Post-illumination Pupil Response Research Articles

Melanopsin-mediated pupil function is impaired in Parkinson\u2019s disease

Parkinson’s disease (PD) is characterised by non-motor symptoms including sleep and circadian disruption. Melanopsin-expressing intrinsically photosensitive Retinal Ganglion Cells (ipRGC) transmit light signals to brain areas controlling circadian rhythms and the pupil light reflex. To determine if non-motor symptoms observed in PD are linked to ipRGC dysfunction, we evaluated melanopsin and rod/cone contributions to the pupil response in medicated participants with PD (n = 17) and controls (n = 12). Autonomic tone was evaluated by measuring pupillary unrest in darkness. In the PD group, there is evidence for an attenuated post-illumination pupil response (PIPR) amplitude and reduced pupil constriction amplitude, and PIPR amplitudes did not correlate with measures of sleep quality, retinal nerve fibre layer thickness, disease severity, or medication dosage. Both groups exhibited similar pupillary unrest. We show that melanopsin- and the rod/cone-photoreceptor contributions to the pupil control pathway are impaired in people with early-stage PD who have no clinically observable ophthalmic abnormalities. Given that ipRGCs project to brain targets involved in arousal, sleep and circadian rhythms, ipRGC dysfunction may underpin some of the non-motor symptoms observed in PD.

The ipRGC-Driven Pupil Response with Light Exposure, Refractive Error, and Sleep.

We investigated links between the intrinsically photosensitive retinal ganglion cells, light exposure, refractive error, and sleep. Results showed that morning melatonin was associated with light exposure, with modest differences in sleep quality between myopes and emmetropes. Findings suggest a complex relationship between light exposure and these physiological processes. Intrinsically photosensitive retinal ganglion cells (ipRGCs) signal environmental light, with pathways to the midbrain to control pupil size and circadian rhythm. Evidence suggests that light exposure plays a role in refractive error development. Our goal was to investigate links between light exposure, ipRGCs, refractive error, and sleep. Fifty subjects, aged 17-40, participated (19 emmetropes and 31 myopes). A subset of subjects (n = 24) wore an Actiwatch Spectrum for 1 week. The Pittsburgh Sleep Quality Index (PSQI) was administered, and saliva samples were collected for melatonin analysis. The post-illumination pupil response (PIPR) to 1 s and 5 s long- and short-wavelength stimuli was measured. Pupil metrics included the 6 s and 30 s PIPR and early and late area under the curve. Subjects spent 104.8 ± 46.6 min outdoors per day over the previous week. Morning melatonin concentration (6.9 ± 3.5 pg/ml) was significantly associated with time outdoors and objectively measured light exposure (P = .01 and .002, respectively). Pupil metrics were not significantly associated with light exposure or refractive error. PSQI scores indicated good sleep quality for emmetropes (score 4.2 ± 2.3) and poor sleep quality for myopes (5.6 ± 2.2, P = .04). We found that light exposure and time outdoors influenced morning melatonin concentration. No differences in melatonin or the ipRGC-driven pupil response were observed between refractive error groups, although myopes exhibited poor sleep quality compared to emmetropes. Findings suggest that a complex relationship between light exposure, ipRGCs, refractive error, and sleep exists.

Impact of blue-depleted white light on pupil dynamics, melatonin suppression and subjective alertness following real-world light exposure

