Rods are the retina's highly sensitive light receptors, numbering about 90-120 million per eye. They contain the pigment rhodopsin and can respond to a single photon, making them ideal for night vision. They are absent from the foveola and most numerous in the mid-peripheral retina.
| Location | Outer retina, throughout except the foveola, densest about 20 degrees from the fovea |
|---|---|
| Parts |
|
| Nerve Supply | Synapse with rod bipolar and horizontal cells; signals leave via the optic nerve (CN II) |
| Blood Supply | Choriocapillaris (short posterior ciliary arteries) |
Detect low levels of light and motion in peripheral vision, providing night (scotopic) vision.
Rods do not distinguish colour, which is why colours fade in dim light. Vitamin A is needed to regenerate rhodopsin, so deficiency causes night blindness. Inherited rod diseases such as retinitis pigmentosa begin with poor night vision and narrowing of the peripheral field.
A group of inherited diseases in which rods degenerate first, causing night blindness and tunnel vision, with later loss of cones.
Lack of vitamin A impairs rhodopsin regeneration, causing poor vision in dim light; severe deficiency also damages the cornea.
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