The fovea is the central part of the retina, which contains only cones (zone free of rods). Creates a site that provides the sharpest image and the largest color discrimination. It is in the middle of a yellow spot.
Illustration of the distribution of conical cells in the central well of a person with normal color vision (left) and retinal color (protanopia). Note that there are very few blue-sensitive cones in the center of the wall. In the primate (including humans) the ratio of ganglion cells to photoreceptors is about 2.5; almost every coil cell receives data from a single cone, and each one feeds from 1 to 3 coil cells.
Therefore, the foveal visual acuity limit only with the density of the conical mosaic, and the dimple is the area of the eye with the highest sensitivity to small details. Cones in the middle hole express pigments sensitive to green and red light. These cones are “dwarf” paths that also support the high sharpness of the well.
The hole is used for accurate vision in the direction in which it is directed. It covers less than 1% of the size of the retina, but it occupies more than 50% of the visual cortex in the brain. Fovea only sees the middle two degrees of field of view (about twice as much as your miniature at your fingertips).
If the object is large and therefore covers a large angle, the eyes must constantly shift the eyesight to then insert the different parts of the image into the fovea (as in reading).
Another Fovea function
Arrangement of rods and cones along the line passing through the middle hole and the blind spot of the human eye Because the hole has no rods, it is not sensitive to poor lighting. Hence, to observe dark stars, astronomers use inverted vision, looking at the side of the eyes, where the density of rods is larger, and therefore weaker objects are easier to see.
Fovea function has a high concentration of yellow carotenoid pigments, lutein, and zeaxanthin. They concentrate the Henle fiber layer (photoreceptor axons that run radially outward from the well) and to a lesser extent in the cones. They believe to play a protective role against the effects of high-intensity blue light that can damage sensitive cones.
The pigments also increase the sharpness of the good hole, reducing the sensitivity of the well to short wavelengths and counteracting the effect of chromatic aberration. This is accompanied by a lower density of blue cones in the middle of the hole. The maximum density of blue cones occurs in the ring around the well. Therefore, the maximum sharpness for blue light is lower than for other colors and is approximately 1 ° Celsius
Entoptic effects in the hole
The presence of pigment in the radially aligned axons of the Henle fiber layer makes it dichroic and birefringent to the blue light. This effect is visible through the Haidinger brush when the dimple points to a polarized light source.
The combined effect of the macular pigment and the distribution of short-waved cones causes the well to be less sensitive to blue light (blue light scarlet). Although this is not visible under normal conditions due to the brain’s “filling” of information, under certain blue light patterns, a dark spot is visible in the focus. Furthermore, if a mixture of red and blue light is viewed (by viewing white light through a dichroic filter), the focal point of the well will have a central red spot surrounded by several red stripes. This is called Maxwell’s place after James Clerk Maxwell who discovered it.