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Fumiatsu Maeda, Carina Kelbsch, Torsten Strasser, Tobias Peters, Barbara Wilhelm, Helmut Wilhelm; Chromatic Pupil Light Reflex in Hemianopsia Patients with Homonymous Visual Field Defects. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4116.
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According to the classical theory, it is widely recognized that the pupil light reflex is a simple subcortical reflex arc. However, many previous studies proved that patients in isolated occipital lesions with homonymous visual field defects showed pupillary hemiakinesia that is reduced or absent pupil light reflex to perimetric stimuli in the blind part of the visual field. Our hypothesis is that the pupillary afferent system consists of two systems: one of these via intrinsically photosensitive retinal ganglion cells (ipRGCs) directly reaching the dorsal midbrain, the other running through the normal ganglion cells via the visual cortex. The purpose of this study was to test the hypothesis of these two separate pupillomotoric pathways.
The subjects were 11 hemianopsia patients (58.0±19.3 years, mean age±SD) with homonymous visual field defects due to postgeniculate lesions of the visual pathway and age-matched 17 normal controls (55.6±11.7 years). The parameters of the stimuli were as follows: intensity was 28 lux, duration was 4.0 sec, and colors were blue (420±20 nm) and red (605±20 nm) in order to activate ipRGCs and other RGCs, respectively. The stimulus provided by an LED stimulator to one eye under mesopic conditions. The consensual pupil light reflex of the non-stimulated eye was measured for 16 seconds by the Compact Integrated Pupillograph (CIP, AMTech). The examined pupil parameters were baseline pupil diameter (mm), latency (msec), relative amplitude at maximal constriction (%), at 3 sec after stimulus onset (%), at stimulus offset (%), at 3 sec after stimulus offset (%), and at 7 sec after stimulus offset (%).
Regarding to red response, the relative amplitude at maximal constriction (35.9±6.1% vs 42.1±6.0%, P=0.013), at 3 sec after stimulus onset (30.5±9.0% vs 38.6±6.2%, P=0.009) and at stimulus offset (28.6±9.2% vs 38.1±6.4%, P=0.003) of hemianopsia patients were significantly smaller than age-matched normal controls. Regarding to blue response, there was no significant difference between hemianopsia patients and normal controls.
Our results confirm the hypothesis of two separate pupillary pathways. The cortical lesions of our patients impaired responses driven by the cortical pathway far more while the subcortically (ipRGCs) driven responses were well-preserved.
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