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To investigate the effect of mild cataract and its surgery on the ISCEV standard electroretinogram (ERG) by comparing pre- and postoperative ERGs elicited from fully dilated eyes. Twenty-two patients participated. Each eye had cataract of grade 2 according to Emery-Little classification. None had complications during and after phacoemulsification and intraocular lens implantation. According to the ISCEV standard, pre- and 1-week postoperative full-field ERGs, dark adapted (DA) 0.01, DA 3, DA 3 oscillatory potentials (OPs), DA 10, and light adapted (LA) 3, and LA 3 flicker, were elicited from fully dilated eyes using skin electrodes. Photopic negative response (PhNR) 1 amplitude was measured from the baseline to the trough before the i-wave in the LA 3 ERG waveform. Statistical analysis was performed using SigmaPlot version 11.0 (Systat Software, Inc., San Jose, CA, USA). Pre- and postoperative data were compared using a paired t-test. Non-normally distributed data were evaluated using the Wilcoxon signed rank test. The pre- and 1-week postoperative amplitudes in each component were as follows: DA 0.01: 48.4 ± 19.5 μV and 57.1 ± 20.0 μV (p = 0.002), a-wave of DA3: 51.5 ± 14.8 μV and 58.3 ± 17.3 μV (p = 0.003), b-wave of DA3: 88.3 ± 27.5 μV and 101.5 ± 29.7 μV (p = 0.003), DA 3 ΣOPs (sum of DA 3 OP1, OP2, and OP3 amplitude): 30.7 ± 16.3 μV and 37.1 ± 21.9 μV (p

Light-adapted (LA) electroretinograms (ERGs) from 90 individuals with autism spectrum disorder (ASD), mean age (13.0 ± 4.2), were compared to 87 control subjects, mean age (13.8 ± 4.8). LA-ERGs were produced by a random series of nine different Troland based, full-field flash strengths and the ISCEV standard flash at 2/s on a 30 cd m−2 white background. A random effects mixed model analysis showed the ASD group had smaller b- and a-wave amplitudes at high flash strengths (p

Mai A Mohammed,1 Mohamed Saad Morsy,1 Nashwa Shehata Zeater,2 Nader Bayoumi1 1Ophthalmology Department, Faculty of Medicine, Alexandria University, Alexandria, Egypt; 2Resident of Ophthalmology, Damanhour Eye Hospital, Damanhour, EgyptCorrespondence: Mai A Mohammed 36 Kamaleldin Salah, Semouha, Alexandria, EgyptTel +201221081590Fax +203 42 444 41Email mai.abdalnabi@yahoo.comBackground: To evaluate the VEP parameters in operated controlled primary congenital glaucoma (PCG) eyes and compare them to normal age similar children eyes.Methods: A cross-sectional comparative study conducted on 34 (19 right) eyes of 26 (19 males) children operated for PCG and 30 (17 right) eyes of 22 (12 males) age similar control children in a university-based practice. All study participants were subjected to a standard protocol of examination and electrophysiological testing (single flash VEP response, light adapted, pupils not dilated), reporting on the P2 implicit time, N1-P1 and N2-P2 (amplitude).Results: The mean±SD of the age of the study children and controls was 43.22± 33.2 and 55.68± 35.2 months respectively (p=0.217). The mean±SD IOP and cup/disc ratio of the study children were 18.4± 5.2 and 5.2± 3.3mmHg and 0.7± 0.2 and 0.3± 0.3 at presentation and at testing, respectively. The VEP testing was conducted after 21.5± 21.3 months of surgery for PCG. There was no statistically significant differences in P2, N1-P1 and N2-P2 between patients and controls (p=0.941, 0.916,0.945, respectively). There was no statistically significant correlation between most of the clinical characteristics of the study eyes and any of the studied VEP parameters.Conclusion: Operated controlled PCG eyes have VEP parameters that match their normal fellow children.Keywords: primary congenital glaucoma, visual evoked potentials, optic nerve, electrophysiology

