I have a patient with keratoconus who has a very steep inferiorly displaced apex—every corneal lens rides low, as expected. Which approach would you recommend as an alternative? Would a hybrid work, or would a scleral be a better option?
“An inferiorly displaced apex in keratoconus is a challenge to fit—corneal lenses often will not center, as they position over the steepest part of the cornea,” says Dennis Burger, OD, clinical professor of optometry at the University of California at Berkeley. Fortunately, just a small percentage of keratoconic patients have a markedly inferior-decentered corneal apex, and there are now new options for fitting lenses to corneas of this type. These include specialized soft, hybrid and scleral lenses.
• Large diameter lens. Optometrist Edward S. Bennett prefers to start with an intralimbal diameter design, such as Rose K2IC (Blanchard) or Dyna Intra-Limbal (Lens Dynamics). Designed to fit within the limbus, these large-diameter lenses (11.2mm) share many fitting characteristics with standard rigid gas permeable lenses, while providing the comfort and irregular corneal masking that is characteristic of sclerals. If that design decenters, which may have been the case with this patient, a scleral or hybrid design would be indicated.
• Hybrid lens. “A hybrid design is sometimes a viable alternative; although it’s important to ensure that the lens is not fitting too tightly, resulting in patient awareness and possibly peripheral corneal complications,” says Dr. Bennett, associate professor and co-chief of the Contact Lens Service at the University of Missouri-St. Louis College of Optometry. “My preference would be for some type of mini-scleral design (i.e., 14mm to 16mm), as good centration, comfort and vision is often achieved.”
• Scleral lens. When dealing with a very steep inferiorly displaced apex, Dr. Burger finds that a scleral lens is the best option. “The rigid surface of the scleral provides good vision; the lenses are durable and they can also be custom designed,” he says. “By using the scleral lens, I am able to vault the cornea and rest the lens on the sclera—this prevents lens decentration.”
This image shows a patient with a displaced apical center and cone diameter greater than 5mm to 6mm.
Although the fitting goal is to vault the entire cornea, bearing still may occur on a displaced apex. If this happens, Dr. Burger uses a reverse geometry design. Reverse geometry scleral lenses are indicated in patients with displaced corneal apices, pellucid marginal degeneration, corneal transplants, post-radial keratotomy and any condition where the peripheral cornea is steep. “These lenses have a steeper secondary curve, allowing for the lens to fit steeper in the peripheral cornea,” he says. “They allow for clearance of the cone.”
Scleral edges must be designed to prevent blood vessel blanching, as tight lenses will lead to discomfort. “Diagnostic lens fitting is mandatory, as empirical fitting does not work,” Dr. Burger warns. “When fit properly, the scleral lens is very comfortable for the patient to wear—the combination of large lens stability, excellent optics, customizable parameters and good comfort make the scleral option the lens of choice for this patient.”
With the recent introduction of many new scleral lens designs, most laboratories have consultants who can help guide you through the fitting process. In addition, many major contact lens meetings offer hands-on fitting workshops. Finally, organizations such as the Scleral Lens Education Society (
www.sclerallens.org) and GP Lens Institute (
www.gpli.info) have helpful resources available on their websites.