Rate Of Dark Adaptation Research Articles

Conditional deletion of Des1 in the mouse retina does not impair the visual cycle in cones.

Cone photoreceptors are essential for vision under moderate to high illuminance and allow color discrimination. Their fast dark adaptation rate and resistance to saturation are believed to depend in part on an intraretinal visual cycle that supplies 11-cis-retinaldehyde to cone opsins. Candidate enzymes of this pathway have been reported, but their physiologic contribution to cone photoresponses remains unknown. Here, we evaluate the role of a candidate retinol isomerase of this pathway, sphingolipid δ4 desaturase 1 (Des1). Single-cell RNA sequencing analysis revealed Des1 expression not only in Müller glia but also throughout the retina and in the retinal pigment epithelium. We assessed cone functional dependence on Müller cell–expressed Des1 through a conditional knockout approach. Floxed Des1 mice, on a guanine nucleotide-binding protein subunit α transducin 1 knockout (Gnat1−/−) background to allow isolated recording of cone-driven photoresponses, were bred with platelet-derived growth factor receptor α (Pdgfrα)-Cre mice to delete Des1 in Müller cells. Conditional knockout of Des1 expression, as shown by tissue-selective Des1 gene recombination and reduced Des1 catalytic activity, caused no gross changes in the retinal structure and had no effect on cone sensitivity or dark adaptation but did slightly accelerate the rate of cone phototransduction termination. These results indicate that Des1 expression in Müller cells is not required for cone visual pigment regeneration in the mouse.—Kiser, P. D., Kolesnikov, A.V., Kiser, J. Z., Dong, Z., Chaurasia, B., Wang, L., Summers, S. A., Hoang, T., Blackshaw, S., Peachey, N. S., Kefalov, V. J., Palczewski, K. Conditional deletion of Des1 in the mouse retina does not impair the visual cycle in cones.

The ARMS2 A69S Polymorphism Is Associated with Delayed Rod-Mediated Dark Adaptation in Eyes at Risk for Incident Age-Related Macular Degeneration

To examine the association between sequence variants in genetic risk factors for age-related macular degeneration (AMD) and delayed rod-mediated dark adaptation (RMDA), the first functional biomarker for incident AMD, in older adults with normal macular health and early AMD. Cross-sectional. Adults 60 years of age or older showing normal macular health (defined as both eyes at step 1 on the Age-Related Eye Disease Study 9-step AMD classification system) and those with AMD in one or both eyes (defined as steps 2-9). Single nucleotide polymorphisms were genotyped in the complement factor H (CFH) and ARMS2 genes using a Taqman assay. Rod-mediated dark adaptation was assessed in 1 eye after photobleach with targets centered at 5° on the inferior vertical meridian. Rate of dark adaptation was defined by rod intercept time (RIT), duration (in minutes) required for sensitivity to reach a criterion sensitivity level in the latter half of the second component of rod recovery. Associations between CFH and ARMS2 polymorphisms and RMDA were adjusted for age and smoking. Rod intercept time. The sample consisted of 543 participants having both genotype and RIT determination; 408 showed normal macular health and 135 demonstrated AMD, most having early AMD (124 of 135). For the combined sample, higher RIT (slower RMDA) was observed for both the A69S variant in ARMS2 and the Y402H variant in CFH (adjusted P= 0.0001 and P= 0.0023, respectively). For healthy participants, the A69S variant in ARMS2 was associated with higher RIT (adjusted P= 0.0011), whereas the Y402H variant in CFH was not (adjusted P=0.2175). For AMD patients, the A69S variant of ARMS2 and the Y402H variant of CFH were associated with higher RIT (adjusted P=0.0182 and P= 0.0222, respectively). Those with a larger number of high-risk ARMS2 and CFH alleles showed higher RIT, in both healthy and AMD groups (adjusted P= 0.0002 and P < 0.0001, respectively). We report a novel association wherein older adults with high-risk ARMS2 and CFH genotypes are more likely to demonstrate delayed RMDA, the first functional biomarker for incident early AMD. Before the AMD clinical phenotype is present, those showing normal macular health with the ARMS2 A69S allele demonstrate delayed RMDA. Understanding ARMS2 function is a research priority.

