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Blind point

9. Februar 2017 - Eye, Ophthalmology

The blind spot , also known as optic papilla , blind spot or optic disc , is the area of ​​the retina from which the optic nerve arises .

This area of the back of the eye has no light – sensitive cells, both cones as canes , thus losing all the optical sensitivity. Normally we do not perceive its existence because the blind spot of one eye is supplied by the visual information that the other gives us. It is also difficult to perceive it with one eye, because in the absence of visual information in the area of ​​the blind spot, the brain virtually recreates and fills that small area in relation to the surrounding visual environment.

Experimental verification

An easy experiment can be made by drawing a cross on a folio and a point with a certain distance between them. Then the paper is placed about 20 cm from the left eye, closes the right eye and, fixing the view at the point to the right with the left eye, the paper is slowly approaching and you can see how it disappears Another point when entering the area without optical sensitivity; As the paper moves closer, the dot reappears. The experiment does not always work because the brain is self-deceptive, and once it reaches the blind spot, the point does not disappear because the brain believes it is seeing it, but in reality it is not.

Instructions: You may need to reduce the size of the browser window if your screen is too large or high resolution. Your face should be very close to the screen. Cover your right eye and focus the X with the left. Now, move slowly away from the screen. About 15 cm, the O should disappear, while A is still visible on the left side. When it moves further, the O must reappear. (Note that you do not see a hole. Instead of the O , you should see something like background color uniform gray color. The hole should be „covered“ by your brain. Make sure that there is no reflection on the screen. )

Evolution

The blind spot exists in humans and other animals, but not in all. The evolution of the eye began 540 million years ago. The appearance of the first eye with a genuine formation of the image provoked strong competition, which favored the simultaneous evolution of various types of eyes. The eyes of squid and cuttlefish are an example similar to the eyes of humans for evolutionary convergence , but which prevent the formation of a blind spot.