Corneal distortions

Thursday, April 17, 2008

Recent advances help solve corneal distortions early

Imagine yourself in a fair, visiting the room of “magic mirrors”. Specially created mirrors reflect bizarre images of your body and face — stretched horizontally to look fat, vertically to look thin and also curved in different angl es to produce fantastic distortions. Everyone has a good laugh at these optical illusions.

But what if these became real? What if these imperfections are present in the cornea of your eye? The normally clear, uniformly curved cornea allows us to perceive the various objects in the environment by producing an orderly refraction of the incoming rays of light. If the cornea was distorted, then one would see a distorted image of our surroundings — not something to laugh at.

Genetically determined

The chance of us suffering from this problem is approximately one in 2000, and the condition is termed Keratoconus. This is a genetically determined entity and usually occurs in young adults. People with allergic eye diseases, Down’s syndrome, and those who habitually rub their eyes are more prone for this condition, which results in thinning and conical protrusion of the cornea.

If affected by this condition, vision tends to get increasingly blurry and distorted, and spectacles often do not help as the corneal shape is quite irregular. Although the condition often presents in the early teens, it may progress gradually for a decade or two, before it stabilises.

In the early stages, when the cone is mild to moderate, newer designs of contact lens can help. If the condition progresses, the increasingly irregular corneal shape makes contact lens difficult or impossible to use and surgical replacement of the affected cornea can help.

Traditionally, this is performed by replacing the entire central cornea in the affected eye and is termed penetrating keratoplasty. This works well, but rejection of the corneal graft can sometimes compromise the outcome.

Recent advances

A recent advance in surgical technique allows replacement of only the anterior corneal layers. Retaining the healthy posterior part of the patient’s cornea offers many significant advantages. These include greater safety for the eye, both during and after the procedure, a more regular corneal shape after surgery resulting in quicker visual rehabilitation, and less risk of rejection of the graft.

This procedure is termed Deep Anterior Lamellar Keratoplasty (DALK), and is at present only offered in select centres, owing to technical complexity. While such surgery offers hope for those with advanced keratoconus, newer imaging modalities like corneal topographers and the Pentacam allow the clinician to diagnose keratoconus at a very early stage.

If diagnosed early, a recent procedure offers the possibility of stabilising the corneal disorder and preventing its progression. Termed Corneal Collagen Cross-Linking with Riboflavin (C3R), the procedure is fairly simple to perform. It uses the photosensitiser riboflavin as drops to saturate the corneal tissues, which are then exposed to Ultraviolet A (UVA) rays.

How it works

Under the influence of the UVA, chemical bonds form in the corneal collagen lamellae, which are the structural backbone of the corneal tissue, strengthening the cornea and stiffening the tissue.

The increase in tissue rigidity appears to slow or stop the progression of the corneal thinning and shape change that normally occurs in keratoconus.

Although introduced recently in India, this procedure has been performed in the U.S. and Europe for a while now, and patients have been followed up for up to five years, during which time disease progression has been stopped.

As yet, it is only performed in a handful of centres in India, but as experience with this new modality of treatment increases, it is likely to increase in popularity.

Keratoconus is a debilitating condition that affects vision in people starting their careers. However, with recent advances in instrumentation, early diagnosis is possible, and with improvements in contact lens design, the introduction of the new procedure of C3R, and the improved surgical approach of DALK, a complete suite of solutions for the condition exist.


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