The word fovea refers to any small pit or depression in the surface of a structure or organ. The Fovea Centralis is a small depression in the center of the macula lutea of the retina. The average diameter is 0.3 mm and the area is rod-free area with very thin, densely packed cones, allowing for a point of maximal focus.

Measured density curves for the rods and cones on the retina display an extremely high density of cones in the fovea centralis. Cones in this area are also slightly smaller in size than anywhere else on the retina (with diameters of 0.0030mm to 0.0015mm). Since both colour vision and the highest visual acuity are associated with the cones, an image must be focussed on the fovea centralis .

The field of vision is typically around 200 degrees but the acuity over most of that range is poor. For examination of intricate detail, the light must fall on the fovea, and that limits the acute vision angle to about 15 degrees. The total absence of rods makes the fovea a second blind spot since cones have very low light sensitivity.

Ref : Hecht, Eugene, Optics, 2nd Ed, Addison Wesley, 1987

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