Detection of cone dysfunction induced by digoxin in dogs by multicolor electroretinography

Abstract

It is difficult to detect discrete cone function with the present conventional electroretinography (ERG) examination. In this study, we developed contact electrodes with a built-in color (red (644 nm), green (525 nm), or blue (470 nm)) light source (color LED-electrode), and evaluated an experimental model of digoxin in the dog. First, 17 normal Beagle dogs were used to determine which electrode works well for color ERG measurement on dogs. Then, color ERG was performed on seven normal Beagle dogs at various points during a 14-day period of digoxin administration. A single daily dose of 0.0125 mg/kg/day, which is within the recommended oral maintenance dosage range for dogs, was administered orally for 2 weeks. Ophthalmic examination, measurement of plasma concentration of digoxin, and color ERG examination were performed. On first examination, amplitudes of all responses were significantly (P < 0.01) lower with the red, than with the blue and green electrodes during ERG recording. In ERG using the red electrode, the standard deviation was large. According to these preliminary results, the red electrode was not used in the experimental dog model with digoxin. In the digoxin administrated animals, no significant change was observed in the ophthalmic examination findings. The digoxin level increased steadily throughout the dosing period but was always within the therapeutic range for dogs. In rod ERG, no abnormalities were detected with any electrode. In standard combined ERG, decreased amplitude of the a-wave was detected with every electrode. In single flash cone ERG, prolongation of implicit time was detected by color ERG with the blue and green electrodes. In 30-Hz flicker ERG, decreased amplitude was detected only by color ERG with the blue electrode. The decreased amplitude and prolonged implicit time recovered after termination of digoxin administration. Cone dysfunction induced by digoxin in the dog was revealed by multicolor ERG using blue and green LED-electrodes. Multi-color ERG was useful for detecting cone type-specific dysfunction in the dog.

Comparison of Two Electroretinography Systems Used in Dogs: The HMsERG and the RETIport

“…The contact lens part embraces a corneal ring electrode, in which the opalescent part of the lens (diameter=12 mm) has been made to work as a light diffusing lens. In theory, the combination of the LED array and the opaque corneal lens makes the distribution of the light rays which reach the cornea equal to the distribution of a Ganzfeld dome [12,16,21]. There is also a report that the Kooijman-Damhof contact lens under a Ganzfeld dome can illuminate the retina nearly even regardless of the pupil size [15].…”

“…Many light stimulating systems or photostimulators have been developed in order to obtain stimulation of the retina, such as xenon strobes, tungsten bulbs and the light-emitting diodes (LEDs) [16][17][18]21].…”

ERG findings in three hypothyroid adult dogs with and without levothyroxine treatment

“…It is true that we did not have access to baseline (before the hypothyroidism) ERG measures from the three dogs and therefore two scenarios are possible, namely, normal ERG in S2 and delayed in S1 (hypothyroidism effect) or normal ERG in S1 and faster in S2 (drug effect). Of interest, a brief survey of the literature 20–22 indicates that the peak times of the cone ERG in dogs (irrespective of breed) will vary between 11 and 14 ms for the a‐wave and 25–34 ms for the b‐wave compared to 47–67 ms for the rod b‐wave. These values are well within the range of our S1 ERG measures, suggesting that LTh intake accelerated the retinal responses.…”

Functional Disorder of the Retina in Manganese-Deficient Japanese Quail Revealed by Electroretinography using a Contact Lens Electrode with Built-In Light Source

“…Very small or no waves were observed upon weaker stimulation intensity (-3.04 log cd/ m 2 /msec), while stronger stimulation (-1.66 log cd/m 2 / msec) evoked both a-waves and b-waves simultaneously, implying cone origin. This was the same for other dark adaptaion times (30 min, 4 hr), while time adopted for dark adaptation was 30 min for humans and dogs [16] and 2 or 4 hr for several diurnal and nocturnal birds [20][21][22][23].…”

“…Recently, a contact lens electrode with a built-in high-luminance diode (LED electrode) has been developed for reliable and economical ERG recording. LED-electrodes have already been applied in the veterinary area to dogs to demonstrate their usefulness [15,16].…”