BackgroundThe non-image forming system, which conveys light information to circadian and sleep centers in the brain, is optimized to respond to short wavelengths of light (blue). Exposure to white light with reduced blue content can cause lower than expected circadian and sleep responses. These findings, however, come from controlled laboratory conditions that may not be entirely accurate when attempting to apply them to most real-world settings. It was our intention to examine whether, under ecologically-valid circumstances, a blue-depleted white light had a diminished impact on sleep and circadian functions as compared to an equiluminant white light.MethodsIn Study 1, seven healthy, young individuals were exposed to a series of one-minute light pulses (32, 100 or 140 lx) produced either by a standard white light emitting diode (LED) or an LED light with reduced blue content. Pupil responses were measured with an infrared pupillometer. In Study 2, ten healthy, young individuals participated in two overnight evaluations. On one of the nights, participants received three hours of 150 lx of a standard white LED starting at habitual bedtime. The protocol on the alternate night was identical except an LED with reduced blue content was used (both lights were identical to those used in Study 1). Saliva samples were collected every 20–30 min for determination of melatonin concentrations and subjective sleepiness was assessed hourly with the Stanford Sleepiness Scale. In both studies, pre-light exposure baseline was real-world ambulatory light exposure.ResultsStudy 1. The post-illumination pupil response (PIPR) to 32 lx was increased in response to the standard as compared to blue-depleted LED (p < 0.05, paired t-test). PIPR did not differ between lighting conditions at higher illuminances. Study 2. Neither salivary melatonin concentrations nor subjective sleepiness scores were different between lighting conditions.ConclusionsWhile the absence or reduction of blue light has the physiologic capacity to reduce the impact of light on non-image forming photoreceptive functions, under a pre-exposure lighting environment closer to that which is found in the real world, no such differences are observed except for pupil responses to moderately dim light.Trial registrationClinicalTrials.gov #NCT02936674, NCT02636140.

Effect of Intermittent versus Continuous Light Exposure on Pupillary Light Response, As Evaluated by Pupillometry.

Continuous and intermittent stimuli with green light affect the pupillary light response (PLR) differently. Since the majority of pupillometric studies use blue and red lights, we investigated the effect of continuous and intermittent stimulations on the PLR using red and blue lights. Seventeen healthy subjects underwent continuous- and intermittent light stimuli, using red (643 nm) and blue light (463 nm). To avoid the influence of pupil size on the amount of light entering the eye, the procedures were repeated with the stimulus-eye in dilated condition. The maximal pupillary constriction and the early redilation phase of post-illumination pupillary response (PIPREarly) represented the mixed response of melanopsin and rod-cone photoreceptors. The late redilation phase of PIPR (PIPRLate) was the marker of melanopsin-containing retinal ganglion cells. Intermittent stimuli with blue light elicited significantly larger maximal contraction during dilated condition (P = 0.001), and larger sustained pupillary contraction under dilated as well as undilated condition (P < 0.001) compared to continuous light exposure. Except the PIPREarly during undilated condition, none of the PIPR metrics were significantly different between intermittent and continuous blue light stimuli. Intermittent red light stimuli elicited also a more sustained pupillary contraction regardless of mydriatic instillation (P ≤ 0.02). In addition, intermittent red light exposure resulted in a slightly larger PIPREarly under undilated condition (P = 0.02) and a slightly larger PIPRLate under dilated condition (P = 0.049). Except the PIPRLate to continuous red light stimulus, all PIPR parameters were larger when the light was presented after induction of unilateral mydriasis. PLR parameters during and after light exposures depend on both the light stimulation mode and the entrance pupillary size.

Melanopsin-Mediated Acute Light Responses Measured in Winter and in Summer: Seasonal Variations in Adults with and without Cataracts.

Seasonal adaptation is a ubiquitous behavior seen in many species on both global hemispheres and is conveyed by changing photoperiods. In humans this seasonal adaptation is less apparent, in part because changes in daylength are masked by the use of electrical lighting at night. On the other hand, cataracts which reduce light transmission, may compound seasonal changes related to the reduced daylength of winter. To better understand the effects of different photoperiod lengths in healthy adults without and with cataracts, we tested their melanopsin-mediated light responses in summer vs. winter. Fifty-two participants (mean age 67.4 years; 30 with bilateral cataracts and 22 age-matched controls with clear lenses; pseudophakes) were tested twice, once in summer and once in winter. At each test session we assessed the electroretinogram and pupil responses during daytime and we determined melatonin suppression, subjective sleepiness and mood in response to light exposure in the evening. Circadian rest-activity cycles and sleep from activity recordings were also analyzed for both seasons. Both groups had similar visual function. There were no seasonal differences in the electroretinogram. For the pupil responses to bright blue light, the post-illumination pupil response (PIPR) was greater in winter than summer in pseudophakes, but not in cataract participants, whereas melatonin suppression to acute light exposure showed no differences between both groups and seasons. Overall, intra-daily variability of rest-activity was worse in winter but participants felt sleepier and reported worse mood at the laboratory in evening time in the summer. Those with cataracts had poorer sleep quality with lower sleep efficiency, and higher activity during sleep in winter than summer. In this study, the PIPR showed a seasonal variation in which a larger response was found during winter. This variation was only detected in participants with a clear intraocular lens. In the cataract group, visual function was not impaired yet these participants showed a lack of seasonal changes in the pupil response to blue light and poorer sleep in winter. These findings raise the question for tailored lighting conditions for cataract patients in order to counter potentially deleterious effects of living with chronically lower light exposure.

