Quantitative histology of optic nerve, optic tract and lateral geniculate nucleus of man.

Although the distribution of nerve fibres and neurones in the visual system has been amply documented on a descriptive basis (Minkowski, 1920), few quantitative studies have been made. Krause (1876) estimated the total number of fibres in the optic nerve of man by a simple computation of average fibre size and the overall optic nerve diameter. His estimate of 1000000 nerve fibres is the most commonly cited figure despite the fact that he later revised it to 440347 noting that this figure included only the large or 'thick' fibres. Forty years later, Kappers (1921) reported 550000 fibres in the optic nerve, while Zwanenburg (1915), using a similar Weigert-Pal myelin stain, counted only 440 000 nerve fibres. Arey & Bickel (1935) reported an average of 1165221 fibres based on the counts of three optic nerves stained with silver. Soon after, Bruesch & Arey (1942) stated that the number of fibres in the optic nerve may vary from 564775 to 1140030. Less information is available for the optic tract. Ramon y Cajal (1899) estimated the ratio of crossed to uncrossed nerve fibres in the optic tract of man to be 2: 1. Later Sa'ntha (1933) estimated this ratio to be 3:2. The first study on the lateral geniculate nucleus of man using quantitative methods was carried out by Balado & Franke (1937), who reported that the nucleus contained 568 845 cells. By referring to the optic nerve fibre counts of Krause, Kappers and Zwanenburg they concluded that a 1:1 ratio existed between the optic nerve axons of the retinal ganglion cells and the post-synaptic cells in the lateral geniculate nucleus. More recently, Chacko (1948) reported the cell count for a human lateral geniculate nucleus of 1210000. The ratio of lateral geniculate cells of crossed to uncrossed laminae was 56:43. She-concluded that despite the broad range of optic nerve fibre counts of Bruesch & Arey, the optic nerve fibre : geniculate cell ratio was 1:1. One other count of the lateral geniculate nucleus of man gave an estimate of 1018 190 cells (Sullivan et al. 1958). The present study presents quantitative data of nerve fibre and cell counts in the optic nerve, optic tracts and lateral geniculate nuclei in a case of unilateral enucleation. Conclusions are drawn as to the density distribution patterns of nerve fibres and cells in this portion of the visual system as well as the ratio of crossed to uncrossed fibres in the optic chiasma.