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L.E. Galle, X. Vaegan, K. Narfström; A–Max to Scotopic I–Max Is the Best Detector of Photoreceptor Dystrophy: Comparison of A–Wave Measures in Normal and Affected Abyssinian Cats . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3444.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Discrimination analysis of ERG data from an Abyssinian cat population, bred so that 50% were affected with recessive rod cone degeneration, later verified by fundus examination, showed that a–max to the brightest available scotopic flash (4 cd.s.m–2) was the most efficient possible detector of disease. Since recent work suggests the b–wave could reduce a–max so the leading edge of the a–wave may be a better index of phototransduction, we studied which a–wave measure is most efficient in a larger data set. Methods: Cats were dark–adapted, anaesthetized and binocular ERGs recorded using a long protocol (age >5 months, 1–6 sessions/cat). Five groups were used: normal cats (n=15, 26 sessions), F2 cats (bred from homozygous, affected and known heterozygous cats), classed as unaffected (N=17, 65 sessions); affected (N=21, 62 sessions), uncertain (N=7, 7 sessions), and progenitor affected (N=15, 35 sessions). Amplitudes at fixed times (7–10 msec) at a–max were evaluated, and a–max time and age. Average from 1–4 msec was taken as baseline and measures were averaged over eyes. Analysis of variance for repeated measures and principal components factor analysis were performed. Discrimination efficiency was evaluated from size of the overlap between groups, t and F–statistics, or size of loading on the 1st factor. A–max had a significant loading with peak time on a 2nd factor. Results: A–max was the most efficient measure except for loadings on the 1st factor and the only measure where there was no overlap between groups. Variance within and between groups decreased as a function of time. Peak time was not important; it varied randomly from 8–10 msec in early disease and only increased in a few cases of very advanced disease. The uncertain cases showed that a repeat test was necessary for certainty and a third test when they were in conflict. Conclusions: Parameters estimated from curves fitted to data from earlier time points are more variable than measures at a–max itself. A–max to the brightest available scotopic flash is a more efficient discriminator of retinal dystrophy than any other point along the a–wave and therefore of any other parameter reflecting phototransduction.
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