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Background In modern times, horses are utilized not only for labour and transportation purposes but also for recreational activities such as competition and pleasure riding. In these various pursuits, the role of vision plays a crucial role. Electroretinography is the most used test to diagnose diseases of the retinal outer segment. There is a wide variety of devices to perform the electroretinography differing one from each other in the corneal electrode and the light stimulation. The Koijman electrode has been tested in dogs but not in horses. The main purpose of this study was to compare electroretinography parameters from horses sedated with detomidine alone or in combination with butorphanol, during a standardized protocol using the Koijman electrode and RETI-port® system. Seven mares were allocated to the detomidine and detomidine plus butorphanol group in a randomised, controlled, crossover study. Friedman and Willcoxon-signed ranked tests were used to compare the electroretinogram parameters. A Student’s t-test was used to compare differences in the number of artefacts to valid values ratio obtained under both sedation protocols. Results Dark adaptation peaked after 16 min under scotopic conditions in both groups. No significant differences in electroretinogram parameters between groups were observed. During the mixed rod and cone response evaluation under scotopic conditions, all mares made a movement of the head resulting in a high number of artefacts. The detomidine plus butorphanol group showed a non-significant tendency to have fewer artefacts and a longer duration of sedation compared to the detomidine group. Conclusions Detomidine alone or combined with butorphanol may be suitable to use Koijman electrode and the RETI-port® to perform a standardized long protocol in horses with some adaptations.

Patients deficient in the peroxisomal membrane protein ACBD5 regularly exhibit a dystrophy of the retina along with decline in visual acuity. Despite the prevalent retinal phenotype, information on the pathogenesis of the retinodystrophy is limited. To gain insight into the cellular, subcellular and molecular alterations occurring in the retina, we analyzed an ACBD5-deficient mouse model by immunofluorescence microscopy, electron microscopy, full-field electroretinography (ffERG) and as well as analytical and spatial mass spectrometry (MS)-based lipidomics techniques. Histological results implied that ACBD5-deficient mice exhibit a moderate degeneration of photoreceptor, bipolar, ganglion and retinal pigment epithelial cells accompanied, however, by a prominent activation of astroglia and microglia. Reduced a- and b-wave amplitudes from ffERG point to a severe functional dysregulation of retinal signal transduction with a focus at the level of the information-processing cell of the inner retina. At the lipidome level, very long-chain polyunsaturated fatty acids (VLC-PUFA) accumulated in phosphatidylcholines from retina homogenates, most likely disrupted by a decline in peroxisome functions. Remarkably, as revealed by MALDI MS imaging, these lipidome changes affected neither the whole retina nor the photoreceptor outer segments (POS), where VLC-PUFAs display the highest concentration in phospholipids of POS membrane discs. In contrast, VLC-PUFAs in ACBD5-deficient mice consistently accumulated in the inner retinal region from the outer (OPL) to inner plexiform layer (IPL). In line with VLC-PUFA-accumulations, photoreceptor ribbon synapses in the OPL showed morphological signs of degeneration on the ultrastructural level. Hence, peroxisomal dysfunction appears to affect cell type-specific lipid homeostasis, thereby disrupting local retinal membrane physiology leading to a severe neuroinflammation of the ACBD5-deficient mouse retina.

Diabetic retinopathy (DR) is a major source of retinal disease and vision loss worldwide. Current treatments fail to address the loss of neurons and are associated with significant side effects. Here, we investigated whether retinal progenitor cells (RPCs) could improve anatomic and functional outcomes in a rat model of DR. Male Long Evans (LE) rats were given streptozotocin (STZ), and the induction of diabetes was confirmed prior to the intravitreal injection of RPCs, either allogeneic (no immunosuppression) or human (with cyclosporin A), at 1 week post-induction. Animals were tested at 6 weeks post-induction via electroretinogram (ERG), optomotor response (OR), and contrast sensitivity (CS). Retinas were harvested post-mortem, 8 weeks post-STZ induction, and analyzed using immunohistochemistry (IHC). In rat RPC-treated eyes, ERG (b-wave, oscillatory potentials), OR, and CS all showed a positive effect for cell treatment versus controls. IHC showed a markedly diminished extravasation of albumin, a decreased VEGF expression, and an improved morphology in cellular and synaptic layers. Human RPC-treated eyes replicated a subset of these results. Together, this provides evidence of both anatomic and functional treatment effects in a rat model of DR, encompassing retinal neuroprotection as well as improved vascular integrity, thereby supporting the further investigation of intravitreal RPCs for the treatment of this condition.

