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Eye (London, England) Feb 2016Under twenty-first-century metropolitan conditions, almost all of our vision is mediated by cones and the photopic system, yet cones make up barely 5% of our retinal... (Review)
Review
Under twenty-first-century metropolitan conditions, almost all of our vision is mediated by cones and the photopic system, yet cones make up barely 5% of our retinal photoreceptors. This paper looks at reasons why we additionally possess rods and a scotopic system, and asks why rods comprise 95% of our retinal photoreceptors. It considers the ability of rods to reliably signal the arrival of individual photons of light, as well as the ability of the retina to process these single-photon signals, and it discusses the advantages that accrue. Drawbacks in the arrangement, including the very slow dark adaptation of scotopic vision, are also considered. Finally, the timing of the evolution of cone and rod photoreceptors, the retina, and the camera-style eye is summarised.
Topics: Animals; Color Vision; Contrast Sensitivity; Dark Adaptation; Humans; Light; Night Vision; Retinal Cone Photoreceptor Cells; Retinal Rod Photoreceptor Cells; Vision, Ocular
PubMed: 26563661
DOI: 10.1038/eye.2015.236 -
Taiwan Journal of Ophthalmology 2022A wide spectrum of phenotypic manifestations characterizes age-related macular degeneration (AMD). Drusen is considered the hallmark of AMD and is located underneath the... (Review)
Review
A wide spectrum of phenotypic manifestations characterizes age-related macular degeneration (AMD). Drusen is considered the hallmark of AMD and is located underneath the retinal pigment epithelium (RPE). In contrast, subretinal drusenoid deposits (SDDs), also known as reticular pseudodrusens, are located in the subretinal space, on top of the RPE. SDDs are poorly detected by clinical examination and color fundus photography. Multimodal imaging is required for their proper diagnosis. SDDs are topographically and functionally related to rods. SDDs cause a deep impairment in retinal sensitivity and dark adaptation. SDDs are dynamic structures that may grow, fuse with each other, or regress over time. An intermediate step in some eyes is the development of an acquired vitelliform lesion. The presence of SDD confers an eye a high risk for the development of late AMD. SDD leads to macular neovascularization, particularly type 3, geographic atrophy, and outer retinal atrophy.
PubMed: 35813798
DOI: 10.4103/tjo.tjo_18_22 -
Experimental Eye Research Oct 2020A significant proportion of research on the visual system focuses on general principles that apply to samples and/or populations. Many questions, however, are more... (Review)
Review
A significant proportion of research on the visual system focuses on general principles that apply to samples and/or populations. Many questions, however, are more suited to the specific characteristics of an individual. The visual system, like most systems of the body, is extremely variable with respect to function and susceptibility to disease. Understanding this variation is an important avenue to better measurement, disease prevention and treatment.
Topics: Adaptation, Ocular; Humans; Individuality; Macula Lutea; Vision, Ocular
PubMed: 32781197
DOI: 10.1016/j.exer.2020.108186 -
Journal of Clinical Medicine Mar 2022Dark adaptation (DA) refers to the slow recovery of visual sensitivity in darkness following exposure to intense or prolonged illumination, which bleaches a significant... (Review)
Review
Dark adaptation (DA) refers to the slow recovery of visual sensitivity in darkness following exposure to intense or prolonged illumination, which bleaches a significant amount of the rhodopsin. This natural process also offers an opportunity to understand cellular function in the outer retina and evaluate for presence of disease. How our eyes adapt to darkness can be a key indicator of retinal health, which can be altered in the presence of certain diseases, such as age-related macular degeneration (AMD). A specific focus on clinical aspects of DA measurement and its significance to furthering our understanding of AMD has revealed essential findings underlying the pathobiology of the disease. The process of dark adaptation involves phototransduction taking place mainly between the photoreceptor outer segments and the retinal pigment epithelial (RPE) layer. DA occurs over a large range of luminance and is modulated by both cone and rod photoreceptors. In the photopic ranges, rods are saturated and cone cells adapt to the high luminance levels. However, under scotopic ranges, cones are unable to respond to the dim luminance and rods modulate the responses to lower levels of light as they can respond to even a single photon. Since the cone visual cycle is also based on the Muller cells, measuring the impairment in rod-based dark adaptation is thought to be particularly relevant to diseases such as AMD, which involves both photoreceptors and RPE. Dark adaptation parameters are metrics derived from curve-fitting dark adaptation sensitivities over time and can represent specific cellular function. Parameters such as the cone-rod break (CRB) and rod intercept time (RIT) are particularly sensitive to changes in the outer retina. There is some structural and functional continuum between normal aging and the AMD pathology. Many studies have shown an increase of the rod intercept time (RIT), i.e., delays in rod-mediated DA in AMD patients with increasing disease severity determined by increased drusen grade, pigment changes and the presence of subretinal drusenoid deposits (SDD) and association with certain morphological features in the peripheral retina. Specifications of spatial testing location, repeatability of the testing, ease and availability of the testing device in clinical settings, and test duration in elderly population are also important. We provide a detailed overview in light of all these factors.
