Dark adaptation-induced changes in rod, cone and intrinsically photosensitive retinal ganglion cell (ipRGC) sensitivity differentially affect the pupil light response (PLR)

A multimodal imaging approach to investigate retinal oxygen and vascular dynamics, and neural dysfunction in bietti crystalline dystrophy

BACKGROUND

This study aimed to explore retinal changes in Bietti crystalline dystrophy (BCD) patients, including retinal metabolism, blood flow, vascular remodeling, and pupillary light reflex (PLR) abnormalities.

METHODS

This cross-sectional study included 120 eyes from BCD patients and 120 eyes from healthy controls, utilizing a multimodal imaging system (MEFIAS 3200, SYSEYE, Chongqing, China) to evaluate retinal oxygenation, blood flow, vascular structure, and PLR. Measurements included oxygen saturation, blood flow velocity, vessel diameters, and pulsatility metrics. PLR parameters were assessed under specific light stimuli.

RESULTS

BCD patients demonstrated significantly higher retinal oxygen saturation and content, but lower oxygen utilization and metabolism compared to controls, with more pronounced declines in those over 40 years old. Vascular parameters revealed smaller external diameters and larger lumen diameters, indicating vascular remodeling. Retinal blood flow was lower, while the resistivity index was higher in BCD patients. Additionally, PLR abnormalities were noted, including reduced constriction amplitude, pupil constriction ratio, constriction duration, and maximum constriction velocity, along with prolonged latency were observed in BCD patients.

CONCLUSION

BCD patients had significant retinal and vascular changes, along with PLR impairments, especially in patients over 40. More targeted interventions should be focused in future research.

Altered pupil light and darkness reflex and eye-blink responses in late-life depression

BACKGROUND

Late-life depression (LLD) is a prevalent neuropsychiatric disorder in the older population. While LLD exhibits high mortality rates, depressive symptoms in older adults are often masked by physical health conditions. In younger adults, depression is associated with deficits in pupil light reflex and eye blink rate, suggesting the potential use of these responses as biomarkers for LLD.

METHODS

We conducted a study using video-based eye-tracking to investigate pupil and blink responses in LLD patients (n = 25), older (OLD) healthy controls (n = 29), and younger (YOUNG) healthy controls (n = 25). The aim was to determine whether there were alterations in pupil and blink responses in LLD compared to both OLD and YOUNG groups.

RESULTS

LLD patients displayed significantly higher blink rates and dampened pupil constriction responses compared to OLD and YOUNG controls. While tonic pupil size in YOUNG differed from that of OLD, LLD patients did not exhibit a significant difference compared to OLD and YOUNG controls. GDS-15 scores in older adults correlated with light and darkness reflex response variability and blink rates. PHQ-15 scores showed a correlation with blink rates, while MoCA scores correlated with tonic pupil sizes.

CONCLUSIONS

The findings demonstrate that LLD patients display altered pupil and blink behavior compared to OLD and YOUNG controls. These altered responses correlated differently with the severity of depressive, somatic, and cognitive symptoms, indicating their potential as objective biomarkers for LLD.

Chromatic Pupillometry as a Putative Screening Tool for Heritable Retinal Disease in Rhesus Macaques

Purpose

Non-human primates (NHPs) are useful models for human retinal disease. Chromatic pupillometry has been proposed as a noninvasive method of identifying inherited retinal diseases (IRDs) in humans; however, standard protocols employ time-consuming dark adaptation. We utilized shortened and standard dark-adaptation protocols to compare pupillary light reflex characteristics following chromatic stimulation in rhesus macaques with achromatopsia to wild-type (WT) controls with normal retinal function.

Methods

Nine rhesus macaques homozygous for the p.R656Q mutation (PDE6C HOMs) and nine WT controls were evaluated using chromatic pupillometry following 1-minute versus standard 20-minute dark adaptations. The following outcomes were measured and compared between groups: pupil constriction latency, peak constriction, pupil constriction time, and constriction velocity.

Results

Pupil constriction latency was significantly longer in PDE6C HOMs with red-light (P = 0.0002) and blue-light (P = 0.04) stimulation versus WT controls. Peak constriction was significantly less in PDE6C HOMs with all light stimulation compared to WT controls (P < 0.0001). Pupil constriction time was significantly shorter in PDE6C HOMs versus WT controls with red-light (P = 0.04) and white-light (P = 0.003) stimulation. Pupil constriction velocity was significantly slower in PDE6C HOMs versus WT controls with red-light (P < 0.0001), blue-light (P < 0.0001), and white-light (P = 0.0002) stimulation. Dark adaptation time only significantly affected peak (P = 0.008) and time of pupil constriction (P = 0.02) following blue-light stimulation.

