Question

While on a camping trip in Moab, Utah, Starr Gazer was admiring all the stars that could be seen in the night sky. She noticed an interesting, fuzzy looking cluster of stars at the edge of her vision. When she looked directly at that part of the sky, however, she could not see the cluster. When she looked toward the stars, but not directly at them, she could see them. Explain what is happening.

Answer 1

Cones are concentrated at the center of retina called fovea centralis where no rod cells are present.

The retina is the innermost lining of the eye, made up of thousands of light-sensitive cells, with an inner part of nerve tissue and a pigmented outer part. It plays a fundamental role in the formation of images, which will be projected and then sent to the brain, through electrical impulses.

The retina consists of three types of layers: bipolar neurons, ganglion neurons and photosensitive cells.

Bipolar neurons promote the union of photosensitive cells with ganglion neurons, which are grouped with nerve fibers and thus originate the optic nerve. It carries nerve impulses to the brain. Photosensitive cells, due to their shape, are named in two types: cones and rods.

There are about 6 million cones that are concentrated in a small depression located in the macula lutea (center of the retina) called the fovea. They have an elongated and cylindrical shape, with conical outer segments. It is in this region that the image is most clearly formed, as they are stimulated by the most intense light. Cones are specialized in the accuracy of daytime vision and in recognizing color. There are three types of cones that have fundamental photopigments that respond to light of wavelengths (λ): cyanopigment - S cones (short λ) - sensitive to blue color, chloropigment - M cones (medium λ) - sensitive to green color and erytopigment - cones L (λ long) - sensitive to red color. The brain interprets the signals received by these cones, which allows it to process color differentiation.