Light Out of Sight: Signaling Mechanisms for Nonvisual Opsins.

Background: Intrinsically photosensitive retinal ganglion cells (ipRGCs) control the pupillary light reflex (PLR) and synchronize sleep-wake cycles, melatonin secretion, and metabolic processes to the 24-h day. PLR abnormalities in diabetic retinopathy (DR) suggest ipRGC dysfunction. We explored whether ipRGC dysfunction in DR is associated with impaired sleep, circadian rhythms and metabolic functioning. Methods: Healthy controls (n=6), type 2 diabetes (T2D) without DR (n=8), or T2D with at least moderate DR (n=11) participated. PLR inferred ipRGC function, HbA1c, and nocturnal urinary 6-sulfatoxymelatonin (aMT6s/creatinine ratio) were measured. Sleep was recorded by 7-day actigraphy. Dim light melatonin onset (DLMO) was assessed by sampling saliva in the 7 hours before self-reported bedtime. Results: Mean age was 54.6±5.4 yr. The relative PLR was significantly smaller in T2D-DR (control vs. T2D-noDR vs. T2D-DR: 0.32(0.10) vs. 0.26 (0.09) vs. 0.13 (0.11), p=0.003). Nocturnal aMT6s [8.3 (3.1) vs. 14.6 (14.3) vs. 1.9 (2.1) ng/mg, p=0.001] was significantly lower in T2D-DR. Sleep was more disturbed in T2D-DR than others as reflected by higher wake time after sleep onset (p=0.024), higher fragmentation index (p=0.007) and lower sleep efficiency (p=0.030). HbA1c was similar between T2D groups. T2D-DR were more likely to have no detectable rise of salivary melatonin in the evening (normal 16% vs. DM-noDR 14% vs. DM-DR 67%, p=0.049). Smaller PLRs correlated with lower aMT6s (r=0.652, p=0.001). Among T2D, lower aMT6s and smaller PLR associated with lower sleep efficiency (p=0.029-0.046) and more fragmented sleep (p=0.028-0.066). There was no relationship between PLR or aMT6s with HbA1c in T2D. PLR was smaller in those without vs. with DMLO [0.11 (0.09) vs. 0.29 (0.09), p<0.001]. Conclusion: T2D with DR had dysregulated melatonin rhythm and disrupted sleep, which significantly correlated with the degree of ipRGC dysfunction. Disclosure S. Reutrakul: None. J.C. Park: None. F. Chau: None. T. Baynard: None. M. Priyadarshini: None. S. Crowley: None. J. McAnany: None. Funding University of Illinois at Chicago