Conclusions

Chromatic pupillometry following 1- and 20-minute dark adaptation is an effective tool for screening NHPs for achromatopsia.

Translational Relevance

Rapid identification of NHPs with IRDs will provide animal research models to advance research and treatment of achromatopia in humans.

[Assessment of a pupillometric method for the screening of glaucoma]

BACKGROUND

Glaucoma is a progressive optic neuropathy, remaining asymptomatic for a long time, which makes its early diagnosis difficult. Visual field testing is still the gold standard but is less than ideal. The goal of this study is to assess a pupillometric test, administered passively to the subject for one minute, to measure its sensitivity and specificity in the classification of healthy eyes and glaucomatous eyes, and to evaluate its tolerability compared to visual field testing.

METHODS

Forty-five participants were included in this single-center, interventional, prospective study. They underwent 3 monocular pupillometric tests with light stimulation: 6 pupillary responses were recorded during full-field multifocal stimulation (performed twice) and pupillary hippus cycle study.

RESULTS

Analysis of spectral power and pupillary measurements with full-field multifocal stimulation provides a 0.94 sensitivity and a 0.88 specificity, a virtually perfect discrimination for early stages of glaucoma. Analysis of pupil cycle time provides a 0.92 sensitivity and a 0.88 specificity for early stages. Acceptability of this test by patients is superior to visual field testing.

CONCLUSION

These results show that data from our pupillometric recordings provide a good classification of healthy and glaucomatous eyes and must be confirmed on a larger population.

Development and Implementation of a Handheld Pupillometer for Detection of Optic Neuropathies

Purpose: Quantitative pupillometry has utility in research settings for measuring optic nerve and autonomic function. We configured a portable device to perform quantitative pupillometry with application to detecting unilateral optic neuropathies in the clinical setting.Materials & methods: Light stimuli were delivered, and pupil diameter responses recorded using customized software implemented on a commercial portable electroretinography device. Increasing pupillary constriction occurred with increasing duration and intensity of full field blue light (470 nm) stimuli in healthy subjects. Flashes of 1 s dim (50 cd/m2) and bright (316 cd/m2) blue light were administered to both eyes of subjects with unilateral optic neuropathies (n = 10) and controls (n = 5). Maximum pupillary constriction (Cmax) for each stimulus was compared between control eyes and optic neuropathy eyes. Cmax for the inter-eye difference curve (Cdiffmax) was compared between control and optic neuropathy subjects.Results: The pupil protocol lasted 15 minutes and was well tolerated by subjects. Cmax for bright and dim stimuli was reduced in eyes with optic neuropathy compared to fellow and control eyes (p < .0005 for all). Inter-eye Cdiffmax was larger in optic neuropathy subjects than control subjects for both dim and bright stimuli (p = .002, <0.0005). There was no overlap between groups for Cmax and Cdiffmax for either stimulus.Conclusions: A portable pupillometer was implemented on a commercial portable electroretinography platform and applied in a pilot manner to subjects with and without unilateral optic neuropathies. Optic neuropathy eyes were distinguished from non-optic neuropathy eyes both within and between subjects.

Intrinsically photosensitive retinal ganglion cell-driven pupil responses in patients with traumatic brain injury

Previous findings regarding intrinsically photosensitive retinal ganglion cell (ipRGC) function after traumatic brain injury (TBI) are conflicting. We examined ipRGC-driven pupil responses in civilian TBI and control participants using two pupillography protocols that assessed transient and adaptive properties: (1) a one second (s) long wavelength "red" stimulus (651 nm, 133 cd/m²) and 10 increasing intensities of 1 s short wavelength "blue" stimuli (456 nm, 0.167 to 167 cd/m²) with a 60 s interstimulus interval, and (2) two minutes of 0.1 Hz red stimuli (33 cd/m²), followed by two minutes of 0.1 Hz blue stimuli (16 cd/m²). For Protocol 1, constriction amplitude and the 6 s post illumination pupil response (PIPR) were calculated. For Protocol 2, amplitudes and peak velocities of pupil constriction and redilation were calculated. For Protocol 1, constriction amplitude and the 6 s PIPR were not significantly different between TBI patients and control subjects for red or blue stimuli. For Protocol 2, pupil constriction amplitude attenuated over time for red stimuli and potentiated over time for blue stimuli across all subjects. Constriction and redilation velocities were similar between groups. Pupil constriction amplitude was significantly less in TBI patients compared to control subjects for red and blue stimuli, which can be attributed to age-related differences in baseline pupil size. While TBI, in addition to age, may have contributed to decreased baseline pupil diameter and constriction amplitude, responses to blue stimulation suggest no selective damage to ipRGCs.