Characterization of Rod Function Phenotypes Across a Range of Age-Related Macular Degeneration Severities and Subretinal Drusenoid Deposits

PurposeTo examine spatial changes in rod-mediated function in relationship to local structural changes across the central retina in eyes with a spectrum of age-related macular degeneration (AMD) disease severity.MethodsParticipants were categorized into five AMD severity groups based on fundus features. Scotopic thresholds were measured at 14 loci spanning ±18° along the vertical meridian from one eye of each of 42 participants (mean = 71.7 ± 9.9 years). Following a 30% bleach, dark adaptation was measured at eight loci (±12°). Rod intercept time (RIT) was defined from the time to detect a −3.1 log cd/m2 stimulus. RITslope was defined from the linear fit of RIT with decreasing retinal eccentricity. The presence of subretinal drusenoid deposits (SDD), ellipsoid (EZ) band disruption, and drusen at the test loci was evaluated using optical coherence tomography.ResultsScotopic thresholds indicated greater rod function loss in the macula, which correlated with increasing AMD group severity. RITslope, which captures the spatial change in the rate of dark adaptation, increased with AMD severity (P < 0.0001). Three rod function phenotypes emerged: RF1, normal rod function; RF2, normal scotopic thresholds but slowed dark adaptation; and RF3, elevated scotopic thresholds with slowed dark adaptation. Dark adaptation was slowed at all loci with SDD or EZ band disruption, and at 32% of loci with no local structural changes.ConclusionsThree rod function phenotypes were defined from combined measurement of scotopic threshold and dark adaptation. Spatial changes in dark adaptation across the macula were captured with RITslope, which may be a useful outcome measure for functional studies of AMD.

Dark adaptation in relation to choroidal thickness in healthy young subjects: a cross-sectional, observational study.

BackgroundDark adaptation is an energy-requiring process in the outer retina nourished by the profusely perfused choroid. We hypothesized that variations in choroidal thickness might affect the rate of dark adaptation.MethodCross-sectional, observational study of 42 healthy university students (mean age 25 ± 2.0 years, 29 % men) who were examined using an abbreviated automated dark adaptometry protocol with a 2° diameter stimulus centered 5° above the point of fixation. The early, linear part of the rod-mediated dark adaptation curve was analyzed to extract the time required to reach a sensitivity of 5.0 × 10−3 cd/m2 (time to rod intercept) and the slope (rod adaptation rate). The choroid was imaged using enhanced-depth imaging spectral-domain optical coherence tomography (EDI-OCT).ResultsThe time to the rod intercept was 7.3 ± 0.94 (range 5.1 - 10.2) min. Choroidal thickness 2.5° above the fovea was 348 ± 104 (range 153–534) μm. There was no significant correlation between any of the two measures of rod-mediated dark adaptation and choroidal thickness (time to rod intercept versus choroidal thickness 0.072 (CI95 -0.23 to 0.38) min/100 μm, P = 0.64, adjusted for age and sex). There was no association between the time-to–rod-intercept or the dark adaptation rate and axial length, refraction, gender or age.ConclusionChoroidal thickness, refraction and ocular axial length had no detectable effect on rod-mediated dark adaptation in healthy young subjects. Our results do not support that variations in dark adaptation can be attributed to variations in choroidal thickness.Electronic supplementary materialThe online version of this article (doi:10.1186/s12886-016-0273-6) contains supplementary material, which is available to authorized users.

Increased Macular Pigment Optical Density and Visual Acuity following Consumption of a Buttermilk Drink Containing Lutein-Enriched Egg Yolks: A Randomized, Double-Blind, Placebo-Controlled Trial.