Primary open-angle glaucoma as a causal factor for circadian disruption: Living by the clock, in alignment with external time cues is an important condition for human health and well-being. Periodic changes in the ambient light serve as a key factor to synchronize the endogenously generated circadian rhythms. The retina perceives the photic signals and transmits them to the central body clock, the suprachiasmatic nuclei (SCN), via the retinohypothalamic tract. Primary open angle glaucoma (POAG) is an optic neuropathy, in which disease progression can be monitored by assessing damage to the retinal ganglion cells (RGCs) (Pérez-Rico et al., 2010; Feigl et al., 2011; Kankipati et al., 2011). Damage of retinal ganglion cells, particularly of intrinsically photosensitive RGCs (ipRGCs), is also one of the causes of circadian disruption. Pathophysiological mechanisms of POAG are complex, including elevated intraocular pressure (IOP), which adds mechanical stress, causing damage, dysfunction, and death of the RGCs (Figure 1). Glaucoma progression affects both image-forming and non-image-forming visual functions of RGCs. A central role of ipRGCs is to convey non-image-forming photic information to the clock. Their damage reduces light signaling to the SCN. Already in early stages of glaucoma, ipRGCs are dysfunctional (Pérez-Rico et al., 2010; Feigl et al., 2011; Kankipati et al., 2011).Figure 1: Melatonin potential to counteract complex circadian alterations with aging, neurodegeneration, specifically in glaucoma.ipRGCs: Intrinsically photosensitive retinal ganglion cells; SNPs: single nucleotide polymorphisms.As RGCs are progressively altered, and non-image-forming function is affected, circadian rhythms are disrupted, sleep is impaired, and mood is altered (Graticelli et al., 2015; Gubin et al., 2019, 2021). Circadian rhythm alterations are found in POAG as compared to age-matched healthy peers (Gubin et al., 2019). Circadian disruption worsens in advanced POAG (Gubin et al., 2019, Neroev et al., 2020), correlating to the increasing loss of ipRGCs with disease progression (Obara et al., 2016). Circadian rhythms also change with increasing age. Age-dependent circadian alterations are not necessarily related to retinal damage, as photic transduction to the central clock is not always compromised. When they are related to retinal damage, they can be due to either neurodegenerative ipRGCs damage, or to ipRGC damage caused by increased mean or deregulated circadian IOP. The intriguing principal difference between the presence or absence of retinal damage in aging is that the reduced light transmitted to the SCN by damaged ipRGCs phase-delays circadian rhythms, but ipRGC-uncompromised aging is commonly associated with phase-advanced circadian rhythms (Gubin et al., 2019). Since individual differences in sensitivity to light, and/or in endogenous melatonin production may interfere with this theoretical modeling, the search for specific genetic factors that may determine such individual differences constitutes a promising approach. In conditions where photic entrainment is compromised, not only is the alignment with external time cues altered, so can be the variability of overt physiologic functions. We showed that large inter-individual variability obscured the circadian IOP rhythm in POAG (Neroev et al., 2020). Circadian IOP rhythms had specific alterations manifested in advanced, but not in mild POAG, which were associated with the progressive damage and dysfunction of RGCs. In patients with RGCs' global loss volume above 15%, as assessed by high-definition optical coherence tomography, the 24-hour IOP rhythm peaked during the night, whereas in patients with stable POAG and a two-eye mean RGCs' global loss volume less than 10%, the IOP peaked predominantly during the daytime. Misalignment between circadian rhythms in body temperature and IOP increased as a function of global loss volume loss. Higher nocturnal IOP in POAG may adversely affect the disease state, fostering damage to RGCs (Neroev et al., 2020). Depending on individual genetic factors, these changes may manifest themselves to a different degree. Individual clock properties depend on numerous genetic factors, comprising clock genes and melatonin receptor genes, melatonin nuclear receptor 1b (MTNR1b) in particular, which may account for large individual differences in light sensitivity. Our pilot study of gene polymorphisms in POAG showed that the D-allele of the Angiotensin-converting enzyme holding a deletion of the 16th intron Alu repeat was significantly associated with alterations of the circadian IOP rhythm. It may also account for the resistance to IOP-lowering therapy (Neroev et al., 2020). Endogenous melatonin production in primary open-angle glaucoma: Glaucoma patients experienced reduced post-illumination pupil response (Kankipati et al., 2011) and reduced nocturnal melatonin suppression by light (Pérez-Rico et al., 2010). Clinical evidence for changes in the timing and mean values of endogenous melatonin production in POAG was also evident (reviewed in Gubin et al., 2021): in POAG, salivary melatonin can be lower than in age-matched controls without POAG; even greater alterations were observed In advanced stages of the disease. The main alteration concerned the time of maximal secretion of melatonin. Such altered melatonin production in POAG and other neurodegenerative pathologies can stem from different factors, including diminished light signaling due to a reduced sensitivity to light. The presence of certain gene polymorphisms can increase the susceptibility of carriers to these factors. We investigated 24-hour profiles of salivary melatonin under controlled lighting conditions and analyzed several clock genes and polymorphisms of the melatonin receptor gene MTNR1b (Gubin et al., 2021). Patients diagnosed with stable POAG had unaltered circadian rhythms of salivary melatonin and body temperature, which peaked at the anticipated time. Circadian rhythms of both variables were delayed, however, in patients diagnosed with advanced POAG (Gubin et al., 2019, 2021). Their 24-hour mean value and circadian amplitude of melatonin were also reduced (Gubin et al., 2021). Analysis of selected polymorphisms in clock and melatonin receptor genes revealed that these changes were observed specifically in carriers of the MTNR1B rs10830963 G-allele with advanced POAG. Overt changes of circadian phenotypes in POAG patients occur when several factors are present in combination: for example, when RGC loss exceeds a certain threshold in carriers of those genotypes, known to be associated with a prolonged duration of melatonin production. The MTNR1B rs10830963 G-allele is mainly known for its association with an elevated fasting glucose and the risk of type 2 diabetes, but it is also listed as a factor predicting POAG independently of diabetes (Shen et al., 2016), a fact supporting the assumption that melatonin may have pleiotropic physiological functions in the development of POAG. Melatonin to counteract non-image-forming visual function deterioration in primary open-angle glaucoma: To enhance circadian entrainment, morning light therapy and evening melatonin administration can both be effective. While studies aimed at estimating the merit of morning light therapy or outdoor light exposure in POAG are lacking, some studies provide evidence for a beneficial effect of exogenously administered melatonin in glaucoma and neurodegenerative pathologies (González Fleitas et al., 2021; Gubin et al., 2021). Melatonin transmits environmental light signals, thus facilitating the synchronization of peripheral clocks. It can thus mitigate several conditions such as glaucoma and its progression: disruption of circadian rhythms, compromised sleep, and mood (Tosini et al., 2012; Gubin et al., 2021) (Figure 1). Melatonin improves internal synchronization, ameliorating circadian alignment between local (IOP) and systemic (temperature) circadian rhythms (Gubin et al., 2021), which were progressively desynchronized with greater RGCs loss in POAG (Neroev et al., 2020). Melatonin is produced endogenously with a pronounced 24-hour rhythm governed by the SCN. Peak production occurs at night. Its specific timing may differ among individuals. Exact endogenous factors that predetermine these differences are not known but may include single nucleotide polymorphisms within candidate genes or melatonin receptors that influence sensitivity to light. Melatonin receptors (MTNR1B) are widespread in numerous brain regions. Their structure may determine the specific response to (both endogenous and exogenous) melatonin. We investigated the effect of oral melatonin administration (daily at 10:30 p.m. for 90 days) on the circadian rhythms of IOP, body temperature, and the pattern electroretinogram in patients diagnosed with stable or advanced POAG, also assessing effects on sleep and mood (Gubin et al., 2021). Melatonin administration increased the stability of the circadian body temperature rhythm, improving its alignment with the circadian IOP rhythm. Melatonin decreased IOP to a different extent at different times of the day and decreased the standard deviation of IOP with statistical significance. Larger changes were found in patients with initially higher 24-hour mean values of IOP. Melatonin improved RGCs function in patients with advanced POAG by increasing the amplitude of pattern electroretinogram that correlated positively with the degree of RGCs loss. Melatonin had more pronounced positive effects on sleep and mood in patients with advanced POAG, who had greater damage of their RGCs. Taken together melatonin has the potential to restore disrupted circadian rhythms in POAG. Its systemic effect is distinct from its local effect on the retinal circadian rhythms. Similar to light exposure, physiological effects of melatonin depend on the time of its administration. Personalizing melatonin administration in terms of its timing and dosing, accounting for the genetic profile, is expected to further refine its multiple benefits. Melatonin may provide beneficial effects in POAG stemming from both its ability to reduce IOP and its potential to prevent RGC damage derived from mechanisms of neurodegeneration (Hardeland, 2021) (Figure 1). These effects may not only mitigate circadian disruption but also improve other aspects of health and well-being. Circadian alignment may strengthen human physiological functions and help slow neurodegeneration. The choice of an optimal melatonin dosing, however, is not yet clear (Hardeland, 2021). Consideration of the best timing should be based on internal circadian parameters and on genes that may account for personal differences in melatonin efficacy. Concluding remarks: In assessing disruptions in the non-image-forming visual system in POAG patients, one needs to discriminate between different situations. There may be complex, non-specific changes in circadian rhythms with age. Changes related to neurogenerative disease, including Alzheimer's disease, Parkinson's disease, and POAG, might promote alterations in neural structures: SCN, pineal, retina. Changes specific to POAG include additional RGC damage caused by the elevated IOP, together with abnormal circadian patterns of physiological variables such as IOP, body temperature, pattern electroretinogram, and melatonin (Figure 1). The circadian IOP pattern with relatively higher values during the resting span may foster harmful effects of IOP on RGCs, since tissue sensitivity may vary depending on circadian time (Neroev et al., 2020). Numerous candidate gene polymorphisms may play a role, alone or in combination with others, affecting the susceptibility to POAG itself (as a primary pathology of vision), or POAG-associated alterations of circadian rhythms, sleep, and mood, linked to non-visual pathways. To answer this question, clinical data combined with circadian profiles of melatonin and other physiological variables, chronotype questionnaires, sleep and mood information, to be checked against single nucleotide polymorphisms databases, should be collected on large cohorts. Constructive collaboration among ophthalmologists, chronobiologists, and geneticists is therefore advocated. The present work was supported by the Russian Foundation for Basic Research (grant No. 19-015-00329) (to DG), and by Government of Tyumen District, Decree of 20.11.2020 No. 928-rp (to DG). The authors have no proprietary or commercial interest in any materials discussed in this article.

