Ocular Surgery News U.S. Edition, April 25, 2016

Richard L. Lindstrom, MD

Corneal ectasia is an important corneal pathology, and like so many other diseases, its diagnosis and treatment are currently evolving rapidly. Corneal ectasia includes keratoconus, pellucid marginal degeneration, posterior keratoconus and post-laser refractive surgery ectasia. Estimates of the number of patients with this diagnosis vary widely. The classic prevalence number is 1:2,000, meaning that there are about 180,000 patients with keratoconus in the U.S. I think this number is low, and some sources have suggested a prevalence as high as 1:400, which would increase the number to 900,000. If we include the so-called forme fruste keratoconus or keratoconus suspect, the number may be higher yet.

Large LASIK centers and practices report that at least 10% of patients are denied laser refractive surgery because of a cornea that is too thin or has an atypical topography that makes the surgeon nervous. Because only myopes and hyperopes are usually seen at these centers, the number might be smaller for the overall population, but in my opinion, as much as 1% to 2% of the population may fit into the forme fruste keratoconus or keratoconus suspect category. That moves the number of at-risk patients in the U.S. up to 3.6 million to 7.2 million. This makes the patient with frank corneal ectasia or risk factors for ectasia more common than classically taught, and as treatment options become safer and more readily available, clinicians will need to decide which of these patients deserve treatment with soon-to-be FDA-approved (we hope) approaches such as corneal collagen cross-linking (CXL).

The classical diagnosis of keratoconus includes progressive thinning with development of corneal steepening, increased astigmatism/coma and usually induced myopia. We currently screen for at-risk patients, or perhaps those with early keratoconus, using pachymetry, retinoscopy, keratometry and especially computerized corneal topography. The Ocular Response Analyzer from Reichert is used in some clinics to elucidate reduced corneal stiffness, and there is exciting research using Brillouin spectroscopy by Intelon and Avedro that promises more accurate measurement of corneal elasticity. This diagnostic technology could help us in the future determine which corneas with atypical topography are really at risk of progressive ectasia and deserve treatment with CXL.

The optical treatment of corneal ectasia typically starts with spectacles and advances to contact lenses. Usually patients with meaningful corneal ectasia see best with a rigid gas permeable contact lens, and many specialty contacts have been designed. A scleral contact lens can correct many patients with even severe keratoconus. My classic corneal training was to be very aggressive with contact lens fitting and reserve surgery for only those patients who are truly contact lens intolerant or are unable to wear contacts long enough to function in their daily life activities. In the face of newer treatments, which I will discuss below, I now usually recommend CXL or CXL combined with adjunct therapy as soon as the diagnosis of corneal ectasia is made. After stabilizing the cornea, contact lens wear can be resumed if needed.

I now consider it inappropriate to allow a patient to progress from mild to moderate to severe keratoconus, even if vision is good with a contact lens. The patient deserves to be informed and offered CXL as soon as the diagnosis is made. According to Eye Bank Association of America statistics, penetrating keratoplasty remains the dominant surgery for corneal ectasia, although deep anterior lamellar keratoplasty is slowly gaining advocates. Fortunately for the patient with corneal ectasia, outcomes with lamellar or penetrating keratoplasty are quite good. 

Still, those of us who do a significant number of corneal transplants know that this procedure is a lot of work for the patient and surgeon, and there are many complications, both early and late, including several that are sight-threatening. We would all love to have a minimally invasive treatment available that would arrest this disease before keratoplasty, or perhaps even before it induces any visual loss. While there is still much to be learned, one or another form of CXL shows promise to be such a treatment.