Surface Coverage with Single vs. Multiple Gaze Surface Topography to Fit Scleral Lenses
Gregory W. DeNaeyer OD, Donald R. Sanders MD PhD, Timothy S. Farajian MS/p>
Until very recently, scleral lens fitting has depended upon the use of a diagnostic fitting set utilizing a trial-and-error process. The measurement of the anterior ocular surface is necessary to measure two critical parameters key to scleral lens fitting: the sagittal height of the eye (SAG) at the diameter of the scleral lens1 and the shape of the sclera. There are currently 2 corneo-scleral elevation topography systems commercially available:
Eye Surface Profiler (Eaglet Vision, Roermond, Netherlands) Relies on a single straight-gaze view to obtain surface topography
sMap3D® (Precision Ocular Metrology LLC, Cedar Crest, NM) Takes three images and stitches them together to product a single wide field topographic image
Both of these systems measure corneal and scleral SAG and toricity. Unlike placido-based (reflection) corneal topography systems, both of these systems are based upon the fluorescence (fluorescein) detection of the ocular surface abnormalities, or corneal scarring or irregularity; virtually any surface can be scanned.
To determine if data obtained from a single straight-gaze examination provides a sufficient area of measurable sclera (coverage) within a given diameter to provide accurate data for mini-scleral and full scleral lens fitting.
Twenty-five eyes of 23 patients that presented for scleral lens fitting were retrospectively analyzed. All patients were measured with the sMap3D instrument using recommended exam procedure: three image acquisitions (up, straight and down gaze) with the application of a fluorescein and anesthetic solution. Examinations were performed by a scleral lens fitter who had experience using the instrument on a routine basis weekly for 10 months before the patients in this study were examined. Acquisition time for all 3 images was usually less than 2 minutes. The extent of readable sclera and cornea and the limbal outline were identified for each image. The 3 images were aligned using a proprietary stitching algorithm.