| optic nerve drusen | Basophilic, calcareous, laminated acellular bodies within the optic nerve anterior to the scleral lamina cribrosa. (05 Mar 2000) |
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| optic nerve glioma | <radiology> F = M, child / young adult (75% less than 10 yrs, 90% less than 20 yrs), fusiform, isodense mass, with or without enhancement, rarely calcified associated with neurofibromatosis Cf: optic nerve meningioma (12 Dec 1998) |
| optic nerve head | The portion of the optic nerve seen in the fundus with the ophthalmoscope. It is formed by the meeting of all the retinal ganglion cell axons as they enter the optic nerve. Because the retina at the optic disk has no photoreceptors there is a corresponding blind spot in the visual field. (12 Dec 1998) |
| optic nerve hypoplasia | Congenitally small optic disk resulting from failure of development of retinal ganglion cells, with a reduced number of axons; visual impairment may be marked. See: de Morsier's syndrome. (05 Mar 2000) |
| optic nerve meningioma | <radiology> Female (80%), middle age, (24% occur before 10 yrs, but are associated with neurofibromatosis), tubular, hyperdense mass, intense tramtrack enhancement, ** Cf: optic nerve glioma (12 Dec 1998) |
| optic nerve sheath decompression | A venting of the optic nerve sheath into the retrobulbar space, by slitting or by fenestrating the sheath. See: optic nerve sheath fenestration. (05 Mar 2000) |
| optic nerve sheath fenestration | The cutting of a window in the dura of the optic nerve sheath to relieve papilledema and prevent further loss of optic nerve fibres. (05 Mar 2000) |
| optic neuritis | <pathology> Inflammation of the optic nerve. This may occur secondary to a wide variety of causes: multiple sclerosis, posterior uveitis, vascular lesions of the optic nerve (interruption of blood supply to the optic nerve), temporal arteritis, central retinal artery occlusion, methyl alcohol poisoning, drug side effects and acute demyelinative disease of the optic nerves (destruction of optic nerve sheath). (27 Sep 1997) |
| optic neuroma | A benign tumour of the optic nerve. (12 Dec 1998) |
| optic neuropathy, ischemic | A severely blinding disease resulting from loss of the arterial blood supply to the optic nerve as a result of occlusive disorders of the nutrient arteries. Optic neuropathy is divided into anterior, which causes a pale oedema of the optic disk, and posterior, in which the optic disk is not swollen and the abnormality occurs between the globe and the optic chiasm. Ischemic anterior optic neuropathy usually causes a loss of vision that may be sudden or occur over several days; ischemic posterior optic neuropathy is uncommon and the diagnosis depends largely upon exclusion of other causes, chiefly stroke and brain tumour. (12 Dec 1998) |
| optic papilla | The portion of the optic nerve seen in the fundus with the ophthalmoscope. It is formed by the meeting of all the retinal ganglion cell axons as they enter the optic nerve. Because the retina at the optic disk has no photoreceptors there is a corresponding blind spot in the visual field. (12 Dec 1998) |
| optic part of retina | The internal layer of the retina containing the neural elements, as distinguished from the outer leaf of the retina, or pigmented layer. Synonym: pars optica retinae, neural layer of retina, optic part of retina, stratum cerebrale retinae. (05 Mar 2000) |
| optic pit | A congenital structural defect of the optic nerve head. (05 Mar 2000) |
| optic placodes | Paired ectodermal placode's that become invaginated to form the embryonic lens vesicles. Synonym: optic placodes. (05 Mar 2000) |
| optic radiation | The massive, fanlike fibre system passing from the lateral geniculate body of the thalamus to the visual cortex (striate or calcarine cortex, area 17 of Brodmann); the fibres follow the retrolenticular and sublenticular limbs of the internal capsule into the corona radiata but they curve back along the lateral wall of the temporal and occipital horns of the lateral ventricle to the striate cortex on the medial surface and pole of the occipital lobe. Synonym: radiatio optica, geniculocalcarine radiation, geniculocalcarine tract, Gratiolet's fibres, Gratiolet's radiation, occipitothalamic radiation, Wernicke's radiation. (05 Mar 2000) |