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Purpose: To determine the utility of ophthalmology evaluation, dark-adapted threshold, and full-field electroretinogram for early detection of Usher syndrome in young patients with bilateral sensorineural hearing loss. Methods: We identified 39 patients with secure genetic diagnoses of Usher Syndrome. Visual acuity, spherical equivalent, fundus appearance, dark-adapted threshold, and full-field electroretinogram results were summarized and compared to those in a group of healthy controls with normal hearing. In those Usher patients with repeated measures, regression analysis was done to evaluate for change in visual acuity and dark-adapted threshold with age. Spherical equivalent and full-field electroretinogram responses from dark- and light-adapted eyes were evaluated as a function of age. Results: The majority of initial visual acuity and spherical equivalent results were within normal limits for age. Visual acuity and dark-adapted threshold worsened significantly with age in Usher type 1 but not in Usher type 2. At initial test, full-field electroretinogram responses from dark- and light-adapted eyes were abnormal in 53% of patients. Remarkably, nearly half of our patients (17% of Usher type 1 and 30% of Usher type 2) would have been missed by tests of retinal function alone if evaluated before age 10. Conclusions: Although there is an association of abnormal dark-adapted threshold and full-field electroretinogram at young ages in Usher patients, it appears that a small but important proportion of patients would not be detected by tests of retinal function alone. Thus, genetic testing is needed to secure a diagnosis of Usher syndrome.

To study whether rod- and cone-driven electroretinogram (ERG) responses are altered in myopia patients. Dark- and light-adapted ERGs were recorded from 57 myopic eyes of 32 patients aged 22–30 and 19 emmetropic eyes of 10 age-matched normal subjects. The myopic eyes were divided into 3 groups according to spherical equivalent (SE) of manifest refraction: 18 low myopia eyes (≤ − 3.00 diopter (D), 23 moderate myopia eyes (− 3.25 to − 6.00 D), and 16 high myopia eyes (> − 6.25 D). The amplitudes of the dark- and light-adapted ERG a- and b-waves, as well as the frequency spectra of the cone-driven and rod-driven oscillatory potentials (OPs), were analyzed by fast Fourier transform. The peak frequency, implicit time, and total power of the OPs were determined. The axial length was measured with an IOL Master. The ERG parameters including those of the cone- and rod-driven OPs were compared among three groups. The amplitudes of the a-wave and b-wave of the dark-adapted ERGs were increased with refractive power (P

Forensic practitioners are recommended to dark adapt their eyes prior to conducting evidential searches in the dark. The dark adaptation process remains poorly standardised across the discipline, with little quantified regarding the benefits of such preparative steps. Herein, we report the findings of a study that recruited 50 participants to assess the effectiveness of the Crime-lite Eye™, a darkness adaptation device developed to assist forensic practitioners both in the laboratory and in field. Participants were tasked with searching for the fluorescent signatures left by reaction of 1,8-diazafluoren-9-one (DFO) with amino acids, in a manner akin to the fluorogenic fingerprint treatment of porous evidence. Using an Epson Stylus Photo R265 inkjet printer, ink cartridges were filled with alanine solutions of various concentrations, allowing different motifs to be printed onto copy paper and subsequently developed using DFO. Participants searched for this ‘evidence’ both with and without dark adapted vision. On average, participants were able to locate and correctly recognise 16% more evidence once dark adapted using the Crime-lite Eye™. The increase in evidence located by participants once dark adapted suggests that crime scene officers should be dark adapting in order to visualise as much as possible. The time taken to dark adapt, 10 min on average during this study, is not excessively long, and should not significantly slow the investigation.

Purpose Functional studies of rods in age-related macular degeneration using the Medmont Dark-Adapted Chromatic Perimeter (DACP) have demonstrated impairments in scotopic sensitivities and dark adaptation (DA). We investigated the intersession repeatability of scotopic sensitivity and DA parameters including the rod intercept time recorded from the Medmont DACP. Methods Scotopic thresholds (14 test points) and DA using a 30% photobleach (eight test points) were measured on two separate days from participants 50 years of age or older with a range of age-related macular degeneration severity at loci superior and inferior to the fovea. Repeatability coefficients were calculated for prebleach scotopic sensitivity, and for DA parameters including rod intercept time. Results Twelve participants (mean age, 79.7 ± 8.1 years) repeated Medmont DACP testing within 50 days. Repeatability coefficients for prebleach scotopic sensitivity to long wavelength (red, 625 nm) and short wavelength (cyan, 505 nm) were 5.9 dB and 7.2 dB, respectively. The DA curve-derived repeatability coefficients for cone threshold was 3.9 dB, final threshold 5.3 dB, with an R value of 0.075 decades/min, rod intercept time 7.6 minutes, and RITslope 0.54 min/degree. Conclusions This study establishes repeatability coefficients for scotopic thresholds and multiple DA parameters obtained with the Medmont DACP in patients with age-related macular degeneration. These repeatability coefficients will serve as the basis for determining clinically meaningful change in rod function in future clinical trials. Translational relevance Measures of repeatability parameters of scotopic thresholds and DA are essential to the accurate interpretation of results in future studies and trials using these measures.

The full-field electroretinogram (ff-ERG) is a widely used clinical tool to evaluate generalized retinal function by recording electrical potentials generated by the cells in the retina in response to flash stimuli and requires mydriasis. The purpose of this study was to determine the intra-visit reliability and diagnostic capability of a handheld, mydriasis-free ERG, RETeval (LKC Technologies, Gaithersburg, MD, USA), in comparison with the standard clinical ff-ERG by measuring responses recommended by the International Society for Clinical Electrophysiology of Vision (ISCEV).This prospective, cross-sectional study included 35 patients recruited at the Hospital for Sick Children (median age = 17, range 11 months-69 years) who had undergone a clinical ff-ERG according to ISCEV standards. For RETeval (n = 35), pupils were undilated in most (n = 29) and sensor strip electrodes were placed under the inferior orbital rim. Stimulus settings on RETeval were equivalent to those used in the clinical ERG. Fifty-seven control participants (median age = 22, range 8-65 years) underwent undilated RETeval ERG to establish standard values for comparison. Patient waveform components with amplitudes 5th percentile, or implicit times 95th percentile of normal relative to control data were classified as abnormal for the RETeval system.The RETeval system demonstrated a high degree of within-visit reliability for amplitudes (ICC = 0.82) and moderate reliability for implicit times (ICC = 0.53). Cohen's Kappa analysis revealed a substantial level of agreement between the diagnostic capability of RETeval in comparison with clinical ff-ERG (k = 0.82), with a sensitivity and specificity of 1.00 and 0.82, respectively. Pearson's correlations for clinical ERG versus RETeval demonstrated a positive correlation for amplitudes across the rod (r = 0.65) and cone (r = 0.74) ERG waveforms. Bland-Altman plots showed no bias between the mean differences across all amplitude and implicit time parameters of the two systems.The present study demonstrated that RETeval is a reliable tool with reasonable accuracy in comparison with the clinical ERG. The portable nature of RETeval system enables its incorporation at resource-limited centers where the ff-ERG is not readily available. The avoidance of sedation and pupillary dilation are added advantages of RETeval ERG.

