Keratoconus is a non-inflammatory eye condition where the normally round dome shaped cornea progressively steepens, causing a cone-like bulge. The result is significant visual impairment. The cornea is the “windshield” of the eye. It is responsible for refracting most of the light coming into the eye. Therefore, abnormalities of the cornea can severely affect the way we see the world.
It can make simple tasks like watching TV, driving and reading a book very difficult. In the early stages of keratoconus, a person may experience slight distortion and blurring of vision along with increased sensitivity to light and glare. Symptoms are usually first seen in the persons late teens to mid twenties. Keratoconus is a progressive disease and can affect one person more or less than another. Each eye can be affected differently.
In the early stages, eyeglasses or soft contact lenses can be used to correct for the mild nearsightedness and astigmatism. As the disorder progresses, the cornea will continue to thin and change shape. Gas permeable lenses will be needed to correct vision more adequately.
In severe cases, patients may become contact lens intolerant or not be able to achieve the vision needed to perform daily tasks. At this point a corneal transplant may be needed where the cornea is replaced with a healthy donor tissue.
Methods of Correction
Keratoconus is managed with many different contact lens designs. There is no one design that is best for every patient. Since each lens design has its own unique characteristics, the practitioner will need to evaluate each patients needs to determine the lens that would offer the best combination of visual acuity, comfort and corneal health.
- GlassesIn the early stages a person can be corrected with glasses or soft contacts lenses but as the disorder progresses it becomes difficult to correct vision caused by the irregular corneal surface. At this point more complex contact lens designs will be needed.
- Soft LensesThe role of soft lenses in keratoconus is limited because the soft lens drapes over the irregular corneal surface. Therefore, the front surface of the lens assumes the same irregular surface as the cornea without trapping a fluid reservoir so the effective refracting surface shows no improvement over the original corneal surface. There are some specially designed soft lenses that are thicker and retain more of a rigid shape and may contribute to the liquid lens affect to some extent. These soft lenses are generally only used in mild to moderate cases of keratoconus.
- RGP Lenses ( Rose K, Rose K2, Rose K2 IC, Centracone)Rigid Gas Permeable lenses are the primary option for correcting keratoconus. The rigid gas permeable lens masks the underlying irregular cornea and serves as a new refractive surface of the eye. The tear film fills in the space the back of the contact and the front of the eye. As seen above, there are many RGP designs. The design is determined by the severity of the disease.
- Piggy-backsThis is where an RGP lens is worn on top of a soft lens. The RGP lens provides crisp vision and the soft lens acts as a cushion providing increased comfort. With new RGP designs and materials, the “piggy-back” system is not used very often.
- Hybrid Lenses (Soft perm, Synergize)This is a lens that has an RGP center with a soft lens skirt. The idea of this lens design is to give good vision thru the RGP lens with the comfort of a soft due to the “skirt”.
- Scleral Lenses (MSD, Jupiter)We were the first practice in the United States to use the MSD Lens! These are large diameter lenses that rest on the “white” part of the eye, called the sclera. The idea of this lens is that it vaults over the cornea. The scleral lenses have many advantages. Because of their size, they do not fall out. Dust or dirt particles cannot get behind them during wear. They are surprisingly comfortable to wear because the edges of the lens rests above and below the lids giving little to no lens awareness. The key to its effectiveness is the artificial tear-filled reservoir that it maintains over the diseased cornea functions as a soothing and healing liquid eye bandage.