Color Pupillography in Dorsal Midbrain Syndrome

The purpose of this study was to evaluate the pupil response to chromatic stimuli in patients with lesions in the dorsal midbrain and possibly gain new insights into the afferent pupillary pathways. Color pupillography was performed in 5 patients with dorsal midbrain syndrome (DMS), and their results were compared with those of 20 healthy control subjects. We used full-field red stimuli (605 nm) that primarily address the rod/cone system and blue stimuli (420 nm) that preferentially activate intrinsically photosensitive retinal ganglion cells (ipRGCs) directly, with a duration of 4 seconds and a stimulus intensity of 28 lx corneal illumination under mesopic conditions. One eye was stimulated, and the consensual pupil response was recorded and analyzed. The pupillary light reflex in patients with DMS was reduced, differed in shape, and showed a prolonged latency time compared to normal subjects. The blue response was less affected than the red response: the mean maximal relative amplitude (M) was 15.8% (SD = 7.8) in patients with DMS compared with 43.0% (SD = 5.5) in normal subjects for red stimulation, and M = 40.8%, SD = 8.4 (DMS) with M = 58.3%, SD = 4.8 (normals) for blue stimulation. The reduction was 63% for red stimulation but only 30% for blue stimulation in patients with DMS. Moreover, there was a preserved postillumination pupil response to blue stimulation in DMS patients. In DMS, the melanopsin-mediated ipRGC pathway appeared relatively preserved.

Attenuation of short wavelengths alters sleep and the ipRGC pupil response.

Exposure to increasing amounts of artificial light during the night may contribute to the high prevalence of reported sleep dysfunction. Release of the sleep hormone melatonin is mediated by the intrinsically photosensitive retinal ganglion cells (ipRGCs). This study sought to investigate whether melatonin level and sleep quality can be modulated by decreasing night-time input to the ipRGCs. Subjects (ages 17-42, n=21) wore short wavelength-blocking glasses prior to bedtime for 2weeks. The ipRGC-mediated post illumination pupil response was measured before and after the experimental period. Stimulation was presented with a ganzfeld stimulator, including one-second and five-seconds of long and short wavelength light, and the pupil was imaged with an infrared camera. Pupil diameter was measured before, during and for 60s following stimulation, and the six-second and 30s post illumination pupil response and area under the curve following light offset were determined. Subjects wore an actigraph device for objective measurements of activity, light exposure, and sleep. Saliva samples were collected to assess melatonin content. The Pittsburgh Sleep Quality Index (PSQI) was administered to assess subjective sleep quality. Subjects wore the blue-blocking glasses 3:57±1:03h each night. After the experimental period, the pupil showed a slower redilation phase, resulting in a significantly increased 30s post illumination pupil response to one-secondshort wavelength light, and decreased area under the curve for one and five-second short wavelength light, when measured at the same time of day asbaseline. Night time melatonin increased from 16.1±7.5pgmL-1 to 25.5±10.7pgmL-1 (P<0.01). Objectively measured sleep duration increased 24min, from 408.7±44.9 to 431.5±42.9min (P<0.001). Mean PSQI score improved from 5.6±2.9 to 3.0±2.2. The use of short wavelength-blocking glasses at night increased subjectively measured sleep quality and objectively measured melatonin levels and sleep duration, presumably as a result of decreased night-time stimulation of ipRGCs. Alterations in the ipRGC-driven pupil response suggest a shift in circadian phase. Results suggest that minimising short wavelength light following sunset may help in regulating sleep patterns.

