How Can I Treat Keratoconus? What is Collagen Cross Linking?
Keratoconus is the ultimate example of irregular astigmatism. In irregular astigmatism, the “bowtie” on the Pentacam or corneal topography is not symmetrical. In keratoconus, the inferior part of the bowtie is a lot more steep than the superior part of the bowtie which is flatter. It leads to worsening vision, that at some point cannot be corrected with just glasses.
How to approach treating Keratoconus?
There is a two- part approach to treating keratoconus and both are equally important. The first part has to do with preventing the disease from progressing and getting worse and the second part has to do with correcting vision. Keratoconus is naturally a slowly progressive disease in which the eye continues to get more “ectatic” or weaker and thinner. We know that disease progression typically occurs in adolescence and early adulthood, but can last through the 30s, 40s and even 50s. It is hard to predict when the disease will reach a halt. That is why screening, early recognition and treatment is crucial.
The goal of Collagen Cross Linking, a revolutionary technology for Keratoconus, is to strengthen the collagen within the cornea and to prevent the progression. The FDA-approved Avedro protocol is an hour long procedure per eye. The top layer of the cornea, the epithelium is first removed and then for the first 30 minutes, riboflavin drops (Photrexa) are placed on the eye every 2 minutes. If the cornea is on the thinner side, Photrexa Viscous (Riboflavin with 20% dextran) is used to help thicken the cornea. At the end of the 30 minutes, the cornea is checked at the slit lamp to ensure proper absorption of the Riboflavin. The corneal thickness is checked and if the thickness and absorption are adequate, then the second half of the procedure, the UV irradiation begins for 30 minutes, with Photrexa being continuously installed every 2 minutes. At the end of the procedure, a bandage contact lens is placed on the eye. This lens is safe to sleep in and is removed in the office in 5-7 days. Antibiotic and steroid drops are used for several weeks after, and people are able to go about their day to day activities the next day. While the uncorrected visual acuity may actually improve after Collagen Cross Linking, that is not the true goal of the procedure. The goal is strengthen the cornea and prevent the keratoconus from progressing.
Why consider Collagen Cross Linking?
Collagen cross linking is recommended for anybody with progressing keratoconus. You may notice progression as worsening vision, or your prescription constantly changing. Your doctor will notice progression as your prescription changing, and the Pentacam, or corneal topography changing.
There is a point at which the keratoconus is too progressive and the cornea is too thin for Collagen cross linking to be a safe procedure. The cornea, which on average is 540 microns and is thinner in keratoconus, cannot be thinner than 400 microns to safely do the procedure. That is why it is important to catch and perform the procedure early if progressive keratoconus is detected.
The other part about treating keratoconus has to do with visual optimization. Initially, the vision resulting from keratoconus is correctible with glasses, then eventually soft contact lenses. Since soft contact lenses mold to the cornea, eventually when the irregular astigmatism gets advanced, soft lenses can no longer correct the vision, and rigid gas permeable or scleral lenses are needed. These create a perfect tear film below the lens.
In terms of order, it is advisable to perform collagen cross linking first before changing the prescription of the glasses or contacts.