The Visual Process
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There are three separate processes that make up the visual process:
The Mechanical Process
The first part of the visual process is mechanical.
Light passes through the cornea and the pupil to the lens.
The cornea's shape focuses the incoming light slightly before it enters the lens.
Some people have an irregularly shaped cornea, which changes the refractive power in that area.
This results in blurred vision, known as astigmatism, which can be corrected for.
The iris determines the size of the pupil.
In bright light, the iris shrinks the pupil, which lets in less light.
In dim light, the iris expands the pupil, letting in more light.
The light then passes through the lens, which bends it and focuses it onto the photoreceptors.
The ciliary muscles and ligaments cause the lens to change shape, which allows the lens to focus light from both distant and nearby objects onto the retina.
This process is called accommodation.
As your body ages, the lens becomes less flexible.
Accommodation is reduced, and the eye’s ability to focus on nearby objects is lessened.
This condition is known as presbyopia, and is corrected with reading glasses or bifocals.
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The Chemical Process
The second part of the visual process is chemical.
The photoreceptors receive the light and convert it into electrical signals.
The cones are active in bright light conditions.
They detect and interpret colors, can pick up small changes (visual acuity), such as threading a needle, and are the photoreceptors that pick up the signals coming from the center of the visual field.
The rods are active in dim conditions, picking up small bits of light from here and there, and are used for peripheral vision.
Rods cannot provide visual acuity, and thus, seeing in the dark and at the edges of vision are usually fuzzy and slightly unfocused.
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The Electrical Process
The third part of the visual process is electrical.
Once the photoreceptors convert the light into electrical signals, the nerve cells that sit on top of the rods and cones pick up the signals and carry them to the optic nerve.
The optic nerve takes the signals to the visual cortex, where the brain reinterprets the signals as what you are seeing.
The follow are other pages on Protect Your Eyesight about the visual-process, please take a look.
Amsler Grid
Eye Anatomy
Refractive Error
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visual process - protect your eyesight