Purpose. To study the effect of 1-year daily consumption of a dairy drink containing lutein-enriched egg yolks on macular pigment optical density (MPOD) and visual function parameters in elderly subjects with ocular drusen and/or retinal pigment abnormalities. Methods. One hundred and one subjects were recruited to participate in this randomized, double-blind, placebo-controlled parallel intervention trial. Statistical analyses were performed with 46 subjects in the lutein group and 43 in the control group. MPOD, best corrected visual acuity (BCVA, logMAR), and dark adaptation were measured at the start of the study, after 6 months and after 12 months. Plasma lutein and zeaxanthin concentrations were assessed at baseline and at the end of the study. Results. In the lutein group, plasma lutein concentrations increased significantly from 205 ng/mL at baseline to 399 ng/mL after twelve months of intervention. MPOD increased significantly from 0.45 to 0.52 and BCVA improved significantly from −0.04 to −0.09 LogMar. Differences in rod dark adaptation rate between both groups were not significant. Conclusion. Daily consumption of a dairy drink containing lutein-enriched egg yolks for one year improves visual acuity, MPOD, and plasma lutein concentration in elderly subjects with drusen and/or retinal pigment epithelial abnormalities.

Assessment of retinal function and morphology in aging Ccl2 knockout mice.

The chemokine Ccl2, or monocyte chemoattractant protein-1 (MCP-1), has previously been identified as playing a potential role in many ocular diseases; however, its role in mice is less clear. We sought to correlate changes in retinal pigment epithelium (RPE) and retinal morphology with changes in function in aging Ccl2(-/-) mice. Ccl2(-/-) mice on a C57BL6J background were genotyped for Crb1(rd8/rd8) and were free of this mutation. Ccl2(-/-) mice and wild-type (WT) C57BL6J mice were investigated for changes in the retinal fundus and histology as a function of age. The function of the rod and cone pathways, and the rate of dark adaptation, was assessed using the electroretinogram (ERG) up to 15 months of age. Fifteen-month-old Ccl2(-/-) mice had fundus lesions, more subretinal microglia/macrophages, and an increase in RPE cell size, indicative of RPE cell loss, when compared with WT mice. Within the retina, gross morphology was normal but there was an increase in Müller cell gliosis and microglial activation. These morphological changes in the Ccl2(-/-) RPE/retina did not correlate with a change in either rod or cone ERG pathway function, or with the rate of dark adaptation. These data show that Ccl2 is important for preserving RPE and glial morphology with age, yet retinal function and gross morphology are maintained. Altered signaling in this chemokine pathway may, however, increase RPE and retinal vulnerability to disease.

AAV-mediated RLBP1 gene therapy improves the rate of dark adaptation in Rlbp1 knockout mice

Recessive mutations in RLBP1 cause a form of retinitis pigmentosa in which the retina, before its degeneration leads to blindness, abnormally slowly recovers sensitivity after exposure to light. To develop a potential gene therapy for this condition, we tested multiple recombinant adeno-associated vectors (rAAVs) composed of different promoters, capsid serotypes, and genome conformations. We generated rAAVs in which sequences from the promoters of the human RLBP1, RPE65, or BEST1 genes drove the expression of a reporter gene (green fluorescent protein). A promoter derived from the RLBP1 gene mediated expression in the retinal pigment epithelium and Müller cells (the intended target cell types) at qualitatively higher levels than in other retinal cell types in wild-type mice and monkeys. With this promoter upstream of the coding sequence of the human RLBP1 gene, we compared the potencies of vectors with an AAV2 versus an AAV8 capsid in transducing mouse retinas, and we compared vectors with a self-complementary versus a single-stranded genome. The optimal vector (scAAV8-pRLBP1-hRLBP1) had serotype 8 capsid and a self-complementary genome. Subretinal injection of scAAV8-pRLBP1-hRLBP1 in Rlbp1 nullizygous mice improved the rate of dark adaptation based on scotopic (rod-plus-cone) and photopic (cone) electroretinograms (ERGs). The effect was still present after 1 year.

