Blind spot (vision)
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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.) | |||||
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[edit] Blind Spot size is an indication of brain function
From a practical stance, the smaller the blind spot we have, the better we are able to see and hence the safer we are.
The eyes, being direct extensions of the brain physically, via the optic nerves, and vision being a function not only of the eye but also of the of the brain, Blind spot mapping gives an insight to the physiological activity of the brain. Blind spot mapping is one of the tools that enables this part of the brain's activity to be evaluated.
When one compares blind spot maps, (Examples of blind spot maps) Robb, PA (2009-05-16). "Jennetics and Stress". http://www.headbacktohealth.com/Jennetics.html. Retrieved on 2009-06-01. and if there is one small blind spot compared to a larger one, the smaller one is (in the absence of any pathology of the eye,) considered to have better function.
[edit] Blind spot size can be improved by physical means
Chiropractic cervical spinal adjustments Carrick, FR (1997). "Changes in brain function after manipulation of the cervical spine". J Manipulative Physiol Ther. 1997 Oct;20(8):529-45. http://www.ncbi.nlm.nih.gov/pubmed/9345682?dopt=Abstract&holding=f1000,f1000m,isrctn. Retrieved on 2009-05-01.
Light touch Jennetics chiropractic adjustment Robb, PA (2009-05-16). "Jennetics and Stress". http://www.headbacktohealth.com/Jennetics.html#Blind_spot_mapping. Retrieved on 2009-06-01.
[edit] Related topic
Expansion of visual fields Light frequencies have been used to expand the visual fields of people with vision defects as well as to improve other physical and neurological disabilities, diseases or injuries. Liberman, Jacob. Light: Medicine of the Future. pp. 42. ISBN 089087-762-9 1996.Liberman, Jacob; Presner S and others. Light years ahead. ISBN 089087-762-9 1996.
[edit] External links
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