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A.J. Lang, T. Miller; First Order Design of Intracorneal Inlays: Dependence on Keratometric Flap and Corneal Properties . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3591.
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© ARVO (1962-2015); The Authors (2016-present)
Outline the general issues regarding intracorneal inlay optical design, derive a first order model and discuss the first order effects.
Outline a general formalism for describing the desired change to the anterior corneal surface, based on a desired change in refraction. First–order assumptions regarding the inlay’s interaction with the overlying keratometric flap and lamellar bed include: conformance of the inlay’s posterior surface to the bed geometry, constancy of the inlay’s center thickness with deformation, and one–to–one projection of the inlay’s thickness profile axially through the overlying flap. With these assumptions, a first–order model of inlay design and the dependence on the corneal parameters are discussed. This new formalism is compared with the published design method by Warsky, et al, [Invest Ophthal & Vis Sci, Vol 26, No 2, 1985] who proposed a radial displacement model; i.e., the anterior corneal radius of curvature is equal to the inlay’s anterior radius of curvature plus the flap thickness. Clinical data is used to compare the prediction of each model.
The desired change in the anterior corneal surface is shown to be relatively independent of the pre–operative corneal power. With the above assumptions, the design of the intracorneal inlay using the axial displacement model is suggested to be independent of the keratometric flap geometry. Both the axial and radial displacement models can be used to predict expected post–operative refractions, which are compared to the actual post–operative refractive spherical equivalents in a clinical study. The standard deviation of the difference is a measure of the effectiveness of each model. Phase II data from a US IDE study (ReVision Optics Hyperopic inlay) involving subjects with know implants demonstrates the following ratios of predicted to actual standard deviations: a) axial model – 97% mechanical keratome and 94% Intralase keratome , b) radial model – 158% mechanical and 163% Intralase.
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