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Marc Friedman, David Usher, Radha Pertaub, David Muller; Riboflavin Dosimetry in the Cornea using a KXL-II and the Scheimpflug Principle. Invest. Ophthalmol. Vis. Sci. 2013;54(15):532.
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To determine the feasibility of a new device (KXL-II) that combines custom UVA illumination patterns with a Scheimpflug imaging system for measuring riboflavin (RF) diffusion rates in the cornea.
A proprietary corneal imaging device was developed. A UVA LED source illuminates a digital micromirror device (DMD) and is in turn projected on to a subject’s eye. Two digital cameras are mounted ±45° to the apex of the cornea. The mirrors on the DMD are configured such that UVA illumination forms a series of slits. As the UVA passes through the cornea the resultant fluorescence profiles change with the cross-sectional distribution of RF. Profiles of multiple slits observed simultaneously map the distribution of riboflavin in the radial direction (Figure 1). The two off axis cameras employ a Scheimpflug principle whereby their focal planes are tilted in order to optimize the system’s optical design in terms of focal depth (Figure 2). Whole porcine eyes were placed at the device’s focal plane. Images from the side cameras were recorded at regular intervals after the application of RF solution.
Sequences of images recorded at regular intervals during and after the application of RF solution showed increased fluorescence at increased depths within the cornea. A focal plane angle of 18.2° to the apex of the eye was found to increase the useable depth of field of the system by a factor of over 2.5.
An advanced riboflavin dosimetry device is presented. The KXL-II system combines the use of UVA projection via a DMD with side cameras that monitor riboflavin fluorescence in the cornea. The camera’s tilted focal plane relaxes the constraints on the systems depth of field. The DMD allows for rapid alternation between illumination profiles intended for cross-linking treatment and slit configurations intended for fluorescent dosimetry. With this device it may be possible to respond and compensate to live dosimetry readings as riboflavin is consumed and measured at various depths within the cornea. Real time dosimetry measurements will play a significant role in determining the underlying mechanisms of corneal cross-linking and assist with the development of additional riboflavin formulations.
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