Optic nerve structure

Topical application is the most common route of administration for ophthalmic drugs. Advantages include convenience, simplicity, noninvasive nature, and the ability of the patient to self-administer. Because of blood and aqueous losses of drug, topical medications typically do not penetrate in useful concentrations to posterior ocular structures and therefore are of no therapeutic benefit for diseases of the retina, optic nerve, and other posterior segment structures. 

Structural Assessment of the Optic Nerve Head and Retinal Nerve Fiber Layer... 

It is important to approach the assessment of these structures in a consistent and organized manner with several key parameters noted for every optic nerve. One way to keep this assessment organized is the mnemonic CARVES, because glaucoma carves out the optic nerve (Courtesy of Nick Holdeman, OD, MD, and Jade Schiffman, MD) ... 

Do not expect visual field findings to correspond to the structural assessment of the optic nerve or retinal nerve fiber layer in early glaucoma. 

Direct interstitial infusion has been applied to the treatment of patients with advanced Parkinson s disease, and the design of the protocol is instructive (29). Motor control is severely compromised in these patients because degradation of the substantia nigra ultimately results in massive overinhibition of the motor cortex by the globus pallidus interna (Gpi). One therapeutic approach is to thermally ablate a portion of the Gpi to reduce this inhibition and restore freedom of movement. However, thermal ablation also risks destroying the optic nerve that forms the floor of the Gpi structure. Hence, a chemical means of destroying the Gpi has been evaluated as a potentially more selective alternative. 

The ganglion cell layer (GCL) contains the cell bodies of retinal ganglion cells, with their axons running across the retinal surface (nerve fiber layer) toward the optic nerve head, and on through the optic nerve to the lateral geniculate nucleus in the mid-brain. The inner retinal blood supply (outside the foveal avascular zone), the nerve fiber layer, and a thin membrane (the inner limiting membrane) form the most superficial retinal structures. 

The LGN and cortical areas exist in duplicate in the two halves of the brain. Each deals with one half of the visual world the optic nerves from the two eyes meet in a structure called the optic chiasm, where fibers from the tw o nasal retinas cross over to combine with those from the temporal retina of the fellow eye consequently each LGN and cortical hemisphere receive visual information from Cw o corresponding retinal halves on their own side, and thus from the contralateral half of the visual field. 

Several disorders may mimic glaucomatous ONH and/or visual field changes. Those that resemble structural glaucomatous optic neuropathy or interfere wdth assessment of glaucomatous cupping include optic disc anomalies, tilted discs, optic nerve drusen, optic nerve pits, optic nerve colobomas, myelinated nerve fibers, ischemic optic neuropathy and optic atrophy. 

Dietary exposure of rats to 2.2 mg Hg/kg/day as mercuric chloride for 3 months resulted in inactivity and abnormal gait (Goldman and Blackburn 1979). However, it is unclear whether the effects observed in this study were the direct result of effects on the nervous system, or whether they may have been secondary to other toxic effects. No evidence of neurotoxicity (clinical signs of neurotoxicity and optic and peripheral nerve structure) was seen in mice administered 0.74 or 2.2 mg Hg/kg/day as mercuric chloride in the drinking water for 110 days (Ganser and Kirschner 1985). The investigators increased the... 

Black JA, Waxman SG, Hildebrand C1985 Axo-glial relations in the retina-optic nerve junction of the adult rat freeze-fracture observations on axon membrane structure. J Neurocytol 14 887-907... 

Another phenomenon of recent interest and debate which may benefit from a habit routine interpretation is filling in. In its simplest aspect, it has long been known that due to the particular structure of the eye, there is a small blind spot on each retina at the position of its attachment to the optic nerve. The portion of the visual scene projected here is therefore not represented in the visual cortex of the brain, yet we have no awareness that there are two blank spots in our field of view. (A simple experiment that all children are taught shows the reality of the blind spot.) The process whereby the brain nevertheless produces an apparent continuous field of view is called filling-in, and some examples of recent research and controversy are by Francis Crick. (14) Although the blind spot may be a quite simple process (the retina itself may play some... 

L. Beaudet, H.I. Browman, C.W. Hawryshyn (1993). Optic nerve response and retinal structure in rainbow trout of different sizes. Vision Res., 33,1739-1746. 

Na /K ATPase motivated membrane pumps which maintain the essential ionic balance within these electrically active tissues. Both the lens and optic nerve are normally rich in potasium ions and the introduction of thallium ions enables binding to melanin-type pigments within the structures of fhe eye and generally affects function and precipitates damage resulting in swelling of fhe optic disc and visual deterioration. 

Adverse effects of drugs may involve external ocular functions and structures, such as oculomotor function, eyeUds, lacrimation, conjunctiva, and cornea or internal structures, such as trabecular meshwork, cihary body, iris, lens, retina, and optic nerve. Higher-than-therapeutic doses and long duration of administration enhance the incidence of drug-induced oculotoxicity. 

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