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Mhairi Day, Dirk Seidel, Lyle S. Gray, Niall C. Strang; A Headmounted, Open-field, Binocular Device To Measure And Analyse Eye Movements, Pupil Size And Refractive Error In Real-time. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2824.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a portable, accurate, headmounted device that measures pupil size, eye movements and refractive error simultaneously
Infrared (IR) LEDs are used to illuminate the eyes via hot mirrors allowing binocular, unobstructed viewing. Two compact, lightweight IR CCD cameras in front of each eye collect reflected IR light via a mirror. The video signals are transmitted to a PXI-1409 video card and a customised program within LabView 9.0 allows real-time analysis. Purkinje images are used to monitor eye movements and pupil diameter is monitored using an edge detection algorithm. Refractive error is measured using the luminance gradient of relected IR light form the retina within the pupil. A model eye is used to simulate pupil diameters (2 to 8mm) and refractive errors (-7D to +6D). Additional measurements were obtained from adult subjects (-5D to +5D). Continuous recordings of 60seconds were obtained at a sampling frequency of 20Hz.
Measurement of pupil diameters 2-8mm were obtained to an accuracy of 0.035±0.01mm (mean±SD) in the model eye. The mean rms for measurement of pupil diameter and eye movements in human subjects was 0.11mm. The linear range for measurement of eye movements was ±40deg. Luminance gradients within the pupil were linearly correlated with refractive error within the range -7D to +6D (r2≥0.930, p<0.01) using the model eye. Refractive error measurements in human subjects are dependent upon the brightness and distance of the IR light from the eye. Simulataneous measures of pupil diameter, eye movements and refractive errors can be made without any reduction in sampling frequency.
High resolution measurements of pupil diameter, eye movements and refractive error can be obtained simultaneously and binocularly under open-field viewing conditions. Real-time anaylsis including removal of blinks and frequency analysis can be conducted during recording. Future developments, including calculation of astigmatism and peripheral refraction, should result in a device that can provide a comprehensive assessment of the ocular motor system during real-life viewing.
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