How does the eye work?
Our eyes pick up signals from the environment and transmit them to our brain through the optic nerve. There, the signals from both eyes are converted into perceptions; in other words, into vision.
You can compare the eye to a camera. An eye has two lenses: the cornea and the actual eye lens. You zoom in and out (accommodate) with the eye lens, allowing you to see images sharply at any distance. The “diaphragm” (pupil) sits between the two lenses. The “film plate,” or retina, is located on the inside of the eyeball. With the help of the lenses, a sharp image forms on our retina.
The iris is the colored part of the eye that controls the size of the pupil and thus the amount of incoming light. In bright light, the pupil becomes smaller; in darkness, the pupil becomes larger. This allows us to see well in bright sunlight as well as at dusk. The color of the iris is unique and varies from person to person. With a lot of pigment in the eyes, the iris is brown. With little pigment, one may have blue or gray eyes.
The pupil is a small (black) opening in the iris that determines the amount of light that enters the eye. In bright light, the pupil becomes smaller; in darkness, the pupil becomes larger. This allows us to see well in bright sunlight as well as at dusk.
The retina is a light-sensitive layer on the inside of the eye. It contains millions of rods and cones. These capture the light that enters the eye and convert it into electrical signals that go to our brain.
The retina has about 6 million cones that we use in daylight or good artificial light. The cones allow us to see colors and distinguish details of things that are right in front of us. Reading and watching TV, for example, are done with the cones.
The cones are responsible for seeing in daylight conditions. The rods are for night vision. We cannot perceive details with rods.
The cornea is the transparent front layer of the eye and is an important protective layer.
The hard eye skirt or sclera is the outer wall of the eyeball that protects the eye and provides stability. At the front, the sclera merges into the cornea.
The optic nerve transmits signals from the eye to the brain. This runs through the back of the eyeball to the brain.
It’s not always a refractive defect that causes you to see less sharply. Sometimes there’s something else going on.
There are several ways to examine your eyes. An initial exam is often done using an autorefractor.
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