The International Society for Clinical Electrophysiology of Vision (ISCEV) standard for full-field electroretinography (ERG) describes a minimum procedure, but encourages more extensive testing. This ISCEV extended protocol describes an extension to the ERG standard, namely the dark-adapted (DA) red flash ERG. The DA red flash ERG can be incorporated conveniently within the ISCEV standard ERG protocol after a minimum of 20-min DA and recorded after the DA 0.01 ERG to a flash strength of 0.3 phot cd s m−2, eliciting a waveform with two positive peaks in healthy individuals. The first positive component is the cone-mediated x-wave with a peak at 30–50 ms; the second is a rod-mediated b-wave with a peak time of approximately 100 ms. Shorter DA times may be desirable to shorten the recording time or to alter the prominence of the early cone-mediated x-wave relative to the rod-mediated b-wave. The DA red flash ERG is used to aid the diagnosis of achromatopsia (rod monochromacy), cone dystrophy and other forms of cone system dysfunction, including “Bradyopsia” (RGS9/R9AP-retinopathy), when the DA red flash ERG x-wave is preserved in the absence of ISCEV standard LA ERGs. The DA red flash ERG can also help determine the origin of residual DA ERGs in cases of severe rod dysfunction, for example in disorders such as vitamin A deficiency, fundus albipunctatus (RDH5-retinopathy), Oguchi disease (SAG- or GRK1-retinopathy) and some rod-cone dystrophies. To shorter DA periods, the x-wave may be elicited without the following rod b-wave, shown to be helpful in abbreviated protocols for children.

Purpose Macular telangiectasia type 2 (MacTel) is a bilateral neurodegenerative disorder of the central macula. Previous findings indicated more functional impairment in low light conditions. We sought to further characterize retinal dysfunction using dark-adapted two-color fundus-controlled perimetry ("scotopic microperimetry"). Methods Participants of the MacTel Natural History Observation Registry study and age-matched healthy controls underwent retinal imaging including dual wavelength autofluorescence macular pigment optical density (MPOD) measurement. Retinal sensitivity was assessed with scotopic microperimetry using cyan (505 nm) and red (627 nm). Disease was graded into classes of MPOD loss (0 to 3). For perimetry analysis, the differences of the mean sensitivities (MacTel minus controls) were compared at each test location and the results were aggregated to global indices. Results Thirty-four eyes (19 patients, mean age 62.2 years) were compared with 25 eyes (25 controls, mean age 61.5 years). Both cyan and red sensitivity were lower in MacTel. This was more pronounced at one- and three-degree eccentricity. Eyes with MPOD class 0 did not exhibit a functional deficit. Class 1 had impaired cyan, but normal red sensitivity. Class 2 and 3 behaved similarly and had impaired cyan and red sensitivity with a relatively higher cyan impairment. Conclusions Rods might be compromised to a greater extent than cones. Linking to previous studies, our results might also hint toward (postreceptoral) dysfunction of the cone system in very early disease stages. Macular pigment loss and global perimetry indices seemed to reflect functional impairment and might be useful as adjunct measures for disease progression.

The International Society for Clinical Electrophysiology of Vision (ISCEV) standard for full-field electroretinography (ERG) describes a minimum protocol for clinical testing but encourages more extensive testing where appropriate. This ISCEV extended protocol describes an extension of the ISCEV full-field ERG standard, in which methods to record and evaluate the growth of the dark-adapted (DA) ERG b-wave with increasing stimulus energy are described. The flashes span a range that includes the weakest flash required to generate a reliable DA ERG b-wave and that required to generate a maximal b-wave amplitude. The DA ERG b-wave stimulus–response series (also known historically as the “intensity–response” or “luminance–response” series) can more comprehensively characterize generalized rod system function than the ISCEV standard ERG protocol and may be of diagnostic or prognostic value in disorders that cause generalized rod system dysfunction.

Purpose The purpose of this study was to characterize changes in the full-field flash electroretinogram (ERG) in association with psychophysical dark-adapted visual thresholds in patients with genetically characterized Duchenne muscular dystrophy (DMD) either lacking Dp427 (Up 30) or at least Dp260 in addition to Dp427 (Down 30). Methods Twenty-one patients with DMD and 27 age-similar controls participated in this study. Dark-adapted (0.01, 3.0, and 10 cd.s/m² flashes) and light-adapted (3.0 cd.s/m² flash) ERGs were recorded following International Society for Clinical Electrophysiology of Vision (ISCEV) standard protocols. Visual detection thresholds to 625-nm (cone function) and 527-nm (rod function) light-emitting diode (LED) flashes (2 degree diameter) were measured during a dark adaptation period after a 1-minute exposure to a bleaching light (3000 cd/m²). Initially, 8 minutes of interleaved 625-nm and 527-nm thresholds were measured. After an additional 5 minutes of dark-adaptation, a second set of threshold measurements to 527-nm stimuli was performed during the subsequent 6 minutes. Results Dark-adapted b-wave amplitude was significantly reduced to all strengths of flash and a-wave in response to the strong flash stimulus was delayed (15.6 vs. 14.7 ms, P < 0.05) in patients with Down 30 compared with controls. Dark-adapted cone thresholds did not differ among the groups (−2.0, −1.8, and −1.7 log cd/m² for Down 30, Up 30, and controls, respectively, P = 0.21). In contrast, dark-adapted rod thresholds were elevated (F(2,36) = 8.537, P = 0.001) in patients with Down 30 (mean = −3.2 ± 1.1 log cd/m²) relative to controls (mean = −4.2 ± 0.3 log cd/m²). Dark-adapted b-wave amplitudes were correlated with dark-adapted rod sensitivity in patients with DMD (Spearman Rho = 0.943, P = 0.005). The changes were much smaller or absent in patients with intact Dp260. Conclusions Dp260 is particularly required for normal rod-system function in dark adaptation.

Our aim was to compare the electroretinographic (ERG) responses of two eyes obtained by consecutive unilateral recordings to those obtained by a simultaneous bilateral recording in sheep. Eight sheep underwent two full-field ERG recordings, using two recording strategies of the standard ISCEV protocol: consecutive unilateral recordings of one eye after the other, and simultaneous bilateral recording of both eyes. The order of recording strategy within an animal (unilateral/bilateral), eye recording sequence in the unilateral session (OD/OS), and amplifier channel assignment for each eye were all randomized. To test whether duration of dark adaptation and/or anesthesia affect the results, the ISCEV protocol was recorded bilaterally in six additional eyes following 38 min of patched dark adaptation, as was done for the second eye recorded in the consecutive unilateral recordings. The second recorded eye in the unilateral session had significantly higher scotopic b-wave amplitudes compared to the first recorded eye and to the bilaterally recorded eyes. A-wave amplitudes of the dark-adapted mixed rod–cone responses to a high-intensity flash were also significantly higher in the second eye compared to the first eye recorded unilaterally and to the bilaterally recorded eyes. Light-adapted responses were unaffected by the recording strategy. When the ISCEV protocol was recorded after 38 min of dark adaptation, the scotopic responses were higher than in the first eyes, and similar to those of the second eyes recorded unilaterally, suggesting that indeed the longer duration of anesthesia and dark adaptation are responsible for the increased scotopic responses of the second eye. Consecutive unilateral ERG recordings of two eyes result in higher amplitudes of the dark-adapted responses of the eye recorded second, compared to the eye recorded first and to bilaterally recorded eyes. The differences in scotopic responses can be attributed to different duration of dark adaptation and/or anesthesia of the two consecutively recorded eyes. Photopic responses are not affected. Therefore, simultaneous bilateral ERG responses should be recorded when possible, especially for evaluation of scotopic responses.

