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David Usher, Radha Pertaub, Marc Friedman, Ronald Scharf, David Muller; Topographically Guided Corneal Cross-Linking. Invest. Ophthalmol. Vis. Sci. 2013;54(15):529.
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To determine the feasibility of a topographically guided corneal cross-linking device.
A proprietary corneal cross-linking device was developed. A UVA LED source illuminates a digital micromirror device (DMD). Light reflected from the DMD is projected on to a subject’s eye. The system controls the configuration of the DMD’s mirrors such that an arbitrary UVA pattern can be projected on to the eye and modulated at video rates. A digital camera is used to record views of the subject’s eye. A Graphical User Interface allows an operator to import topographies from a third party corneal topographer and define UVA irradiation patterns based on the imported topography data set. A common reference frame between the cross-linking device and the topographer is established via a registration algorithm. Images of the subject’s iris exported by the topographer are compared to images recorded by the cross-linking device’s digital camera. Iris textures and limbus boundaries visible within each dataset are used to calculate a geometrical relationship between the two camera views. Eye motion during the application of the UVA light is accounted for by tracking the location of the eye in the cross-linking device’s digital camera. This detected eye motion forms feedback for modulating the DMD mirrors such that the incident UVA illumination tracks relative to the eye. Eye motion, in terms of pupil displacements, was calculated for 20 eyes from 10 subjects each over 30 second periods.
An average frame-to-frame (60 Hz) eye motion of 23.9 um (Range: 16.6 - 38.0) was recorded across subjects. Rotations of 2.1° and 2.8° were measured for two subjects where images were recorded by both the cross-linking device and the corneal topographer.
The proposed UVA treatment system demonstrates unique features that will be able to advance the science of corneal cross-linking. Each individual mirror of the DMD can be controlled to correct beam uniformity through irradiance calibrations. Its flexibility allows a surgeon complete freedom when configuring the UVA dose across different areas of the cornea to a high degree of accuracy. The eye tracking preserves this accuracy by accounting for eye motion. The integration of the topography data allow a surgeon to use variables such as corneal elevations, power maps, k readings, corneal thickness maps, and epithelial thickness maps when creating patent specific cross-linking pretreatment plans and procedures.
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