The pupil constricts or dilates in response to a luminance increase or decrease, and these transient pupillary responses are controlled by the parasympathetic and sympathetic pathways. Although pupillary responses of the two eyes are highly correlated, they are not always identical (referred to as anisocoria). For example, there are unequal direct and consensual pupillary constriction responses after an increase in luminance to one eye. While contraction anisocoria (i.e. constriction) has been demonstrated in the pupillary light reflex, it is not yet known if there is also dilation anisocoria in the pupillary darkness reflex. Unlike previous studies that focused on the pupillary light reflex, we examined response anisocoria in both pupillary light and darkness reflexes. While requiring participants to maintain central fixation, we presented a light or dark stimulus to either the right or left visual field to induce transient pupillary constriction or dilation. Both the pupillary light and darkness reflexes had significantly larger ipsilateral responses compared to the contralateral responses relative to the stimulated visual field. The observed ipsilateral effects occurred significantly faster in the light than darkness reflex, suggesting that larger ipsilateral pupillary dilation after a luminance decrease cannot be only attributed to the inhibition of the parasympathetic system, but is also mediated by the excitation of the sympathetic system. Together, our results demonstrated a larger ipsilateral pupil response in both the pupillary light and darkness reflex, indicating an asymmetry in ipsilateral and contralateral neural circuitry of the pupillary darkness reflex.

