Keratoconus is an eye disease that is characterized by thinning and steepening of the cornea. The cornea is the front surface of the eye and the most important focusing element of the vision system. In patients who have keratoconus their cornea is cone-shaped. The name keratoconus is derived from the Greek work for cornea (kerato) and cone-shaped (conus). Keratoconus results in visual distortion often not correctable by traditional glasses. The thinning and steepening of the cornea causes the front surface to become progressively more irregular in shape. The corneal surface irregularity is what induces the distortion and blurriness of vision experienced in keratoconus.
It is often argued if keratoconus runs in families. There is no gender preference, an equal number of men and women have the disease. Keratoconus is most commonly seen in people with atopic or severe allergies, especially ocular allergies. Keratoconus is initially diagnosed just after puberty and can progress through the third to fourth decade of life.
If the disease is mild and doesn’t progress, good vision can be maintained with glasses and soft contact lenses. Most cases however cause more significant corneal changes creating dramatic vision distortion. Specialized contact lenses are required to provide adequate vision, these lenses include, rigid gas permeable, hybrid or scleral lenses.
In more advanced cases of keratoconus the cornea develops scarring and/or contact lenses can’t be tolerated. These cases require surgical corneal transplantation. Fortunately, new medical technology such as collagen corneal cross-linking with Riboflavin hold promise to controlling progressive cases of keratoconus.
The National Keratoconus Foundation has more information available.
Why is it that glasses don’t always work for patients with keratoconus? In many instances, individuals with keratoconus do not achieve excellent visual performance with spectacles or traditional soft contact lenses. One cause for the failure of these corrections is that the changes in corneal shape that accompany keratoconus induce refractive errors which traditional spectacles simply cannot correct. So, even when sphere and cylinder in the keratoconic eye are well-corrected, these “other refractive errors” or “other aberrations” remain uncorrected and can lead to a blurred retinal image and blurred vision. Collectively these other aberrations can be referred to as higher order aberration, while the aberrations that are typically corrected with spectacles and soft contact lenses are referred to as lower order aberration. Rigid gas permeable, scleral lenses and hybrid contact lens are options to provide clearer vision for the irregular cornea.
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