| visual extinction | A condition in which individual stimuli are seen correctly, but when the nasal visual field of one eye and the temporal visual field of the fellow eye are stimulated simultaneously, one field is blind. Synonym: visual extinction. (05 Mar 2000) |
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| visual field | The area simultaneously visible to one eye without movement; often measured by means of a bowl perimeter located 330 mm from the eye. (05 Mar 2000) |
| visual field test | <ophthalmology> A test which measures the extent of visual field loss. This test may be performed by a number of methods including confrontation, tangent screen exam and automated perimetry. Diseases that affect visual field include stroke, diabetes, hypertension, multiple sclerosis, glaucoma, hyperthyroidism, Jacob-Creutzfeldt disease and optic glioma. (27 Sep 1997) |
| visual image | A collection of foci corresponding to all the luminous points of an object. (05 Mar 2000) |
| visual orbicularis reflex | Contraction of the orbicularis oculi muscle caused by a sudden visual stimulus. See: wink reflex. (05 Mar 2000) |
| visual organ | The eye and its adnexa. Synonym: organum visus, organ of vision. (05 Mar 2000) |
| visual pathway | Neural paths and connections within the central nervous system, beginning with the retina and terminating in the occipital cortex. (05 Mar 2000) |
| visual perception | The selecting and organizing of visual stimuli based on the individual's past experience. (12 Dec 1998) |
| visual pigments | The photopigments in the retinal cones and rods that absorb light and initiate the visual process. (05 Mar 2000) |
| visual projection | A perceptual synthesis involving visual mechanisms. (05 Mar 2000) |
| visual purple | <protein> Light sensitive pigment formed from retinal linked through a Schiff's base to opsin: rhodopsin is an integral membrane protein found in the discs of retinal rods and cones, comprising some 40% of the membrane. Vertebrate opsins are proteins of 38 kD. See: bacteriorhodopsin. (18 Nov 1997) |
| visual receptor cells | The rod and cone cell's of the retina. (05 Mar 2000) |
| visual-spatial agnosia | The inability to localise objects or to appreciate distance, motion, and spatial relationships; caused by lesion in the occipital lobe. Compare: simultanagnosia. (05 Mar 2000) |
| visual threshold | Threshold of visual sensation, the minimal light intensity evoking a visual sensation. Synonym: achromatic threshold, minimum light threshold. (05 Mar 2000) |
| visual violet | A visual pigment, composed of 11-cis-retinal bound to an opsin, found in the cones of the retina. Synonym: visual violet. Origin: G. Ion, violet, + ops, eye, + -in (05 Mar 2000) |