The Scleral Lens Vault
Fitting Back-Surface Toric Scleral Lenses
BY GREGORY W. DENAEYER, OD, FAAO
Scleral lenses are routinely fit using diagnostic lenses to estimate the corneal vault and haptic alignment. In the United States, the majority of scleral lens fitting sets have spherical back surfaces. The use of spherical back-surface designs has been relatively successful since the reintroduction of modern scleral lenses. However, optical coherence tomography data has shown that the sclera is not spherical, but rather non-rotationally symmetrical (van der Worp, 2010). The development of corneo-scleral topography has confirmed that in most cases, the sclera is astigmatic and asymmetric in elevation.
In a recent study by Ritzmann et al (2015), they measured the corneo-scleral shape of 80 normal eyes and showed that the average amount of scleral toricity at 15.0mm was 4.00D (0.8mm) and its location was surprisingly random, anywhere 360º around the sclera. In addition, they found, along the horizontal meridian, that the nasal quadrant was higher in its elevation compared to the temporal quadrant; along the vertical meridian, the superior sclera was higher than the inferior.
Visser et al (2006) highlighted the value of using toric back-surface scleral designs to avoid air bubbles and localized conjunctival vessel blanching. In 27 eyes that had worn a spherical scleral lens, patients reported increased comfort and wear time after being refit with a back-toric design.
Another study by Visser et al (2007) demonstrated high patient satisfaction using modern scleral lenses to manage corneal disorders. However, patients showed a preference toward back-surface toric scleral lens designs. For 99 eyes that were switched from back-surface spherical to back-surface toric scleral lenses, patients reported increased comfort, visual quality, and overall satisfaction. Patients who were fit with back-surface torics also took fewer lens breaks—defined as removal to clean the lens—compared to those wearing spherical back-surface designs.
Fitting the Lenses
Historically, a guesstimate was made based on the appearance of diagnostic lenses to determine prescribed back-surface haptic toricity. This rudimentary judgment can be challenging, especially considering that scleral toricity can range from 0.00D to 6.50D, in my personal experience.
The advent of corneo-scleral topography will allow practitioners to measure the amount and direction of scleral toricity (Figure 1). Fitting software can custom design back-surface toric lenses for each individual eye. Custom back-surface toricity can be used to rotationally stabilize a lens if front-surface toricity is needed to correct residual astigmatism.
Figure 1. This images shows 6.50D of with-the-rule scleral astigmatism measured at a 16mm chord.
Fitting custom back-surface toric lenses will improve fitting success by reducing localized blanching and edge lift, which also translates into better comfort and less reservoir debris. CLS
I would like to thank Pat Caroline, FAAO, for his help with this article.
For references, please visit www.clspectrum.com/references and click on document #240.
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 email@example.com.