| LHON | Leber hereditary optic neuropathy |
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| LL | large lymphocyte; lateral leminiscus; left lateral; left leg; left lower; left lung; lepromatous [in... |
| LML | large and medium lymphocytes; left mediolateral; left middle lobe |
| LOA | leave of absence; Leber optic atrophy; left occipitoanterior [fetal position] |
| LUL | left upper eyelid; left upper limb; left upper lobe; left upper lung |
| optic agnosia | The inability to recognise objects by sight; usually caused by bilateral parieto-occipital lesions. Synonym: optic agnosia. (05 Mar 2000) |
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| optic ataxia | An inability to guide the hand toward an object using visual information; seen in Balint's syndrome. (05 Mar 2000) |
| optic atrophy | Atrophy of the optic disk resulting from degeneration of the nerve fibres of the optic nerve and optic tract. (12 Dec 1998) |
| optic atrophy, hereditary | An inherited disorder in which optic atrophy is associated with muscle weakness, peroneal muscular atrophy and, in some patients, lancinating pains. In these patients the peripheral sensory neurons are probably affected. (12 Dec 1998) |
| optic axis | The axis of the eye connecting the anterior and posterior poles; it usually diverges from the visual axis by five degrees or more. Synonym: axis opticus. (05 Mar 2000) |
| optic canal | 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 capsule | The concentrated zone of mesenchyme around the developing optic cup; the primordium of the sclera of the eye. (05 Mar 2000) |
| 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) |