Morphometry of nerve fiber bundle pores in the optic nerve head of the human.

The axons of retinal ganglion cells form fascicles that leave the globe through pores in the optic nerve head formed by beams of glia and collagen. In eyes obtained at time of autopsy of 17 normal subjects of various ages, these pores were counted and measured in the lamina choroidalis and lamina scleralis of the nerve heads. The number of pores at the scleral level was 1.48 times (0.18, 95% confidence interval) greater than at the choroidal level, and the pores were proportionately smaller at the scleral level. No significant change in the numbers of pores or the area of the nerve head at either level was found with age. The proportion of the nerve head devoted to pores decreased significantly with age. Since the pores contain primarily nerve fibers, the slope of this decrease suggests the loss to be about 5% of fibers per decade after age 30.