To evaluate rod and cone contributions to the dark-adapted 15-Hz flicker electroretinogram (ERG) across a broad range of stimulus luminances by comparing rod-isolating (ERGR), cone-isolating (ERGC), and non-receptor-specific (ERGR+C) responses.Dark-adapted, full-field 15-Hz ERGs were obtained from four normally sighted subjects (ages 29-36 years) using a four-primary LED-based stimulating system. The primaries were either modulated sinusoidally in phase (ERGR+C) or were modulated in counter-phase to achieve rod isolation (ERGR) or cone isolation (ERGC) by means of triple silent substitution. Measurements were made for a broad range of luminances (-2.5 to 1.8 log scot. cd/m(2) in 0.2 log unit steps). Fourier analysis was used to obtain the amplitude and phase of the fundamental response component at each stimulus luminance.Stimulus luminance had different effects on response amplitudes and phases under the three paradigms. Specifically, ERGC amplitude and phase increased monotonically as luminance increased. The effects on ERGR+C and ERGR were complex: ERGR+C and ERGR amplitude was small and the phase decreased for low luminances, whereas amplitude and phase increased sharply at moderate luminances. For high luminances, ERGR+C amplitude and phase increased, whereas ERGR amplitude decreased and phase was approximately constant.At low luminances, the ERGR+C and ERGR functions can be attributed to interactions between two rod pathways. At high luminances, the functions can be accounted for by interactions between rod and cone pathways (ERGR+C) or rod insensitivity (ERGR). The ERGR paradigm minimizes cone intrusion, permitting assessment of rod function over a large range of luminance levels.

Purpose To determine the effective dynamic range (EDR), retest reliability, and number of discriminable steps (DS) for mesopic and dark-adapted two-color fundus-controlled perimetry (FCP) using the S-MAIA (Scotopic-Macular Integrity Assessment) "micro-perimeter." Methods In this prospective cross-sectional study, each of the 52 eyes of 52 subjects with various macular diseases (mean age 62.0 ± 16.9 years; range, 19.1-90.1 years) underwent duplicate mesopic (achromatic stimuli, 400-800 nm), dark-adapted cyan (505 nm), and dark-adapted red (627 nm) FCP using a grid of 61 stimuli covering 18° of the central retina. The EDR, the number of DS, and the retest reliability for point-wise sensitivity (PWS) were analyzed. The effects of fixation stability, sensitivity, and age on retest reliability were examined using mixed-effects models. Results The EDR was 10 to 30 dB with five DS for mesopic and 4 to 17 dB with four DS for dark-adapted cyan and red testing. PWS retest reliability was good among all three types of retinal sensitivity assessments (coefficient of repeatability ±5.79, ±4.72, and ±4.77 dB, respectively) and did not depend on fixation stability or age. PWS had no effect on retest variability in dark-adapted cyan and dark-adapted red testing but had a minor effect in mesopic testing. Conclusions Combined mesopic and dark-adapted two-color FCP allows for reliable topographic testing of cone and rod function in patients with various macular diseases with and without foveal fixation. Retest reliability is homogeneous across eccentricities and various degrees of scotoma depth, including zones at risk for disease progression. These reliability estimates can serve for the design of future clinical trials.

Author(s): Panorgias, Athanasios; Tillman, Megan; Sutter, Erich E; Moshiri, Ala; Gerth-Kahlert, Christina; Werner, John S | Abstract: PurposeTo investigate the topographic changes of the dark-adapted multifocal electroretinogram (mfERG) across adulthood in the central retina and compare the topography between macular versus extramacular, nasal versus temporal, and inferior versus superior retinal areas.MethodsSixty-five subjects (18-88 years) received a comprehensive dilated eye examination to ensure the health of their retina and were tested with a dark-adapted mfERG protocol using a 61-hexagon pattern. The lens absorption of each subject was also estimated using a heterochromatic flicker photometry (HFP) paradigm.ResultsThe response amplitude and latency of the dark-adapted mfERG showed a significant change with age, which was best described with a linear model. All the retinal areas examined demonstrated similar aging effects. The extramacular and temporal retina showed higher response amplitude and faster response latency when compared with the macular and nasal retinae, respectively. No difference was found in response amplitude and latency between the inferior and superior retina. The HFP results also showed a significant correlation with age, consistent with senescent increases in short wavelength absorption by the crystalline lens. However, the change in lens absorption did not exceed the magnitude of the change in response amplitude and latency.DiscussionOur results indicate that there is a decline in dark-adapted retinal activity as measured with the mfERG. These aging processes affect rods and rod-bipolar cells. Their decrease in response can be attributed to both optical and neural factors.

This paper reports the first electrolysis-based oxygen generation and transportation device for the treatment of retinal ischemia; containing an isolated biocompatible electrolyte and inductive power transfer for on-demand oxygen. A finite element model of the retina along with oxygen delivery data demonstrates the feasibility of the device. The estimated therapeutic window for the device was found to be 210 minutes for the light adapted retina, and 55 minutes for the dark adapted retina.

Purpose: To determine whether the pupillary light reflex (PLR) can serve as an indicator of photoreceptor function in patients with advanced typical retinitis pigmentosa (RP). Methods: Dark-adapted transient PLRs elicited by blue or white light over a luminance range of 4 log units were recorded from 27 eyes of 19 patients with advanced RP. Retinas were characterized according to fundus autofluorescence (AF) and dark-adapted perimetry. We qualitatively analyzed whether PLR thresholds were correlated with AF patterns or scotopic sensitivity. Quantitative analysis included correlations between relative pupillary constrictions (RPCs) elicited by blue light (≤–1 log cd/m2) and the area of abnormal ring or central AF, and between RPCs elicited by white light and perimetric mean sensitivity. Results: The PLRs of all patients showed varying degrees of threshold elevation and relative afferent pupil defects. We classified three types of abnormal fundus AF: abnormal ring AF, abnormal central AF, and fragmentary AF. PLR thresholds were largely consistent with the patterns of AF and scotopic sensitivity. Rod-mediated RPCs were not correlated with the area of the abnormal ring AF (p > 0.05), but were correlated with the area of abnormal central AF (p < 0.05). RPCs elicited with a white stimulus (–0.3 or 0.7 log cd/m2) were significantly correlated with the mean sensitivity of the dark-adapted perimetry. Conclusions: PLR testing is a powerful technique for assessing photoreceptor dysfunction. The high correlation with AF and dark-adapted perimetry suggests that the key to quantifying photoreceptor function using the transient PLR is to optimize the luminance of the stimulus.

Based on a proposed model of the operation of the retina of a dark-adapted eye, the absolute sensitivity of the eye is calculated and is compared with that of a camera based on a cooled electron-multiplying CCD array. It is shown that the lowest observable brightnesses coincide in the two cases. The main factors that provide high visual sensitivity are indicated: a molecular light detector, a large detector area with a special noise-suppression system, and the absence of losses to scattering accompanying night vision.

