Cones are the retina's daylight receptors, about 6 million per eye, concentrated in the fovea. There are three types, most sensitive to short (blue), medium (green) and long (red) wavelengths. Comparing their signals gives colour vision, and their dense foveal packing gives sharp detail.
| Location | Outer retina, densest in the fovea and sparse in the periphery |
|---|---|
| Parts |
|
| Nerve Supply | Synapse with cone bipolar and horizontal cells; signals leave via the optic nerve (CN II) |
| Blood Supply | Choriocapillaris (short posterior ciliary arteries) |
Provide colour vision and fine detail in bright light (photopic vision).
Red-green colour vision deficiency, from altered medium or long wavelength cone pigments, is X-linked and affects about 8 percent of men of Northern European descent. Cone dystrophies cause reduced acuity, light sensitivity and poor colour vision. Ishihara plates screen for red-green defects.
An inherited X-linked change in red or green cone pigments that makes these colours hard to tell apart. It is common and usually mild.
Inherited progressive loss of cone function causing reduced central vision, glare sensitivity and colour vision loss.
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