A blind spot, also known as a scotoma, is an obscuration of the visual field. A particular blind spot known as the blindspot, or physiological blind spot, 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 fills in with surrounding detail and with 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 when 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.

Demonstration of the blind spot
A	O		X
Instructions: You may need to reduce the size of your browser window if your screen is large or at a high resolution. Your face should be very close to the screen. Cover right eye and focus the left eye on the X. Now slowly move away from the screen. The O will disappear, while the A which is further to the left is still visible. As you move further away, the O will reappear. (Observe that you do not see a hole. Instead of the O you see a uniform grey background. The "hole" is filled in by your brain. Make sure there is not a glare on the screen as it will obscure the whole vision.)

[edit] See also

• Horizontal eccentricity

[edit] References

[edit] External links

• Blind spots

v • d • e Phenomena of the visual system Entoptic phenomena Blind spot · Phosphene · Floater · Afterimage · Haidinger's brush · Prisoner's cinema · Blue field entoptic phenomenon · Purkinje images Other phenomena Form constant · Scintillating scotoma · Palinopsia · Visual snow · Afterimage on empty shape

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