The Relation Between Light-Induced Lacrimation and the Melanopsin-Driven Postillumination Pupil Response.

To investigate the chromatic characteristics and intensity-response function of light-induced reflex lacrimation and its correlation with the melanopsin-driven postillumination pupil response (PIPR). Eleven visually normal participants completed the experiment. Lacrimation was measured in one eye by placing a calibrated filter paper strip in the conjunctival sac over a 1 minute-interval (Schirmer's test) during which participants received either no light stimulation (baseline trial) or one flash of blue or red light stimuli presented binocularly with a Ganzfeld stimulator, while the pupil response was recorded simultaneously from the fellow eye by using an eye tracker. Light stimulation trials were presented in alternating fashion at seven incremental intensity steps (0.1, 1, 3.16, 10, 31.6, 100, and 400 cd/m2). Postillumination pupil response was defined as the mean pupil constriction from 10 to 30 seconds post illumination. The amount of lacrimation in response to 10 to 400 cd/m2 blue light was significantly greater than baseline and increased monotonically with increasing light intensity. Red light did not induce significant reflex lacrimation until the brightest stimulation at 400 cd/m2. There was a positive linear correlation between PIPR and lacrimation in response to blue light (r = 0.74, P < 0.001) but not to red light (r = 0.13, P = 0.25). The chromatic characteristics and intensity-response of light-induced lacrimation are highly consistent with the features of melanopsin phototransduction. This finding is the first in vivo evidence in humans, supporting the hypothesis that light-induced reflex lacrimation is mediated primarily by melanopsin photoactivity, and provides new insight into the putative mechanisms of photophobia.

Intrinsically Photosensitive Retinal Ganglion Cell Function, Sleep Efficiency and Depression in Advanced Age-Related Macular Degeneration.

Melanopsin expressing intrinsically photosensitive retinal ganglion cells (ipRGC) input to multiple brain regions including those for pupil control, circadian rhythms, sleep and mood regulation. Here we measured ipRGC function and its relationship to sleep quality and depression in patients with advanced AMD. The melanopsin-mediated post-illumination pupil response (PIPR) was measured in 53 patients with advanced AMD (age 78.8 ± 8.8 years) and in 20 healthy controls (age 72.5 ± 3.3 years). Sleep quality and efficiency was assessed using the Pittsburgh Sleep Quality Index (PSQI). Risk of depression was determined using the Center for Epidemiologic Studies Depression questionnaire. The group with AMD showed significantly reduced pupil constrictions (P = 0.039); PIPR amplitudes (P = 0.003); global sleep scores (P = 0.01); and higher levels of depression (P < 0.001) than the control group. There was a significant correlation between the PIPR amplitude and global sleep score in the AMD group (P = 0.01). The amplitude of PIPR significantly correlated with sleep efficiency (P = 0.008; regression, P = 0.01, R2 = 0.13), but not sleep quality (P = 0.23) in the AMD group. There was no correlation between PIPR and depression scores. Intrinsically photosensitive RGC dysfunction in advanced AMD contributes to the observed reduction in sleep efficiency. The correlation between the melanopsin-mediated PIPR and sleep may indicate reduced photic input to the suprachiasmatic nucleus and ventrolateral preoptic area due to ipRGC dysfunction in AMD.

The Preferential Impairment of Pupil Constriction Stimulated by Blue Light in Patients with Type 2 Diabetes without Autonomic Neuropathy.

