| IOT | intraocular tension; intraocular transfer; ipsilateral optic tectum |
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| LHON | Leber hereditary optic neuropathy |
| LOA | leave of absence; Leber optic atrophy; left occipitoanterior [fetal position] |
| 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... |
| optic recess | A diverticulum extending forward from the anterior part of the third ventricle above the optic chiasm. Synonym: recessus opticus. (05 Mar 2000) |
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| 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 tract | The continuation of the optic nerve fibres beyond (behind) the latter's hemidecussation in the optic chiasm; each of the two symmetrical optic tracts is composed of fibres originating from the temporal half of the retina of the ipsilateral eye and a nearly equal number of fibres from the nasal half of the contralateral retina; it forms a compact, somewhat flattened fibre band passing caudolaterally alongside the base of the hypothalamus and over the basal surface of the crus cerebri; most of its fibres terminate in the lateral geniculate body; a smaller number of fibres enter the brachium of the superior colliculus, to terminate in the superior colliculus and the pretectal region. Synonym: tractus opticus. (05 Mar 2000) |
| 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) |
| 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) |
| lateral root of optic tract | The larger division of the posterior end of the optic tract that terminates in the lateral geniculate body. Synonym: radix lateralis tractus optici. (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) |
| abdominal part of aorta | <anatomy> The largest arterial conduit below the diaphragm. This term refers to the portion of the aorta below the diaphragm to the bifurcation into the right and left common iliac arteries. It supplies blood to the abdominal viscera, pelvic organs and lower extremities. (20 Jun 2000) |
| abdominal part of oesophagus | The part of the oesophagus inferior to the diaphragm. See: oesophagus. Synonym: pars abdominalis oesophagi. (05 Mar 2000) |
| abdominal part of thoracic duct | The part of the thoracic duct between the cisterna chyli and the aortic hiatus of the diaphragm. Synonym: pars abdominalis ductus thoracici. (05 Mar 2000) |
| abdominal part of ureter | The part of the ureter between the renal pelvis and the brim of the pelvis. Synonym: pars abdominalis ureteris. (05 Mar 2000) |
| accessory flower part | <plant biology> Sepal and petal organs found on flowers. The sepals and petals are not essential for pollination but may aid in attracting insects or other organisms. (15 Jan 1998) |