Dopamine modulation of retinal signaling has been shown to be an important part of retinal adaptation to increased background light levels, but the role of dopamine modulation of retinal inhibition is not clear. We previously showed that light adaptation causes a large reduction in inhibition to rod bipolar cells, potentially to match the decrease in excitation after rod saturation. In this study, we determined how dopamine D1 receptors in the inner retina contribute to this modulation. We found that D1 receptor activation significantly decreased the magnitude of inhibitory light responses from rod bipolar cells, whereas D1 receptor blockade during light adaptation partially prevented this decline. To determine what mechanisms were involved in the modulation of inhibitory light responses, we measured the effect of D1 receptor activation on spontaneous currents and currents evoked from electrically stimulating amacrine cell inputs to rod bipolar cells. D1 receptor activation decreased the frequency of spontaneous inhibition with no change in event amplitudes, suggesting a presynaptic change in amacrine cell activity in agreement with previous reports that rod bipolar cells lack D1 receptors. Additionally, we found that D1 receptor activation reduced the amplitude of electrically evoked responses, showing that D1 receptors can modulate amacrine cells directly. Our results suggest that D1 receptor activation can replicate a large portion but not all of the effects of light adaptation, likely by modulating release from amacrine cells onto rod bipolar cells. NEW & NOTEWORTHY We demonstrated a new aspect of dopaminergic signaling that is involved in mediating light adaptation of retinal inhibition. This D1 receptor-dependent mechanism likely acts through receptors located directly on amacrine cells, in addition to its potential role in modulating the strength of serial inhibition between amacrine cells. Our results also suggest that another D2/D4 receptor-dependent or dopamine-independent mechanism must also be involved in light adaptation of inhibition to rod bipolar cells.

The effects of dopamine D2-class receptor blockade by sulpiride on the electroretinographic (ERG) b-wave (ON response) and d-wave (OFF response) were investigated in light-adapted turtle (Trachemys scripta elegans) and frog (Rana ridibunda) eyecups. For turtle ERG, sulpiride (240 μM) produced an amplitude increase of the b- and d-waves, while the 40 μM and 120 μM of sulpiride were ineffective. Alternatively, for frog ERG, a well-developed and dose-dependent b- and d-wave amplitude decrease was obtained with 40 μM and 240 μM sulpiride. In both species, 240 μM sulpiride significantly affected the maximal voltage range of the ERG responses without altering their relative sensitivity (determined by the semi-saturation point). The absolute sensitivity of the ON and OFF responses (evaluated by threshold estimation) was not significantly altered for turtle ERG, but it was decreased for frog ERG. The time characteristics of the ERG responses were unchanged in both species. Our results show important differences between dopamine D2-class receptor-mediated pathways in turtle and frog retina (revealed by ERG).

The International Society for Clinical Electrophysiology of Vision (ISCEV) standard for full-field electroretinography (ERG) describes a minimum protocol for clinical testing but encourages additional ERG testing when appropriate. This ISCEV extended protocol describes methods to record and evaluate a light-adapted (LA) ERG stimulus–response series with increasing flash strengths. The LA ERG stimulus–response series (also referred to as the luminance–response or intensity–response series in the published literature) can characterise generalised cone system function more comprehensively than the ISCEV standard LA ERGs alone. The amplitude of LA ERG a-waves, arising from cones and cone off-bipolar cells, typically shows a saturating function. The LA ERG b-wave amplitudes, which arise primarily from activity of retinal bipolar cells, show an amplitude peak followed by a nonzero plateau (the “photopic hill” phenomenon). This ISCEV extended protocol specifies a stimulus–response series suitable to evaluate generalised dysfunction affecting the LA retina, to aid in distinguishing between the on- and off-responses of the cone system and to monitor ERG changes in these characteristics. The LA ERG stimulus–response series for a- and b-waves is recorded to a sequence of nine flash stimuli ranging from 0.03 to 300 cd s m−2, superimposed on a standard background of 30 cd m−2. A shorter protocol is also presented to measure the mid-range of the function (the “photopic hill”) using 5 flash stimuli.

During adaptation from dim to bright environments, changes in retinal signaling are mediated, in part, by dopamine. Dopamine is released with light and can modulate retinal receptive fields, neuronal coupling, inhibitory receptors, and rod pathway inhibition. However, it is unclear how dopamine affects inner retinal inhibition to cone bipolar cells, which relay visual information from photoreceptors to ganglion cells and are important signal processing sites. We tested the hypothesis that dopamine (D)1 receptor activation is sufficient to elicit light-adapted inhibitory changes. Local light-evoked inhibition and spontaneous activity were measured from OFF cone bipolar cells in dark-adapted mouse retinas while stimulating D1 receptors, which are located on bipolar, horizontal, and inhibitory amacrine cells. The D1 agonist SKF38393 reduced local inhibitory light-evoked response magnitude and increased response transience, which mimicked changes measured with light adaptation. D1-mediated reductions in local inhibition were more pronounced for glycinergic than GABAergic inputs, comparable with light adaptation. The effects of D1 receptors on light-evoked input were similar to the effects on spontaneous input. D1 receptor activation primarily decreased glycinergic spontaneous current frequency, similar to light adaptation, suggesting mainly a presynaptic amacrine cell site of action. These results expand the role of dopamine to include signal modulation of cone bipolar cell local inhibition. In this role, D1 receptor activation, acting primarily through glycinergic amacrine cells, may be an important mechanism for the light-adapted reduction in OFF bipolar cell inhibition since the actions are similar and dopamine is released during light adaptation. NEW & NOTEWORTHY Retinal adaptation to different luminance conditions requires the adjustment of local circuits for accurate signaling of visual scenes. Understanding mechanisms behind luminance adaptation at different retinal levels is important for understanding how the retina functions in a dynamic environment. In the mouse, we show that dopamine pathways reduce inner retinal inhibition similar to increased background luminance, suggesting the two are linked and highlighting a possible mechanism for light adaptation at an early retinal processing center.

