CONTACT LENS CASE REPORTS
SCLERAL SHAPE 360º AROUND
PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
In the fitting of modern scleral lenses, it is important to select a lens with an appropriate design and sagittal height that will vault the entire corneal surface as well as the adjacent limbus. In this way, the full weight, pressure, and bearing of the lens will come to rest on the bulbar conjunctiva and sclera. In fitting a 16.5mm scleral lens, the point of maximum lens bearing will take place at a chord of approximately 15.0mm. The lens periphery then departs the ocular surface for 0.75mm in concave “ski” fashion so as to avoid impingement “blanching” of the conjunctival vessels (Figure 1).
Figure 1. A 16.5mm scleral lens has a “fitting chord” of 15.0mm. A 0.75mm wide periphery jettisons the edge away from the ocular surface.
In the future, it will be important for practitioners to measure and understand the shape of the sclera 360º around. Previously, topographical studies related to scleral shape have been limited to measurements along the horizontal and vertical meridians.
In a poster at the 2016 Global Specialty Lens Symposium in Las Vegas, Dr. Sheila Morrison, Markus Ritzmann, and colleagues provided us with a more complete picture of scleral shape through measurements obtained by three anterior segment instruments: Carl Zeiss Meditec’s Visante, Eaglet Eye’s Eye Surface Profiler (ESP), and Visionary Optics’ sMap3D (Figure 2).
Figure 2. Three techniques to quantitate the shape/height of the sclera in the eight primary meridians.
The Visante instrument uses optical coherence tomography (OCT) imaging and manual digitizing to provide 360° measurements of the sagittal height of the sclera at a chord of 15.0mm. The ESP and the sMap3D are profilometry techniques that use sodium fluorescein and a projected pattern to map the scleral surface.
Figure 3 shows the right eye mean sagittal height results of the Visante, ESP, and sMap3D in the eight primary meridians: nasal, superior-nasal, superior, superior-temporal, temporal, inferior-temporal, inferior, and inferior-nasal at a chord of 15.0mm. Figure 4 shows the left eye data. The results of this 360° eye evaluation showed:
1) A consistency between the data from all three measurement techniques at a 15.0mm chord.
2) There were some differences noted between right and left eyes.
Figure 3. Right eye data showing the sagittal height data comparison of the three techniques in each meridian.
Figure 4. Left eye data showing the same comparison as in Figure 3.
It is clear that as our industry moves in the direction of quadrant-specific scleral lens designs that knowledge of the scleral shape 360° around will take on an increased level of importance. CLS
For references, please visit www.clspectrum.com/references and click on document #250.
Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant to Contamac.
Mark André is an associate professor of optometry at Pacific University. He is also a consultant to CooperVision