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Christine W Sindt, Bruno Lay, Ronan Danno, David Slater; Modeling the limbus as an elliptical toric to optimize scleral lens fitting. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3080.
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© ARVO (1962-2015); The Authors (2016-present)
Highly astigmatic eyes have an elliptical limbal shape, as well as toric configuration. All current scleral lenses assume a planar circular limbus of a standard diameter, which will either overestimate or underestimate the limbal clearance of the lens. Underestimation, resulting in limbal touch, can create stem cell failure. Overestimation results in lens displacement, negative pressure and conjunctival prolapse, which also can result in stem cell failure, debris accumulation and discomfort. Our hypothesis is to design the entire lens based on the limbal shape, thus securing the appropriate vault 360 degrees, to improve the lens centration and protect the limbal stem cells.
Using impression technology to capture true 3-D ocular surface topography, 5+ points are chosen to define the limbal shape.Using these points, an elliptical regression algorithm is run to find the best fit ellipse.A minimum acceptable clearance value is entered to create a best fit toric ellipse 360 degrees.The virtual toric ellipse is displayed on the 3-D model showing the x,y,z axes. The user visually validates the ellipse-limbus relationship.The computation of the Transition Zone, the area between the optic zone and the scleral landing area, guarantees clearance over the limbus is in each meridian.The Landing Zone diameter is equidistant from the elliptical limbal definition, thus creating an elliptical lens.The Landing Zone outer diameter minimum value is based upon the ellipse major axis. Once the back surface is modeled, the lens front surface is computed using standard elevation specific technology.10 patients with highly toric globes fit with circular limbal zones and experiencing over or under limbal vaulting complications were refit into toric elliptical limbal designs
Toric elliptical limbal scleral lens designs minimized conjunctival prolapse and posterior tear film debris. Patients subjectively reported improved lens comfort and wearing time.
Poor lens to limbus relationships result in significant scleral lens complications. Using the limbal shape to define lens shape results in better outcomes
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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