Abstract
Abstract: :
Purpose: Retinal disease must be classified with 100% certainty for efficient genetic analysis. In Abyssinian cats with recessive rod cone degeneration, an ERG can be used. It is reduced before the fundus changes. We recorded long protocol, ganzfeld bilateral white flash ERGs in 21 homozygous/heterozygous cross cats (50% affected, age 8–24 months, 40 sessions, 1–3 repeats, 3 months apart). We derived a score to classify them using iterative principal components factor analysis. An equation combinined 12 measures from ERGs to the 3 brightest scotopic and the brightest photopic flashes. The score separated cats, later verified by fundus exams, to have a retinal degeneration, from phenotypically unaffected litter mates with a wide gap and consistently classified doubtful cases. We evaluated the equation by applying it, blind, to new data. Methods: We recorded more ERGs in 23 cats (16 new, 50 sessions, 1–3 repeats) using the same protocol. Amplitude and peak time of a– and b– waves to stimuli used in the equation were measured and b/a ratios calculated. These measures, and the parameters defining the equation from the first group, were used to calculate one score for each cat in the second group The scores were compared to subsequent funduscopic exams by a third person, blind to the scoring and the hypothesis being tested. Results: The scores split into two distinct distributions. The gap between the lowest score in the high group and the highest score in the low group was as large as before (16.56%). Two animals with normal fundi crossed over, one from borderline abnormal to normal and one from abnormal to normal on two subsequent ERGs. A cat from the initial group, with a questionable fundus and one normal ERG became abnormal in both fundus appearance and in three more ERGs. Two new animals had doubtful fundi. One had a single very abnormal ERG score. Another had one abnormal ERG and two subsequent normal ERGs. One cat, with an abnormal fundus, had a single normal ERG. Conclusions: A composite score derived from factor analysis, separated a new set of ERGs into 2 distinct populations. There were uncertain cases. Repeated testing showed that scores from at least 2 ERG sessions need to be in agreement, and a third used where the two are in conflict, to make a 100% definite and correct diagnosis of this retinal dystrophy with ERGs. Support: Allergan (V) Foundation Fighting Blindness, National Cancer Institute (KN)
Keywords: electroretinography: non–clinical • retinal degenerations: hereditary • gene screening