The Scleral Lens Vault
Stabilizing Scleral Lens Rotation
BY GREGORY W. DENAEYER, OD, FAAO
Scleral lens design and fitting approaches have become more complex as technology has advanced and practitioners have become more experienced. Scleral lenses that incorporate front-surface toricity require on-eye rotational stability. In the case of wavefront-guided front-surface correction, the lenses need to have both rotational and translational stability to accurately correct higher-order aberrations.
The most traditional and common ballast method to stabilize rotation of a scleral lens is the use of double slab-off prism (Figure 1). This design incorporates thinned zones in the superior and inferior areas of the lens, which allows the lids to effectively squeeze the lens into position.
Figure 1. Scleral lens with double slab-off prism.
Although relatively successful, this technique has some disadvantages. Some patients find the thickness differences to be uncomfortable, especially if an increased thickness differential is required to improve stability. Additionally, the changes to the front surface make it difficult for patients to get small plungers to attach to the lens for removal.
A second way to stabilize a lens for front-surface toricity or wavefront-guided correction is to use back-surface-toric haptics. Most scleras are toric (Ritzmann et al, 2015), and measuring scleral topography enables practitioners to prescribe custom toric back surfaces that will not only improve fit and comfort, they also help stabilize a scleral lens (Figures 2 and 3).
Figure 2. Scleral elevation map showing 2.50D of scleral toricity.
Figure 3. Back-surface-toric lens on the eye measured in Figure 2. Toric orientation matches measured toricity.
Ticak et al (2015) reported that three different toric stabilization methods provided superior stability over a spherical design. They concluded that back-surface-toric stabilization can potentially stabilize a scleral lens that has wavefront-guided correction.
A final way to achieve rotational stabilization is to fit a lens designed from a mold of the eye being fit. This complete customization of the fit allows the lens to lock in place without additional modifications.
Prism-ballasted scleral lenses will be increasingly replaced by more sophisticated back-surface profiles that will be specific for each individual eye. Corneo-scleral topography will allow for designing custom back-surface toricity that will not only improve comfort and fit, it will also be a successful platform for adding front-surface toricity or wavefront-guided correction to scleral lenses. More extreme cases may be successfully corrected using molding techniques for complete back-surface customization. CLS
For references, please visit www.clspectrum.com/references and click on document #242.
Dr. DeNaeyer is the clinical director for Arena Eye Surgeons in Columbus, Ohio and a consultant to Visionary Optics, Alcon, B+L, and Aciont. He is also a shareholder in Precision Ocular Metrology LLC. You can contact him at firstname.lastname@example.org.