The cornea acts as the eye’s outermost lens. It functions like a window that controls and focuses the entry of light into the eye. The cornea contributes between 65- 75 percent of the eye’s total focusing power. When light strikes the cornea, it bends–or refracts–the incoming light onto the lens.
Sometimes, however, the structure of the cornea is not strong enough to hold this round shape. Over time, the normal round curvature of the surface of the eye can bulge outward like a cone. This condition is called keratoconus.
Keratoconus usually is detected in the teenage years or 20’s, but it can also start in childhood. In some cases, keratoconus is diagnosed at a later age, but usually only when it is mild. The changes in the shape of the cornea occur over several years, but at a more rapid rate in younger patients.
Keratoconus changes vision in two ways:
- As the cornea changes from a ball shape to a cone shape, the smooth surface also warps. This change is called irregular astigmatism, which cannot be fully corrected with glasses.
- As the front of the cornea steepens, the eye becomes more nearsighted (poor vision at distance; only nearby objects can be seen clearly). As a result, the person may need new eyeglasses more often.
DIAGNOSIS OF KERATOCONUS
Special photographic tests, such as corneal topography, record images to create a detailed shape map of your cornea. Corneal pachymetry can measure the thickness of your cornea.
A treatment for keratoconus which has shown great success is Corneal Collagen Crosslinking with Riboflavin (C3-R), a one-time application of riboflavin eye drops to the eye. The riboflavin, when activated by approximately 10 minutes illumination with UV-A light, augments the collagen cross-links within the stroma and so recovers some of the cornea’s mechanical strength.
Collagen cross-linking treatment is not a cure for keratoconus rather, it aims to slow or even halt the progression of the condition. This is important to understand. Patients may need to continue to wear spectacles or contact lenses (although a change in the prescription may be required) following the cross-linking treatment but it is hoped that it could limit further deterioration in the patient’s vision and reduce the case for keratoplasty.The main aim of this treatment is to arrest progression of keratoconus, and thereby prevent further deterioration in vision and the need for corneal transplantation.