Quantification of the early pupillary dilation kinetic to assess rod and cone activity

Rods, cones and melanopsin contribute in various proportions, depending on the stimulus light, to the pupil light response. This study used a first derivative analysis to focus on the quantification of the dynamics of pupillary dilation that immediately follows light-induced pupilloconstriction in order to identify novel parameters that reflect rod and cone activity. In 18 healthy adults, the pupil response to a 1 s blue light stimulus ranging from − 6.0 to 2.65 log cd/m² in dark-adapted conditions and to a 1 s blue light stimulus (2.65 log cd/m²) in light-adapted conditions was recorded on a customized pupillometer. Three derivative parameters which describe the 2.75 s following the light onset were quantified: dAMP (maximal amplitude of the positive peak), dLAT (latency of the positive peak), dAUC (area under the curve of the positive peak). We found that dAMP and dAUC but not dLAT have graded responses over a range of light intensities. The maximal positive value of dAMP, representing maximal rate of change of early pupillary dilation phase, occurs at − 1.0 log cd/m² and this stimulus intensity appears useful for activating rods and cones. From − 0.5 log cd/m² to brighter intensities dAMP and dAUC progressively decrease, reaching negligible values at 2.65 log cd/m² indicative of a melanopsin-driven pupil response that masks the contribution from rods and cones to the early phase of pupillary dilation.

Pupillary light reflex as a diagnostic aid from computational viewpoint: A systematic literature review

This work presents a detailed and complete review of publications on pupillary light reflex (PLR) used to aid diagnoses. These are computational techniques used in the evaluation of pupillometry, as well as their application in computer-aided diagnoses (CAD) of pathologies or physiological conditions that can be studied by observing the movements of miosis and mydriasis of the human pupil. A careful survey was carried out of all studies published over the last 10 years which investigated, electronic devices, recording protocols, image treatment, computational algorithms and the pathologies related to PLR. We present the frontier of existing knowledge regarding methods and techniques used in this field of knowledge, which has been expanding due to the possibility of performing diagnoses with high precision, at a low cost and with a non-invasive method.

Effects of Narrowband Light on Choroidal Thickness and the Pupil

Purpose

To determine the effects of narrowband light exposure on choroidal thickness and the pupil response in humans.

Methods

Twenty subjects, ages 21 to 43 years, underwent 1 hour of exposure to broadband, short wavelength “blue,” or long wavelength “red” light, or darkness. Choroidal thickness, imaged with spectral domain optical coherence tomography, axial length, determined from biometry, and rod/cone- and intrinsically photosensitive retinal ganglion cell-driven pupil responses were measured before and after exposure. Pupil stimuli were six 1 second alternating red (651 nm) and blue (456 nm) stimuli, 60 seconds apart. Pupil metrics included maximum constriction and the 6 second post-illumination pupil response (PIPR).

Results

Compared with before exposure, the choroid significantly thinned after broadband light, red light, and dark exposure (all P < 0.05), but not after blue light exposure (P = 0.39). The maximum constriction to 1 second red stimuli significantly decreased after all light exposures (all P < 0.001), but increased after dark exposure (P = 0.02), compared with before exposure. Maximum constriction and 6-second PIPR to 1 second blue stimuli significantly decreased after all light exposures compared with before exposure (all P < 0.005), with no change after dark exposure (P > 0.05). There were no differences in axial length change or 6-second PIPR to red stimuli between exposures.

Conclusions

Narrowband blue and red light exposure induced differential changes in choroidal thickness. Maximum constriction, a function of rod/cone activity, and the intrinsically photosensitive retinal ganglion cell-mediated PIPR were attenuated after all light exposures. Findings demonstrate differing effects of short-term narrowband light and dark exposure on the choroid, rod/cone activity, and intrinsically photosensitive retinal ganglion cells.

