The Scleral Lens Vault
Scleral Lenses and the Limbus
BY GREGORY W. DENAEYER, OD, FAAO
The corneal limbus contains stem cells that renew the basal cells of the cornea, which continuously replace the epithelial layers (Hart, 1992). The cornea gradually transitions to the bulbar conjunctival and scleral tissue. Mini-scleral and full scleral lenses ideally vault the cornea, including the limbus, which allows them to rest on the sclera. Not all successful fits have complete corneal clearance.
Scleral lenses often slightly decenter down and out 1mm to 2mm, resulting in a sectional area of limbal touch at the superior-nasal quadrant. In addition, corneo-scleral lenses share bearing between the cornea and the sclera, which would include the limbus.
However, practitioners need to avoid harsh bearing on the limbus to avoid significant corneal complications such as corneal limbal edema, neovascularization, and keratitis. Complications from limbal compromise tend to result from circumferential bearing, in which the weight of the scleral lens is bearing on the limbal area.
Evaluating adequate limbal clearance can be a clinical challenge. To start, use a diffuse cobalt light with a #12 Wratten filter to rule out limbal bearing (Figure 1). Using a slit beam helps evaluate limbal clearance (Figure 2), but accurate assessment may be difficult if the vault is minimal. Diffuse white light shows fluorescein that extends beyond the cornea when a scleral lens has generous limbal vault (Figure 3). Keep in mind: the amount of limbal clearance will be significantly less than the central corneal clearance. Optical coherence tomography (OCT) is the most accurate way to assess limbal clearance (Figure 4).
Figure 1. A scleral lens with circumferential limbal bearing.
Figure 2. Evaluating limbal vault with a slit beam.
Figure 3. Fluorescein beyond the limbus.
Figure 4. An OCT image showing limbal clearance.
If circumferential limbal bearing is observed, adjust the design to avoid complications. A larger diameter improves overall corneal vault. Increasing the optic zone or midperipheral curve widths will often be all that is necessary to successfully vault the limbal area.
If you are unsure whether you have limbal vault, monitor the patient carefully to look for signs of keratitis, neovascularization, or edema. Instruct patients to return to the office immediately if they have symptoms of redness and intolerance to the scleral lens. CLS
For references, please visit www.clspectrum.com/references and click on document #230.
Dr. DeNaeyer is the clinical director for Arena Eye Surgeons in Columbus, Ohio, and a consultant to Visionary Optics, B+L, and Aciont. You can contact him at email@example.com.