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Focus on Keratoconus
Keratoconus is a non-inflammatory condition, and is usually caused by a progressive thinning of the central corneal tissues. Occasionally it may have other causes such as improperly fitting hard contact lenses. The etiology of the corneal thinning is not known, though in some cases it appears to be hereditary. Keratoconus usually occurs in both eyes, though one eye may be more affected than the other.
Keratoconus is a relatively rare condition, and is said to afflict less than 1 person out of 2 thousand. However, because the severity of Keratoconus varies greatly, milder cases are not be always diagnosed. The condition normally begins after puberty and may progress slowly over of a period of many years.
Keratoconus is suspected when frequent changes in glass prescription, requiring more correction for near sightedness with a marked increase in astigmatism, are necessary and the maximum visual acuity diminishes even with the best prescription.
The condition may be easily diagnosed by using instruments such as the keratometer which measures the central corneal curvature. As the condition progress the curvature readings become steeper and begin to appear irregular. The peripheral corneal shape and curvature can also be measured by various methods such as the keratoscope, which measures corneal topography, to ascertain the size and the configuration of the cone.
Because the corneal surface of a keratoconic eye is distorted and irregular, the best visual acuity can only be achieved by replacing it as the primary refractive surface. This can usually be achieved by covering the corneal surface with a contact lens or replacing its central section with a corneal transplant supplied by a donor. Refractive surgery techniques such as LASIK are contra-indicated in cases of Keratoconus, because they do not work well when used on irregularly shaped corneas.
When contact lenses are used, hard lenses are the lens of choice rather than soft lenses which are thin and flexible and follow the contour of the eye, and therefore are usually not effective when used as a correction for Keratoconus. Very occasionally, soft lenses are used in conjunction with hard lenses which are “piggy backed” on top of the soft lens surface.
The preferred materials for use in fabricating hard lenses is usually a gas permeable plastic which permits oxygen to pass through the lens and therefore help maintain the normal metabolism of the corneal surface. These lenses must be custom made to provide the optimum fit over the irregular corneal surface of a keratoconic cornea. In some cases, if properly fitted, they may help also to retard the progression of Keratoconus by putting a “cap” on the top of the cone. Unfortunately, the recent advances in the plastic used for lenses are not always combined with the best in custom fitting, and many contact lens wearers with Keratoconus suffer unnecessary discomfort and sometimes even the inability to wear the lenses that they depend on for normal vision.
Advanced Keratoconus may result in corneal scars and opacities which may lead to the need for a corneal transplant. It is important that the transplant be performed before the area surrounding the central cornea becomes too thin.
All told, approximately 10,000 corneal transplants are performed each year in the United States for various conditions, including Keratoconus. Corneal transplant surgery is an art as well as a science, and it is important that those seeking such surgery find an experienced and successful surgeon. When performed properly, the surgery is relatively non-traumatic, and is over 90% successful. After the surgery many Keratoconus patients experience normal vision though most will require the additional use of contact lenses or glasses.