Utilize Scleral Profilers for Scleral Lens Selection
Scleral topographers, or profilers, are instruments that image the cornea and scleral topography. Both the depth and shape of the cornea are displayed as well as the shape of the sclera. These instruments are valuable to determine if toricity is needed in the scleral landing zone.
Two instruments are currently available to obtain scleral topography and employ the obtained map to create scleral lenses – the sMap3D by Precision Ocular Metrology (New Mexico, US) and the Eye Surface Profiler by Eaglet Eye (Netherlands).
In order to obtain optimal data collection, the sMap3D takes three images of the ocular surface using fluorescein. The images are then stitched together to create a single image of the ocular surface. After a scleral lens is applied to determine the over-refraction needed, the software is used to design a scleral lens. The lens design software identifies the amount of scleral toricity, integrating this information into the landing curves if needed. The software designs the best fit lens based upon the Europa Scleral® lens (Visionary Optics) to determine initial lens parameters (Figure X).
Further modifications can be made by using the software after the scleral lens is evaluated on the patient.
A single image of the cornea and sclera in primary gaze is captured by the Eye Surface Profiler (ESP). Corneal and scleral curvature and height data is then used to select a lens from existing designs in the software. The instrument generates the initial lens diameter based on corneal size, as well as the recommended initial lens SAG value and amount of toricity in the scleral landing zone for optimal fit (Figure Y). The toricity in the landing zone is derived not just from scleral shape alone, but from the total SAG of each of the major meridians of the eye, allowing for precise landing in each meridian. The suggested lens can be placed on the eye and an over refraction completed to finalize the initial lens order.
Beginning the scleral lens fitting process can be overwhelming to the novice practitioner. With scleral topography, determining the initial lens to select can be simplified. Evaluation of the initial lens, even if suboptimal, makes subsequent lens selection more straightforward. Scleral topography saves the practitioner, patient and staff time, thus simplifying the scleral lens fitting process and creating a positive impression about scleral lenses.
Figure X. Scleral lens design software on the sMap3D scleral profiler.
Figure Y. The Eye Surface Profiler initial lens selection screen provides the desired lens SAG, diameter, and the peripheral curves for the two major meridians.
Dr. Melissa Barnett is a Principal Optometrist at the UC Davis Eye Center in Sacramento, specializing in anterior segment disease and specialty contact lenses. Dr. Barnett is the Past President of The Scleral Lens Education Society. She lectures and publishes extensively on topics including dry eye, anterior segment disease, contact lenses and creating a healthy balance between work and home life for women in optometry.