Crizotinib reduces the rate of dark adaptation in the rat retina independent of ALK inhibition.

Crizotinib (Xalkori) is a tyrosine kinase inhibitor of both anaplastic lymphoma kinase (ALK) and mesenchymal-epithelial transition factor (c-Met). Though not predicted from standard nonclinical toxicological evaluation, visual disturbance became a frequently observed adverse event in humans. To understand the possible mechanism of this vision effect, an in vivo electroretinogram (ERG) study was conducted to assess retinal functional changes following oral administration of crizotinib. Immunohistochemical (IHC) staining of ALK and c-Met in the neural retinas of human, non-human primate, dog, rat, and mouse was used to aid in the animal model selection. ALK IHC staining was identified predominantly in the ganglion cell and inner nuclear layers of most species evaluated, in the inner plexiform layer in human and rodent, and in the nerve fiber layer in human and rat only. There was no apparent staining of any layer of the neural retina for c-Met in any of the species evaluated. ERG measurements identified a significant reduction in b-wave amplitude during the initial phase of dark adaptation in the crizotinib-treated rats. ERGs were also taken following oral administration of PF-06463922 (an ALK-selective inhibitor), for an understanding of potential kinase involvement. ERG effects were not observed in PF-06463922-treated animals when comparable exposures in the vitreous humor were achieved. Collectively, our results suggest that the ERG b-wave amplitude decreases during dark adaption following crizotinib administration may be related to signaling changes within the retina in rats, likely independent of ALK inhibition.

Low aqueous solubility of 11-cis-retinal limits the rate of pigment formation and dark adaptation in salamander rods

We report experiments designed to test the hypothesis that the aqueous solubility of 11-cis-retinoids plays a significant role in the rate of visual pigment regeneration. Therefore, we have compared the aqueous solubility and the partition coefficients in photoreceptor membranes of native 11-cis-retinal and an analogue retinoid, 11-cis 4-OH retinal, which has a significantly higher solubility in aqueous medium. We have then correlated these parameters with the rates of pigment regeneration and sensitivity recovery that are observed when bleached intact salamander rod photoreceptors are treated with physiological solutions containing these retinoids. We report the following results: (a) 11-cis 4-OH retinal is more soluble in aqueous buffer than 11-cis-retinal. (b) Both 11-cis-retinal and 11-cis 4-OH retinal have extremely high partition coefficients in photoreceptor membranes, though the partition coefficient of 11-cis-retinal is roughly 50-fold greater than that of 11-cis 4-OH retinal. (c) Intact bleached isolated rods treated with solutions containing equimolar amounts of 11-cis-retinal or 11-cis 4-OH retinal form functional visual pigments that promote full recovery of dark current, sensitivity, and response kinetics. However, rods treated with 11-cis 4-OH retinal regenerated on average fivefold faster than rods treated with 11-cis-retinal. (d) Pigment regeneration from recombinant and wild-type opsin in solution is slower when treated with 11-cis 4-OH retinal than with 11-cis-retinal. Based on these observations, we propose a model in which aqueous solubility of cis-retinoids within the photoreceptor cytosol can place a limit on the rate of visual pigment regeneration in vertebrate photoreceptors. We conclude that the cytosolic gap between the plasma membrane and the disk membranes presents a bottleneck for retinoid flux that results in slowed pigment regeneration and dark adaptation in rod photoreceptors.

PH dependence of Anabaena sensory rhodopsin: retinal isomer composition, rate of dark adaptation, and photochemistry.

