Keratoconus

Overview

Keratoconus is a progressive disease in which the cornea becomes stretched, thinned, and eventually takes on a somewhat conical shape. Keratoconus typically begins to appear in the teens or early twenties and worsens with time. The cause of keratoconus is not well understood, but there appears to be a genetic link in some instances.

The normal shape of the cornea is that of a sphere. As keratoconus progresses, the cornea thins and as a result, the normal pressure within the eye pushes against the thinned cornea and stretches it. The resulting shape of the cornea tends to appear like that of a cone. As a result of this change in shape, the light rays that hit the light sensitive retina at the back of the eye cause distorted vision and severe irregular astigmatism.

Forme Fruste Keratoconus

Forme fruste keratoconus is the term used to describe patients who are at risk of developing keratoconus. In the early days of laser eye surgery, some patients who underwent to procedure actually developed keratoconus as a result of a decrease in the amount of corneal tissue – the laser eye surgery actually accelerated the development of full-blown keratoconus. Consequently, forme fruste keratoconus is now a contraindication for laser eye surgery.

Signs & Symptoms of Keratoconus

Keratoconus is such a gradual disease that it is difficult to detect in the early stages. Typical symptoms of early keratoconus include progressive nearsightedness and mild astigmatism, causing blurred and distorted vision. Additional symptoms that may or may not occur include glare and light sensitivity. Patients with keratoconus usually need a prescription change with each visit to the optometrist. Usually both eyes are affected by keratoconus.

Detection & Diagnosis of Keratoconus

Due to the slow progression of keratoconus, it is often an eye disease with a delayed diagnosis. Eye doctors depend on regular changes in prescription, progressively worse astigmatism, and corneal topography mapping to diagnosis of keratoconus. In corneal topographers, a map of the curvature of the cornea can be determined and with regular visits to the optometrist, the progression of keratoconus can be monitored with a corneal topographer. A pachymeter is also used to measure the thickness of the cornea.

Patients with moderate to severe keratoconus will also exhibit what is known as the Munson sign. To test for this, the patient is asked to look down at the ground: upon doing this, the marked conical shape of the cornea becomes readily evident.

Keratoconus Treatment

Unfortunately, there is no cure for keratoconus. Current keratoconus treatment is therefore focused on ensuring that patients with keratoconus have the best vision possible as their eye disease progresses.

In the early stages of keratoconus, glasses or soft toric contact lenses will be sufficient to make vision clear for patients with keratoconus. As the eye condition progresses, however, eyeglasses and soft contacts will no longer be sufficient.

For moderate forms of keratoconus, patients are moved over to rigid gas permeable (RGP) contact lenses. These hard contacts significantly improve vision. RGP contact lenses, unfortunately, are difficult to fit to patients with keratoconus, and require repeated visits with the optometrist to fine-tune the prescription.

Once keratoconus has progressed to the point where RGP contact lenses no longer work, or for patients who simply cannot tolerate RGP lenses, the next option is a corneal transplant (penetrating keratoplasty).

A relatively new treatment for keratoconus is corneal inserts (Intacs). Corneal inserts are small plastic tube-like structures that are placed just below the surface of the peripheral cornea. The corneal inserts act to pull on the cornea, and flatten the central cornea. This reduces nearsightedness and astigmatism. Although this surgery does have its risks, including infection, glare, haloes, and foreign body sensation, Intacs may very well postpone the necessity of a corneal transplant.

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