- A type of specialized light-sensitive cell (photoreceptor) in the retina of the eye that provides side vision and the ability to see objects in dim light (night vision). By contrast, the cones are the retinal photoreceptors that provide sharp central vision and color vision.
* * *1. A slender cylindric structure or device. 2. The photosensitive, outward-directed process of a rhodopsin-containing r. cell in the external granular layer of the retina; many millions of such rods, together with the cones, form the photoreceptive layer of rods and cones. SYN: r. cell of retina. [A.S. r.]- analyzing r. a device used with a surveyor to determine the relative positions of parallel surfaces and undercuts when designing removable partial dentures.- enamel rods SYN: prismata adamantina, under prisma.- Maddox r. a glass r., or a series of parallel glass rods, that converts the image of a light source into a streak of light perpendicular to the axis of the r.. The position of this streak in relation to the image of the light source seen by the fellow eye indicates the presence and amount of heterophoria.- surgical r. a cylindric implant, usually composed of metal, used to align and internally fix fractures of long bones. SEE ALSO: nail, pin.* * *record of decision
* * *rod 'räd n1) a straight slender pole or bar2) any of the long rod-shaped photosensitive receptors in the retina responsive to faint light compare CONE (2a)3) a bacterium shaped like a rod
* * *n.one of the two types of light-sensitive cells in the retina of the eye (compare cone). The human eye contains about 125 million rods, which are necessary for seeing in dim light. They contain a pigment, rhodopsin (or visual purple), which is broken down (bleached) in the light and regenerated in the dark. Breakdown of visual purple gives rise to nerve impulses; when all the pigment is bleached (i.e. in bright light) the rods no longer function. See also dark adaptation, light adaptation.
* * *(rod) 1. a straight, slim mass of substance. 2. retinal r.
Medical dictionary. 2011.