| IOA | inner optic anlage; International Osteopathic Association |
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| ION | ischemic optic neuropathy |
| IOT | intraocular tension; intraocular transfer; ipsilateral optic tectum |
| LHON | Leber hereditary optic neuropathy |
| LOA | leave of absence; Leber optic atrophy; left occipitoanterior [fetal position] |
| 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) |
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| 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) |
| 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) |
| optic recess | A diverticulum extending forward from the anterior part of the third ventricle above the optic chiasm. Synonym: recessus opticus. (05 Mar 2000) |
| optic sign | <microscopy> For uniaxial materials, by definition, the sign is positive if the value epsilon minus omega is positive, and negative if epsilon - omega is negative. For biaxial materials, the sign is positive if gamma is the acute bisectrix, and negative if alpha is the acute bisectrix, or positive if gamma - beta greater than beta - alpha and negative if gamma - beta less than beta - alpha (05 Aug 1998) |
| optic stalk | The constricted proximal portion of the optic vesicle in the embryo; it develops into the optic nerve. Pineal stalk, the attachment of the pineal body to the roof of the third ventricle; it contains the pineal recess of the third ventricle. Pituitary stalk, a process comprising the tuberal part investing the infundibular stem that attaches the hypophysis to the tuber cinereum at the base of the brain. Yolk stalk, the narrowed connection between the intraembryonic gut and the yolk sac; its walls are splanchnopleure. Synonym: umbilical duct, vitelline duct, vitellointestinal duct. (05 Mar 2000) |