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 photopic On–Off ERG, and outlines common clinical applications. A light stimulus duration of 150–200 ms is used in the presence of a rod-suppressing background to elicit cone-driven On- and Off-system ERG components. The On-response occurs after the stimulus onset and has a negative a-wave and positive b-wave. The Off d-wave is a positive component evoked by stimulus offset. Common diagnoses that may benefit from additional photopic On–Off ERG testing include retinal dystrophies and retinal disorders that cause dysfunction at a level that is post-phototransduction or post-receptoral. On–Off ERGs assess the relative involvement of On- and Off-systems and may be of use in the diagnosis of disorders such as complete and incomplete congenital stationary night blindness (complete and incomplete CSNB), melanoma-associated retinopathy, and some forms of autoimmune retinopathy. The photopic On–Off ERGs may also be useful in X-linked retinoschisis, Batten disease, Duchenne muscular dystrophy, spinocerebellar degeneration, quinine toxicity, and other retinal disorders.

The CRISPR/Cas9 system is a robust, efficient, and cost-effective gene editing tool widely adopted in translational studies of ocular diseases. However, in vivo CRISPR-based editing in animal models poses challenges such as the efficient delivery of the CRISPR components in viral vectors with limited packaging capacity and a Cas9-associated immune response. Using a germline Cas9-expressing mouse model would help to overcome these limitations. Here, we evaluated the long-term effects of SpCas9 expression on retinal morphology and function using Rosa26-Cas9 knock-in mice. We observed abundant SpCas9 expression in the RPE and retina of Rosa26-Cas9 mice using the real-time polymerase chain reaction (RT-PCR), Western blotting, and immunostaining. SD-OCT imaging and histological analysis of the RPE, retinal layers, and vasculature showed no apparent structural abnormalities in adult and aged Cas9 mice. Full-field electroretinogram of adult and aged Cas9 mice showed no long-term functional changes in the retinal tissues because of constitutive Cas9 expression. The current study showed that both the retina and RPE maintain their phenotypic and functional features in Cas9 knock-in mice, establishing this as an ideal animal model for developing therapeutics for retinal diseases.

PurposesNorth Carolina macular dystrophy (NCMD) is a rare autosomal dominant inherited disorder characterized by macular impairment with a variety of phenotypic manifestations. The aims of this study were to assess the clinical features of a Chinese family with NCMD and to identify the underlying genetic cause of the disease.MethodsThree patients from a Chinese family were included in this study. Detailed ophthalmological examinations were performed, including best corrected visual acuity (BCVA), slit lamp, dilated indirect ophthalmoscopy, fundus photography, optical coherence tomography (OCT), fundus autofluorescence, full-field electroretinography (ERG), and electrooculography (EOG). Genomic DNA was extracted from peripheral blood samples. Whole-genome sequencing and long-read genome sequencing were applied to detect the pathogenic variants. Sanger sequencing was performed to confirm the breakpoints.ResultsAll three patients had macular involvement ranging from patchy yellowish-white lesions to big-area thinning, which are typical for NCMD. The BCVA ranged from 20/50 to 20/20. OCT revealed varying degrees of macular structure disorganization. The ERG responses were normal, and the Arden ration of the EOG was reduced. A novel 134.6 kb (g.99932464-100067110dup) tandem duplication on chromosome 6 (NC_000006.11) encompassing the entire CCNC and PRDM13 genes and a DNase 1 hypersensitivity site in the MCDR1 locus was identified.ConclusionA novel large tandem duplication in MCDR1 locus was confirmed in a Chinese family with NCMD with a variety of macular phenotypes.

A set of electrophysiological studies of the visual system was run before and after the eight-month SIRIUS 20/21 international experiment, with recording of standard photopic electroretinograms (ERG), fl icker ERG for flickering at frequencies of 8.3, 10, 12, and 24 Hz, photopic negative response, and pattern ERG. The aim of the study was to obtain objective assessments of changes in the functional activity of retinal neurons in ground station crew members associated with long-term isolation and the influence of a set of stress factors. Moderate activation of the bioelectrical activity of photoreceptors and bipolar cells was fund, along with a slight decrease in the functioning of retinal ganglion cells after release from isolation. These changes may reflect adaptation of the visual sensory system of the test subjects to physical and psychoemotional stress in the experimental conditions. Further studies of the specific characteristics of changes in electroretinographic markers with increasing duration of the period of isolation are required to expand our understanding of visual system stress resistance and adaptation during long-term exposure of people to extreme environmental conditions.

