| LOA | leave of absence; Leber optic atrophy; left occipitoanterior [fetal position] |
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| MOD | magnetic optic disk; maturity onset diabetes; Medical Officer of the Day; mesio-occlusodistal |
| OA | obstructive apnea; occipital artery; occipito-anterior; occiput anterior; octanoic acid; ocular albi... |
| OAK | Kjer optic atrophy |
| OC | obstetrical conjugate; occlusocervical; office call; on call; only child; optic chiasma; oral contra... |
| optic placodes | Paired ectodermal placode's that become invaginated to form the embryonic lens vesicles. Synonym: optic placodes. (05 Mar 2000) |
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| 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) |
| optic tectum | <anatomy> A region of the midbrain in which input from the optic nerve is processed. Because the retinally derived neurons of the optic nerve map onto the optic tectum in a defined way, the question of how this specificity is determined has been a long standing problem in cell biology. Although there is some evidence for adhesion gradients and for some adhesion specificity, the problem is unresolved. (11 Jan 1998) |
| optic vesicle | In the embryo, one of the paired evaginations from the ventrolateral walls of the forebrain from which the sensory and pigment layers of the retina develop. Synonym: vesicula ophthalmica, ocular vesicle, optic vesicle. (05 Mar 2000) |
| orbital part of optic nerve | <anatomy, nerve> The part of the optic nerve between the eye and the optic canal. Synonym: pars orbitalis nervi optici. (05 Mar 2000) |
| excavation of optic disc | The normally occurring depression or pit in the centre of the optic disc. Synonym: excavatio disci, depression of optic disk, excavatio papillae, physiologic cup, physiologic excavation. (05 Mar 2000) |
| external sheath of optic nerve | <anatomy, nerve> The outer sheath around the optic nerve, continuous with the dura mater. Synonym: vagina externa nervi optici, dural sheath of optic nerve. (05 Mar 2000) |
| Leber's hereditary optic atrophy | Hereditary degeneration of the optic nerve and papillomacular bundle with resulting rapid loss of central vision, progressive for several weeks, then usually stationary with permanent central scotoma; age of onset is variable, most often in the third decade; more males than females are affected and transmission is cytoplasmic and strictly on the female side. Mutation on the mitochondrial chromosome involved, which presumably interacts with an X-linked mutant. This mechanism may explain the bizarre sex ratio, which differs significantly from one country to another. (05 Mar 2000) |
| lenticulo-optic | Relating to the lentiform nucleus and the optic tract; specifically refers to branches of the middle cerebral artery considered to supply these structures. (05 Mar 2000) |
| alimentary tract | The passage leading from the mouth to the anus through the pharynx, oesophagus, stomach, and intestine. Synonym: alimentary canal, alimentary tract, digestive tube, tubus digestorius. (05 Mar 2000) |
| alimentary tract smear | A group of cytologic specimens containing material from the mouth (oral smear), oesophagus and stomach (gastric smear), duodenum (paraduodenal smear), and colon, obtained by specialised lavage techniques; used principally for the diagnosis of cancer of those areas. (05 Mar 2000) |
| anterior corticospinal tract | Uncrossed fibres forming a small bundle in the pyramidal tract. See: pyramidal tract. Synonym: tractus corticospinalis anterior, tractus pyramidalis anterior, anterior corticospinal tract, anterior pyramidal fasciculus, direct pyramidal tract, fasciculus corticospinalis anterior, fasciculus pyramidalis anterior, Turck's bundle, Turck's column, Turck's tract. (05 Mar 2000) |