||This article needs additional citations for verification. (November 2011)
In vertebrate eyes, the nerve fibers route before
, blocking some light and creating a blind spot where the fibers pass through the retina and out of the eye. In octopus
eyes, the nerve fibers route behind
, and do not block light or disrupt the retina. In the example, 4
denotes the vertebrate blind spot, which is notably absent in the octopus eye. In vertebrates, 1
denotes the retina
the nerve fibers, including the optic nerve (3
), whereas in octopodes, 1
denote the nerve fibers and retina respectively.
A blind spot, scotoma, is an obscuration of the visual field. A particular blind spot known as the blindspot, or physiological blind spot, or "blind point", or punctum caecum in medical literature, is the place in the visual field that corresponds to the lack of light-detecting photoreceptor cells on the optic disc of the retina where the optic nerve passes through it. Since there are no cells to detect light on the optic disc, a part of the field of vision is not perceived. The brain interpolates the blind spot based on surrounding detail and information from the other eye, so the blind spot is not normally perceived.
Although all vertebrates have this blind spot, cephalopod eyes, which are only superficially similar, do not. In them, the optic nerve approaches the receptors from behind, so it does not create a break in the retina.
The first documented observation of the phenomenon was in the 1660s by Edme Mariotte in France. At the time it was generally thought that the point at which the optic nerve entered the eye should actually be the most sensitive portion of the retina; however, Mariotte's discovery disproved this theory.
The blind spot is located about 12–15° temporal and 1.5° below the horizontal and is roughly 7.5° high and 5.5° wide.
Blind spot test 
|Demonstration of the blind spot
|Instructions: Close one eye and focus the other on the appropriate letter (R for right or L for left). Place your eye a distance from the screen approximately equal to 3× the distance between the R and the L. Move your eye towards or away from the screen until you see the other letter disappear. For example, close your right eye, look at the "L" with your left eye, and the "R" will disappear.
See also 
- ^ Gregory, R., & Cavanagh, P. (2011). "The Blind Spot". Scholarpedia. Retrieved on 2011-05-21.
- ^ MIL-STD-1472F, Military Standard, Human Engineering, Design Criteria For Military Systems, Equipment, And Facilities (23 Aug 1999) PDF
External links