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E. L. Markwell, B. Feigl, S. S. Smith, A. J. Zele; Circadian Modulation of the Intrinsically Photosensitive (Melanopsin) Retinal Ganglion Cell Driven Pupil Light Response. Invest. Ophthalmol. Vis. Sci. 2010;51(13):671.
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© ARVO (1962-2015); The Authors (2016-present)
Melanopsin retinal ganglion cells (ipRGCs) provide the primary environmental light input to the suprachiasmatic nucleus for circadian photoentrainment and contribute to the post-stimulus sustained constriction of the pupil light response (PLR). This study determines the circadian dynamics of the ipRGC (inner retina) and rod and cone photoreceptor (outer retina) control of the PLR in humans.
Eleven participants (18-30 years; 4M, 7F) recorded their habitual sleep pattern with actigraphy and a sleep diary for 1 week prior to testing. Consensual pupil light responses were measured with 10 sec, 7.15º stimuli (488 nm; 14.2 log photon.cm-2.s-1) using a Maxwellian view optical system and infrared camera and analysed with custom developed software. The dynamic PLR parameters (baseline diameter, constriction amplitude and post-stimulus sustained constriction) were determined every hour for 24 hrs. External circadian cues were controlled (10 lux; kJ intake < 500/hr) during the 24 hr test. Circadian time (aligned to each participant’s circadian rhythm) was determined from hourly salivary melatonin levels and habitual wake time. Data were analysed using a mixed model univariate ANOVA.
Baseline pupil diameter and constriction amplitude do not significantly vary with time. Post-stimulus sustained constriction demonstrates a significant dependence on time of day (p < 0.05).
Outer retinal rod and cone photoreceptor contributions to the pupil light response do not vary during a 24 hour maintained wake period under controlled illumination. Inner retinal ipRGC contributions to the post-stimulus sustained pupil response show dynamic changes that suggest circadian modulation.
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