Microbial rhodopsins are photoactive proteins, and their binding site can accommodate either all-trans or 13-cis retinal chromophore. The pH dependence of isomeric composition, dark-adaptation rate, and primary events of Anabaena sensory rhodopsin (ASR), a microbial rhodopsin discovered a decade ago, are presented. The main findings are: (a) Two pKa values of 6.5 and 4.0 assigned to two different protein residues are observed using spectroscopic titration experiments for both ground-state retinal isomers: all-trans, 15-anti (AT) and 13-cis, 15-syn (13C). The protonation states of these protein residues affect the absorption spectrum of the pigment and most probably the isomerization process of the retinal chromophore. An additional pKa value of 8.5 is observed only for 13C-ASR. (b) The isomeric composition of ASR is determined over a wide pH range and found to be almost pH-independent in the dark (>96% AT isomer) but highly pH-dependent in the light-adapted form. (c) The kinetics of dark adaptation is recorded over a wide pH range, showing that the thermal isomerization from 13C to AT retinal occurs much faster at high pH rather than under acidic conditions. (d) Primary photochemical events of ASR at pH 5 are recorded using VIS hyperspectral pump-probe spectroscopy with <100 fs resolution and compared with the previously recorded results at pH 7.5. For AT-ASR, these are shown to be almost pH-independent. However, photochemistry of 13C-ASR is pH-dependent and slowed down in acidic environments.

Brightness discrimination in the South African fur seal (Arctocephalus pusillus)

Underwater, the contrast between object and background is much larger reduced with increasing distance between object and observer than in air. For marine predators, such as pinnipeds, it would therefore be advantageous to possess a high sensitivity for brightness differences, since this would increase the distance at which prey can be detected visually. Few studies have examined the brightness discrimination thresholds of pinnipeds. Two studies with phocid seals have confirmed low brightness discrimination thresholds in pinnipeds whereas the threshold obtained for the South African fur seal seems to be twice as high as that of the phocids. However, the experiments with the South African fur seal have been conducted under inadequate conditions which likely resulted in an underestimation of the brightness discrimination ability of this species. The study at hand reinvestigated the brightness discrimination threshold of the South African fur seal under well controlled conditions. In a two alternative forced choice task, one fur seal was trained to indicate the position of the brighter of two gray discs presented on a black background on a monitor. The thresholds were determined for 11 standard intensities each tested against 8 lower comparison intensities. It was found that the fur seal was able to perceive brightness differences of 8-10%, which is better than the phocid species tested so far. For low standard intensities, however, the threshold increased which could to be due to a relative slow dark adaptation rate of the fur seal. The results are discussed in terms of the relevance of visual information for pinnipeds during foraging dives and are directly compared to the results obtained for the harbor seal which has been tested under the same conditions as the fur seal in a previous study.

Leukemia Inhibitory Factor Coordinates the Down-regulation of the Visual Cycle in the Retina and Retinal-pigmented Epithelium

Leukemia inhibitory factor (LIF), an interleukin-6 family neurocytokine, is up-regulated in response to different types of retinal stress and has neuroprotective activity through activation of the gp130 receptor/STAT3 pathway. We observed that LIF induces rapid, robust, and sustained activation of STAT3 in both the retina and retinal pigmented epithelium (RPE). Here, we tested whether LIF-induced STAT3 activation within the RPE can down-regulate RPE65, the central enzyme in the visual cycle that provides the 11-cis-retinal chromophore to photoreceptors in vivo. We generated conditional knock-out mice to specifically delete STAT3 or gp130 in RPE, retina, or both RPE and retina. After intravitreal injection of LIF, we analyzed the expression levels of visual cycle genes and proteins, isomerase activity of RPE65, levels of rhodopsin protein, and the rates of dark adaptation and rhodopsin regeneration. We found that RPE65 protein levels and isomerase activity were reduced and recovery of bleachable rhodopsin was delayed in LIF-injected eyes. In mice with functional gp130/STAT3 signaling in the retina, rhodopsin protein was also reduced by LIF. However, the LIF-induced down-regulation of RPE65 required a functional gp130/STAT3 cascade intrinsic to RPE. Our data demonstrate that a single cytokine, LIF, can simultaneously and independently affect both RPE and photoreceptors through the same signaling cascade to reduce the generation and utilization of 11-cis-retinal.