In zebrafish, the expression of long-wavelength cone (LC) opsin mRNA fluctuated rhythmically between the day and night. In a 24-h period, expression was high in the afternoon and low in the early morning. This pattern of fluctuation persisted in zebrafish that were kept in constant darkness, suggesting an involvement of circadian clocks. Functional expression of Clock, a circadian clock gene that contributes to the central circadian pacemaker, was found to play an important role in maintaining the circadian rhythms of LC opsin mRNA expression. In zebrafish embryos, in which the translation of Clock was inhibited by anti-Clock morpholinos, the circadian rhythms of LC opsin mRNA expression diminished. CLOCK may regulate the circadian rhythms of LC opsin mRNA expression via cyclic adenosine monophosphate (cAMP)-dependent signaling pathways. In control retinas, the concentration of cAMP was high in the early morning and low in the remainder of the day and night. Inhibition of Clock translation abolished the fluctuation in the concentration of cAMP, thereby diminishing the circadian rhythms of opsin mRNA expression. Transient increase of cAMP concentrations in the early morning (i.e. by treating the embryos with 8-bromo-cAMP) restored the circadian rhythms of LC opsin mRNA expression in morpholino-treated embryos. Together, the data suggest that Clock plays important roles in regulating the circadian rhythms in photoreceptor cells.

Like other mammals,human has obvious circadian rhythm,and light is recognized as the principal circadian synchronizer.Rod/cone photoreceptors of the outer retina and the melanopsin-containing retinal ganglion cells(mcRGCs) of the inner retina mediate non-image forming visual responses including entrainment of the circadian clock to the ambient light,the pupillary light reflex (PLR),and light modulation of activity by means of a set of mcRGCs projecting to the suprachiasmatic nucleus (SCN)through retinohypothalamic tract (RHT).Glaucoma is a group of diseases which cause degenerative changes and loss of RGCs including mcRGCs,so the circadian rhythm of patients with glaucoma will be interrupted.The progress in the study on the effect of glaucoma and experimental hypertension on circadian rhythm was reviewed. Key words: Glaucoma; Circadian rhythm; Melanopsin

