The cornea is the clear, dome-shaped covering of the eyeball. In order to see clearly with or without glasses or contact lenses, the cornea must be clear as well as maintain this dome shape. For some patients, the cornea becomes thin and eventually bulges forward like a cone. This disease is called keratoconus.
What causes keratoconus? Usually there is no cause but it can be hereditary. Keratoconus has also been linked to chronic eye rubbing and Down syndrome. It occurs equally between males and females and generally affects both eyes
Keratoconus usually begins in the late teenage years however it can occur in the twenties or early thirties. Patients usually notice a very slow progression of distorted vision. To a patient, objects appear distorted. They will also notice haloes or star bursts around bright lights. An optometrist or ophthalmologist makes a diagnosis of keratoconus based on the patient’s observations as well as results from a complete eye examination. Patients usually have an increase in the astigmatism portion of their eyeglass prescription. The cornea shape is examined manually by a machine called a keratometer. Computer-generated 3D maps of the cornea can also be performed using a topographer. These tests will indicate how curved or cone-shaped the cornea has become.
How is keratoconus treated? There is no cure for keratoconus. In the early stages we prescribe new eyeglasses. As the disease progresses, soft and then hard contact lenses are considered. Hard contact lenses or rigid gas permeable lens (RGPs) work best since they maintain their shape and can help to mask the corneal irregularity that results from keratoconus. Some patients find hard contact lenses uncomfortable and need specialty contact lenses. One type of specialty contact lens has a hard material in the center and a soft material on the periphery. Another contact lens option available requires wearing a soft contact lens with a hard contact lens over top.
Scleral contact lenses are another specialty lens option for keratoconic patients who struggle with lens stability. Since the cornea is cone-shaped in keratoconus, some traditional RGP lenses are unstable on the eye. Think of the apex of the cone as the center of a teeter-totter. The RGP can rock over the cone and is prone to falling out of the eye. Scleral contact lenses have a much larger diameter than traditional RGPs and extend on to the sclera (white part of the eyeball) which provides much greater stablitiy.
For some patients, the keratoconus progresses to the point where contact lens wear does not provide them with adequate vision, or they may simply find the contact lenses too uncomfortable. These patients are then considered for corneal transplant surgery. Any patient who has any sign of keratoconus should not have laser eye surgery.
A surgical procedure available in Canada to prevent the progression of keratoconus. It is called corneal collagen cross-linking with riboflavin and UV-A light (CXL-UVA). In this procedure, the front layer of the cornea is gently removed. Then riboflavin eye drops are applied to the cornea. A safe amount of UV-A light is applied to the cornea. Riboflavin when activated with the UV-A light, increases the corneal cross links within the cornea. This strengthens the links or bonds of neighboring filaments within the cornea making it more rigid and less likely to bulge forward into a cone shape. The goal of CXL-UVA is not to totally reverse the disease but to prevent further progression to enhance spectacle or contact lens wear. It may defer the need for a corneal transplant.
Keratoconus does not result in blindness. Improving a keratoconic’s vision requires patience and persistence on the part of the patient and optometrist since no single treatment option works on every patient.