Low aqueous solubility of 11-cis-retinal limits the rate of pigment formation and dark adaptation in salamander rods

We report experiments designed to test the hypothesis that the aqueous solubility of 11-cis-retinoids plays a significant role in the rate of visual pigment regeneration. Therefore, we have compared the aqueous solubility and the partition coefficients in photoreceptor membranes of native 11-cis-retinal and an analogue retinoid, 11-cis 4-OH retinal, which has a significantly higher solubility in aqueous medium. We have then correlated these parameters with the rates of pigment regeneration and sensitivity recovery that are observed when bleached intact salamander rod photoreceptors are treated with physiological solutions containing these retinoids. We report the following results: (a) 11-cis 4-OH retinal is more soluble in aqueous buffer than 11-cis-retinal. (b) Both 11-cis-retinal and 11-cis 4-OH retinal have extremely high partition coefficients in photoreceptor membranes, though the partition coefficient of 11-cis-retinal is roughly 50-fold greater than that of 11-cis 4-OH retinal. (c) Intact bleached isolated rods treated with solutions containing equimolar amounts of 11-cis-retinal or 11-cis 4-OH retinal form functional visual pigments that promote full recovery of dark current, sensitivity, and response kinetics. However, rods treated with 11-cis 4-OH retinal regenerated on average fivefold faster than rods treated with 11-cis-retinal. (d) Pigment regeneration from recombinant and wild-type opsin in solution is slower when treated with 11-cis 4-OH retinal than with 11-cis-retinal. Based on these observations, we propose a model in which aqueous solubility of cis-retinoids within the photoreceptor cytosol can place a limit on the rate of visual pigment regeneration in vertebrate photoreceptors. We conclude that the cytosolic gap between the plasma membrane and the disk membranes presents a bottleneck for retinoid flux that results in slowed pigment regeneration and dark adaptation in rod photoreceptors.

Abstract 4385: Effect on retinal function as a mechanism for vision disorders with crizotinib (PF-02341066)

Abstract Crizotinib is a small-molecule receptor tyrosine kinase inhibitor of anaplastic lymphoma kinase (ALK) and c-Met. Crizotinib has been shown to be effective in patients with ALK-positive non-small cell lung cancer. One common adverse event that has been observed is a grade 1 vision disorder (∼45% of patients) characterized as seeing shadows or streaks during changes in lighting conditions. Onset occurs during the first weeks of treatment, with most cases improving with continued treatment and not requiring treatment discontinuation. Such vision disorders were not predicted from preclinical toxicological evaluation of crizotinib. To further understand the possible mechanism of this vision disorder, a rat electroretinography (ERG) study was conducted to determine if retinal function is altered following repeat-dose administration of crizotinib. Male Long-Evans rats (8/group) were administered crizotinib by oral gavage at a dose of 100 mg/kg/day for up to 29 days, during which an evaluation of in-life parameters (clinical signs, body weight, and food consumption), ophthalmic examinations, and ERG were performed. As part of the ERG assessment, five light-stimulation protocols were applied to test scotopic (dark-adapted) and photopic (light-adapted) luminance responses, photopic and scotopic adaptometry, and photopic flicker responses. Terminal plasma and vitreous fluid were examined for crizotinib concentrations in main study animals, and a toxicokinetic profile was obtained from a satellite group of 6 animals. Results of the ERG measurements identified a statistically significant (∼30%) reduction in mean b-wave amplitude relative to control during the initial 16 and 32 minutes of dark adaptation on Days 15 (p&amp;lt;0.05) and 29 (p&amp;lt;0.01), respectively. The magnitude of the reduction did not worsen between Days 15 and 29. Following 2 hours of dark adaptation, b-wave amplitudes were comparable between control and crizotinib-treated animals on both Days 15 and 29. There were no crizotinib-related effects observed for any other ERG parameters or during ophthalmologic examinations. Plasma exposures were ∼6-fold those associated with vision disorders in patients, and vitreous humor concentrations were 0.66-fold those in plasma at an equivalent time post-dose. Results from this preclinical model show that crizotinib causes significant reductions in the rate of retinal dark adaptation, but not the ability to achieve full dark adaptation. Vision disorders reported in the clinical setting may thus be due to direct effects on the retina rather than a central CNS effect. Whether this is a pharmacologically mediated effect at ALK or c-Met receptors expressed in retina or an off-target effect is not clear. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4385. doi:10.1158/1538-7445.AM2011-4385