In this PhD thesis 3 projects were addressed focusing on the melanopsin retinal ganglion cells (mRGCs) system and its relevance for circadian rhythms and sleep in neurodegeneration. The first project was aimed at completing the characterization of mRGCs system in hereditary optic neuropathies (LHON and DOA). We confirmed that mRGCs are relatively spared also in post-mortem retinal specimens of a DOA case and pupillometric evaluation of LHON patients showed preservation of the pupillary light reflex, with attenuated responses compared to controls. Cell studies failed to indicate a protective role exerted by melanopsin itself. The second project was aimed at characterizing the possible occurrence of optic neuropathy and rest-activity circadian rhythm dysfunction in Alzheimer (AD) and Parkinson disease (PD), as well as, at histological level, the possible involvement of mRGCs in AD. OCT studies demonstrated a subclinical optic neuropathy in both AD and PD patients, with a different pattern involving the superior and nasal quadrants in AD and the temporal quadrant in PD. Actigraphic studies demonstrated a tendency towards an increased intradaily variability (IV) and reduced relative amplitude (RA) of rest-activity circadian rhythm in AD and a significant increased IV a reduced RA in PD. Immunohistochemical analysis of post-mortem retinal specimens and optic nerve cross-sections of neuropathologically confirmed AD cases demonstrated a significant loss of mRGCs and a nearly significant loss of axons in AD compared to controls. The mRGCs were affected in AD independently from age and magnitude of axonal loss. Overall these results suggest a role of the mRGCs system in the pathogenesis of circadian dysfunction in AD. The third project was aimed at evaluating the possible association between a single nucleotide polymorphism of the OPN4 gene and chronotype or SAD, failing to find any significant association with chronotype, but showing a non-significant increment of TT genotype in SAD.

Continuous measurement of pupil size and light reflex during CPR in out-of-hospital cardiac arrest patients

An automated infrared pupillometer measures quantitative pupillary light reflex using a calibrated light stimulus. We examined whether the timing of performing quantitative pupillary light reflex or standard pupillary light reflex may impact its neuroprognostic performance in postcardiac arrest comatose patients and whether quantitative pupillary light reflex may outperform standard pupillary light reflex in early postresuscitation phase. PubMed and Embase databases from their inception to July 2020. We selected studies providing sufficient data of prognostic values of standard pupillary light reflex or quantitative pupillary light reflex to predict neurologic outcomes in adult postcardiac arrest comatose patients. Quantitative data required for building a 2 × 2 contingency table were extracted, and study quality was assessed using standard criteria. We used the bivariate random-effects model to estimate the pooled sensitivity and specificity of standard pupillary light reflex or quantitative pupillary light reflex in predicting poor neurologic outcome during early (< 72 hr), middle (between 72 and 144 hr), and late (≧ 145 hr) postresuscitation periods, respectively. We included 39 studies involving 17,179 patients. For quantitative pupillary light reflex, the cut off points used in included studies to define absent pupillary light reflex ranged from 0% to 13% (median: 7%) and from zero to 2 (median: 2) for pupillary light reflex amplitude and Neurologic Pupil index, respectively. Late standard pupillary light reflex had the highest area under the receiver operating characteristic curve (0.98, 95% CI [CI], 0.97-0.99). For early standard pupillary light reflex, the area under the receiver operating characteristic curve was 0.80 (95% CI, 0.76-0.83), with a specificity of 0.91 (95% CI, 0.85-0.95). For early quantitative pupillary light reflex, the area under the receiver operating characteristic curve was 0.83 (95% CI, 0.79-0.86), with a specificity of 0.99 (95% CI, 0.91-1.00). Timing of pupillary light reflex examination may impact neuroprognostic accuracy. The highest prognostic performance was achieved with late standard pupillary light reflex. Early quantitative pupillary light reflex had a similar specificity to late standard pupillary light reflex and had better specificity than early standard pupillary light reflex. For postresuscitation comatose patients, early quantitative pupillary light reflex may substitute for early standard pupillary light reflex in the neurologic prognostication algorithm.

