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Keratoconus

Fig. 1 Cornea bulging lower eyelid.

What is keratoconus?

Keratoconus is a condition that is due to progressive steepening of the cornea resulting in a "cone" shaped appearance [See figure 1]. The cornea becomes thin near the center and may lead to myopia (near sightedness) and/or severe astigmatism. It is usually bilateral and typically begins to develop during adolescence.

What causes keratoconus?

The exact cause of keratoconus in not known but is thought to be due to combination of factors that lead to corneal thinning. Abnormal function of enzymes involved in maintenance of the cornea (lysozymes and proteolytic inhibitors) has been implicated, as well as abnormalities in collagen structure. Eye rubbing and contact lens wear have been associated with keratoconus.

Is keratoconus hereditary?

Most cases of keratoconus are sporadic (nonfamilial), but occasionally it is transmitted as an autosomal dominant trait.

Is Down syndrome associated with keratoconus?

The incidence of keratoconus is higher in Down syndrome patients than in the general population. It is unclear whether excessive eye rubbing may predispose to keratoconus in this group.

How is keratoconus diagnosed?

Keratoconus is diagnosed by careful eye examination and corneal topography. Severe cases of keratoconus produce protrusion of the lower lid on downgaze (Munson sign) as well as conical reflection of the nasal part of the cornea when a light is shown temporally (Rizutti's sign). The cornea is thin, a pigmented arc may be present inferiorly (Fleischer ring), and stress lines may be seen in the stroma (Vogt striae). Subtle cases are usually diagnosed by obtaining a corneal topographic map.

What are typical symptoms of keratoconus?

Poor vision not corrected with glasses or soft contact lens is the most common symptom of keratoconus. Mild keratoconus typically causes slight blurring and distortion of vision, as well as photophobia (light sensitivity). In severe cases, eye pain and redness occur due to formation of corneal blister (hydrops). Scarring may cause decreased vision.

How long does it take for keratoconus to progress?

Although there is a great deal of variability (including between eyes of an individual), keratoconus usually progresses over a 10-20 year period.

What are the treatment options for keratoconus?

Mild cases of keratoconus may be treated with glasses or soft contact lenses. Most require rigid gas permeable contact lenses to provide best vision. In cases of corneal scarring and severe keratoconus, a corneal transplant may be performed.

Can laser treatment cure keratoconus?

Refractive surgery such as LASIK or PRK are generally not recommended in suspected. Certain refractive procedures (such as thermal keratoplasty) may be appropriate for a select group of patients.

Where can I learn more about keratoconus?

National Keratoconus Foundation
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