Optic Nerve Size and Constituent Components: Posterior Is More

Abstract

Purpose: To divide the human optic nerve into its constituent fractions and describe the relative contributions of each as the nerve increases in diameter as it courses back from its retrobulbar origin towards the optic chiasm. Methods: Seven human optic nerves were examined via a semiautomatic, computer-assisted morphometric analysis system. Results: The cross-sectional area, the axonal area, and the axonal population of the pre-chiasmic region relative to the retrobulbar region of the nerve increased by 45.2%, 35.4%, and 17.1%, respectively (p values: 0.044, 0.049, and 0.03, respectively). The other constituents in the nerve, namely myelin and the extra-axonal matrix, showed increases of 48.6% and 44.6%, respectively (p values: 0.016 and 0.094, respectively) in the posterior portion. Conclusions: Nearly equivalent increases in the three main constituents of the human optic nerve (axons, myelin, and extra-axonal matrix) are responsible for the increase in diameter of the human optic nerve as it courses posteriorly from the retrobulbar area towards the optic chiasm.

KEYWORDS:

• Axonal population
• component
• human
• morphometric
• optic nerve