The main aim of the present paper is to examine whether the pupillary light reflex (PLR) mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs) is impaired in type 2 diabetic patients. One hundred and three diabetic patients without diabetic autonomic neuropathy (DAN) and 42 age-matched controls underwent a series of detailed neurological examinations. The patients were stratified into three groups: stage I, no neuropathy; stage II, asymptomatic neuropathy; stage III, symptomatic but without DAN. The PLR to 470 and 635 nm light at 20 cd/m2 was recorded. Small fiber neuropathy was assessed by corneal confocal microscopy and quantifying corneal nerve fiber (CNF) morphology. The 470 nm light induced a stronger and faster PLR than did 635 nm light in all subjects. The PLR to both lights was impaired equally across all of the diabetic subgroups. The postillumination pupil response (PIPR) after 470 nm light offset at ≥1.7 sec was attenuated in diabetic patients without differences between subgroups. Receiver operating characteristic analysis revealed that the PIPR mediated by ipRGCs in patients with stage II and stage III neuropathy was different from that of the control subjects. Clinical factors, nerve conduction velocity, and CNF measures were significantly correlated with PLR parameters with 470 nm light. PLR kinetics were more impaired by stimulation with blue light than with red light in diabetic patients without DAN.

The Effects of Short-Term Light Adaptation on the Human Post-Illumination Pupil Response.

We determine the effect of short-term light adaptation on the pupil light reflex and the melanopsin mediated post-illumination pupil response (PIPR). Inner and outer retinal photoreceptor contributions to the dark-adapted pupil response were estimated. In Experiment A, light adaptation was studied using short wavelength lights ranging from subthreshold to suprathreshold irradiances for melanopsin signaling that were presented before (5-60 seconds) and after (30 seconds) a melanopsin-exciting stimulus pulse. We quantified the pupil constriction and the poststimulus response amplitudes during dark (PIPR) and light (poststimulus pupil response, PSPR) adaptation. In Experiment B, colored prestimulus adapting lights were univariant for melanopsin or rod excitation. Increasing the prestimulus duration and irradiance of adapting lights increased the pupil constriction amplitude when normalized to the dark-adapted baseline but reduced its amplitude when normalized to the light-adapted baseline. Light adaptation at irradiances suprathreshold for melanopsin activation increased the PIPR amplitude, with larger changes at longer adaptation durations, whereas the PSPR amplitude became more attenuated with increasing irradiances, independent of duration. Rod versus melanospin univariant adaptation did not alter the constriction amplitude but increased the PIPR amplitude in the rod condition. Correlations between millimeter pupil constriction and PIPR amplitudes were eliminated when normalized to the baseline diameter. The findings have implications for standardizing light adaptation paradigms and the choice of pupil metrics in both laboratory and clinical settings. Light and dark adaptation have opposite effects on the pupil metrics, which should be normalized to baseline to minimize significant correlations between constriction and PIPR amplitudes.

Analysis of retinal function using chromatic pupillography in retinitis pigmentosa and the relationship to electrically evoked phosphene thresholds.

To analyse pupil responses to specific chromatic stimuli in patients with advanced retinitis pigmentosa (RP) to ascertain whether chromatic pupillography can be used as an objective marker for residual retinal function. To examine correlations between parameters of the pupil response and the perception threshold of electrically evoked phosphenes. Chromatic pupillography was performed in 40 patients with advanced RP (visual acuity<0.02 or visual field ≤5°, non-recordable ERGs) and 40 age-matched healthy subjects. Pupil responses to full-field red (605nm) and blue (420nm) stimuli of 28 lx corneal illumination were recorded and analysed for two stimulus durations (1 and 4seconds). The perception threshold of phosphenes to transcorneal electrostimulation was ascertained and correlated to the pupil responses and visual acuity. Patients with RP showed significantly reduced pupil responses to red and blue stimuli compared with the controls. With red stimuli, pupillary escape could be observed; blue stimuli resulted in a well-preserved postillumination pupil response. Phosphene thresholds were significantly increased in patients with RP and correlated with the parameters of the pupil response if all subjects were considered. Within the RP group alone, this relationship was less pronounced and statistically not significant. Chromatic pupillography demonstrated a significant decrease in outer retinal photoreceptor responses but a persisting and disinhibited intrinsic photosensitive retinal ganglion cell function in advanced RP. These phenomena may be useful as an objective marker for the efficacy of any interventional treatment for hereditary retinal diseases as well as for the selection of suitable patients for an electronic retinal implant.

