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Pieter Poolman, John N Pienta, Jan M Full, Susan C Anderson, Randy H Kardon; The Influence of Eyelid Position and the Photic Blink Reflex Upon the Pupil Light Reflex. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4098.
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Recently, we reported that pupil entrance size and anisocoria can influence retinal illuminance and the relative afferent pupil defect (RAPD) in patients with darkly pigmented irides, but not lightly pigmented irides. We also reported how pupil size interacts with iris mechanics to limit the amount of pupil contraction to light stimuli and how the % pupil contraction can minimize this efferent effect. We now report how eyelid position and pigmentation influence the amount of light entering the eye and hence, modulate retinal illuminance and the pupil light reflex.
Normal subjects and patients from the University of Iowa Neuro-ophthalmology Clinic participated in this study. A binocular, computerized pupillometer (DP2000, Neuroptics Inc) was used to provide light stimuli (1.0 and 0.2 s in duration) and record infrared video of both eyes (and eyelids). Seven light intensities, given in 0.5 log unit steps (2.6 log unit range, starting at 1 Lux), were presented alternately to the right and left eye. Pupil tracings were plotted as a function of light intensity and the RAPD was derived. Pupil size was determined using two different methods: 1) for estimation of afferent light input, the pupil borders were outlined with image analysis accounting for both pupil size and for eyelid effects when the upper eyelid border occluded part or all of the pupil, 2) for estimation of the efferent pupil response to light, the pupil borders were outlined according to an extrapolated round geometry, even when the eyelid partly occluded the pupil.
With increased light intensity, a partial or full eyelid reflex excursion occurred with a latency of 100 ms, representing the photic blink reflex. It was more pronounced with 1 s duration blue light (480 nm) compared to red light (620 nm), matched for photopic luminance. In cases where a photic eyelid reflex occurred, the resulting pupil response was decreased due to reduction in retinal illuminance. This effect significantly affected the RAPD.
The photic blink reflex is a naturally occurring eyelid reflex response to light that can function as an accessory pupil, further limiting retinal illuminance in addition to pupil size. Since the photic blink reflex has a shorter latency than the pupil light reflex, it may play a greater role in modulating retinal illuminance during both a light stimulus and also during steady state light, when squinting occurs.
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