The relatively large eye and pupil of the Piked Dogfish, Squalus acanthias, is visually arresting. However, knowledge of its basic visual characteristics lags far behind other areas in this generally well studied species. This study quantifies pupil dilation in a species that is naturally exposed to a broad range of light intensities and finds that the pupil area in the dark adapted state is 35.3% of the total eye area, an increase of 12.4% from the light adapted state. The anterior and posterior extents of the horizontal visual field are assessed and compared with both morphological and electrophysiological techniques and the results are integrated with the measured head yaw to derive the anterior convergence distance and blind area. The position of the eyes and the triangular, pointed snout of S. acanthias provides excellent anterior vision, which likely facilitates foraging upon its mobile prey.

Two EOG parameters - The Arden ratio (A) and an expression devised by Gliem (G) - from a sample of normal human subjects are studied. Their relations to the EOG potential and time parameters and to sex, age, pupillary diameter, degree of iris pigmentation, refractive error and axial length, ocular protrusion and interpupillary distance were assessed. Right eye and left eye distributions were congruent, although individual differences were sometimes appreciable, especially in the case of G. The two ratios were positively correlated and both showed a negative correlation to the interval between the dark trough and the light peak. Correlations to the EOG potential parameters, especially the light induced potential rise of the dark adapted eye, were also established. In the case of A, a higher level was disclosed in the male half of the sample. A negative age correlation, predominant in the female part of the sample, characterized both ratios. The two ratios were positively correlated to the pupil diameter, negatively correlated to the degree of refractive errror, and positively correlated to the degree of ocular protrusion. The consequences for the clinical EOG test are discussed, and it is concluded that the present EOG procedure is a qualitative rather than a quantitative test.

Purpose To determine the effects of a standardized intravenous dose of an α-2 agonist (Domitor®, Orion Pharma, distributed by Pfizer Animal Health, Exton, PA) on the electroretinogram (ERG) response in normal dogs. Methods Twenty-five normal dogs were used to collect ERG responses including a- and b-wave implicit times (IT) and amplitudes (AMP) before and after administration of medetomidine. Dogs were dark adapted for 20 min and ERGs were obtained using the HMsERG (RetVetCorp Inc., Columbia, MO). The QuickRetCheck protocol (Narfstrom) was employed to provide the following flash intensities: 10 mcd s/m2, 3 cd s/m2, and 10 cd s/m2. ERGs were repeated after 375 µg/m2 of medetomidine intravenously. Statistical analysis of the difference between the responses before and after medetomidine at all flash intensities was performed using a mixed effects model for anova. Results The P value for the effect of medetomidine on each of the ERG responses was

Glial Ca2+ excitability plays a key role in reciprocal neuron–glia communication. In the retina, neuron–glia signalling is expected to be maximal in the dark, but the glial Ca2+ signal characteristics under such conditions have not been evaluated. To address this question, we used bioluminescence imaging to monitor spontaneous Ca2+ changes under dark conditions selectively in Muller cells, the principal retinal glial cells. By combining this imaging approach with network analysis, we demonstrate that activity in Muller cells is organized in networks of coactive cells, involving 2–16 cells located distantly and/or in clusters. We also report that spontaneous activity of small networks (2–6 Muller cells) repeat over time, sometimes in the same sequential order, revealing specific temporal dynamics. In addition, we show that networks of coactive glial cells are inhibited by TTX, indicating that ganglion and/or amacrine neuronal cells probably regulate Muller cell network properties. These results represent the first demonstration that spontaneous activity in adult Muller cells is patterned into correlated networks that display repeated sequences of coactivations over time. Furthermore, our bioluminescence technique provides a novel tool to study the dynamic characteristics of glial Ca2+ events in the retina under dark conditions, which should greatly facilitate future investigations of retinal dark-adaptive processes.

Dopamine (DA) is an important modulator of light-adaptation in the vertebrate retina. A known source of DA in the retina is amacrine or interplexiform cells, but another potential source is the ret...

Structural and biophysical studies of rhodopsin have long depended upon the ready availability of bovine retina from the meat-packing industry and the relative ease of obtaining homogenous preparations of rhodopsin in the quantities and purities necessary for such study. Herein we present a modular purification methodology employing a combination of several strategies, beginning with sucrose gradient isolation of rod outer segments (ROS) from bovine retina, detergent solubilization of ROS, selective extraction of rhodopsin starting from this detergent-solubilized ROS, and further purification via size-exclusion chromatography, resulting in a preparation of high-purity rhodopsin at high concentration suitable for crystallization or other biophysical study.

Dark-adapted rods in the area surrounding a luminance-modulated field can suppress flicker detection. However, the characteristics of the interaction between rods and each of the cone types are unclear. To address this issue, the effect that dark-adapted rods have on specific classes of receptoral and postreceptoral signals was determined by measuring the critical fusion frequencies (CFF) for receptoral L-, M-, and S-cone and postreceptoral luminance ([L+M+S] and [L+M+S+Rod]) and chromatic ([L/(L+M)]) signals in the presence of different levels of surrounding rod activity. Stimuli were generated with a two-channel photostimulator that has four primaries for a central field and four primaries for the surround, allowing independent control of rod and cone excitation. Measurements were made either with adaptation to the stimulus field after dark adaptation or during a brief period following light adaptation. The results show that dark-adapted rods maximally suppressed the CFF by ∼6 Hz for L-cone, M-cone, and luminance modulation. Dark-adapted rods, however, did not significantly alter the S-cone CFF. The [L/(L+M)] postreceptoral CFF was slightly suppressed at higher surround illuminances, that is, higher than surround luminances resulting in suppression for L-cone, M-cone, or luminance modulation. We conclude that rod-cone interactions in flicker detection occurred strongly in the magnocellular pathway.

Purpose: To determine the individual variability of the dark-adapted pupil diameter over 2 testing sessions using a standardized dark-adaptation protocol. Setting: Texas Tech University Health Sciences Center, Lubbock, Texas, USA. Methods: In this prospective observational cohort study, 40 volunteers with no history of ocular disease, surgery, or injury other than requirement for refractive correction were included. The right eye was tested. A standardized dark-adaptation protocol was used that controlled for accommodation and patient alertness. Infrared, still digital photographs were taken after 5 and 10 minutes of dark adaptation and analyzed independently by 2 investigators using digital-image software. Two test sessions were performed 1 to 7 days apart. Lifestyle factors such as sleep, diet, and exercise were not controlled. Results: The mean subject age was 31.5 years (range 20 to 49 years). There were 20 men; 27 subjects wore correction for myopia, and 13 wore no correction. The mean interval between test sessions was 2 days (range 1 to 7 days). The mean difference and 95% confidence intervals for pupil diameter difference between sessions were as follows: 5-minute readings, +0.032 mm (−0.030 to +0.094); 10-minute readings, −0.006 mm (−0.059 to +0.047); mean of 5- and 10-minute readings, +0.013 mm (−0.038 to +0.064). Using the paired t test, the pupil diameter did not differ significantly between sessions in 5-minute dark adaptation ( P = .2980), 10-minute dark adaptation ( P = .8263), or the mean ( P = .6049). Conclusion: Using a consistent dark-adaptation protocol that controlled for alertness, individuals aged 20 to 49 years showed no significant variation in dark-adapted pupil diameter when tested twice in 1 week.

