keratoconus

A topographical map of the front surface of the eye in a patient with keratoconus. The red indicates the steepest part of the cornea (the cone).

What is keratoconus?

Keratoconus is a degenerative disease in which the cornea (the clear tissue of the front of the eye) progressively thins and bulges. This area of bulging resembles a cone. The National Keratoconus Foundation (NKCF) has a good introductory video here.

What are the symptoms?

The cornea is normally smooth and dome-shaped, and this allows light to focus clearly on the retina. With keratoconus, the irregularity of the cornea prevents light from focusing clearly on the retina, causing blurred and distorted vision. Glare and light-sensitivity may occur as well. Symptoms usually present in the late-teens/early-twenties. The disease generally affects both eyes, though one eye can be more severely affected than the other.

How is it treated?

Early in the disease process, eyeglasses or soft contact lenses may do the job. But as the cone progresses, the cornea becomes more irregular, and vision cannot be adequately corrected with glasses or soft contacts. Thus, you need something that will help mask the irregularity of the front surface of the eye. That’s where rigid gas permeable (RGP or GP) contact lenses come in.

Image from NKCF

The type of contact lens that is best depends on the severity of the disease and the location of the cone. Some of the options available include:

• Custom soft contact lenses- custom-made soft lenses specifically designed for keratoconus.
• Corneal GP lenses– small rigid lenses that sit on the clear part of the eye (cornea).
• Scleral GP lenses– large-diameter rigid lenses that sit on the white part of the eye (sclera).
• Hybrid lenses– lenses with a GP center and a soft periphery, or skirt.
• “Piggybacking”– when a GP lens is placed on top of a soft lens for increased comfort.

Fitting a keratoconic patient in any of these contact lenses is typically considered a specialty fitting, so you can expect to spend a little more time and money on the process and the lenses compared to a standard soft contact lens fitting. Be sure to discuss the options with your optometrist to figure out what is best for your individual case. If he/she is not able to perform the specialty fitting, he/she can certainly refer you to an optometrist in your area that can.

What are the surgical treatment options?

For various reasons, some cases of keratoconus cannot be treated with the above methods. In such cases, surgery may be indicated.

• Intacs® are small, semi-circular inserts that are implanted into the middle layer of the cornea to flatten the cone-like area. Intacs are FDA approved for the treatment of keratoconus.

Intacs®

• Collagen cross-linking (CXL) is a treatment procedure that involves administering riboflavin eyedrops and then exposing the cornea to UV-A light. This promotes cross-linking of the collagen fibers of the cornea, which stiffens the cornea and prevents further bulging. The outer layer of the cornea is removed in epithelium-off CXL, and left intact in epithelium-on CXL. CXL is now FDA-approved in the US.

• Conductive keratoplasty (CK) involves using heat in the form of radiofrequency energy to change the curvature of the cornea. Using a thin probe, radiofrequency energy is applied to small areas of the cornea in a circular pattern, creating constriction of the corneal tissue and reducing astigmatism. This procedure is being done by some doctors (off-label) in conjunction with CXL and/or Intacs.

• Corneal transplants may be necessary in 10-20% of keratoconus cases. In a full-thickness corneal transplant, or penetrating keratoplasty (PK), the diseased cornea is removed and replaced with a healthy donor cornea.  Deep anterior lamellar keratoplasty (DALK) is a partial-thickness corneal transplant that leaves the bottom layer of the patient’s cornea intact, only transplanting a portion of the donor cornea. This potentially allows for a faster healing time and less risk for graft rejection (1).

Photo of a patient post-PK

CliffsNotes: Keratoconus is an eye disease that causes irregularity in the front surface of the eye. The best treatment is determined on a case-by-case basis, so talk to your eye doctor about what your options are.

Additional Recommended Resources:

• National Keratoconus Foundation
• AOA: Keratoconus
• All About Vision: Keratoconus