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GA Cull, GA Cioffi, J Dong, A Turpin, L Wang, G Yan; Estimating Normal Optic Nerve Axon Numbers In Non-Human Primate Eyes . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2627.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Due to the large number of fibers, over 1 million in the primate optic nerve (ON), estimating the number of axons has been difficult and time consuming. In this study, using an image analysis system, a novel sampling method for estimating the ON counts is presented. Methods:Five normal optic nerves of adult Rhesus monkeys were analyzed using a Bioquant Imaging System,a light microscope, and 1µm thick ON cross sections stained with p-phenylenediamine. A grid of 45 x 45µm square regions was placed over the ON section and every 2nd grid region was selected. Axon numbers, areas and center of area x-y coordinates were recorded. Approximately 650,000 axons were counted per ON representing a 50% sampling of the total ON area. Sampling at 5%, 6%, 7%, 8%, 10%, 12.5%, 17%, and 25% was compared to the 50% count and the total, the total estimated axon numbers were calculated. The percentage difference of the total estimated axon numbers for each sampled area to the 50% estimated total axon number was calculated. A mean (S.D.) was calculated for all the optic nerves, for all of the sampled areas at 5%, 6%, 7%, 8%, 10%, 12.5%, 17%, 25%. The difference and the % difference to the mean with its 95% confidence interval was calculated. Results:The mean cross sectional area of the 5 ONs was 7.26µ m2 0.6 (S.D.) and the mean total count estimated from 50% of the ON area counts was 1,320,438 94,663 fibers (ranging 1,188514 to 1,406278). With estimates derived from the 7% to 25% counts, the percentage difference to the mean ranged from 0.71% to 2.67%. This increased to 5.16% and 7.07% at the 6% and 5% sampled areas respectively. Conclusion:This study has shown that sampling a 7% or greater area of the ON accurately reflects the total number of axons within the normal ON of the primate.
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