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G. Hofmann, J. Wang, M. Shen, J. Perez, C. Riley; Feasibility of in-vivo Lens and Corneal Shape Measurements With Lens Position Using Long Scan Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3418.
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© ARVO (1962-2015); The Authors (2016-present)
The feasibility of using a long scan SD-OCT to measure corneal shapes and in-vivo lens profiles, while determining the lens position, has been demonstrated. In-vivo lens and corneal shape data along with the lens position are needed to understand how an in-vivo lens flexes; an important step toward understanding how lens flexure affects fit and lens performance.
Contact lenses were made with a circular fiducial (groove, ~180 µm wide, indented into the front surface of the lens) that was concentric with the lens center. Two types of senofilicon A lenses were made: 1 mm and 4 mm diameter fiducials. Etafilicon A lenses (1 mm diameter fiducial) were also fabricated.A long scan SD-OCT, capable of at least 15 mm wide scans and 7.2 mm scan depths, was used to obtain cross sectional images (horizontal and vertical) of in-vivo lenses and bare eyes. Each image was comprised of 2048 A-scans. Enface images were also obtained.OCT images were processed with custom Matlab software to yield in-vivo lens cross sectional surfaces (~8 mm wide) the bare eye surfaces (~10 mm wide) and the fiducial mark locations (intersection of circular fiducial with image plane) relative to the corneal apex .The surface data were fit to a conic and the fiducial locations were used to define lens position.
While all fiducial marks were visible, regardless of lens type, the 4 mm diameter fiducials worked best since their location was farthest from the central reflux at the corneal apex. Additionally, the fiducials were present as a ring in the reconstructed enface view showing the position of the lens with respect to the corneal apex.Contact lens and bare eye shapes were found to be prolate ellipses, with typical conic parameters: apex radius 7.8 mm and conic constant -0.24. Regions outside the corneal surface were also imaged.
It has been demonstrated that long scan SD-OCT can be used to measure the in-vivo lens and corneal shapes with lens position. This provides the framework for development of 3D SD-OCT shape capabilities that may extend beyond the corneal surface and dynamic lens tracking.
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