The dark-adapted cone electroretinogram (ERG) is difficult to isolate because of unwanted rod intrusion. We compare dark-adapted cone estimates derived using three techniques. The first uses the cone response on a moderate rod saturating background to estimate the dark-adapted cone response. The second uses red and blue flashes to tease apart cone and rod responses (red-minus-blue technique, [Investigative Ophthalmology and Visual Science 31 (1990) 2283]). The third uses a bright flash to temporarily saturate rods, followed by a test flash that generates a putative cone-only response (2-flash technique [Investigative Ophthalmology and Visual Science 36 (1995) 1603]). By subtracting the cone estimates from ‘mixed’ ERG responses in the dark, rod isolated responses can be derived. The rod phototransduction parameters, derived using a computational model, are similar using the light-adapted and 2-flash cone estimates, but differ using the red-minus-blue estimates. The 2-flash cone estimate gives a cone waveform similar to the dark-adapted response of a patient with Oguchi stationary night blindness (a patient with no rod ERG responses and normal cone ERG responses). The growth of the cone response during light adaptation to steady backgrounds causes significant differences between the light-adapted and 2-flash cone waveforms at times beyond the first few milliseconds.

One of the purposes of this study was to examine whether b-wave measurements can be used in the evaluation of scotopic spectral sensitivity in Prussian carp measurements when the eyes were surgically deprived of cornea, lens, and most of the vitreous. Another goal was testing the new fitting procedure for A2-based photopigments. Using fitted amplitude-log intensity functions for threshold calculation, and two models for computer-assisted fitting of spectral sensitivity curves, no significant differences in λ max were found between rod photopigments and b-wave-based spectral sensitivity.

BACKGROUND: The retinal response to flickering stimuli (steady state ERG) recruits many retinal elements and is a sensitive indicator of early retinal dysfunction. This study reports the post-natal maturation of the steady state ERG response in guinea pigs. METHODS: The steady state ERG response to flickering stimuli (0.6 to 20 Hz) was recorded from dark adapted (more than 12 hrs) English Shorthair guinea pigs (n = 7) using flashes that produced rod and cone dominated responses. Temporal sensitivity functions and critical fusion frequencies (CFF) were derived over a range of ages from postnatal day (PND) 1 to 45. RESULTS: Guinea pig rod and cone temporal sensitivity functions show shape characteristics and CFF similar to humans. Furthermore, the post-natal development of the guinea pig temporal characteristics is also similar to that of humans - they are present at birth and mature rapidly post-natally. The time-course of CFF maturation is similar for rod and cone mediated responses. CONCLUSIONS: These data show that the temporal response and its maturation in the guinea pig retina is similar to that in humans. Therefore, we propose that the guinea pig is a particularly useful animal model to study retinal disease in early childhood.

A signal-detection procedure was used to measure the influence of rods on S-cone-mediated ("tritan") chro- matic discrimination in normal trichromatic human observ- ers. Rod influence on discriminability of both increments and decrements in S-cone excitation was assessed by com- paring cone-plateau (minimizes rod influence) and dark adapted (maximizes rod influence) conditions. For 1° stim- uli, rods impaired tritan discrimination, especially for S- cone decrements. For 8° stimuli, rods had no systematic effects. This confirms that rods have the same direction of effect (impairment) on tritan discrimination as has been shown for Rayleigh (L-M) discrimination. However, the size dependence of the rod effect on tritan discrimination is opposite to that previously shown for either Rayleigh dis- crimination or hue appearance. This provides further evi- dence for separable rod influences on S-cone and L-M cone pathways. © 2000 John Wiley & Sons, Inc. Col Res Appl, 26, S65-S68

Yang, Xiong-Li and Samuel M. Wu. Response sensitivity and voltage gain of the rod- and cone-bipolar cell synapses in dark-adapted tiger salamander retina. J. Neurophysiol. 78: 2662–2673, 1997. Rods, cones, and bipolar cells were recorded in superfused, flat-mounted isolated retinas of the larval tiger salamander, Ambystoma tigrinum, under dark-adapted conditions. Voltage responses of 24 rods, 15 cones, and 41 bipolar cells in dark-adapted retinas to 500 nm light steps of various intensities were listed and fitted with hyperbolic functions, and their step sensitivities and relative sensitivities (log σ) were estimated. In the linear response-intensity ranges, the step sensitivity of rods, SS (rod), is −1.0 mV photon−1 μm2 s or 0.034 mV Rh*−1 s rod and that of the cones, S S (cone), is ∼0.00146 mV photon−1 μm2 s or 0.000048 mV Rh*−1 s rod. The rod and cone responses were relatively homogenous with little variations in response amplitude and sensitivity. In contrast, bipolar cell responses were heterogenous with large variations in response amplitude and sensitivity. The maximum response amplitude of bipolar cells varied from 5 to 25 mV, and the relative response sensitivity (log σ) varied >6 log units (−8.11 to −2.32). The step sensitivity of bipolar cells in the linear response-intensity range varied from 0.0000438 to 51.82 mV photon−1 μm2 s. Bipolar cells in dark-adapted tiger salamander retinas fell into two groups according to their relative sensitivities with very few cells falling in the intermediate light intensity region. The mixed bipolar cells (DBCM and HBCM) exhibited relative response sensitivity ranged from −8.11 to −5.54, and step sensitivity ranged from 1.22 to 51.82 mV photon−1 μm2 s. The cone-driven bipolar cells (DBCC and HBCC) exhibited relative response sensitivity ranged from −3.45 to −2.32, and step sensitivity ranged from 0.0000438 to 0.00201 mV photon-1 μm2 sec. The chord voltage gain of the rod-DBCM or rod-HBCM synapses near the rod dark membrane potential ranged from 1.14 to 48.43 and that of the cone-DBCC or cone-HBCC synaptic gain near the cone dark membrane potential ranged from 0.03 to 1.38. The highest voltage gains were found near the rod or cone dark membrane potentials. By the use of linear subtraction method, we studied the synaptic inputs from cones to five mixed bipolar cells, and the voltage gains of the cone synapses in each of the bipolar cells were very close to the voltage gain of the rod synapses. This result suggests that although the responses of mixed bipolar cells are mediated mainly by rods when lights of short and medium wavelengths are used, their responses to long wavelength lights (>650 nm) are mediated by both rods and cones with comparable synaptic gains. Functional roles of the mixed and cone-driven bipolar cells in information processing in dark-adapted retinas are discussed.

Purpose To investigate the effect of daily brimonidine tartrate 0.15% on the dark-adapted pupil diameter. Design Observational case series. Method Ten normal volunteers administered brimonidine to their right eyes once daily. Four to six hours later, infrared pupil photographs were taken after dark adaptation. Measurements were performed at baseline; on treatment days 1, 5, 11, and 18; and on washout days 1 and 2. Results One subject had no response. The nine responding subjects showed an average maximum antimydriatic effect of −1.63 mm (range, −0.57 mm–−2.30 mm); all subjects experienced tachyphylaxis. Five subjects showed rebound mydriasis (mean maximum rebound +0.87 mm larger than baseline; range 0.50 mm–1.22 mm). The untreated pupil also responded, showing antimydriasis (two subjects), rebound mydriasis (two subjects), or paradoxical direct mydriasis (one subject). Conclusions Once-daily use of brimonidine tartrate to prevent dark-induced pupil dilation can lead to tachyphylaxis and rebound mydriasis.

