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David Usher, Amit Mukherjee, Mikhail Smirnov, Jason Hill, William Eddington, Cailing Liu, Desmond Christopher Adler; Impact of Eye Motion and Active vs. Passive Eye Tracking on Refractive Crosslinking. Invest. Ophthalmol. Vis. Sci. 2019;60(9):327.
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© ARVO (1962-2015); The Authors (2016-present)
Localization of the crosslinking (CXL) effect within a sharply-defined XY zone is critical for maximizing anterior curvature change in refractive crosslinking (PiXL). Uncompensated eye motion imparts an uncontrolled and radially asymmetric two-dimensional blur to the UV beam, degrading spatial localization and reducing the refractive impact. Active tracking compensates for eye motion by measuring pupil location and rapidly repositioning the UV beam. This study provides simulations and ex vivo measurements of PiXL procedures with and without the compensatory action of eye tracking, based on measured motion profiles from a set of human eyes.
Motion profiles were derived from measured pupil trajectories in 130 video recordings of human eyes undergoing screening for CXL. Observed pupil motion from a combination of eye and head motion during treatment was up to several millimeters from mean position. When motion is left uncompensated, blur is imparted to the UV profile. Uncompensated UV profiles were simulated by superimposing a nominal UV beam on the measured pupil trajectories. Compensated UV profiles were simulated in the same way but included the effects of active eye tracking. Impact on refractive change was simulated using a biomechanical model. Impact was also assessed by applying motion-compensated and uncompensated UV profiles to ex vivo porcine eyes and measuring anterior curvature changes with a Pentacam HR tomography system.
Uncompensated motion imparts significant blur to the UV beam, with nasal-temporal blur being largest. Simulations predict a 40% to 100% decrease in anterior curvature change without eye tracking. These findings are confirmed with ex vivo measurements, which show significant decrease in PiXL effect as UV edge blur increases.
Simulations and ex vivo measurements confirm the essential role of active eye tracking in refractive crosslinking. Refractive changes from PiXL are degraded due to uncompensated eye motion when active eye tracking is not provided in the UV delivery system, implying that passive eye tracking is insufficient.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Simulated effects of eye motion, from most stable to least stable, on UV pattern used for hyperopic correction. Active tracking minimizes blur while passive tracking results in UV distortion.
Measured ex vivo curvature changes from PiXL show significant reduction in refractive effect as UV blur increases.
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