ObjectivesPupil light reflex (PLR) has been widely used as a method for evaluating parasympathetic activity. The first aim of the present study is to develop a PLR measurement using a computer screen set-up and compare its results with the PLR generated by a more conventional setup using light-emitting diode (LED). The parasympathetic nervous system, which is known to control the ‘rest and digest’ response of the human body, is considered to be associated with daily life fatigue. However, only few studies have attempted to test the relationship between self-reported daily fatigue and physiological measurement of the parasympathetic nervous system. Therefore, the second aim of this study was to investigate the relationship between daily-life fatigue, assessed using the Need for Recovery scale, and parasympathetic activity, as indicated by the PLR parameters.DesignA pilot study was conducted first to develop a PLR measurement set-up using a computer screen. PLRs evoked by light stimuli with different characteristics were recorded to confirm the influence of light intensity, flash duration, and color on the PLRs evoked by the system. In the subsequent experimental study, we recorded the PLR of 25 adult participants to light flashes generated by the screen set-up as well as by a conventional LED set-up. PLR parameters relating to parasympathetic and sympathetic activity were calculated from the pupil responses. We tested the split-half reliability across two consecutive blocks of trials, and the relationships between the parameters of PLRs evoked by the two set-ups. Participants rated their need for recovery prior to the PLR recordings.ResultsPLR parameters acquired in the screen and LED set-ups showed good reliability for amplitude related parameters. The PLRs evoked by both set-ups were consistent, but showed systematic differences in absolute values of all parameters. Additionally, higher need for recovery was associated with faster and larger constriction of the PLR.ConclusionsThis study assessed the PLR generated by a computer screen and the PLR generated by a LED. The good reliability within set-ups and the consistency between the PLRs evoked by the set-ups indicate that both systems provides a valid way to evoke the PLR. A higher need for recovery was associated with faster and larger constricting PLRs, suggesting increased levels of parasympathetic nervous system activity in people experiencing higher levels of need for recovery on a daily basis.

It is important to assess the severity of hepatic encephalopathy (HE) and to quantitate improvement in HE after therapeutic interventions in a reliable and reproducible manner. The lack of a well standardized method of measurement has led to the use of different techniques by different clinical investigators, making a comparison between studies problematic. Although this issue had been noted more than 2 decades ago,1, 2 it is still unresolved and is reflected in the diversity of end-points and methods used in the assessment of acute HE in clinical trials over the last 15 years, e.g. West Haven criteria, Glasgow coma scale, PSE index with arterial or venous ammonia, and the EEG) (Table 1). Also different conditions have been classified as chronic HE (not reviewed here). The problem of how HE should be assessed, together with the considerable diversity of terms used to define different clinical settings, prompted a gathering of a panel of international experts to reach a consensus. Table 1. Clinical treatment trials of episodic hepatic encephalopathy (precipitated or spontaneous) in the last 15 years. SMT: standard medical treatment Author and Year Type of patients Therapy studied Primary End-point Measurement of HE Kramer, 200115 Stage II and III HE Cirrhosis Sorbent dialysis + SMT vs SMT only Sensory evoked potentials Clinical staging (West Haven), sensory evoked potentials automated EEG Laccetti, 200016 Stage III-IV HE Cirrhosis Flumazenil + SMT vs placebo + SMT Clin ical improvement Glasgow coma scale Barbaro, 199816 Stage IVa HE Cirrho sis Flumazenil + lactulose vs placebo + lactulose Clinical improvement and EEG. EEG and modified Glasgow coma scale (Pappas and Jones), including: verbal ability, eye-opening, pupillary light reflex, corneal reflex, spontaneous eye movements, oculocephalic reflex, motor response, respiration pattern Barbaro, 199818 Stage III-IVa HE Cirrhosis Flumazenil + lactulose vs placebo + lactulose Clinical improvement and EEG EEG and modified Glasgow coma scale (Pappas and Jones), including: verbal abilitiy, eye-opening, pupillary light reflex, corneal reflex, spontaneous eye movements, oculocephalic reflex, motor response, respiration pattern Gyr, 199614 Stage I-III HE Cirrhosis Flumazenil vs placebo (Lactulose permitted in both groups) Clinical improvement Own adapted clinical PSE score, EEG Van der Rijt, 199519 HE staged by EEG (clinical stage varied from 0 to IV) Acute or chronic liver disease Flumazenil vs placebo Clinical improvement and EEG Clinical staging asses sed by own classi ficatio n: stage I: > 2 of inverted sleep pattern, disturbed memory, impaired serial 7’s, slowness of speech, flapping tremor; stage II: > 2 of lethargy, time disorientation, asterixi s; stage III: > 2 of state that subject had to be stimulated repetitively to open eyes or execute commands, place and person disorientation; stage IV: coma. EEG Cadranel, 199520 Stage II-IV HE Cirrhosis Flumazenil vs placebo Clinical improvement and EEG Clinical grading with own classification: I: euphoria/depression, mild confusion, slowness, disordered sleep rhythm; II: drowsiness, inappropriate behaviour, accentuation of grade I; III: stupor, patient sleeps most of time but rousable, incoherent speech, marked confu sion; IVa: coma, coordinated response to pain; IVb: hyperextension and pronosupination to pain stimuli; IVc: no response to pain; V: clinica l decerebration. EEG Pomier-Layrargues, 199421 Stage IV HE Cirrhosis Flumazenil + lactulose vs placebo + lactulose Clinical improvement Modified Glasgow coma score, including: verbal ability, eyeopening, pupillary light, corneal and oculocephalic reflexes, spontaneous eye movements, motor response, respiration pattern. EEG Blanc, 199422 Acute HE Cirrhosis Lactulose + neomycin vs placebo PSE index PSE Index (mental state (West Haven), number conection test, EEG, asterixis and arterial ammonia) Strauss, 199223 Acute HE stages I-IV Cirrhosis Neomycin vs placebo Clinical improvement Clinical criteria (I to IV) but no reference or explanation. Sushma, 199224 Acute HE stages II-IV Cirrhosis Lactulose vs sodium benzoate Clinical improvement Mental state (WH), asterixis, psychometric tests, arterial ammonia, EEG, evoked potentials Vilstrup, 199025 Acute HE stages II-IV Cirrhosis BCAA iv + lactulose vs glucose iv + lactulose Clinical improvement Glasgow coma scale Klotz, 198926 Stage III HE Cirrhosis Flumazenil vs placebo Clinical improvement Coma status evaluated by reactions and reflexes to stimuli (no further explanation or reference) Uribe, 198727 Acute HE (stage II Cirrhosis Lactitol and lactose enemas vs nonacidifying enemas PSE index PSE index: mental state (WH), NCT, asterixis, EEG, fasting arterial ammonia. Morgan, 198713 Acute HE Cirrhosis Lactitol vs lactulose PSE index PSE index: mental state (WH), NCT-A, asterixis, EEG, venous ammonia

