[Clinical electroretinography in the dog. Part 1]. / Klinische Elektroretinographie beim Hund. 1. Teil.

In the first of three parts of this investigation the clinical importance and the principal indications for electroretinography are presented. The histology and ultrastructure of the retina with special emphasis on the photoreceptors and the second order neurons are discussed. A section is devoted to the history of electroretinography in man and animals. The components of the ERG and their origin are discussed.

[Oscillating potentials on the B-wave of the ERG in the dog]. / Oszillierende Potentiale auf der B-Welle des ERG beim Hund.

The oscillatory potentials (OP) on the b-wave of the canine ERG are characterized. Normal values for an OP-index, implicit times and periodicity are given. The OP-index increases during dark adaptation as well as with increasing stimulus intensities for white light flashes. Scotopic blue and red stimuli, although balanced for the maximum b-wave amplitude, surprisingly result in higher OP-indices for red flashes. Implicit times decrease for all OP with increasing stimulus intensities. Scotopic balanced red light results in OP with markedly reduced implicit times compared to blue light stimulation. The intervals between two OPs remain constant during dark adaptation, however, intervals between OPs with longer implicit times tend to be shorter. In contrast, the b-waves for scotopic balanced stimuli show rhythmic oscillations with constant intervals between them, the intervals being shorter for blue light than for red light. The intervals between OPs tend to become shorter with increasing stimulus intensities. This investigation indicates that OPs are influenced but not generated by photoreceptors. The examination of a dog with optic nerve hypoplasia indicates that the ganglion cells do not contribute to the biogenesis of OPs. The prognostic value of OPs in the early diagnosis for hereditary retinal degenerations in the dog is discussed.

[Clinical electroretinography in the dog. Part 3]. / Klinische Elektroretinographie beim Hund. 3. Teil.

In this last part the preparation of the patient for the ERG is shown. Anesthesia, positioning, and retrobulbar injection technique are discussed. The protocol for recording the ERG is presented. The dog is dark adapted for 30 minutes. The level of adaptation is examined using a single flash of dim red light at various times. Rods and cones are stimulated separately by scotopically balanced red and blue flashes. After a single flash of bright white light the rods and cones are studied with flicker trains at 5, 12.5, 15 and 30 Hz. During dark adaptation the maximum b-wave amplitude increased from 13.8 +/- 8.4 microV to 49.3 +/- 16.3 microV. Bright white light stimuli resulted in b-wave amplitudes of 167.7 +/- 75.3 microV. There were always 6 oscillatory potentials visible on the b-wave. Scotopically balanced stimuli produced b-waves of 104 microV (red) and 116 microV (blue). It was found that older dogs had reduced b-wave amplitudes and longer peak times than younger dogs. The most common artefacts in electroretinography are discussed.

[Clinical electroretinography in the dog. Part 2]. / Klinische Elektroretinographie beim Hund. 2. Teil.

The second part of this study deals primarily with the technical aspects of electroretinography. A custom made dark chamber for the patient is presented. The requirements for an optical stimulator are discussed in detail and the recording instrumentation--electrodes, amplifiers, averager, digitalizer--are presented. The display of the signals on a monitor and plotter concludes this technical description. The remainder of part 2 is devoted to the many factors influencing the recording of an ERG, notably pupillary diameter, anesthesia, oxygen and glucose supply to the animal, body temperature of the patient, its intraocular pressure and level of retinal adaptation, and finally the age of the patient. On the technical side the intensity, wavelength and frequency of stimulation play an important role.