Contact Lenses and Keratoconus
One method of treating keratoconus is through the use of contact lenses. Other than glasses, contact lenses are perhaps the simplest method of correcting vision. Since contact lenses come in many different designs, a specialized contact lens practitioner must be consulted to find the contact lens that offers the best combination of acuity, comfort, and corneal health. For patients with keratoconus, fitting a contact lens can be difficult. In progressed cases of keratoconus, the cornea has become thin to the point where it bulges outward. A contact lens must be fit around this bulge and still maintain proper fit, comfort, centration, and acuity.
Standard rigid gas permeable contact lenses are the simplest fitting choice and are often able to achieve success in mild cases of keratoconus. Because of the spherical shape, rigid gas permeable contact lenses provide clear vision when fitted correctly.
Aspheric shaped lens designs are sometimes necessary in cases of moderate and advancing keratoconus. These designs take into account the cone shape of the cornea caused by keratoconus. This lens will cover the apex of the cone allowing better fit. Because of the nonstandard shape of the lens, the contact lens must center well in order to correct a patientís vision adequately.
Piggyback contact lenses are occasionally used to correct keratoconus. At times, a rigid gas permeable contact lens can be uncomfortable, especially for someone with keratoconus. Sometimes a hard contact lens is also unable to remain centered correctly to provide good vision for someone with keratoconus. In these cases, it is occasionally necessary to use two contact lenses simultaneously. A soft lens, often a silicone hydrogel, is placed directly on the eye. This helps maintain the corneaís shape. A second lens, a rigid gas permeable contact lens, is then placed on top of the soft lens to help maintain the shape further and improve visual acuity further.
While keratoconus can be treated with contact lenses, there are some studies that indicate rigid contact lenses might hasten the onset of keratoconus. It has been suggested that the continual contact and rubbing from a contact lens weakens the collagen linking in the cornea and therefore exacerbates the onset of keratoconus. Despite these studies, contact lenses remain a popular treatment for keratoconus.