Purpose The purpose of this study was to develop a convenient means to measure rod (and cone) function by automated perimetry in patients with inherited retinal degenerations (IRDs). Methods A currently available automated perimeter was used to determine sensitivity (in decibels) to a blue target in the dark-adapted (DA) state and a white target in the light-adapted (LA) state. Normal subjects and IRD patients were evaluated with a full-threshold 71-locus strategy (the retinitis pigmentosa [RP] test) and a size III target. Comparisons were made with results from the more commonly used methods of two-color DA perimetry and middle/long-wavelength LA perimetry in the same patients. Results Rod function using the blue target and the RP test was determined for normal subjects by measuring DA sensitivities. If patients detected the blue stimulus in the DA state, it was determined whether the value was rod mediated by using normal data acquired during the cone plateau phase of dark adaptation. If rod mediated, rod sensitivity loss (RSL) was calculated and mapped across the visual field. Light-adapted sensitivities in normal subjects were also measured, permitting cone sensitivity losses (CSL) to be calculated for the patients. Multiple methods were used to compare RSL and CSL results with those from two-color DA perimetry and chromatic LA perimetry, and there was close correspondence between the methods. Conclusions The unmodified automated static perimeter used in the DA and LA states presents a practical approach to accomplish current goals of treatment trials in IRDs. This proof-of-principle study is an initial step toward establishing a clinical method to gather reproducible data on photoreceptor-mediated sensitivity.

The spectral sensitivity of the dark-adapted eye of the snail Helix lucorum L. was investigated in semi-intact "optic cupoptic nerve-cerebral ganglion" preparations. The data of the recording of the electroretinogram in response to monochromatic radiation of varied intensities were used to plot the spectral sensitivity functions. The averaged spectral sensitivity function is well described by a Dartnall nomogram for the photopigment rhodopsin with a sensitivity peak at 496 nm.

Purpose The ISCEV Standard for ERG does not include a measure of dark-adapted cone function. Prior to the introduction of the Standard, use of a red flash under dark-adapted conditions was a well-recognised part of ERG but its use appears subsequently to have declined. The purpose of the presentation is to demonstrate the importance of the dark-adapted red flash ERG in clinical ERG interpretation. Methods Retrospective case based presentation. Use of a red flash under dark adaptation can evoke an ERG in which there the early part of the waveform arises from the dark-adapted cone system and the latter part of the waveform from the rod system. The intensity of the red stimulus can be adjusted so that the rod-system derived part of the waveform has an amplitude similar to that of the rod specific ERG b-wave (DA 0.01). Results Cases will be shown where use of the dark-adapted red flash ERG enabled an improved interpretation of the bright flash ERG (DA 11.0). Disorders addressed will include fundus albipunctatus; vitamin A deficiency; RGS9 mutation (“bradyopsia”) and retinitis pigmentosa. An electronegative ERG waveform can occur arising in dark adapted cones, consistent with the so-called “photopic hill” phenomenon occurring in dark adapted cones exposed by an absence of rod function. The DA 11.0 ERG a-wave can reach in excess of 150µV under such circumstances, giving the potential for misdiagnosis of a form of inner retinal dysfunction such as may occur in CSNB. Conclusion The ISCEV Standard ERG waveforms are intended as a minimum data set. Use of a red stimulus under dark adaptation is a valuable addition to that data set and may prevent misinterpretation of the ISCEV Standard ERGs. The decline in the use of this ERG appears unjustified in routine clinical practice.

The cone-driven flash responses of mouse electroretinogram (ERG) increase as much as twofold over the course of several minutes during adaptation to a rod-compressing background light. The origins of this phenomenon were investigated in the present work by recording preflash-isolated (M-)cone flash responses ex vivo in darkness and during application of various steady background lights. In this protocol, the cone stimulating flash was preceded by a preflash that maintains rods under saturation (hyperpolarized) to allow selective stimulation of the cones at varying background light levels. The light-induced growth was found to represent true enhancement of cone flash responses with respect to their dark-adapted state. It developed within minutes, and its overall magnitude was a graded function of the background light intensity. The threshold intensity of cone response growth was observed with lights in the low mesopic luminance region, at which rod responses are partly compressed. Maximal effect was reached at intensities sufficient to suppress ∼90% of the rod responses. Light-induced enhancement of the cone photoresponses was not sensitive to antagonists and agonists of glutamatergic transmission. However, applying gap junction blockers to the dark-adapted retina produced qualitatively similar changes in the cone flash responses as did background light and prevented further growth during subsequent light-adaptation. These results are consistent with the idea that cone ERG photoresponses are suppressed in the dark-adapted mouse retina by gap junctional coupling between rods and cones. This coupling would then be gradually and reversibly removed by mesopic background lights, allowing larger functional range for the cone light responses.

Summary. 1. As a rule the refractive index for dark adapted retinae of cows was 1.358. 2. In a material of 321 cases the light adapted retina's index was 1.3610 ± 0.0008. 3. The experiments carried out support the supposition expressed by Kuhne Aand Ewald that visual purple exudes water when it is bleached. For this reason the value of the refractive index in light adapted retinae is higher than that in dark adapted ones. 4. The retinal refractive index in newly born calves in a material of 104 samples was 1.3621 ± 0.0012. 5. The refractive index for the retinae of pigs was 1.35733 ± ± 0.00167. The low index value possibly depends on the fact that the retina is poor in rods. 6. The refractive index in horses' eyes was as a rule 1.361.

Purpose: To measure the dark-adapted pupil diameter of normal research participants in their second through ninth decades of life using the NeurOptics pupillometer (Neuroptics Inc). Methods: Individuals aged 18 to 80 years with no history of eye disease or injury, intraocular surgery, or use of systemic antihistamines or opiates were recruited. After 2 minutes of adaptation at 1 lux illumination, the right dark-adapted pupil diameter was measured using the NeurOptics pupillometer, with accommodation controlled by distance fixation. The NeurOptics pupillometer reported a mean dark-adapted pupil diameter and a standard deviation of the mean, which were analyzed as a function of age-decade. Results: Two-hundred sixty-three individuals participated. For participants aged 18 to 19 years (n=6), the mean dark-adapted pupil diameter was 6.85 mm (range: 5.6 to 7.5 mm); 20 to 29 years (n=66), 7.33 mm (range: 5.7 to 8.8 mm); 30 to 39 years (n=50), 6.64 mm (range: 5.3 to 8.7 mm); 40 to 49 years (n=51), 6.15 mm (range: 4.5 to 8.2 mm); 50 to 59 years (n=50), 5.77 mm (range: 4.4 to 7.2 mm); 60 to 69 years (n=30), 5.58 mm (range: 3.5 to 7.5 mm); 70 to 79 years (n=6), 5.17 mm (range: 4.6 to 6.0 mm); and 80 years (n=4), 4.85 mm (range: 4.1 to 5.3 mm). These values were consistent with studies using infrared photography. The standard deviation was >0.1 mm in 10 (3.8%) participants, all of whom were younger than 55 years. Conclusions: The dark-adapted pupil diameter is an important clinical variable when planning refractive surgery. Surgeons can compare a patient’s dark-adapted pupil diameter with the results of this population study to identify outlier measurements, which may be erroneous, and repeat testing prior to surgery.

