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The full-field, flash electroretinogram (ERG) is now a widely used test of canine retinal function for the clinical diagnosis of hereditary retinal dystrophies and other causes of retinal degeneration, assessment of retinal function in patients with opaque media, ruling out of generalized retinal diseases in patients with sudden loss of vision and in ophthalmological research, as well as in pharmaceutical and toxicological screening for deleterious side effects of drugs and other chemical compounds. In 2002, the first guidelines for clinical ERGs in this species adopted by the European College of Veterinary Ophthalmologists were published. This work provides an update of these guidelines. [ABSTRACT FROM AUTHOR]

These procedures described for the dog ERG were approved at the 1st European Conference on Veterinary Visual Electrophysiology in Vienna, Austria, May 30, 2000. Dr. Narfström was Chair of the Committee for a Harmonized ERG Protocol, appointed by the European College of Veterinary Ophthalmology (ECVO), and Dr. Ofri was secretary. The other coauthors are committee members. Guidelines for ERG procedures in other animal species for clinical and laboratory studies are planned for in the future and the present guidelines are planned to be revised on a biannual basis. A brief report of the recommended procedures is available in the Conference Proceedings book. [ABSTRACT FROM AUTHOR]

Introduction: Multifocal electroretinography (MF-ERG) is widely used in the detection of local retinal dysfunction. However, the position of the stimulus on the retina and the stability of fixation are usually not directly accessible. Thus, devices have been designed for a continuous fundus visualization during recording. Methods: MF-ERGs were recorded with a RetiScanTM system connected to two different Scanning-laser ophthalmoscopes (SLOs) that use either a red (633 nm) or green (415 nm) laser for stimulation, and a VERISTM 4 system connected to a piggyback stimulator prototype that added the stimulus to the optical pathway of the SLO by means of a wavelength-sensitive mirror. Fundus visualization was achieved with the infrared lasers of the SLOs (780 and 835 nm). Results: The most extensive study so far with a green laser stimulus in a cat model of retinal degeneration demonstrated the capability of the device to detect retinal landmarks and the different stages of degeneration. Also, the advantages of exactly reproducible stimulus positioning for averaging within and comparison between disease groups became apparent. The results with the same setup in transgenic mice suggest a pure cone origin of the responses. In humans, recordings show that fixation is sufficiently good in most subjects. It is not clear yet whether red or green laser stimulation (or both) is preferable. The results with the prototype were very similar to the MF-ERGs obtained with a standard CRT screen. Conclusions: All three devices allowed us to record MF-ERGs with continuous fundus monitoring. Although further refinements are necessary, it is obvious that fundus controlled methods will improve the reliability of MF-ERG in future research on glaucoma, transplantation studies, and evaluation of gene therapy. [ABSTRACT FROM AUTHOR]

Light-adapted cone ERG in response to white stimuli with long duration (200 ms) was studied in seven normal cats and six cats with early to moderate, inherited retinal dystrophy. The stimuli typically elicited an ERG consisting of an a- and b-wave in response to light onset, whereas light-offset was followed by a cornea-positive d-wave and subsequent negative dip and occasionally a second positive peak in both normal and dystrophic cats, although b- and d- waves had less distinct peaks in cats with moderately advanced retinal dystrophy. Linear regression models indicated a positive correlation between d-wave amplitude and stimulus luminance, whereas a negative correlation was found between amplitude and background light luminance in normal cats. The d-wave implicit time was independent of both stimulus and background light luminance in normal cats. The d-wave amplitude was not significantly different in dystrophic cats, whereas the implicit time was increased when affected cats were compared to normal cats. The significant increase in implicit time in dystrophic cats could not be explained with a reduced sensitivity of the off-pathway to background or stimulus light. This is supported by the finding that d-wave amplitude was not significantly altered in early to moderately advanced dystrophic cats. [ABSTRACT FROM AUTHOR]

Levels of interphotoreceptor retinoid-binding protein (IRBP) protein and message in retinas of Abyssinian cats homozygous for progressive rod-cone degeneration were determined at early ages, well before the onset of clinical retinal degeneration. IRBP gene expression was assessed by immunochemical quantitation of IRBP protein, and by Northern blotting and slot-blotting of total RNA using a human IRBP cDNA probe. Morphology was assessed by electron microscopy and immunocytochemistry. Levels of both IRBP protein and message in affected Abyssinian cat retinas were significantly reduced below normal as early as 4 weeks of age at the earliest stage of retinal disorientation. Opsin mRNA was more abundant in affected Abyssininian cat retinas than in control retinas. This was at least 1 year before the onset of clinical symptoms. The reduction in IRBP gene expression to levels significantly below normal well before the onset of retinal degeneration in affected Abyssinian cat retinas indicates that this represents a primary defect or at least an early problem that could itself cause adverse effects. [ABSTRACT FROM AUTHOR]

Retinae of Abyssinian cats homozygous for a retinal degeneration gene, and normal controls, have been investigated using antibodies directed against opsin, transducin α (TD-α), S-antigen (48K protein), interphotoreceptor retinoid-binding protein (IRBP), and cone outer segments. IRBP-immunoreactivity (IR) is much reduced at stage 2 of the disease in affected retinae; later massive photoreceptor cell death occurs. In cats, at a late stage of the disease, the retina exhibits few S-antigen-IR cells in the peripheral part of the retina whereas, in the central part, some patches of cells exhibiting opsin-IR, TD-α-IR, and S-antigen-IR are present in remnants of the outer nuclear layer (ONL). No IRBP-IR is detectable at this stage. The form and size of the majority of these remaining cells, however, does not resemble that of normal photoreceptors. No, or only rudimentary, inner and outer segments are present; long bifurcating basal protrusions often occur. These cells, which could be remains of cone elements, are S-antigen immunoreactive. Double labelling for different retina-specific proteins reveals a co-localization of opsin, TD-α and S-antigen in some, but not all, remaining photoreceptor elements. Cells exhibiting opsin-IR also show TD-α-IR and S-antigen-IR located within the entire cell and its protrusions. In control retinae and retinae at early stages of the disease, immunoreactions are comparable with all antibodies used. However, TD-α-IR is less intensive in the photoreceptor terminals. S-antigen-IR cones are most frequently present in the peripheral retina. Reduction of IRBP at an early stage of the disease could be one of the factors leading to photoreceptor cell death at later stages. [ABSTRACT FROM AUTHOR]