Quadrant Field Pupillometry Detects Melanopsin Dysfunction in Glaucoma Suspects and Early Glaucoma.

It is difficult to detect visual function deficits in patients at risk for glaucoma (glaucoma suspects) and at early disease stages with conventional ophthalmic tests such as perimetry. To this end, we introduce a novel quadrant field measure of the melanopsin retinal ganglion cell mediated pupil light response corresponding with typical glaucomatous arcuate visual field defects. The melanopsin-mediated post-illumination pupil response (PIPR) was measured in 46 patients with different stages of glaucoma including glaucoma suspects and compared to a healthy group of 21 participants with no disease. We demonstrate that the superonasal quadrant PIPR differentiated glaucoma suspects and early glaucoma patients from controls with fair (AUC = 0.74) and excellent (AUC = 0.94) diagnostic accuracy, respectively. The superonasal PIPR provides a linear functional correlate of structural retinal nerve fibre thinning in glaucoma suspects and early glaucoma patients. This first report that quadrant PIPR stimulation detects melanopsin dysfunction in patients with early glaucoma and at pre-perimetric stages may have future implications in treatment decisions of glaucoma suspects.

Individual Differences in the Post-Illumination Pupil Response to Blue Light: Assessment without Mydriatics.

Melanopsin-containing retinal ganglion cells play an important role in the non-image forming effects of light, through their direct projections on brain circuits involved in circadian rhythms, mood and alertness. Individual differences in the functionality of the melanopsin-signaling circuitry can be reliably quantified using the maximum post-illumination pupil response (PIPR) after blue light. Previous protocols for acquiring PIPR relied on the use of mydriatics to dilate the light-exposed eye. However, pharmacological pupil dilation is uncomfortable for the participants and requires ophthalmological expertise. Hence, we here investigated whether an individual’s maximum PIPR can be validly obtained in a protocol that does not use mydriatics but rather increases the intensity of the light stimulus. In 18 participants (5 males, mean age ± SD: 34.6 ± 13.6 years) we evaluated the PIPR after exposure to intensified blue light (550 µW/cm2) provided to an undilated dynamic pupil. The test-retest reliability of the primary PIPR outcome parameter was very high, both between day-to-day assessments (Intraclass Correlation Coefficient (ICC) = 0.85), as well as between winter and summer assessments (ICC = 0.83). Compared to the PIPR obtained with the use of mydriatics and 160 µW/cm2 blue light exposure, the method with intensified light without mydriatics showed almost zero bias according to Bland-Altman plots and had moderate to strong reliability (ICC = 0.67). In conclusion, for PIPR assessments, increasing the light intensity is a feasible and reliable alternative to pupil dilation to relieve the participant’s burden and to allow for performance outside the ophthalmological clinic.

Rhodopsin and Melanopsin Contributions to the Early Redilation Phase of the Post-Illumination Pupil Response (PIPR).

Melanopsin expressing intrinsically photosensitive Retinal Ganglion Cells (ipRGCs) entirely control the post-illumination pupil response (PIPR) from 6 s post-stimulus to the plateau during redilation after light offset. However, the photoreceptor contributions to the early redilation phase of the PIPR (< 6 s post-stimulus) have not been reported. Here, we evaluated the photoreceptor contributions to the early phase PIPR (0.6 s to 5.0 s) by measuring the spectral sensitivity of the criterion PIPR amplitude in response to 1 s light pulses at five narrowband stimulus wavelengths (409, 464, 508, 531 and 592 nm). The retinal irradiance producing a criterion PIPR was normalised to the peak and fitted by either a single photopigment nomogram or the combined melanopsin and rhodopsin spectral nomograms with the +L+M cone photopic luminous efficiency (Vλ) function. We show that the PIPR spectral sensitivity at times ≥ 1.7 s after light offset is best described by the melanopsin nomogram. At times < 1.7 s, the peak PIPR sensitivity shifts to longer wavelengths (range: 482 to 498 nm) and is best described by the combined photoreceptor nomogram, with major contributions from melanopsin and rhodopsin. This first report of melanopsin and rhodopsin contributions to the early phase PIPR is in line with the electrophysiological findings of ipRGC and rod signalling after the cessation of light stimuli and provides a cut-off time for isolating photoreceptor specific function in healthy and diseased eyes.

