We have compared the time course of dark adaptation of the human scotopic visual system, measured psychophysically and from the b-wave of the electroretinogram (ERG), for bleaches ranging from a few percent to near total. We also measured light adaptation, in order to apply a "Crawford transformation" to convert the raw measurements of dark adaptation into equivalent background intensities. For both the "psychophysical threshold equivalent" intensity and the "ERG b-wave sensitivity equivalent" intensity, the equivalent background declined over much of its range with an "S2" component, though with somewhat different slopes of -0.36 (psychophysical) and -0.22 (ERG) log(10) unit min(-1), respectively. In addition, the magnitude of the equivalent background was approximately 1 log(10) unit lower in the psychophysical experiments than in the ERG experiments. Despite these differences, the two approaches extract a common time course for the decline in level of free opsin following moderately large bleaches. We conclude that the recovery of psychophysical scotopic visual threshold over the S2 region reflects events that are present by the stage of the first synapse of rod vision, stemming ultimately from the presence of unregenerated opsin in the rod outer segments.

The substantial time taken for regaining visual sensitivity (dark adaptation) following bleaching exposures has been investigated for over a century. Psychophysical studies yielded the classic biphasic curve representing recovery of cone‐driven and rod‐driven vision. The electroretinogram (ERG) permits direct assessment of recovery at the level of the retina (photoreceptors, bipolar cells), with the first report over 70 years ago. Over the last two decades, ERG studies of dark adaptation have generated insights into underlying physiological processes. After large bleaches, rod photoreceptor circulating current, estimated from the rod‐isolated bright‐flash ERG a‐wave, takes 30 min to recover, indicating that products of bleaching, thought to be free opsin (unbound to 11‐cis‐retinal), continue to activate phototransduction, shutting off rod circulating current. In contrast, cone current, assessed with cone‐driven bright‐flash ERG a‐waves, recovers within 100 ms following similar exposures, suggesting that free opsin is less able to shut off cone current. The cone‐driven dim‐flash a‐wave can be used to track recovery of cone photopigment, showing regeneration is 'rate‐limited' rather than first order. Recoveries of the dim‐flash ERG b‐wave are consistent also with rate‐limited rod photopigment regeneration (where free opsin, desensitising the visual system as an 'equivalent background', is removed by rate‐limited delivery of 11‐cis‐retinal). These findings agree with psychophysical and retinal densitometry studies, although there are unexplained points of divergence. Post‐bleach ERG recovery has been explored in age‐related macular degeneration and in trials of visual cycle inhibitors for retinal diseases. ERG tracking of dark adaptation may prove useful in future clinical contexts.

Purpose To determine the prevalence and spatial pattern of rod and cone dysfunction in patients with pseudoxanthoma elasticum (PXE) and to correlate these with Bruch's membrane (BrM) calcification. PXE is a rare genetic disorder that causes calcification of Bruch's membrane, which eventually leads to loss of central vision. Understanding the functional implications of BrM calcification is crucial for developing effective treatments. Methods In this prospective natural history study (PROPXE, ClinicalTrials.gov ID: NCT05662085), performed at a tertiary referral center, 26 patients with PXE (14 women, 12 men; median age, 55 years; interquartile range, 43–59 years), diagnosed according to the Plomp criteria, underwent comprehensive ophthalmic evaluations, including best-corrected visual acuity (BCVA), contrast sensitivity testing, and multimodal imaging. Dark adaptometry was tested following a 59% rhodopsin bleach at 8°, 15°, 30°, and 46° eccentricity from the fovea along the temporal retina. The eye without a history of exudative macular neovascularization (MNV) or the better-seeing eye was selected as the study eye. Results Of 26 participants, 12 had no history of exudative MNV in the study eye, while 14 had previous or current treatment for MNV with a median BCVA of −0.07 logMAR and 0.11 logMAR, respectively. In the macula at 8° eccentricity, rod intercept time (RIT) was prolonged in 83.3% of nonexudative and 92.9% of exudative eyes, while BCVA and cone thresholds at 8° eccentricity were affected in only 42.3% and 65.4% of eyes. The delay in RIT was most pronounced in regions at risk of calcification and increased markedly with age. In addition, prolonged cone recovery time constants were evident that correlated with RIT. Conclusions Patients with PXE exhibit significant slowing of both cone- and rod-mediated dark adaptation, particularly in regions prone to BrM calcification. These findings suggest that dark adaptometry and assessment of BrM calcification can serve as clinical tools for evaluating disease severity and monitoring progression in PXE, enabling earlier interventions before the onset of exudative MNV or atrophy.

