Scleral Topography: Improving Scleral Lens Fitting Efficiency and Success
By Gregory W. DeNaeyer, OD
Previous studies using optical coherence tomography (OCT) determined that the sclera is non-rotationally symmetrical and that it increases in asymmetry toward the periphery.1 The relatively recent advent of scleral topography has allowed for the complete topographical measurement of the anterior ocular surface out to 22mm in diameter. Three-dimensional models from scans allow for measurements of sagittal height and surface shape.
The Scleral Shape Study Group (SSSG) published a paper showing that there are four general categories of scleral shape: sphere, toric, asymmetric, and toric with variable periodicity.2 For patients who reported for scleral lens fitting, the study noted that 65% would be best matched with a back-surface quadrant-specific or free-form scleral lens design, while 30% would be matched best with toric landing zones. Only 6% would be best fit using a scleral lens with a spherical landing zone.
The SSSG also recently published a paper on the correlation between ectasia and scleral shape.3 The study authors concluded that normal patients and those who had central ectasias primarily had regular toric scleral shapes. However, ectasia patients who have peripheral apexes (defined as greater than 1.25mm from the corneal center) had scleral shapes with a significant quadrant-specific effect. The quadrant of the sclera in the same meridian as the apex was steeper compared to 180° away. This quadrant-specific effect can negatively affect the fit of a scleral lens with a symmetric design (sphere or toric); many times, this causes the scleral lens to decenter inferiorly. Designing a customized back surface, beyond sphere or toric landing zones, will substantially improve the fit.
Scleral topographers generate sagittal height maps that can be used to assess scleral shape (Figure 1) and to determine the type of scleral lens landing zone that would best match the surface of the eye. Software can be used to customize standard lens designs or to design free-form scleral lenses (Figure 2). Measurement of the ocular surface using topography is necessary for advanced customizations that will increase patient success.
Figure 1. Scleral sagittal height map that has a with-the-rule scleral toricity.
Figure 2. A free-form custom scleral lens for a patient who has a pterygium.
1. van der Worp E. A Guide to Scleral Lens Fitting [monograph online]. Forest Grove, OR: Pacific University; 2010. Available from: http://commons.pacificu.edu/mono/4/
2. DeNaeyer G, Sanders DR, van der Worp E, Jedlicka J, Michaud L, Morrison S. Qualitative assessment of scleral shape patterns using a new wide field ocular surface elevation topographer: the SSSG study. JCLRS. 2017 Nov;1:12-22. Available at http://www.jclrs.org/index.php/JCLRS/article/view/11. Accessed Feb. 15, 2018.
3. DeNaeyer G, Sanders DR, Michaud L, et al. Correlation of Corneal and Scleral Topography in Cases with Ectasias and Normal Corneas. JCLRS. 2019 Apr 22;3:e10-e20. Available at http://www.jclrs.org/index.php/JCLRS/article/view/33. Accessed July 23, 2019.
Dr. DeNaeyer practices at Arena Eye Surgeons in Columbus, OH. He is a shareholder of Precision Ocular Metrology LLC, has proprietary interest in Visionary Optics’ Europa and Elara Scleral Lenses, is a consultant to Visionary Optics, and has received lecture or authorship honoraria from Contamac. You can contact him at firstname.lastname@example.org.