The absence of attenuating effect of red light exposure on pre-existing melanopsin-driven post-illumination pupil response

It has been proposed that after activation by blue light, activated melanopsin is converted back to its resting state by long wavelength red light exposure, a putative mechanism of melanopsin chromophore recovery in vivo. We tested this hypothesis by investigating whether red light attenuates the ongoing post-illumination pupil response (PIPR) induced by melanopsin-activating blue light. Pupillary light responses were tested using “Blue+Red” double flashes and “Blue Only” single flash stimuli in 10 visually normal subjects. For “Blue+Red” conditions, PIPR was induced with an intense blue flash, followed by experimental red light exposure of variable intensity and duration (Experiment 1) immediately or 9s after the offset of the blue flash (Experiment 2). For “Blue Only” conditions, only the PIPR-inducing blue stimuli were presented (reference condition). PIPR was defined as the mean pupil size from 10 to 30s (Experiment 1) and from 25 to 60s (Experiment 2) after the offset of blue light stimuli. The results showed that PIPR from “Blue+Red” conditions did not differ significantly from those of “Blue Only” conditions (p=0.55) in Experiment 1. The two stimulation conditions also did not differ in Experiment 2 (p=0.38). We therefore conclude that red light exposure does not alter the time course of PIPR induced by blue light. This finding does not support the hypothesis that long wavelength red light reverses activated melanopsin; rather it lends support to the hypothesis that the wavelengths of stimuli driving both the forward and backward reactions of melanopsin may be similar.

Melanopsin-mediated post-illumination pupil response in the peripheral retina.

Intrinsically photosensitive retinal ganglion cells (ipRGCs) regulate pupil size by integrating extrinsic rod and cone signals with intrinsic melanopsin-mediated phototransduction. Light adapted pupil diameter is determined by the corneal flux density (CFD), and for central visual field stimulation the melanopsin-mediated post-illumination pupil response (PIPR) follows this same CFD relationship. Rods, cones, and ipRGCs vary in size, density, and distribution across the retina, but how these differences affect the amplitude and timing of the extrinsic and intrinsic pupil light reflex in the central and peripheral retina is unknown. We determined the relationship between stimulus area and photon flux with stimuli constant for CFD, irradiance, or area at central (0°) and peripheral (20°) eccentricities with high and low melanopsin excitation. We show that the pupil constriction amplitude was similar at both eccentricities and the time to minimum diameter increased as melanopsin excitation increased. In contrast, the peripheral PIPR follows a CFD relationship but with lower amplitude compared with that at the fovea. This indicates differences in the spatial and temporal characteristics of extrinsic and intrinsic ipRGC inputs to the pupil control pathway for the central and peripheral retina. The eccentricity-dependent change in PIPR amplitude may be analogous to the hill of vision observed in visual perimetry; such knowledge is an important precursor to the development of pupil perimetry paradigms to measure the PIPR in select regions of the visual field.

Individual Differences in Sleep Timing Relate to Melanopsin-Based Phototransduction in Healthy Adolescents and Young Adults.

Individual differences in sleep timing have been widely recognized and are of particular relevance in adolescents and young adults who often show mild to severely delayed sleep. The biological mechanisms underlying the between-subject variance remain to be determined. Recent human genetics studies showed an association between sleep timing and melanopsin gene variation, but support for functional effects on downstream pathways and behavior was not demonstrated before. We therefore investigated the association between the autonomic (i.e., pupil diameter) and behavioral (i.e., sleep timing) readouts of two different downstream brain areas, both affected by the same melanopsin-dependent retinal phototransduction: the olivary pretectal nucleus (OPN) and the suprachiasmatic nucleus (SCN). Our study population included 71 healthy individuals within an age range with known vulnerability to a delayed sleep phase (16.8-35.7 y, 37 males, 34 females). Pupillometry was performed to estimate functionality of the intrinsic melanopsin-signaling circuitry based on the OPN-mediated post-illumination pupil response (PIPR) to blue light. Sleep timing was quantified by estimating the SCN-mediated mid-sleep timing in three different ways in parallel: using a chronotype questionnaire, a sleep diary, and actigraphy. All three measures consistently showed that those individuals with a later mid-sleep timing had a more pronounced PIPR (0.03 < P < 0.05), indicating a stronger blue-light responsiveness of the intrinsic melanopsin-based phototransduction circuitry. Trait-like individual differences in the melanopsin phototransduction circuitry contribute to individual differences in sleep timing. Blue light-sensitive young individuals are more prone to delayed sleep.