PubMed: 35268448
DOI: 10.3390/jcm11051358 -
Current Eye Research May 2023Studies on age-related macular degeneration often use rod-mediated dark adaptation (RMDA) to evaluate macular functional health, studying eyes with cataract and...
PURPOSE
Studies on age-related macular degeneration often use rod-mediated dark adaptation (RMDA) to evaluate macular functional health, studying eyes with cataract and pseudophakic eyes within the same sample. We examine a poorly understood issue-whether rod intercept time (RIT), a measure of RMDA, changes after cataract surgery and intraocular lens (IOL) insertion as compared to RIT before cataract surgery. Cataract may serve as a filter reducing photo-bleach magnitude prior to surgery, biasing RMDA interpretation.
METHODS
A pre-/post-cataract surgery design was used. Persons with nuclear sclerotic and/or cortical cataract per the electronic health record were enrolled. Prior to cataract surgery, visual acuity, RMDA, and the LOCS III classification documenting cataract presence/severity were measured. Thirty days after surgery (mean), visual acuity and RMDA were repeated, followed by fundus photos to document macular health.
RESULTS
Twenty-four participants (mean age 72.7 years, standard deviation 5.6) enrolled. All eyes had nuclear sclerotic and nuclear color cataract; 68% had cortical cataract. All IOLs were monofocal with 21 having blue blocking characteristics and 3 had clear IOLs. Most eyes had higher RIT post-surgery (15.6 min, SD 6.7) as compared to pre-surgery (13.7 min, SD 6.4), = 0.0006, meaning that RMDA was slower post-surgery. Eyes with moderate cataract (<4 on any LOCS III grade) had RIT that increased on average by 0.7 min; those with more advanced cataract (≥4) had RIT that increased by 3.1 min ( = 0.0116). Results were unchanged when clear IOLs were removed from analysis.
CONCLUSION
RMDA was significantly slower (RIT was greater) following cataract surgery, with the greatest impact on RIT in older eyes after surgery for more advanced cataract. These findings suggest that persons with more advanced cataract may bias results when evaluating RMDA using RIT.
Topics: Humans; Aged; Dark Adaptation; Cataract Extraction; Capsule Opacification; Visual Acuity; Cataract
PubMed: 36662498
DOI: 10.1080/02713683.2023.2171438 -
The Biochemist Oct 2020The retina is famous for its ability to operate under a broad range of light intensities. This is partly due to the presence of two types of photoreceptor cells, rods...
The retina is famous for its ability to operate under a broad range of light intensities. This is partly due to the presence of two types of photoreceptor cells, rods and cones. Rods are used mostly for dim light vision, and cones are used for bright light and colour vision. These cells are also able to adapt to a broad range of light intensities using light- and dark-adaptation mechanisms. Dark adaptation is used by the vertebrate retina to increase its visual sensitivity when moving from a brightly lit environment to a dark environment. The brighter the surrounding light, the longer it takes for the retina to adapt to the dark. Most retina biologists have studied dark adaptation by exposing animals to a 90% bleach, meaning that 90% of the light-sensing proteins in these photoreceptor cells have been activated, followed by transfer of these animals to a dark room and analysis of their light sensitivity using electrophysiological methods. In this report, we introduce the basic elements of the visual system and describe how the system might operate during dark adaptation. We also introduce a novel role for cAMP-mediated phosphorylation of G protein-coupled receptor kinase 1 (GRK1), a major kinase in visual signalling.
