Looking after your eyes. All you need to know for free.

Your eyes are your most important organs after your brain, heart and the essential metabolic organs like the liver, pancreas and kidneys. Good eyesight is essential to maintaining good quality of life. Globally, in 2002 more than 161 million people were visually impaired, of whom 124 million people had low vision and 37 million were blind. However, refractive error as a cause of visual impairment was not included, which implies that the actual global magnitude of visual impairment is greater. These figures are from those compiled by the World Health Organization. Prevention of blindness and visual impairment should be sufficient reason to care for your eyes. If well cared for they will help you keep an eye on the world and give you added years of safe and quality living.

Before I start talking about what to do to keep your eyes healthy I will illustrate the parts of a normal eye. Each of these parts is represented in the diagram and I have described the parts in more detail below. If you intend to look after your eyes, it is essential that you know the important parts.

Picture 1.External Parts of the eye.

Lens

The lens are the transparent bodies located just behind the iris. The iris is a collection of longitudinal and circular muscles which control the amount of light which enters the eyes. The lens bends light rays so that they form a clear image at the back of the eye where the rods and cones are found. The lens are elastic, they can change their shapes, getting fatter (more convex) to focus close objects and thinner for distant objects.

Cornea

The cornea is the transparent membrane which forms the outer coating at the front of the eyeball and covers the iris and pupil. It also focuses light on the retina. There are no blood vessels in the cornea. Oxygenation takes place by diffusion.

Diagram 1 Parts of the Eye. (figure from allaboutvision.com)

Pupil

The pupil is the dark circular hole in the centre of the iris. The pupil adjusts to ambient light situations. When there is more light, the pupil is constricted, when there is less light the pupils become dilated.

Iris

The iris is the colored circle surrounding the pupil. It changes the size of the pupil and allows different amounts of light to enter the eye.

Retina

The retina is the light-sensitive inner lining of the back of the eye. Imagine that the eye is like a camera, and the retina is the film. Rays of light enter the eye and are focused on the retina by the cornea and lens. The retina produces an image which is sent along the optic nerve for the brain to interpret, rather like developing a camera film.

Macula

The macula is the small area at the centre of the retina responsible for what we see straight in front of us, at the centre of our field of vision. The macula is very important as it gives us the vision needed for detailed activities such as reading and writing, and the ability to appreciate colour.

Sclera

The sclera is the white of the eye and forms the outer coating of the eyeball. It is fibrous, is tough and has a protective function.

Conjunctiva

The conjunctiva is a transparent, mucous membrane that covers the exposed front portion of the sclera and lines the inside of the eyelids. It must be moist at all times.

Tear film

The tear film is the moist layer that covers and protects the outer surfaces at the front of the eye.

Vitreous Humour.

The vitreous is the clear, jelly-like substance that fills the inside of the eye from the lens to the retina. It gives shape to the eye.

Aqueous Humor

The aqueous is the thin, watery fluid that fills the space between the cornea and the iris (anterior chamber). It is continually produced by the ciliary body, the part of the eye that lies just behind the iris. This fluid nourishes the cornea and the lens and gives the front of the eye its form and shape. Alterations in pressure in this part of the eye can cause visual disturbances.

Common Problems and Management of the eye.

TRAUMA

The most common problem of the eye is damage to the cornes. Corneal Trauma is a major cause of impaired vision in developing countries. The cornea can be damaged from infection, injury or other disease. The whole cornea can become cloudy or parts can be damaged by scars. If light cannot pass through the cornea, vision will be affected. The result is similar to cataracts; visual acuity is reduced, good contrast is needed and the amount of light affects vision. Glasses are unlikely to improve vision damaged by corneal scars or clouding. The best method to prevent this is to prevent injury to any part of the. Children need to be supervised when playing and adults need to be aware of the fact that flying objects at work and in the home environment are the major causes of blindness. These are preventable by thinking about safety and having safe practices.