Human vision is approximately 10 times less sensitive than toad vision on a cool night. Here, we investigate (1) how far differences in the capacity for temporal integration underlie such differences in sensitivity and (2) whether the response kinetics of the rod photoreceptors can explain temporal integration at the behavioral level. The toad was studied as a model that allows experimentation at different body temperatures. Sensitivity, integration time, and temporal accuracy of vision were measured psychophysically by recording snapping at worm dummies moving at different velocities. Rod photoresponses were studied by ERG recording across the isolated retina. In both types of experiments, the general timescale of vision was varied by using two temperatures, 15 and 25 degrees C. Behavioral integration times were 4.3 s at 15 degrees C and 0.9 s at 25 degrees C, and rod integration times were 4.2-4.3 s at 15 degrees C and 1.0-1.3 s at 25 degrees C. Maximal behavioral sensitivity was fivefold lower at 25 degrees C than at 15 degrees C, which can be accounted for by inability of the "warm" toads to integrate light over longer times than the rods. However, the long integration time at 15 degrees C, allowing high sensitivity, degraded the accuracy of snapping toward quickly moving worms. We conclude that temporal integration explains a considerable part of all variation in absolute visual sensitivity. The strong correlation between rods and behavior suggests that the integration time of dark-adapted vision is set by rod phototransduction at the input to the visual system. This implies that there is an inexorable trade-off between temporal integration and resolution.

Bees are predominantly diurnal; only a few groups fly at night. An evolutionary limitation that bees must overcome to inhabit dim environments is their eye type: bees possess apposition compound eyes, which are poorly suited to vision in dim light. Here, we theoretically examine how nocturnal bees Megalopta genalis fly at light levels usually reserved for insects bearing more sensitive superposition eyes. We find that neural summation should greatly increase M. genalis’s visual reliability. Predicted spatial summation closely matches the morphology of laminal neurons believed to mediate such summation. Improved reliability costs acuity, but dark adapted bees already suffer optical blurring, and summation further degrades vision only slightly. � 2006 Elsevier Ltd. All rights reserved.

Purpose To study retinal function in cats homozygous and heterozygous for a recessively inherited rod-cone degeneration. Methods Dark-adapted electroretinograms (ERGs) were performed on early affected, heterozygous (ophthalmoscopically normal), and clinically normal, nonrelated cats. Responses to blue stimuli over a 3.9-log unit range were recorded. Results Lower b-wave amplitudes than normal were observed in heterozygotes and early affected cats. The amplitudes of the heterozygotes took an intermediate position between normal and early affected cats. Normalized amplitude/intensity data suggest a normal dynamic range in carriers. B-wave implicit times in carriers were comparable to those of normal cats. Conclusions These results show that heterozygotes have an altered retinal function, although they are ophthalmoscopically normal. It is difficult to electrophysiologically differentiate heterozygotes from affected cats with the very early stage of retinal degeneration.

Abundant evidence spanning 25 years demonstrates that hypopigmentation is associated with sensory abnormalities manifested most clearly as elevated absolute dark-adapted thresholds in hypopigmented mice. Here we show that when ocular melanin is increased in the himalayan mouse via α-melanocyte stimulating hormone (α-MSH) injections, dark-adapted thresholds drop in proportion to the change in ocular melanin. We further measured free calcium concentration with calcium-sensitive microelectrodes in both albino and black mouse retinal eyecups in living subjects. The recordings were done in anesthetized animals as the defect is not present in isolated retinas or in the superfused eye preparation. A double-barreled electrode—pCa and Vref—was used to simultaneously record the calcium concentration and the electroretinogram (ERG) at each of many depths as the electrode was driven through the retina. The position of the electrode was confirmed with ERG and 1,1′-dioctadecyl-3, 3,3′,3′-tetramethylindocarbocyanine perchlorate electrode tract reconstruction. Dark-adapted albinos ( n = 6) had 1.4 ± 0.015 mM calcium in the subretinal space compared with 0.80 ± 0.025 mM in black mice ( n = 6). The results of these experiments are consistent with the hypothesis that ocular hypopigmentation causes elevated calcium levels in the subretinal space that in turn mimic light adaptation in hypopigmented mice.

The most sensitive response in the dark-adapted electroretinogram (ERG), the scotopic threshold response (STR) which originates from the proximal retina, has been identified in several mammals including humans, but previously not in the mouse. The current study established the presence and assessed the nature of the mouse STR. ERGs were recorded from adult wild-type C57/BL6 mice anaesthetized with ketamine (70 mg kg(-1)) and xylazine (7 mg kg(-1)). Recordings were between DTL fibres placed under contact lenses on the two eyes. Monocular test stimuli were brief flashes (lambda(max) 462 nm; -6.1 to +1.8 log scotopic Troland seconds(sc td s)) under fully dark-adapted conditions and in the presence of steady adapting backgrounds (-3.2 to -1.7 log sc td). For the weakest test stimuli, ERGs consisted of a slow negative potential maximal approximately 200 ms after the flash, with a small positive potential preceding it. The negative wave resembled the STR of other species. As intensity was increased, the negative potential saturated but the positive potential (maximal approximately 110 ms) continued to grow as the b-wave. For stimuli that saturated the b-wave, the a-wave emerged. For stimulus strengths up to those at which the a-wave emerged, ERG amplitudes measured at fixed times after the flash (110 and 200 ms) were fitted with a model assuming an initially linear rise of response amplitude with intensity, followed by saturation of five components of declining sensitivity: a negative STR (nSTR), a positive STR (pSTR), a positive scotopic response (pSR), PII (the bipolar cell component) and PIII (the photoreceptor component). The nSTR and pSTR were approximately 3 times more sensitive than the pSR, which was approximately 7 times more sensitive than PII. The sensitive positive components dominated the b-wave up to5 % of its saturated amplitude. Pharmacological agents that suppress proximal retinal activity (e.g. GABA) minimized the pSTR, nSTR and pSR, essentially isolating PII which rose linearly with intensity before showing hyperbolic saturation. The nSTR, pSTR and pSR were desensitized by weaker backgrounds than those desensitizing PII. In conclusion, ERG components of proximal retinal origin that are more sensitive to test flashes and adapting backgrounds than PII provide the 'threshold' negative and positive (b-wave) responses of the mouse dark-adapted ERG. These results support the use of the mouse ERG in studies of proximal retinal function.

