| 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) |
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| 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) |
| visual yellow | The orange retinaldehyde resulting from the action of light on the rhodopsin of the retina, which converts the 11-cis-retinal component of the rhodopsin to all-trans-retinal plus opsin. Synonym: trans-retinal, visual yellow. (05 Mar 2000) |