Age-Related Deterioration of Rod Vision in Mice

Even in healthy individuals, aging leads to deterioration in visual acuity, contrast sensitivity, visual field, and dark adaptation. Little is known about the neural mechanisms that drive the age-related changes of the retina and, more specifically, photoreceptors. According to one hypothesis, the age-related deterioration in rod function is due to the limited availability of 11-cis-retinal for rod pigment formation. To determine how aging affects rod photoreceptors and to test the retinoid-deficiency hypothesis, we compared the morphological and functional properties of rods of adult and aged B6D2F1/J mice. We found that the number of rods and the length of their outer segments were significantly reduced in 2.5-year-old mice compared with 4-month-old animals. Aging also resulted in a twofold reduction in the total level of opsin in the retina. Behavioral tests revealed that scotopic visual acuity and contrast sensitivity were decreased by twofold in aged mice, and rod ERG recordings demonstrated reduced amplitudes of both a- and b-waves. Sensitivity of aged rods determined from single-cell recordings was also decreased by 1.5-fold, corresponding to not more than 1% free opsin in these photoreceptors, and kinetic parameters of dim flash response were not altered. Notably, the rate of rod dark adaptation was unaffected by age. Thus, our results argue against age-related deficiency of 11-cis-retinal in the B6D2F1/J mouse rod visual cycle. Surprisingly, the level of cellular dark noise was increased in aged rods, providing an alternative mechanism for their desensitization.

11-cis Retinol as a Substrate for Cone Dark Adaptation

We have determined the effectiveness of 11-cis retinol as a substrate for visual pigment formation in intact vertebrate cone and rod photoreceptors and measured opsin-mediated transducin activation by 11-cis retinol. Methods were of two types. Firstly, visual pigment absorbance spectra were measured microspectrophotometrically in single cone and rod photoreceptor outer segments before and after bleaching of the native visual pigment and following subsequent treatment with 11-cis retinal and 11-cis retinol. Secondly, we expressed human and salamander cone and rod opsins in COS cells and then tested in a cell free assay the effects of these retinoids on the activation of transducin by opsin. We show that 11-cis retinol promotes pigment formation in bleached red and blue salamander cones but not in bleached salamander red or green rods. Transducin activation experiments show that 11-cis retinol acts as an inverse agonist of red and green cone opsins, but has no effect on the activity of blue cone opsins. In contrast, 11-cis retinol acts as an agonist of rod opsin. We conclude that cones have a mechanism for handling retinoids and regenerating visual pigment that is different from rods. 11-cis Retinal and 11-cis retinol are usable substrates for cone pigment regeneration and dark adaptation as both retinoids promote pigment regeneration and neither elicits activation of the transduction cascade by opsin. On the other hand, 11-cis retinol is not useful for rod function since it does not promote pigment regeneration and its opsin-mediated activation of rod transducin may slow the rate of rod dark adaptation.

Effects of Long-Term Administration of 9-cis-Retinyl Acetate on Visual Function in Mice

