Juan Ding, OD, PhD
This case is from one of my favorite patients. He first came to me as a referral from his ENT (ear, nose and throat) doctor, because he complained about dry eyes since his facial nerve palsy on the right side. His ENT doctor was not the one to diagnose facial nerve palsy of course, but since he was undergoing several sinus surgeries he happened to mention this during one of the visits.
In his initial eye visit, I noticed that his vision was not able to be corrected to 20/20 by glasses, and he had a large amount of astigmatism. Retinoscopy showed scissor shaped light reflex, and slit lamp exam showed steepening cornea with prominent nerves and the right cornea actually had a mild scar. Corneal topography later confirmed keratoconus in both eyes, more so in the right eye.
Keratoconus literally means a corneal cone. Cornea is the front transparent layer of our eyes, and it is usually a regularly shaped dome like in the image on the left (Figure 1). But in keratoconus, the cornea gradually becomes thinner and thinner, and bulging more and more like in the image on the right. Because now the cornea is irregular, vision is blurry, even with glasses often still not good, since glasses do not correct this irregular surface of the cornea. Even regular soft contact lenses will not do much in this case because the soft lens material will just drape over the irregular cornea and still showing the irregular optics.
Figure 1. Normal cornea and cornea with keratoconus. Image from www.allaboutvision.com
Fortunately certain rigid contact lenses called rigid gas permeable (RGP) lenses can correct vision. These are stiff and can mask the irregularity of a keratoconus cornea. These are typically small, and often very uncomfortable especially in the beginning while the hard lens rubs against the surface of the eye and the eyelid.
Another type of lens to correct vision for keratoconus is a scleral lens (Figure 2). This is a large lens that sits on the white part of the eye called sclera, therefore causing minimum discomfort to the eye, and it corrects vision because the lens vaults over the irregular cornea to mask its imperfection.
Figure 2. How scleral lens corrects vision in keratoconus. Image from https://visualeyesboca.com/scleral-lenses/
Back to my patient, I initially fitted him with special RGP lenses designed for keratoconus, but due to advanced bulging, these lenses were unstable on the eyes and often popped out when he moved his eyes around or blinked. I then fitted him with Jupiter scleral lenses. These are very simple and easy on the patients as they are a relatively small scleral lens and easier to insert for beginners. However, in his case, the fitting was not ideal because the edge of the cornea kept being pressed close to the back surface of the lens. This is not good in scleral lens fitting, as it may not leave enough space for the cornea to breathe. I then switched to BostonSight scleral lens design, which is larger and more easily vaults over the entire cornea. He was very happy about his vision, with the right eye seeing 20/25 and left eye seeing 20/20. He told me that he ‘hasn’t seen this well since 16’- that was probably when he started developing keratoconus. He’s now in his early 40s, and this was the first time he heard of keratoconus.
Keratoconus is a condition that affects about 1 in 2,000 individuals. It usually starts in teenage years or early 20s, but can happen as early as 8 or 9 years of age. It tends to get progressively worse until stabilization in the mid 30s. There is often a family history, but not always. Both eyes tend to be affected, though one eye may be much worse than the other. We do not know the cause of the disease, but one modifiable risk factor is rubbing of eyes. So I always ask patients not to rub eyes. While it is progressing, an effective treatment called corneal cross linking can stabilize the cornea and halt the worsening of the condition. This procedure is typically done by a corneal specialist. Once cornea is stable, these special contact lenses such as RGPs or scleral lenses can often help patients to see what they used to be able to. Any keratoconus patient should have at least two types of eye doctors, one a corneal specialist, and one an optometrist who fits specialty contact lenses for keratoconus.