| optic capsule | The concentrated zone of mesenchyme around the developing optic cup; the primordium of the sclera of the eye. (05 Mar 2000) |
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| optic chiasm | <anatomy> The anatomic point of crossing or decussation of the optic nerve fibres. most of the nerve fibres cross to the opposite side. (27 Sep 1997) |
| optic cup | The double-walled cup formed by the invagination of the embryonic optic vesicle; its inner component becomes the sensory layer of the retina, its outer layer, the pigment layer. Synonym: caliculus ophthalmicus, ocular cup. (05 Mar 2000) |
| optic decussation | <anatomy> The anatomic point of crossing or decussation of the optic nerve fibres. most of the nerve fibres cross to the opposite side. (27 Sep 1997) |
| optic disk | 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 disk drusen | Hyaline bodies occurring in the intra-ocular portion of the optic nerve. They are distinguished from retinal drusen, which lie beneath the retinal pigment epithelium. This disorder is differentiated also from papilledema by the absence of dilated retinal vessels. (12 Dec 1998) |
| optic fissure | In the embryo, the temporary gap in the ventral margin of the developing optic cup. Synonym: choroid fissure, choroid fissure, choroidal fissure. (05 Mar 2000) |
| optic foramen | The short canal through the lesser wing of the sphenoid bone at the apex of the orbit that gives passage to the optic nerve and the ophthalmic artery. Synonym: canalis opticus, foramen opticum, optic foramen. (05 Mar 2000) |
| optic glioma | <oncology, tumour> A tumour of the optic nerve that can result in blindness to the pressure and destruction (caused by the tumour) of the optic nerve. There is an association between optic gliomas and neurofibromatosis. Surgical excision or radiation therapy is the general coarse of treatment. (27 Sep 1997) |
| optic groove | The groove on the upper surface of the sphenoid bone running transversely between the optic canals bounded anteriorly by the sphenoidal limbus and posteriorly by the tuberculum sellae; forms in relationship to the optic chiasm. Synonym: sulcus prechiasmatis, chiasmatic sulcus, optic groove, prechiasmatic sulcus. (05 Mar 2000) |
| optic layer | A layer of white matter interspersed with nerve-cell bodies, immediately below the superficial gray layer of the superior colliculus, composed of myelinated fibres originating in the retina and striate cortex, the inner layer of the retina, consisting of the fibres originating from the cells of the ganglionic layer of optic nerve; in their further course these fibres combine to form the optic nerve or optic tract. Synonym: stratum opticum. (05 Mar 2000) |
| optic lobe | In invertebrate zoology, a lateral lobe of the forebrain in certain arthropods. In vertebrate zoology, either of the corpora bigemina of lower vertebrates. (12 Dec 1998) |
| 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) |