A Review of Silent Substitution Devices for Melanopsin Stimulation in Humans

One way to study the specific response of the non-visual melanopsin photoreceptors of the human eye is to silence the response of cones and rods. Melanopsin photoreceptors (ipRGC), highlighted in the early 2000s, are intimately linked to the circadian rhythm and therefore to our sleep and wakefulness. Rest and sleep regulation, health and cognitive functions are all linked to ipRGC and play an important role in work and human relationships. Thus, we believe that the study of ipRGC responses is important.We searched and reviewed scientific articles describing instrumentation dedicated to these studies. PubMed lists more than 90,000 articles created since the year 2000 that contain the word circadian but only 252 with silent substitution. In relation to melanopsin, we found 39 relevant articles from which only 11 give a device description for humans, which is incomplete in most cases. We did not find any consensus for light intensity description, melanopsin contrast, sequences of melanopsin light stimulation and optical setup to expose the retina to the light.

The Role of Daylight for Humans: Gaps in Current Knowledge

Daylight stems solely from direct, scattered and reflected sunlight, and undergoes dynamic changes in irradiance and spectral power composition due to latitude, time of day, time of year and the nature of the physical environment (reflections, buildings and vegetation). Humans and their ancestors evolved under these natural day/night cycles over millions of years. Electric light, a relatively recent invention, interacts and competes with the natural light-dark cycle to impact human biology. What are the consequences of living in industrialised urban areas with much less daylight and more use of electric light, throughout the day (and at night), on general health and quality of life? In this workshop report, we have classified key gaps of knowledge in daylight research into three main groups: (I) uncertainty as to daylight quantity and quality needed for "optimal" physiological and psychological functioning, (II) lack of consensus on practical measurement and assessment methods and tools for monitoring real (day) light exposure across multiple time scales, and (III) insufficient integration and exchange of daylight knowledge bases from different disciplines. Crucial short and long-term objectives to fill these gaps are proposed.

Adaptation time, electroretinography, and pupillography in healthy subjects

PURPOSE

To investigate the relationship between adaptation time and the parameters of electroretinography (ERG) and pupillography in healthy subjects.

METHODS

Forty-six eyes of 23 healthy women (mean age 21.7 years) were enrolled. ERG and pupillography were tested in each of the right and left 23 eyes, respectively. ERG with a skin electrode was used to determine amplitude and implicit time by the records of rod-, flash-, cone-, and flicker-responses with white light (0.01-30 cd s/m²). Infrared pupillography was used to record the pupillary light reflex to 1-s stimulation of red light (100 cd/m²). Cone- and flicker- (rod-, flash- and pupil) responses were recorded after light (dark) adaptation at 1, 5, 10, 15, and 20 min.

RESULTS

Amplitude (µV) was significantly different between 1 min and ≥ 5 or ≥ 10 min after adaptation in b-wave of cone- or rod-response, respectively. Implicit time (ms) differed significantly between 1 min and ≥ 5 min after adaptation with b-wave of cone- and rod-response. There were significant differences between 1 min and ≥ 10 or ≥ 5 min after dark adaptation in parameter of minimum pupil diameter (mm) or constriction rate (%), respectively.

CONCLUSIONS

Cone-driven ERG can be recorded, even in 5 min of light adaptation time without any special light condition, whereas rod-driven ERG and pupillary response results can be obtained in 10 min or longer of dark adaptation time in complete darkness.

Standards in Pupillography

The number of research groups studying the pupil is increasing, as is the number of publications. Consequently, new standards in pupillography are needed to formalize the methodology including recording conditions, stimulus characteristics, as well as suitable parameters of evaluation. Since the description of intrinsically photosensitive retinal ganglion cells (ipRGCs) there has been an increased interest and broader application of pupillography in ophthalmology as well as other fields including psychology and chronobiology. Color pupillography plays an important role not only in research but also in clinical observational and therapy studies like gene therapy of hereditary retinal degenerations and psychopathology. Stimuli can vary in size, brightness, duration, and wavelength. Stimulus paradigms determine whether rhodopsin-driven rod responses, opsin-driven cone responses, or melanopsin-driven ipRGC responses are primarily elicited. Background illumination, adaptation state, and instruction for the participants will furthermore influence the results. This standard recommends a minimum set of variables to be used for pupillography and specified in the publication methodologies. Initiated at the 32nd International Pupil Colloquium 2017 in Morges, Switzerland, the aim of this manuscript is to outline standards in pupillography based on current knowledge and experience of pupil experts in order to achieve greater comparability of pupillographic studies. Such standards will particularly facilitate the proper application of pupillography by researchers new to the field. First we describe general standards, followed by specific suggestions concerning the demands of different targets of pupil research: the afferent and efferent reflex arc, pharmacology, psychology, sleepiness-related research and animal studies.

