Scleral lens fitters are increasingly using more sophisticated designs to successfully fit a wide variety of indications. A key design element is the haptic back surface. Spherical, toric, or multi-meridian designs can be manufactured depending on patients’ scleral geometry.
Spherical Versus Toric Back-Surface Haptics
Optical coherence tomography and corneo-scleral topography have shown that the scleral shape is non-rotationally symmetrical (van der Worp, 2010; Ritzmann et al, 2015). Additionally, scleral asymmetry is not related to corneal toricity (Kinoshita et al, 2016; Seibert and Jedlicka, 2017). Multiple manufacturers now offer toric fitting sets, and practitioners seem to be prescribing back-surface toricity with increased frequency. The Visser group has shown that patients often prefer haptic back-surface toricity (Visser et al, 2006; Visser et al, 2007).
In my practice, scleral lenses that I design have dramatically shifted toward back-surface toricity since I started utilizing corneo-scleral topography (Figure 1 a and b). For a six-month period in 2014 without corneo-scleral topography, 93% of my scleral fits had a spherical back surface, whereas 7% had a toric back surface. In contrast, for a six-month period in 2016 when fitting from corneo-scleral topography, 32% of my fits had a spherical back surface versus 68% with a toric back surface. It is important to keep in mind that some scleras have a relatively spherical shape and will be best fit with a spherical haptic back surface. Fitting these patients with a toric back-surface haptic not only will not improve the fit, but could create a fitting complication.
Toric Versus Multi-Meridian Back-Surface Haptics
Some patients have scleras with an asymmetric shape that is not definitively toric (Figure 2 a and b). For these patients, a multi-meridian approach is best. They will be best fit using back-surface haptics with four or more primary meridians, not necessarily equidistant, that are tailored for their scleral geometry.
The future of scleral lens design is utilizing spherical, toric, or multi-meridian designs to best fit each individual eye. CLS
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