Draw a small circle on a white sheet of paper. About 6 cm (2 1/2 inches) to the

Question

Draw a small circle on a white sheet of paper. About 6 cm (2 1/2 inches) to the right of this circle, draw a plus-sign, about 3 mm (1/4 inch) in size. Close your left eye and put your nose on the paper so that your right eye is directly above the circle. Slowly move your head up until you cannot see the plus-sign. Measure and record the distance from your eye to the paper. Move your head farther above the paper until the plus-sign reappears. Measure and record this distance. Why does the plus-sign disappear? Does the plus sign disappear if it is below the circle instead of above it? Explain.

Explanation / Answer

Our eye has an inner lining made up of a sheet of nerves. This sheet of nerves is responsible for our vision and called as RETINA. There is a “hole” in the sheet from where the Optic Nerve enters the eye. This area is called the Optic Nerve Head.

Photoreceptors are cells in the retina that detect light and allow “vision”. On the optic nerve head there are NO photoreceptors. Thus, there is no light or vision detected at this spot in the retina. This is our “Blind Spot”. Every eye has a blind spot….your blind spot in your right eye is slightly on your right and your blind spot in your left eye is slightly on your left.

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