Sheila D. Morrison OD MS, Patrick J. Caroline FAAO, Gregory W. DeNaeyer OD, Donald R. Sanders MD PhD
The advent and use of scleral mapping tools has improved the scientific approach to scleral lens fitting by measuring topographical shape of the sclera beyond the limbus, namely the sagittal height of the eye (SAG) at the diameter of the scleral lens and the amount of scleral asymmetry. SAG is necessary to determine the appropriate scleral lens parameters to achieve a desired central clearance of the lens that optimally vaults the ocular surface. It is generally accepted that most scleral surfaces are asymmetrical, not spherical; the use of a toric peripheral back haptic in scleral lenses can improve landing zone alignment, improve comfort, and increase wearing time.
A toric peripheral back haptic my also decrease debris buildup under the lens and can often provide ‘lock-and-key’ rotational stability for applying a front surface toric optic. However, even when it is obvious that scleral asymmetry is present, determining the exact amount of back haptic toricity to place in the lens is not always clear.
Furthermore, while the majority of patients appear to have some degree of scleral asymmetry, some do have a more spherical shape, with significant inter-eye differences, highlighting the benefit of scleral mapping to optimize efficient lens selection and design.
To determine the repeatability of three scleral topography measurements with the novel sMap3D™ cornea-scleral topographer at a 15mm scleral chord: (1) SAG, (2) sMap3D™ principal toricity magnitude value, and (3) steep axis orientation of the sclera.
Drs. DeNaeyer and Sanders and Mr. Farajian are shareholders in Precision Ocular Metrology, the manufacturer of the sMap3D™ instrument. Dr. Sanders is a shareholder of Visionary Optics and Dr. DeNaeyer is a consultant to Visionary Optics. Visionary Optics distributes the sMap3D™ and helped fund this research.