Age-associated changes in electroretinography measures in companion dogs

Subjective vision assessment in companion dogs using dogVLQ demonstrates age-associated visual dysfunction

“…Dog owners completed the questionnaire on their own in order to consider and observe their dog’s behavior. A subset of dogs were invited to participate in a clinical visit at the University of Wisconsin-Madison School of Veterinary Medicine, for participation in a study on aging of the visual system and retinal electrophysiologic responses ( 24 ). Inclusion criteria for invitation to the clinical visit were dog age over 1 year and health/temperament suited to study procedures without the need for administration of anxiolytic medication (trazadone, gabapentin) which impacts retinal electrophysiologic responses ( 24 , 31 ).…”

“…Unilateral electroretinography (ERG) was performed with mydriasis (Tropicamide, 1%, Akorn, Lake Forest, IL; administered at least 40 min prior to initiation of ERG) and topical corneal analgesia (Proparacaine 0.5%, Akorn, Lake Forest, IL), using a handheld ERG unit (RetEval, LKC Technologies, Gaithersburg, MD) as previously described ( 24 ), apart from studying a wider light stimulus range. The dogs were first tested in ambient room light with a background light of 30 cd/m 2 , with stimuli consisting of flashes of increasing stimulus strength (light-adapted stimuli at 1, 3, and 10 cds/m 2 ; interstimulus interval 0.5 s, 20 flashes averaged), followed by 20 min of dark adaptation and a dark-adapted flash stimulus series (a series of 8 different dark-adapted flash stimuli ranging from 0.003–10 cds/m 2 ; interstimulus interval 2 s, 10 averages for 0.003–0.03 cds/m 2 , interstimulus interval 5 s, 8 averages for 0.1–1 cds/m 2 , interstimulus interval 10 s for 3 cds/m 2 , 20 s for 10 cds/m 2 , both 3 averages).…”

“…The b-wave amplitude was measured from the baseline, or the depth of the a-wave trough (where present) to the peak of the b-wave. The b-wave was selected as it is detectable at a wider range of stimulus strengths to compare to dogVLQ subsection scores ( 24 ). The b-wave represents a summed response of the retinal bipolar cells to input from the photoreceptors and represents a measure of both outer and inner retinal function ( 34 ).…”

“…All purebred dogs and dogs that underwent clinical evaluation were assigned an estimated life stage as previously described ( 24 ). This was performed to account for the variance in lifespan due to breed.…”

“…While capable of detecting extreme vision loss, neither instrument described sensitivity to subtle vision changes, nor validation using objective tests (such as electroretinography, maze navigation skill) or had subsections regarding vision specifically in different lighting environments. Chronic ophthalmic conditions with long clinical courses such as hereditary and age-associated vision loss ( 23 , 24 ), cataracts ( 25 ), and corneal opacification ( 26 ) occur in dogs, like in humans. Because the subtle pre-clinical signs are difficult for owners to determine, many dogs present for clinical evaluation late in disease, rendering treatment more challenging.…”