The determination of dark adaptation time using electroretinography in conscious miniature Schnauzer dogs

Abstract

The optimal dark adaptation time of electroretinograms (ERG's) performed on conscious dogs were determined using a commercially available ERG unit with a contact lens electrode and a built-in light source (LED-electrode). The ERG recordings were performed on nine healthy Miniature Schnauzer dogs. The bilateral ERG's at seven different dark adaptation times at an intensity of 2.5 cd.s/m(2) was performed. Signal averaging (4 flashes of light stimuli) was adopted to reduce electrophysiologic noise. As the dark adaptation time increased, a significant increase in the mean a-wave amplitudes was observed in comparison to base-line levels up to 10 min (p < 0.05). Thereafter, no significant differences in amplitude occurred over the dark adaptation time. Moreover, at this time the mean amplitude was 60.30 +/- 18.47 microV. However, no significant changes were observed for the implicit times of the a-wave. The implicit times and amplitude of the b-wave increased significantly up to 20 min of dark adaptation (p < 0.05). Beyond this time, the mean b-wave amplitudes was 132.92 +/- 17.79 microV. The results of the present study demonstrate that, the optimal dark adaptation time when performing ERG's, should be at least 20 min in conscious Miniature Schnauzer dogs.

Fig. 1

A conscious Miniature Schnauzer dog is positioned on the table, and the head and light stimulator (LED-electrode) is stabilized by the assistant's hand (A). A contact lens, cushioned with 0.3% hydroxypropyl methylcellulose, is applied on the cornea. A ground subdermal electrode is placed on the external occipital protuberance and a reference electrode about 2 cm caudal to the lateral canthus of the tested eye (B).

Fig. 2

Influence of dark-adaptation time on the amplitudes of a-waves in conscious Miniature Schnauzer dogs. a, b : A different superscript on the error bars indicates a statistically significant difference (p < 0.05).

Fig. 3

Influence of dark adaptation time on the implicit times of a-wave in the conscious Miniature Schnauzer dogs. a: The same superscript on the error bars indicates no statistical difference (p < 0.05).

Fig. 4

Influence of dark adaptation time on the amplitudes of the b-wave in conscious Miniature Schnauzer dogs. a, b, c : A different superscript on the error bars indicates a significant statistical difference (p < 0.05).

Fig. 5

Influence of dark-adaptation time on the implicit times of the b-wave in conscious Miniature Schnauzer dogs. a, b, c : A different superscript on the error bars indicates a significant statistical difference (p < 0.05).

Fig. 6

The graph represents the waveforms of the ERG in relation to dark adaptation times (1, 10, 20, 30, 40, 50, and 60 min) at a white light intensity of 2.5 cd·s/m² in Miniature Schnauzer dogs. The light stimulus is given at the beginning of each recording. A) 1:1 min of dark adaptation time; 2:10 min of dark adaptation time; 3:20 min of dark adaptation time B) 4:30 min of dark adaptation time; 5:40 min of dark adaptation time; 6:50 min of dark adaptation time; 7:60 min of dark adaptation time.