Comparative retinal ganglion cell and optic nerve morphology

Abstract

The optic nerve is divided in four regions: intraocular, intraorbital, intracanalicular, and intracranial. The vertebrate retinal ganglion cells are classified by morphology, physiology and soma size. Species differences and similarities occur with retinal ganglion cells. Alpha retinal ganglion cells have large somata, large dendritic fields, large-diameter axons, and are most dense in the peripheral retina. Beta retinal ganglion cells have smaller diameter somata, smaller dendritic fields, small diameter axons, and predominate in the central retina. Gamma retinal ganglion cells are a heterogenous class of cells and have small diameter axons, and slow axon conduction velocities. The spatial distribution and organization of the retinal ganglion cells extends retinotopically through the nerve fiber layer, optic nerve, optic chiasm, optic tract, lateral geniculate nucleus, and visual cortex. The retinal nerve fiber layer thickness decreases from the optic disk toward the periphery of the retina. The retrobulbar optic nerve axon counts and axon density vary by species, with larger nerves having higher axon counts. Decussation of the optic nerve axons at the optic chiasm varies with 100% decussation in most birds and fish, 65% in cats, 75% in dogs, 80-90% in large animals, and 50% in primates. Centrifugal axons also occur in the optic nerve and may represent a method by which the brain can influence retinal activity.

The upregulation of GLAST-1 is an indirect antiapoptotic mechanism of GDNF and neurturin in the adult CNS

“…This may be a consequence of the higher susceptibility of larger RGCs to glutamate excitotoxicity. 7 The density of larger a-RGCs is known to increase toward the outer or peripheral retina, 39 where we observed the most pronounced decrease in RGC density after GLAST-1 siRNA co-treatment.…”

Effects of conventional argon panretinal laser photocoagulation on retinal nerve fibre layer and driving visual fields in diabetic retinopathy

“…With time, laser-induced damage to retinal ganglion cells results in the loss of nerve fibre layer and thinning within peripapillary nerve fibre layer zones. 18 To test our hypothesis that PRP causes axonal damage and progressive loss over time, we examined visual fields in our patients to determine whether nerve fibre layer alterations are associated with any functional loss.…”

“…17,18 After PRP, there is increased oxygenation of the inner retina from the choroid, increasing intra-retinal perfusion around the ganglion cell axons. 21 We hypothesise that direct laser damage and axonal oedema may lead to axonal cell death.…”

Retinogeniculostriate Pathway Components Scale with Orbit Convergence Only in Primates and Not in Other Mammals

“…Although the optic nerve is traditionally named the second cranial nerve, it may be more useful to consider it a white-matter tract of the diencephalon, composed primarily of the axons of retinal ganglion cells streaming away from the eye [e.g. Brooks et al, 1999].…”