The pigmented-rat optic nerve: fibre count and fibre diameter spectrum.

A well distributed electron microscopic sample of 52,000 fibres from the pigmented rat optic nerve cross section indicates a total count of 120,000 +/- 1,600 (S.E.M.) fibres ranging from 0.437 mu to 5.2 mu in diameter. The fibre diameter spectrum is essentially unimodal with a peak at 1.0 mu with a well developed "tail." These results are identical to those available in the literature for the albino rat.