An array of different retinal disorders is present as a threat in quite a number of dog breeds. These often lead to profound visual impairment or blindness. Many of the disorders are genetic, and they are, in Sweden as well as in other countries, subject to breeding programmes. The anatomy of the eye and the retina, as well as current examination techniques (ophthalmoscopy, Electroretinography (ERG) and genetic analysis) are described. The more common retinal disorders encountered in dogs in Sweden are discussed: retinal dysplasia, generalized progressive retinal dystrophy, retinal pigment epithelial dystrophy, collie eye anomaly, sudden acquired retinal degeneration, retinal detachment and choroiditis. The possibly affected breeds are listed. The value of diagnostic findings is discussed and current advances on the subject in ophthalmologic research are accounted for..

Full-field flash Electroretinography is an electrodiagnostic method used to examine the function of retinal cells. Light stimulation of the eye elicits electrical potentials in the retina. By aid of a corneal electrode and a reference electrode close to the back of the eye, the electrical potentials can be recorded and presented as an electroretinogram (ERG). ERGs driven by mainly one type of cones can be used to examine the function of a single cone class. In human beings, studies have shown the cone class sensitive to light of short wavelengths, the S-cones, to be more vulnerable to acquired damage than the other cone classes (Daley et al., 1987; Gouras et al., 1993; Greenstein et al., 1989). Dogs have two cone classes, S-cones, and M/L-cones (most sensitive to medium to long wavelengths).

The aim of the study was to examine the retinal ON- and OFF-pathways of the canine electroretinogram (ERG). The ON- and OFF-pathways are used to distinguish objects from their backgrounds. A dark object is discernible from a lighter background using the OFFpathway and the ON-pathway is used to descry a light object upon a darker background. This study shows that the dog ERG has both ON- and OFF-responses and that these responses can be separated by prolonging the flash duration over 50 ms. The dog OFF-response waveform was more similar to the cat OFF-response than the human OFF-response (Frishman, 2006; Zrenner and Gouras, 1979). In this study six female three-year-old Beagle dogs were included. Both background and flash stimuli were provided by LEDs (light emitting diodes) with a wavelength of 470 nm, a wavelength that is absorbed almost as effectively by the canine M/L-cones as by the S-cones. These stimuli gave ERGs with both ON- and OFF-responses.

Electroretinography is an examination method where the function of the retina is objectively assessed. In 2002 the European College of Veterinary Ophthalmology (ECVO) published a proposition to a standard on how to perform ERG examinations, to facilitate comparison of results and to make it possible to repeat examinations. The purpose of this study was to validate parts of the canine ERG protocol suggested by the ECVO. Our principal aim was to study if there is any interference at the recommended stimulus intervals for dark-adapted rod- and combined rod-/cone responses. The results show that there is an effect on the a- and b-wave amplitudes when different stimulus intervals are employed. When all examined intervals are pooled, there is an increase in the median b-wave to each consecutive dim, white (rod) stimulus in a series of four.