Optogenetic vision restoration has progressed from proof-of-concept to early clinical testing, yet most programmes rely on microbial channels that demand high irradiance and offer limited adaptation. This review synthesizes preclinical and clinical evidence comparing microbial actuators with human opsins (rhodopsin, cone opsins, melanopsin) and outlines vector and safety considerations for translation. Human opsins activate G-protein-coupled cascades, providing intrinsic signal amplification and operation at room-light levels (∼10¹¹-10¹² photons⋅cm^-2⋅s^-1), in contrast to the ≥1015 photons⋅cm^-2⋅s^-1 typically needed for channelrhodopsins. Rhodopsin and MW cone opsin preserve photopic-range sensitivity (rhodopsin > cone opsin) while delivering millisecond-scale kinetics and adaptation across backgrounds, enabling patterned retinal responses without optical intensification devices; clinical validation without external intensification is pending. Such mammalian pigments also confer bleaching-based light adaptation, whereas microbial tools are photocyclic and can desensitize under steady illumination, limiting sustained contrast encoding. Bistable melanopsin enables durable irradiance coding but with slow dynamics; chimeric designs (e.g., melanopsin-mGluR6, Gloeobacter-human rhodopsin) aim to combine amplification with favorable reset properties. In contrast to human opsins, microbial channels warrant safety considerations including light-dose budgeting (particularly at short wavelengths), potential cytotoxicity from proton or calcium loads, and vector-related ocular inflammation; red-shifted actuators improve photochemical safety margins. Targeting opsins to ON bipolar (ON-BP) cells retains inner-retinal computations (center-surround, ON/OFF segregation, temporal filtering). Engineered adeno-associated virus (AAV) capsids (e.g., AAV2-7m8 intravitreally; AAV8.BP2 subretinally) paired with GRM6 or L7 promoters achieve broad ON-BP expression in rodents but a much more limited expression profile in non-human primates. First clinical studies report acceptable early ocular safety with emerging efficacy signals. We propose accelerating phase I safety human trials of human-opsin vectors with prospectively defined light-exposure budgets and low vision functional endpoints such as navigation, face and object recognition, temporal contrast sensitivity, alongside work on chromophore support, cascade integrity in late degeneration, and scalable vector-promoter solutions. Pharmacological noise suppression in degenerating retinas (e.g., gap-junction blockers or retinoic-acid pathway modulators) may further enhance signal-to-noise without altering opsin biochemistry. Together, these steps can move human-opsin optogenetics from experimental promise to clinically meaningful restoration of light sensitivity.

minutes for the eye to adapt from darkness to bright sunlight. This is due to cones obtaining more sensitivity when first entering the dark for the first five In visual physiology, adaptation is the ability of the retina of the eye to adjust to various levels of light. Natural night vision, or scotopic vision, is the ability to see under low-light conditions. In humans, rod cells are exclusively responsible for night vision, as cone cells are only able to function at higher illumination levels. Night vision is of lower quality than day vision because it The human eye can function from very dark to very bright levels of light; its sensing capabilities reach across nine orders of magnitude. This means that the brightest and the darkest light signal that the eye can sense are a factor of roughly 1,000,000,000 apart. However, in any given moment of time, the eye can only sense a contrast ratio of 1,000. What enables the wider reach is that the eye adapts its definition of what is black. The eye takes approximately 20–30 minutes to fully adapt from bright sunlight to complete darkness and becomes 10,000 to 1,000,000 times more sensitive than at full daylight. In this process, the eye's perception of color changes as well (this is called the Purkinje effect). However, it takes approximately five minutes for the eye to adapt from darkness to bright sunlight. This is due to cones obtaining more sensitivity when first entering the dark for the first five minutes but the rods taking over after five or more minutes. Cone cells are able to regain maximum retinal sensitivity in 9–10 minutes of darkness whereas rods require 30–45 minutes to do so. Dark adaptation is far quicker and deeper in young people than the elderly. Rhod…

