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Mircea Mujat, Ankit Patel, Patrick O'Grady, Gopi Maguluri, Nicusor Iftimia, R Daniel Ferguson; OCT-based eye topographer. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1610.
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To develop a novel technology that will allow for precise real-time wide-area measurement of the human eye anterior segment topography. An automated method to measure the complete corneal and scleral topology will provide a valuable tool for both clinicians and scleral lens manufacturers and will help streamline the fitting process.
An Optical Coherence Tomography (OCT) - based topographer has been developed for rapid measurement of the corneal and scleral topography with micron scale resolution. Radial scanning geometry has been chosen for the OCT imager, in which a pair of elliptical mirrors is used to relay the pivot point from the scanners into the center of the eye, such that the laser beam is always near-normal to the eye surface as the beam scans over the eye surface. Several individual patches (9 mm x 16 mm) are acquired from different locations on the cornea/sclera and are stitched together to generate a large area (20 - 24 mm diameter) eye surface topography. The eye position is controlled by a set of LED fixation lights that turn on sequentially. A USB camera monitors the eye position for easy alignment and during the OCT scan for motion artifacts. Custom software automatically segments the OCT data for surface identification and stitches multiple surfaces together.
The imager was tested on phantoms, a calibration sphere, and animal eyeballs. Were found the smoothness and accuracy of the investigated surfaces to be within the instrument lateral and axial resolution range, which falls within the natural shape deformation and tear film variations in the human eye. The mean error between the surface of the calibration sphere and the OCT measured surface was about 10 µm. Figure 1 shows the large-area surface of a porcine eye obtained by stitching together 10 individual patches.
We have developed an automated corneal/scleral surface topographer with which patients with corneal diseases and disorders can be fitted with scleral hard contact lenses providing comfort, care, and increased treatment options for this patient population. Although preliminary, our results demonstrate the capability of our proposed approach for generating accurate surface plots over relatively large areas of the eye, which is not currently possible with any other single, existing platform.
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