea.
- Corneal transplants are used in more severe cases. In this procedure, the cone-shaped cornea is removed and replaced with a donated cornea. The success rate is 90 percent, much higher than that of other organ transplants because the cornea does not contain or require blood. After the operation, almost all patients still require glasses or contacts to further correct their nearsightedness.
- Corneal grafting, medically known as epikeratophakia, consists of an eye surgeon grafting a layer of corneal epithelial (surface or skin-like) cells from the patient's own cornea in the upper layer around the central cone to build up and flatten the slope of the cornea. The success rate compares to that of corneal transplants, but it offers the advantage of not requiring donated tissue.