The pupillary light reflex (PLR) is crucial for protecting the retina from excess light. The intrinsically photosensitive retinal ganglion cells (ipRGCs) in the retina are neurons that are critical to generating the PLR, receiving rod/cone photoreceptor signals and directly sensing light through melanopsin. Previous studies have investigated the roles of photoreceptors and ipRGCs in PLR using genetically-modified mouse models. Herein, we acutely ablated photoreceptors using N-nitroso-N-methylurea (MNU) to examine the roles of ipRGCs in the PLR. We conducted PLR and multiple electrode array (MEA) recordings evoked by three levels of light stimuli before and 5 days after MNU intraperitoneal (i.p..) injection using C57BL6/J wildtype (WT) mice. We also conducted these measurements using the rod & cone dysfunctional mice (Gnat1-/- & Cnga3-/-:dKO) to compare the results to published studies in which mutant mice were used to show the role of photoreceptors and ipRGCs in PLR. PLR pupil constriction increased as the light stimulus intensified in WT mice. In MNU mice, PLR was not induced by the low light stimulus, suggesting that photoreceptors induced the PLR at this light intensity. By contrast, the high light stimulus fully induced PLR, similar to the response in WT mice. In dKO mice, no PLR was evoked by the low-light stimulus and a slow-onset PLR was evoked by the high-light stimulus, consistent with previous reports. Ex vivo MEA recording in the MNU tissue revealed a population of ipRGCs with a fast onset and peak time, suggesting that they drove the fast PLR response. These results suggest that ipRGCs primarily contribute to the PLR at a high light intensity, which does not agree with the previous results shown by mutant mouse models. Our results indicate that the melanopsin response in ipRGCs generate fast and robust PLR when induced by high light.