Chromatic Pupillometry Methods for Assessing Photoreceptor Health in Retinal and Optic Nerve Diseases

The pupillary light reflex is mediated by melanopsin-containing intrinsically-photosensitive retinal ganglion cells (ipRGCs), which also receive input from rods and cones. Melanopsin-dependent pupillary light responses are short-wavelength sensitive, have a higher threshold of activation, and are much slower to activate and de-activate compared with rod/cone-mediated responses. Given that rod/cone photoreceptors and melanopsin differ in their response properties, light stimuli can be designed to stimulate preferentially each of the different photoreceptor types, providing a read-out of their function. This has given rise to chromatic pupillometry methods that aim to assess the health of outer retinal photoreceptors and ipRGCs by measuring pupillary responses to blue or red light stimuli. Here, we review different types of chromatic pupillometry protocols that have been tested in patients with retinal or optic nerve disease, including approaches that use short-duration light exposures or continuous exposure to light. Across different protocols, patients with outer retinal disease (e.g., retinitis pigmentosa or Leber congenital amaurosis) show reduced or absent pupillary responses to dim blue-light stimuli used to assess rod function, and reduced responses to moderately-bright red-light stimuli used to assess cone function. By comparison, patients with optic nerve disease (e.g., glaucoma or ischemic optic neuropathy, but not mitochondrial disease) show impaired pupillary responses during continuous exposure to bright blue-light stimuli, and a reduced post-illumination pupillary response after light offset, used to assess melanopsin function. These proof-of-concept studies demonstrate that chromatic pupillometry methods can be used to assess damage to rod/cone photoreceptors and ipRGCs. In future studies, it will be important to determine whether chromatic pupillometry methods can be used for screening and early detection of retinal and optic nerve diseases. Such methods may also prove useful for objectively evaluating the degree of recovery to ipRGC function in blind patients who undergo gene therapy or other treatments to restore vision.

Correlation between Transient Pupillary Light Reflex and Retinal Function Impairment in Patients with Retinitis Pigmentosa

Purpose

To investigate the relationship between transient pupillary light reflex (PLR) and visual function in patients with retinitis pigmentosa (RP).

Methods

A retrospective study was performed with 137 eyes of 73 patients with RP. Transient pupillary light reflex was measured by the vision monitor system (MonColor; Metrovision, France). Dark-adapted transient PLRs were elicited by four specific levels of stimulus luminance (−5, −3, −1, and 0 log cd/m², blue or white light). Best-corrected visual acuity (BCVA) was recorded based on Early Treatment Diabetic Retinopathy Study (ETDRS) acuity charts. Fixation stability and retinal sensitivity of radial 10° areas were measured with microperimetry. The retinal sensitivity (RS) was divided into central RS (fovea and radial 1° areas) and peripheral RS (radial 3° and 5° areas from the fovea). The patients were further classified into 2 groups (P1 > 75% and P1 < 75%) according to fixation stability. Spearman's correlation was performed to identify significant associations between BCVA, fixation stability, RS, and PLR.

Results

Under the stimuli of the same color light, relative pupillary constriction (RPC), latency, or velocity of constriction in the same patients was statistically different in multiple luminance, respectively. Under the same luminance, blue light induced greater RPC and velocity (except for −3 log cd/m²) than white light. Most patients showed varying degrees of threshold elevation and visual function deficiency. Besides, there was a statistically significant difference in the distribution of BCVA, MRS, or fixation stability under different thresholds. The correlation between pupillary constrictive area (PCA) and retinal sensitivity was mainly determined by the peripheral region. Moreover, patients with stable fixation showed a greater correlation between PCA and RS.

Conclusion

PLR induced by specific colors and luminance may serve as a promising clinical approach for assessing and monitoring rod function in advanced RP patients.

The Melanopsin-Mediated Pupillary Light Response Is Not Changed in Patients with Newly Diagnosed Idiopathic Intracranial Hypertension

Previously, it has been reported that melanopsin-mediated pupillary light response (PLR), measured with pupillometry, is reduced in patients with idiopathic intracranial hypertension (IIH), indicating the clinical utility of the tool in the diagnosis of IIH. In the current study, the authors aimed to measure the PLR in 13 treatment-naive patients with new-onset IIH and 13 healthy controls. In contrast to the previous report, which was based on patients with longstanding IIH (n = 13), the authors found no significant difference in the melanopsin-mediated PLR (p = 0.48).