PubMed: 33840915
DOI: 10.1042/BIO20200067 -
Plant Physiology Aug 2021
Topics: Adaptation, Physiological; Biological Transport; Crops, Agricultural; Dark Adaptation; Dehydration; Dendrobium; Flowers; Plant Breeding; Plant Senescence; Plant Stems; Polygalacturonase; Stress, Physiological; Thiamine; Vitis
PubMed: 35237806
DOI: 10.1093/plphys/kiab265 -
The Journal of International Medical... May 2021Oguchi's disease is a rare form of congenital stationary night blindness, associated with light-dependent golden fundus discoloration. In this report, we describe two... (Review)
Review
Oguchi's disease is a rare form of congenital stationary night blindness, associated with light-dependent golden fundus discoloration. In this report, we describe two cases of Oguchi's disease, both of which had two characteristic features: congenital stationary night blindness and fundoscopic manifestation of the Mizuo-Nakamura phenomenon. In both patients, fundus examination revealed a metallic sheen throughout the retina, which disappeared after 2.5 hours of dark adaptation, suggestive of the Mizuo-Nakamura phenomenon. The characteristic electroretinogram (ERG) changes (i.e., un-recordable rod response and reductions of maximal response, oscillatory potentials, and flicker response) in these patients confirmed the clinical diagnosis of Oguchi's disease. Furthermore, we discuss the results of our literature search for evidence concerning the diagnosis and pathogenesis of this rare disease. Further studies regarding the genes involved in phototransduction and light adaptation are needed to determine the pathogenesis of this rare disease.
Topics: Dark Adaptation; Electroretinography; Eye Diseases, Hereditary; Humans; Night Blindness; Retina
PubMed: 34057838
DOI: 10.1177/03000605211019921 -
Vision Research Nov 2021Following photopigment bleaching, the rhodopsin and cone-opsins show a characteristic exponential regeneration in the dark with a photocycle dependent on the retinal...
Following photopigment bleaching, the rhodopsin and cone-opsins show a characteristic exponential regeneration in the dark with a photocycle dependent on the retinal pigment epithelium. Melanopsin pigment regeneration in animal models requires different pathways to rods and cones. To quantify melanopsin-mediated light adaptation in humans, we first estimated its photopigment regeneration kinetics through the photo-bleach recovery of the intrinsic melanopsin pupil light response (PLR). An intense broadband light (~120,000 Td) bleached 43% of melanopsin compared to 86% of the cone-opsins. Recovery from a 43% bleach was 3.4X slower for the melanopsin than cone-opsin. Post-bleach melanopsin regeneration followed an exponential growth with a 2.5 min time-constant (τ) that required 11.2 min for complete recovery; the half-bleaching level (I) was ~ 4.47 log melanopic Td (16.10 log melanopsin effective photons.cm.s; 8.25 log photoisomerisations.photoreceptor.s). The effect on the cone-directed PLR of the level of the melanopsin excitation during continuous light adaptation was then determined. We observed that cone-directed pupil constriction amplitudes increased by ~ 10% when adapting lights had a higher melanopic excitation but the same mean photometric luminance. Our findings suggest that melanopsin light adaptation enhances cone signalling along the non-visual retina-brain axis. Parameters τ and I will allow estimation of the level of melanopsin bleaching in any light units; the data have implications for quantifying the relative contributions of putative melanopsin pathways to regulate the post-bleach photopigment regeneration and adaptation.
Topics: Adaptation, Ocular; Dark Adaptation; Humans; Light; Photobleaching; Retinal Cone Photoreceptor Cells; Retinal Rod Photoreceptor Cells; Rod Opsins
PubMed: 34315092
DOI: 10.1016/j.visres.2021.07.005 -
Vision (Basel, Switzerland) Sep 2021As life expectancy grows, so too will the number of people adversely affected by age. Although it is acknowledged that many conditions and diseases are associated with... (Review)
Review
As life expectancy grows, so too will the number of people adversely affected by age. Although it is acknowledged that many conditions and diseases are associated with age, this mini-review will present a current update of the various visual changes that generally occur in healthy individuals disregarding the possible effects of illness. These alterations influence how the world is perceived and in turn can affect efficiency or the ability to perform ordinary daily tasks such as driving or reading. The most common physical developments include a decreased pupil size and retinal luminance as well as changes both in intercellular and intracellular connections within the retina along the pathway to the visual cortex and within the visual cortex. The quantity and the physical location of retinal cells including photoreceptors, ganglion and bipolar retinal cells are modified. The clarity of intraocular organs, such as the intraocular lens, decreases. These all result in common visual manifestations that include reduced visual acuity, dry eyes, motility changes, a contraction of the visual field, presbyopia, reduced contrast sensitivity, slow dark adaptation, recovery from glare, variation in color vision and a decreased visual processing speed. Highlighting these prevalent issues as well as current and possible future innovations will assist providers to formulate treatments and thereby conserve maximum independence and mobility in the modern mature population.
PubMed: 34698313
DOI: 10.3390/vision5040046