Eye activity-based within-task cognitive load measurement (CLM) is currently not feasible in everyday situations. One important issue to be addressed to move such CLM beyond controlled laboratory environments is determining practical methods for mitigating the pupillary light reflex (PLR) effect in CLM. In this paper, four approaches to dealing with the PLR effect within a modified verbal digit span task are investigated: ignore the PLR, exclude PLR data, compensate for PLR and use PLR features for measurement. During experimental work, cognitive load and the PLR were induced with a modified verbal digit span task and changes in brightness of a large monitor, respectively. The “exclude PLR,” “compensate for PLR,” and “use PLR features” methods were found to improve classification performance by up to 18.5% relative to the “ignore PLR” method, which yielded the worst classification accuracy of 58% using an average pupil diameter feature. Features derived from the transient properties of the PLR response associated with cognitive load were found to yield the superior classification accuracy of 70%, which is an improvement compared with previously published approaches which treated the PLR responses as interference. The findings from this paper suggest that the PLR cannot be easily ignored or normalized, and clearly demonstrate the importance of PLR-aware feature extraction for the design of future eyewear-based always-on CLM in conditions that are more realistic than a darkened, controlled laboratory.

There are many benefits to facilitating 'always-on' pupillary light reflex (PLR)-aware pupil size measurement in eyewear, including improving the reliability of pupil-based cognitive and affective load monitoring and enabling PLR-based diagnosis of cognitive and eye-related diseases which have neurological symptoms manifested in the form of aberrant PLR responses. However, the detection of PLR responses for application in eyewear devices for everyday usage, beyond PLR measurement in confined clinical sessions, has not been investigated. To this end, a means of characterizing PLRs in less controlled environmental settings is investigated and subsequently a method of PLR detection is developed and evaluated. A low-cost head-mounted Web camera was used to record near-field eye video sequences which were processed with the self-tuning threshold algorithm for pupil diameter estimation and blink detection. PLR was induced by luminance change of a monitor and brightness change of the displayed image on a monitor. A transient model-based PLR detection algorithm which utilizes the general correlation of PLR amplitude and velocity was developed and evaluated on the data sets in terms of false alarm and false rejection rates. The findings from this research suggest that the PLR can be detected reliably using low-cost wearable pupil-measurement systems without using a separate sensor for detecting the luminance conditions. The correlation between pupil diameter amplitude and maximum velocity of PLR was shown to be sufficiently consistent for PLR detection.

This review examines how diabetes affects the ganglion cells of the retina, including the axons that make up the optic nerve. Links between established changes in the morphology of retinal ganglion cells (RGCs) and vision loss, as well as other functions, such as the pupillary light reflex, are considered. RGC morphology and function are significantly altered in both animal models and humans with diabetes. Diabetes affects all parts of the RGC, including the dendrites, the cell body, the axons making up the nerve fiber layer, and the optic nerve. Subtypes of RGCs appear to be affected differently by diabetes, and the morphology and electrophysiological output are more significantly affected in ON-RGCs than in OFF cells, which may explain part of the mechanism underlying the widely documented diabetes-induced reduction in contrast sensitivity. Furthermore, the morphology of the specialized light-sensitive melanopsin-containing RGCs also appears to be affected by diabetes, which may explain deficits in circadian rhythm and the pupillary light reflex. Potential therapeutic approaches aimed at protecting RGCs in diabetes are also discussed. Overall, strong evidence supports the conclusion that diabetes impacts the form and function of RGCs and their axons within the optic nerve, resulting in deficient regulation of circadian rhythms and the pupillary light reflex, in addition to vision.

Purpose: To study UV light–induced and green light–induced pupillary light reflex (PLR) in mice and to measure the illumination thresholds of rod-mediated and cone–mediated PLR responses. Methods: We measured dark-adapted transient PLR- in C57BL/6 mice elicited with ultraviolet and green light over an intensity range of 9 log units. To assist in isolating the responses mediated by rods and cones, we studied the PLRs in mouse models presenting pure cone and pure rod functions. We also characterized ERG signals in these mice under the same experimental conditions. Results: The UV light–induced transient PLR has identical intensity-response curves as green light–induced PLR in all the three mice strains. The threshold (5% PLR) of rod-driven PLR is 107∼108 photons cm2 s−1, which is 1∼2 log units lower than the dark-adapted ERG b-wave. The threshold of cone-driven PLR is ∼1012.5 photons cm−2 s−1 and is similar to that of the cone ERG. Conclusions: We demonstrated that mice have PLR responses under UV stimulation. The cone-elicited PLRs have a threshold that is ∼5 log units higher than that of rod-elicited PLR at both UV and green wavelengths. We observed a divergence between the spectra responses in PLR and ERG. However, the mechanism and implications of this phenomenon are yet to be identified.