Anatomical studies of the developing zebrafish retina have shown that rods approach maturity at about 15 days postfertilization (dpf). Past work has examined the photopic spectral sensitivity function of the developing zebrafish, but not spectral sensitivity under dark-adapted conditions. This study examined rod contributions to the dark-adapted spectral sensitivity function of the ERG b-wave component in developing zebrafish. ERG responses to stimuli of various wavelengths and irradiances were obtained from dark-adapted fish at 6-8, 13-15, 21-24, and 27-29 dpf. The results show that dark-adapted spectral sensitivity varied with age. Spectral sensitivity functions of the 6-8 and 13-15 dpf groups appeared to be cone dominated and contained little or no rod contributions. Spectral sensitivity functions of the 21-24 and 27-29 dpf groups appeared to have both rod and cone contributions. Even at the oldest age group tested, the dark-adapted spectral sensitivity function did not match the adult function. Thus, consistent with anatomical findings, the rod contributions to the ERG spectral sensitivity function appear to develop with age; however, these contributions are still not adult-like by 29 dpf, which is contrary to anatomical work. These results illustrate that the zebrafish is an excellent model for visual development.

A physiological model of dark-adapted and light-adapted photoreceptors in the honeybee worker (Apis mellifera) has been developed. Almost all of the electrophysiological components of photoreceptors known up to date, e.g. the phototransduction cascade, the ion channels of the membrane, phototransduction gain and optical adaptation mechanisms, are adequately described by simple biophysical and biochemical models. The connections of these components were tried out in synthetic simulations for best fits of simulated to intracellularly recorded membrane potentials. Although the parameters of the best model were determined exclusively for the measured membrane potentials of dark-adapted photoreceptors, the model also accurately describes the light-adapted photoreceptor membrane potentials. Furthermore, the model correctly predicts the time-courses of measured photoreceptor responses with respect to squared-modulated flicker lights up to 200 Hz. This clearly demonstrates that the presented photoreceptor model is indeed a physiologically adequate description of the essential components of the phototransduction and the electrical membrane processes in the photoreceptors of the honeybee worker.

To investigate early changes of retinal function in the experimental myopic eyes in chicken, flash electroretinograms (f-ERGs) were recorded. The amplitudes of occluded eyes were larger than those of fellow eyes at the early stage of occlusion; but as th went on, the amplitudes gradually decreased. This result might reflect each retinal cell alteration caused by the disturbance of the development of the occluded eye during the early developing stage.

Intraocular funduscopy and photography permitted serial examination and documentation of time-related changes in the living toadfish (Opsanus tau) eye as it went from the dark-adapted to the light-adapted state. In the present study, the fully dark-adapted eye showed virtually no choroidal, pigment epithelial, or retinal vascular detail. The optic nerve was chalky white with indistinct borders. Grayish brown to chalky white retinal streaks radiated from the optic nerve into the periphery. As light adaptation began, the retinal streaks faded, with the retinal vasculature and the underlying choroidal and pigment epithelial detail becoming more discernible. Once the eye became fully light adapted, the typical geographic orange and black mottled appearance of the underlying pigment epithelium and choroid was visible, and the optic nerve head developed a pink hue with a distinct border. Even in the fully light-adapted eye, a vague radiation of lines could be seen extending from the optic nerve. This was superimposed on a cross-hatched mosaic of black dots seen throughout the fundus, not visible in the fully dark-adapted eye. Histological examination of the retina indicated forward migration of pigment in the pigment epithelium in the light-adapted state.

Chlorophyll a fluorescence is used as an indicator of stress damage to growing plants. Plants or plant samples first must be transported to a laboratory and dark adapted. If stress (e.g., drought) has not been severe enough to permanently damage the photosynthetic apparatus, plants may recover during dark adaption and stress may not be detectable. In situ readings are more reliable. Dark adaptation takes place after the onset of total darkness. The objective of this work was to develop a device that would enable the dark adaptation of plant leaves in situ during hours when stress could occur (...)

Experiments were conducted to verify whether the neurohormone melatonin influences the membrane conductance of photoreceptors isolated from the frog retina. It has been found that 20 microM melatonin decreases membrane conductances both in the linear and non linear ranges by0.4 nS. These actions are estimated to produce in dark adapted photoreceptors an increase of the response to a dim light induced change of the dark current of about 21%, i.e. from 1.3 to 1.62 mV/pA.

Dark adapted rods exert tonic suppressive influences upon cone-mediated vision, i.e. suppressive rod-cone interactions (SRCI). We have intensively studied two forms: (1) sensitivity to rapid flicker progressively decreases during rod-dark adaptation, and increases if rods are adapted to increasing intensity backgrounds. This ‘flicker-SRCF’ is mediated in distal retina and involves a prominent role for horizontal cells; (2) sensitivity to high spatial frequency gratings similarly decreases during rod-dark adaptation, and increases if rods are adapted to increasing intensity backgrounds. However, this ‘grating-SRCF’ is as prominent with interocular adapting fields as with one-eyed stimulation, and psychophysical data are inconsistent with an electrical coupling model accounting for flicker-SRCI. Contrast sensitivity is well-known to increase as the size of the visual display increases. For higher spatial frequencies, we show this influence of display size is likely to reflect a removal of SRCI rather than an effect of display size per se. Although counterintuitive, our data strongly suggests that night-time sensitivity to fine spatial and temporal detail should be improved under everyday conditions by maintaining rods in a slightly light- adapted state.

Although often thought of as a disease that primarily affects the rods, retinitis pigmentosa (RP) delays the implicit times of the cone ERGs very early in progression (see ref. 1 for review). The first two panels of Figure 1 show the cone responses recorded as part of a standard clinical protocol from a normal subject and four patients with RP. Cone ERGs are recorded by presenting a single white flash on a background that suppresses the rods (left panel) or by presenting a 30 Hz pulse train, too fast for the rods to follow, to the dark adapted eye (right panel). The vertical dashed lines in Fig. 1 mark the peak times for the normal observer and the patients’ records were selected to illustrate a range of implicit times. In general, patients with RP show delays in the peak response to both the single flashes and the 30 Hz flicker. These delays have been attributed, at least in part, to cone photoreceptor abnormalities, specifically to a decrease in quantal absorption by the cone outer segments (1–3). Other ERG evidence is more difficult to reconcile with only a change in quantal absorption (4–10).

Studies of the retinal sensitivity, as reflected in the ERG records, have been made, before, during, and after exposure of the eye to an argon laser beam ( > = 488 nm ; intensity 1 mW/cm2 ; durations 0.12 and 0.25 sec). The applied retinal load thus was similar as that during retinal treatments. The ERG records were carried out at different temperatures (10 - 30°C) for both light and dark adapted eyes. The aim of this study was to assess the best suitable conditions for retinal laser treatments without affecting other retinal tissues. The obtained results showed that the argon laser therapy causes some damage to the eye which is paralleled by a noticeable change in the b-wave amplitude (Ab) of the electroretinogram. This damage recovers faster when the laser dose and the eye temperature are reduced. Also it was preferable to perform these treatments in dark adapted eyes rather than in light adapted eyes. Simple calculations of the changes in the external K+ concentration, ΔK, induced by light stimulation were performed, before and after laser treatment, using Nernst equation modified by Miller relating Ab to the logarithm of the external K+ concentration. This led to the conclusion that laser treatment has an indirect effect on the eye through its direct effects on the pigment epithelium and photoreceptor membrane permeabilities to K+. Moreover, calculations of the repair-damage ratio represented by Ab variations, after laser exposure, helped for optimizing the laser conditions during treatments. This indicated that the ERG is a sensitive tool for studying the effects on the eye during treatments.