Acoustic blast overpressure (ABO) injury in military personnel and civilians is often accompanied by delayed visual deficits. However, most animal model studies dealing with blast-induced visual defects have focused on short-term (≤1 month) changes. Here, we evaluated long-term (≤8 months) retinal structure and function deficits in rats with ABO injury. Adult male Long-Evans rats were subjected to ABO from a single blast (approximately 190 dB SPL, ∼63 kPa, @80 psi), generated by a shock tube device. Retinal function (electroretinography; ERG), visual function (optomotor response), retinal thickness (spectral domain–optical coherence tomography; SD-OCT), and spatial cognition/exploratory motor behavior (Y-maze) were measured at 2, 4, 6, and 8 months post-blast. Immunohistochemical analysis of glial fibrillary acidic protein (GFAP) in retinal sections was performed at 8 months post-blast. Electroretinogram a- and b-waves, oscillatory potentials, and flicker responses showed greater amplitudes with delayed implicit times in both eyes of blast-exposed animals, relative to controls. Contrast sensitivity (CS) was reduced in both eyes of blast-exposed animals, whereas spatial frequency (SF) was decreased only in ipsilateral eyes, relative to controls. Total retinal thickness was greater in both eyes of blast-exposed animals, relative to controls, due to increased thickness of several retinal layers. Age, but not blast exposure, altered Y-maze outcomes. GFAP was greatly increased in blast-exposed retinas. ABO exposure resulted in visual and retinal changes that persisted up to 8 months post-blast, mimicking some of the visual deficits observed in human blast-exposed patients, thereby making this a useful model to study mechanisms of injury and potential treatments.

To investigate the effect of ageing on the recovery of ocular blood flow, intravitreal oxygen tension and retinal function during and after intraocular pressure (IOP) elevation. Long Evans rats (3- and 14-month-old) underwent acute stepwise IOP elevation from 10 to 120 mmHg (5 mmHg steps each 3 minutes). IOP was then returned to baseline and recovery was monitored for 2 hours. Photopic electroretinograms (ERG) were recorded at each IOP step during stress and at each minute during recovery. Ocular blood flow and vitreal oxygen tension (pO2) were assayed continuously and simultaneously using a combined laser Doppler flow meter (LDF) and an oxygen sensitive fibre-optic probe, respectively. The combined sensor was placed in the vitreous chamber, proximal to the retina. Data were binned into 3 minute intervals during stress and 1 min intervals during recovery. Recovery data was described using a bi-logistic function. Rats of both ages showed similar susceptibility to IOP elevation, with pO2 showing a closer relationship to ERG than LDF. During recovery, both ages showed a distinctive two-phased recovery for all three measures with the exception of the LDF in 3-month-old rats, which showed only 1 phase. In all animals, LDF recovered fastest (<1 minute), followed by pO2 (<10 minute) and ERG (>1 hour). 14-month-old rats showed surprisingly faster and greater LDF recovery compared to the younger group, with similar levels of pO2 recovery. However, the ERG in these middle-aged animals did not fully recover after two hours, despite showing no difference in susceptibility to IOP during stress compared to the young group. Young and middle-aged eyes showed similar susceptibility to IOP elevation in terms of pO2, LDF and ERG. Despite this lack of difference during stress, older eyes did not completely recover function, suggesting a more subtle age-related susceptibility to IOP.

The purpose of this study was to better understand the role of ocular pigmentation and genetics in light-induced retinal damage. Adult pigmented [Long Evans (LE) and Brown Norway (BN)] and albino [Sprague Dawley (SD) and Lewis (LW)] rats were exposed to a bright cyclic light for 6 consecutive days and where compared with juvenile animals exposed to the same bright light environment from postnatal age 14 to 28. Flash ERGs and retinal histology were performed at predetermined days (D) post-light exposure. At D1, ERGs were similar in all adult groups with no recordable a-waves and residual b-waves. A transient recovery was noticed at D30 in the LW and LE only [b-wave: 18% and 25% of their original amplitude respectively]. Histology revealed that BN retina was the most damaged, while LE retina was best preserved. SD and LW rats were almost as damaged as BN rats. In contrast, the retina of juvenile BN was almost as resistant to the bright light exposure as that of juvenile LE rats. Our results strongly suggest that, although ocular pigmentation and genetic background are important factors in regulating the severity of light-induced retinal damage, the age of the animal at the onset of light exposure appears to be the most important determining factor.