Many demersal fish species undergo vertical shifts in habitats during ontogeny especially after larval metamorphosis. The visual spectral sensitivity shifts with the habitat, indicating a change in colour vision. Colour vision depends on sufficient ambient light and becomes ineffective at a particular low light intensity. It is not known how fishes see colour in dim light. By means of a behavioural experiment on larval African catfish Clarias gariepinus in the laboratory, we determined colour vision and colour discrimination in dim light. Light-adapted larvae were subjected to classical conditioning to associate a reward feed with a green or a red stimulus placed among 7 shades of grey. The larvae learned this visual task after 70 and 90 trials. A different batch of larvae were trained to discriminate between green and red and then tested for the ability to discriminate between these colours, as the light intensity was reduced. The larvae learned this visual task after 110 trials in bright light and were able to discriminate colours, as light was dimmed until 0.01 lx, the minimal illuminance measurable in this study, and similar to starlight. The retinae of the larvae were found to be light adapted at 0.01 lx; thus indicating cone-based colour vision at this illuminance. For comparison, three human subjects were tested under similar conditions and showed a colour vision threshold at between 1.5 and 0.1 lx. For the larvae of C. gariepinus, the ability of colour discrimination in dim light is probably due to its retinal tapetum, which could increase the sensitivity of cones.

To analyze the effects of different methods of measurement on the photopic negative response (PhNR), recorded as part of a standard ISCEV Photopic 3.0 ERG responses from patients with a variety of clinical diagnoses. ERGs were recorded from both eyes of 97 patients (187 eyes) as part of a standard clinical assessment. The average age was 56.4 ± 15.7 years, the gender balance was 35 M, 62F, and only recordable responses of acceptable quality were included. PhNR was measured at an identifiable trough before (PhNR1) and after the i-wave (PhNR2), and the amplitudes and peak times were compared with a-, b- and i-wave corresponding parameters. PhNR components were measured: from baseline and from b-wave peak. Correlation between PhNR troughs and with ERG parameters were tested for right eyes. The possibility to predict and substitute PhNR2 amplitude from PhNR1 amplitude was also tested. PhNR1 was recordable in 97.3% of eyes and PhNR2 in 85.6%. An identifiable PhNR2 peak was found to occur before 65 ms at ~ 50% of the records, while in ~ 38% of the cases was within 65–75 ms in ~ 12%—after 75 ms. The correlation between the PhNR1 and PhNR2 peaks was quite strong (with coefficients 0.81–0.98, depending on method of measurement, and slopes close to 1). The average difference between predicted and measured PhNR2 was reasonably small in absolute (

Visual abilities of the honey bee have been studied for more than 100 years, recently revealing unexpectedly sophisticated cognitive skills rivalling those of vertebrates. However, the physiological limits of the honey bee eye have been largely unaddressed and only studied in an unnatural, dark state. Using a bright display and intracellular recordings, we here systematically investigated the angular sensitivity across the light adapted eye of honey bee foragers. Angular sensitivity is a measure of photoreceptor receptive field size and thus small values indicate higher visual acuity. Our recordings reveal a fronto-ventral acute zone in which angular sensitivity falls below 1.9°, some 30% smaller than previously reported. By measuring receptor noise and responses to moving dark objects, we also obtained direct measures of the smallest features detectable by the retina. In the frontal eye, single photoreceptors respond to objects as small as 0.6° × 0.6°, with >99% reliability. This indicates that honey bee foragers possess significantly better resolution than previously reported or estimated behaviourally, and commonly assumed in modelling of bee acuity.

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.