3. Subjects will then be dark adapted for 20-30 minutes. During this time they may be blindfolded (depending on darkness of the room) and sitting in a dark room. Music options will be available to help pass the time and ease potential discomfort. 4. After 20-30 minutes, the blindfold will be removed (if used) and patient will have monocular dark-adapted (scotopic) testing done with the OCD, left eye followed by right eye. The non-tested eye may be covered during testing. 5. After scotopic testing, the light of the OCD will be increased and light-adapted (photopic) testing will be performed in the same manner. This visit should take approximately 90 minutes to complete. Second Research Visit (approximately 1 month after the first research visit): 1. Pelli-Robson Contrast Sensitivity Testing. This is a form of stationary central vision contrast sensitivity that is a commonly used testing modality for photopic contrast in many ophthalmologic clinical studies. We hypothesize that there will be similarities in contrast performance between Pelli-Robson and OKR testing which will help validate our testing strategy. 2. OKR-based contrast testing.

Dark adaptation and falls in the elderly. The human eye is capable of adjusting to wide variations in light intensity by altering the pupil size and the sensitivity of the retina to light. Falls are one of the commonest problems of old age, and the causes are multifactorial. As falls often occur at night, this study was designed to compare dark adaptation in groups of elderly fallers and non-fallers. Twenty-two female patients in a geriatric assessment ward were included in the study and classified as 'fallers' or 'non-fallers'. A full ophthalmic examination was performed on each subject, and dark adaptation measured, in a single-blind fashion, using the Friedmann visual field analyser; following initial bleaching of the retinal photoreceptors, the room was placed in total darkness and retinal sensitivity measured every minute for 20 min. The values, expressed as log filter density, were plotted against duration of time in the dark. The mean values at 5 min were 0.9 in the fallers and 1.4 in the non-fallers (p less than 0.02 unpaired t test) and at 20 min 2.2 and 3.2, respectively (p less than 0.04).

The quantity of rhodopsin in young human eyes. The rhodopsin content of 20 eyes of infants and children ages 27 weeks gestation to 8 years (11 donors) was assayed and compared to the rhodopsin content of adults (36 eyes; 19 donors). Infants have significantly lower rhodopsin contents than adults. On average the rhodopsin content of young infants is about a third of adults. Previously reported full-field b-wave sensitivity of young infants is about 0.5 log units, that is about a third, less than adults. Thus, as previously found in infant rats, photon capture by rhodopsin appears to limit the dark adapted sensitivity of young human infants. Published in Current eye research (1991)

snouts and tails that are compressed on the sides, with their eyes, ears, and nostrils at the top of the head. Alligators and caimans tend to have broader Crocodylia or Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They appeared 83.5 million years ago in the Late Cretaceous period (Campanian stage) and are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria. Members of the crocodilian total group, the clade Pseudosuchia, appeared about 250 million yea The eyes, ears and nostrils of crocodilians are at the top of the head; this placement allows them to stalk their prey with most of their bodies underwater. When in bright light, the pupils of a crocodilian contract into narrow slits, whereas in darkness they become large circles, as is typical for animals that hunt at night. Crocodilians' eyes have a tapetum lucidum that enhances vision in low light. When the animal completely submerges, the nictitating membranes cover its eyes. Glands on the nictitating membrane secrete a salty lubricant that keeps the eye clean. When a crocodilian leaves the water and dries off, this substance is visible as "tears". While eyesight in air is fairly good, it is significantly weakened underwater. Crocodilians appear to have undergone a "nocturnal bottleneck" early in their history, during which their eyes lost traits like scleral rings, an annular pad of the lens and coloured cone oil droplets, giving them dichromatic vision (red-green colourblindness). Since then, some…