The Human Eye: How it Works
As with other eyes found in nature, the human eye is called a ‘camera type eye’. Similar to the lens of a camera, light is focused onto a film – in the human eye this is called the cornea – which in turn focuses the light onto a retina (a light-sensitive membrane in the eye).
How the Human Eye Works
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Every students should be familiar with the anatomy of the human eye. Following is the detailed structure of an eye.
Eye – Structure (Anatomy of the Human Eye)
Cornea is transparent and located at the front of the eye. It focuses incoming light. The cornea is able to focus most light, and from there the light goes through the lens.
The lens is a transparent structure called the crystalline lens.
Aqueous humor is a clear fluid found between the iris and the cornea.
The iris is a ring-shaped membrane behind the cornea.
The pupil is an adjustable opening in the iris, which can enlarge or get smaller, and will control the amount of light that enters the eye.
Ciliary muscles are around the lens. As well as keeping the lens in position, they have another role in vision. When relaxed they flatten the leans and this allows us to see objects in the distance. For closer objects they contract and make the lens thicker.
Vitreous humor is a tissue that is like jelly, filling the interior area of the eyeball. Before reaching the retina the light travels through the vitreous humor.
There are three layers of tissue that make up the eye. The sclera, or white part, is the most outer layer, along with the cornea. Between the retina and the sclera is the choroid. The blood vessels in the choroid provide nutrition and oxygen to the retina and also removes waste.
There are millions of cells in the retina. They are sensitive to light and are mostly rods and cones. Rods give us monochrome vision, which is needed when the light is poor, and cones add colour and finer details. Cones can be found in the area called the fovea. It is the fovea that gives us good central vision.
Once light gets to the rods or cones, the optic nerve creates an electric signal that goes directly to the brain. The brain translates this signal into what we see.
Vision – possible problems and diseases
There are 4 main vision problems:
- myopia – being nearsighted,
- hyperopia – being farsighted,
- astigmatism – a defect caused when the curvature is not spherical, and
- presbyopia – being farsighted, but it is related to age; most people develop this in the middle years and many will need reading glasses. The ciliary muscles are not able to do their job so effectively, as we age.
Blindness can be caused by the following:
- cataracts (the lens becomes clouded),
- macular degeneration, age related (the central retina deteriorates),
- glaucoma (optic nerve damage), and
- diabetic retinopathy (the blood vessels in the retina are damaged).
There are two other common disorders – lazy eye (amblyopia) and crossed eyes (strabismus).
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