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Keratoconus

Keratoconus

What is Keratoconus?
Keratoconus is an eye condition in which the normally round dome-shaped clear window of the eye (cornea) progressively thins causing a cone-shaped bulge to develop. Exactly why this happens is unknown, but genetic factors play a role and it is more common in people with allergic diseases such as asthma, in Down’s syndrome and in some disorders of connective tissue such as Marfan’s disease. It affects up to one in 1,000 people and is more common in people of Asian heritage. It is usually diagnosed in teenagers and young people.

Despite its uncertainties, keratoconus can be successfully managed with a variety of clinical and surgical techniques, and often with little or no impairment to the patient’s quality of life.

Keratoconus (from Greek: kerato- horn, cornea; and konos cone) = cone shaped cornea

The cornea is the clear window on the front of the eye. It is usually a regular spherical dome in shape. The substance of the cornea consists of hundreds of layers that are linked to each other by a substance called collagen. If these collagen cross-links between layers are lost due to keratoconus, there is a progressive corneal thinning and stretching which gradually progresses, often in both eyes. Normal pressure within the eye causes the cornea to bulge forward into an irregular cone shape. When light enters the eye, it first passes through the cornea. If the cornea has turned conical, there is distortion of the image. The eye develops astigmatism (cylindrical errors) and myopia (shortsightedness) and the vision may become severely blurred.

A simulation of the multiple images seen by a person with keratoconus.

Symptoms

  • Early stages just having the need for spectacle correction.
  • As the disease progresses, the vision deteriorates.
  • Visual acuity becomes impaired at all distances, and night vision is sometimes quite poor.
  • Some individuals have vision in one eye that is markedly worse than that in the other eye.
  • Some develop photophobia (sensitivity to bright light), eye strain from squinting in order to read, or itching in the eye.
  • There is usually little or no sensation of pain.
  • Keratoconus can cause substantial distortion of vision, with multiple images, streaking and sensitivity to light.

Diagnosis

This is usually done by an ophthalmologist with a detailed eye examination. Diagnosing early keratoconus can be tricky, since mild disease often does not show any identifiable signs on slit-lamp examination; however, recent and a more definitive diagnosis can be obtained using corneal topography, in which an automated instrument projects an illuminated pattern onto the cornea and determines its shape from analysis of a digital image. The topographical map reveals distortions or scarring in the cornea, with keratoconus revealed by a characteristic steepness of curvature which is usually below or around the centre of the cornea. The topography record of the degree and extent of the deformation is used for assessing its rate of progression. Unilateral cases tend to be uncommon. Sometimes it’s a mild condition in the better eye, below the limit of clinical detection. It is common for keratoconus to be diagnosed first in one eye and not until later in the other. At our hospital, we use a very sensitive Pentacam Occulyser which records data from 25,000 points on the cornea.

Progress of the Disease

Keratoconus is always, almost a progressive condition. In about 10% to 20% of patients, the keratoconus becomes very advanced. The cornea may become extremely steep, thin and irregular or the vision cannot be improved and also posing a risk of the transplant rejection.

Treatment

Keratoconus is a known progressive disorder. All modalities of treatment whether it is glasses, contact lenses, INTACS or Phakic IOL’s, all correct the refractive error secondary to the cone formation; they DO NOT treat the keratoconus. Reason tells us that anything which is progressive first needs to be stopped and for that there is only one treatment that is available which is C3R or CXL.

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Corneal collagen crosslinking (C3R/ CXL) is a well-accepted and welcome addition to treatment options for keratoconus. Before C3R was approved, treatment options to rehabilitate vision were quite limited, mostly to contact lenses and when they failed one needed to undergo a penetrating keratoplasty.