Pupillary responses driven by ipRGCs and classical photoreceptors are impaired in glaucoma.

The aim was to investigate the involvement of intrinsically photosensitive retinal ganglion cells (ipRGCs) in patients with manifest glaucoma and ocular hypertension (OH) using specific parameters of the pupil light reflex to chromatic stimuli. Twenty-five patients with manifest glaucoma, 16 patients with OH and 16 healthy control subjects were stimulated with 28lx red (605nm) or blue (420nm) light with a duration of either 1s or 4s. The consensual pupil light reaction was recorded by means of infrared pupillometry. The maximal relative amplitude (MRA), the post-illumination pupil response PIPRblue-red, and the slope of the response during exposure to the 4s red stimulus (SORRS) were calculated and compared using ANOVA and Tukey-Kramer post-hoc tests. Correlations between pupil parameters and visual field defects were analyzed using Pearson correlation coefficient r. PIPRblue-red was reduced in glaucoma patients compared to normals (p < 0.001) and OH (p < 0.01). There was no significant difference between OH and normals. Glaucoma patients showed additionally reduced MRA for red and blue light (p < 0.05) and a pupillary escape during exposure to red light (increased SORRS, p < 0.0005). This pupillary escape could also be seen in single subjects with OH. Significant correlations between pupil parameters and visual field defects were detected. The reduced PIPRblue-red indicates a characteristic impairment of the melanopsin-driven pathway of ipRGCs in glaucoma patients, whereas the reduced MRA and increased SORRS suggest a disturbed synaptic function and altered interaction between outer photoreceptors, RGCs, and ipRGCs.

Melanopsin-Mediated Post-Illumination Pupil Response in Early Age-Related Macular Degeneration.

To determine whether melanopsin-expressing intrinsically photosensitive retinal ganglion cell (ipRGC) inputs to the pupil light reflex (PLR) are affected in early age-related macular degeneration (AMD). The PLR was measured in 40 participants (20 early AMD and 20 age-matched controls) using a custom-built Maxwellian view pupillometer. Sinusoidal stimuli (0.5 Hz, 11.9 seconds duration, 35.6° diameter) were presented to the study eye and the consensual pupil response was measured to lights with high melanopsin excitation (464 nm [blue]) and with low melanopsin excitation (638 nm [red]) that biased activation to the outer retina. Two melanopsin PLR metrics were quantified: the phase amplitude percentage (PAP) during the sinusoidal stimulus presentation and the post-illumination pupil response (PIPR). The PLR during stimulus presentation was analyzed using latency to constriction, the transient pupil response and maximum pupil constriction metrics. Diagnostic accuracy was evaluated using receiver operating characteristic (ROC) curves. The blue PIPR was significantly less sustained in the early AMD group (P < 0.001). The red PIPR was not significantly different between groups (P > 0.05). The PAP and blue stimulus constriction amplitude were significantly lower in the early AMD group (P < 0.05). There was no significant difference between groups in the latency or transient amplitude for both stimuli (P > 0.05). ROC analysis showed excellent diagnostic accuracy for the blue PIPR metrics (area under the curve > 0.9). This is the initial report that the melanopsin-controlled PIPR is dysfunctional in early AMD. The noninvasive, objective measurement of the ipRGC controlled PIPR has excellent diagnostic accuracy for early AMD.