Corneal Thinning Diseases
I would like to focus on two of the most prominent corneal thinning diseases affecting people today. Both of them are unique in their own right, but the primary reason for the symptoms caused are due to thinning of the cornea, the clear tissue at the front of they eye.
Keratoconus is a Greek term, literal defined as “cornea” and “cone”. This appropriate name describes the structural changes that are most commonly seen with keratoconus. What we see is a localized bulging of the cornea in areas where corneal thinning is taking place. The bulge, or cone, is formed by the pressure on the cornea exerted by fluid on the inside of the eye. The areas where the cornea is thinner do not have the inherent strength that the rest of the cornea has, and therefore can not resist the pressure to maintain its traditional shape.
Vision Effects of Keratoconus
Keratoconus adversely affects vision by creating an irregular optical surface that is difficult to correct utilizing traditional glasses and contact lenses. Traditionally, rigid gas permeable contact lenses have been used to improve the vision for those suffering from keratoconus. One of the primary setbacks of using the smaller lenses is they actually rest on the front part of the eye. This can lead to significant discomfort, resulting in tearing and poor adaptation to contact lens wear. In addition, some studies have shown an increased risk for corneal scarring because of the pressure that is being applied by the contact lens to the front part of the eye. The amount of this risk is up for debate, with many clinicians still incorporating contact lens fitting philosophies that results in pressure on the front part of the eye.
In our office we like to utilize scleral contact lenses as the initial fitting strategy for patients who have been diagnosed with keratoconus when traditional contact lenses or glasses do not improve their vision. As detailed in the link above, scleral contact lenses can be a more comfortable option for those suffering from the visual effects of keratoconus. The fact they vault over the cornea improves comfort and may decrease the risk of developing corneal scarring secondary to keratoconus.
Pellucid Marginal Degeneration
Pellucid is another corneal thinning disease that disrupts vision due to irregular corneal shape. In this condition the lower part of the cornea is thinner, causing the entire cornea to slump down on itself.
Vision Effects of Pellucid
We see similar symptoms from our patients, blurry vision, halos around lights, and poor night vision. Similar to keratoconus, it is difficult to improve our patients vision utilizing traditional contact lenses or glasses. Contact lenses are once again utilized in an effort to decrease the effect of the irregular corneal surface.
Prognosis of Keratoconus and Pellucid
The prognosis of keratoconus is difficult to define with a few primary risk factors for progression identified in the Collaborative Longitudinal Evaluation of Keratoconus Study. Even using the identifiers defined in CLEK, it is still difficult to predict which cases will progress. Long term concerns with both conditions are progressive thinning, steepening of the cornea, or stromal scarring. Sometimes vision can be affected enough that corneal transplantation is required to improve the vision.