| retinal | 1. <anatomy> Pertaining to the retina. 2. <biochemistry> The aldehyde of retinol, derived by the oxidative enzymatic splitting of absorbed dietary carotene and having vitamin A activity. In the retina, retinal combines with opsins to form visual pigments. One isomer, 11 cis retinal combines with opsin in the rods (scotopsin) to form rhodopsin or visual purple. Another, all trans retinal (trans r.), visual yellow, xanthopsin) results from the bleaching of rhodopsin by light, in which the 11 cis form is converted to the all trans form. Retinal also combines with opsins in the cones (photopsins) to form the three pigments responsible for colour vision. (18 Nov 1997) |
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| retinal adaptation | Adjustment to degree of illumination. (05 Mar 2000) |
| retinal anlage tumour | A benign neoplasm of neuroectodermal origin that most often involves the anterior maxilla of infants in the first year of life. It presents clinically as a rapidly growing blue-black lesion producing a destructive radiolucency; histologically, it is characterised by small round undifferentiated tumour cells interspersed with larger polyhedral melanin-producing cells arranged in an alveolar configuration. Synonym: melanoameloblastoma, pigmented ameloblastoma, pigmented epulis, progonoma of jaw, retinal anlage tumour. (05 Mar 2000) |
| retinal artery | <anatomy, artery> Central retinal artery and its branches. It arises from the ophthalmic artery, pierces the optic nerve and runs through its centre, enters the eye through the porus opticus and branches to supply the retina. (12 Dec 1998) |
| retinal artery occlusion | Occlusion or closure of the central retinal artery causing sudden, usually nearly complete, loss of vision in one eye. Occlusion of the branch retinal artery causes sudden visual loss in only a portion of the visual field. (12 Dec 1998) |
| retinal blood vessels | The blood vasculature of the retina, including the branches and tributaries of the central retinal artery and vein, respectively, and the vascular circle of the optic nerve. Synonym: vasa sanguinea retinae. (05 Mar 2000) |
| retinal camera | An instrument for photographing the ocular fundus. (05 Mar 2000) |
| retinal cone | <ophthalmology, physiology> One of the two photoreceptor cell types in the vertebrate retina. In cones the photopigment is in invaginations of the cell membrane of the outer segment. Cones are less sensitive to light than rods, and are differentially sensitive to particular wavelengths of light and therefore important for colour vision. They provide vision with higher spatial and temporal acuity, and it is the combination of signals from cones with different pigments that facilitates colour vision. There are three types of cones, each type sensitive to red, green or blue. Present in large numbers in the fovea. (03 Jul 1999) |
| retinal degeneration | <ophthalmology> A retrogressive pathological change in the retina, focal or generalised, caused by genetic defects, inflammation, trauma, vascular disease, or aging. Degeneration affecting predominantly the macula lutea of the retina is macular degeneration. (03 Jul 1999) |
| retinal dehydrogenase | An oxidoreductase catalyzing the interconversion of retinaldehyde and NAD+ to retinoic acid and NADH; thus affecting growth and differentiation. Synonym: retinaldehyde dehydrogenase. (05 Mar 2000) |
| retinal detachment | <ophthalmology> A painless disorder (when spontaneous) where the patient complains of a gradual raising or lowering of a curtain over the visual field of the affected eye. May also occur as the result of trauma. (27 Sep 1997) |
| retinal disease | <ophthalmology> A general term which describes any retinal changes (haemorrhages or exudates) that can affect vision (for example diabetic retinopathy, hypertensive retinopathy). (27 Sep 1997) |
| retinal disparity | The slight difference in retinal images that arises because of the lateral separation of the two eyes that stimulates stereoscopic vision. (05 Mar 2000) |
| retinal drusen | <ophthalmology> Colloid or hyaline bodies lying beneath the retinal pigment epithelium. They may occur either secondary to changes in the choroid that affect the pigment epithelium or as an autosomal dominant disorder of the retinal pigment epithelium. (12 Dec 1998) |
| retinal dysplasia | <ophthalmology> Congenital, often bilateral, retinal abnormality characterised by the arrangement of outer nuclear retinal cells in a palisading or radiating pattern surrounding a central ocular space. This disorder is sometimes hereditary. (12 Dec 1998) |