Long-term effects of treatment with 9-cis-retinyl acetate (9-cis-R-Ac), an artificial retinoid prodrug, were tested on changes in rod and cone visual functions in mice. The acetyl ester of the functional geometric chromophore 9-cis-retinal was delivered by oral gavage to C57BL/6 female mice. In initial experiments, 10-month-old mice were used for the single treatment with 9-cis-R-Ac or the control vehicle. In long-term experiments, 4-month-old mice were treated with 9-cis-R-Ac monthly for 6 and 10 months. Photoreceptor status was evaluated by various electroretinographic (ERG) techniques, retinoid analyses, and retinal morphology. Opsin, the predicted target of oxidized 9-cis-R-Ac, was purified and its chromophore was characterized. Age-related changes observed in vehicle-treated mice at 10 months of age, compared with those in 4-month-old mice, included a progressive decline in ERG responses, such as a decreased rate of dark adaptation and a lowered rhodopsin/opsin ratio. Administration of 9-cis-R-Ac increased the rhodopsin regeneration ratio, and improved ERG responses and dark adaptation. Compared with vehicle-treated control animals, 10- and 14-month-old mice treated monthly with 9-cis-R-Ac for 6 or 10 months exhibited improved dark adaptation. In 14-month-old mice treated monthly, changes in the expression of retina-specific genes in the eye were detected by mRNA expression profiling, but no significant effects in gene expression were detected in the liver and kidney. Deteriorating photoreceptor function documented in mice at 10 and 14 versus 4 months of age was improved significantly by long-term, monthly administration of 9-cis-R-Ac. These findings suggest a potential therapeutic approach to prevent age-related retinal dysfunction.

Circadian Light Sensitivity and Rate of Retinal Dark Adaptation in Indoor and Outdoor Workers

Circadian Light Sensitivity and Rate of Retinal Dark Adaptation in Indoor and Outdoor Workers

Improvement in Rod and Cone Function in Mouse Model ofFundus albipunctatusafter Pharmacologic Treatment with 9-cis-Retinal

To assess changes in rod and cone visual functions in a mouse model of Fundus albipunctatus with disrupted 11-cis-retinol dehydrogenase (RDH) genes after pharmacologic treatment with an artificial retinal chromophore. Retinoid levels and photoreceptor functions of Rdh5-/-Rdh11-/- mice at a variety of light intensities were analyzed with normal-phase HPLC and ERG techniques. Production of 11-cis-retinal, the visual pigment chromophore, was suppressed with a potent inhibitor of the retinoid cycle, all-trans-retinylamine (Ret-NH2). The chromophore was replaced by a functional geometric isomer, 9-cis-retinal, delivered by oral gavage. Aberrant cone responses were detected in 12-month-old Rdh5-/-Rdh11-/- mice raised in a 12-hour light/12-hour dark cycle. This cone defect was exacerbated in conditions of low levels of 11-cis-retinal. Administration of 9-cis-retinal increased the rate of dark adaptation and improved cone function in Rdh5-/-Rdh11-/- mice. Disruption of 11-cis-RDHs causes a slowly developing cone dystrophy caused by inefficient cone pigment regeneration. Rod and cone visual function improved significantly in the mouse model of F. albipunctatus after treatment with 9-cis-retinal, suggesting a potential approach to slow the progression of cone dystrophy in affected humans.

The Scotopic Sensitivity Tester‐1 and the detection of early age‐related macular degeneration1

Previous research shows that dark adaptation is a marker of early age-related macular degeneration (ARMD), even when visual acuity remains good. This study evaluates whether a commercially available, off-the-shelf device for measuring dark adaptation, the Scotopic Sensitivity Tester-1 (SST-1), which uses a full-field stimulus, detects early ARMD as defined by fundus appearance. Fundus appearance is the gold standard method for defining the presence of ARMD. Dark adaptation was measured using the SST-1 in 12 young adults (mean age 23 years), 17 old adults with normal retinal health (mean age 69) and 19 old adults with early ARMD (mean age 74). Normal retinal health and presence of early ARMD were defined by masked grading of dilated fundus photographs using the Wisconsin Age-Related Maculopathy Grading System. Older adults in normal retinal health exhibited slower dark adaptation as compared with young adults. No difference in the rate of dark adaptation was found between early ARMD patients and older adults in normal retinal health. Although the SST-1 differentiated between young and older adults, it failed to detect dark adaptation abnormalities in early ARMD when referenced against older adults in normal retinal health. This may be attributable to the full-field stimulation used by the SST-1, which may be better suited for characterizing retinal degenerations affecting large retinal areas than for focal macular diseases like ARMD.