Information on the human eye

You should never take your eyes for granted; don't wait until you have a problem to have a vision exam. You should have your eyes checked annually.

The eye is very delicate and in order to see well, all parts must be able to function properly. Always try to protect your eyes. Did you know that the bones in your head protect your eyes from injury; even the eyelids close out unwanted light and also dirt. Your tears from nearby tear ducts work hard to keep the eye's surface moist and clean.

The pupil is a round opening surrounded by muscles that regulate the amount of light that enters the eye; pupils will enlarge if the light is too dim and if the light is too bright, pupils become small to keep out too much light. The iris controls the size of the pupil and is a colored circle containing many muscles. It can appear gray, green, blue, or brown. The muscles in the iris receive their nourishment from blood vessels in the middle layer of eye tissue that contains many blood vessels; this tissue is the choroid. There is a lens behind the pupil suspended by the middle layer of the eye, and it is a flexible structure that aligns the light rays so that they come together in the inner layer of the eye. The focus is the point at which all of the light rays intersect. After light passes through the lens, it falls on the retina, the part of the eye that absorbs light rays and changes them into the electrical messages that then create images.

There are receptors in the retina called photoreceptors. These are of two types: rods and cones. Rods are cells that are very sensitive to light but can only distinguish black from white, and cones detect color but are not very sensitive to light. At the center back of the retina is a small yellow spot called the fovea, which contains no rods; it allows the eye to view things in great detail. There is also a blindspot at the point at which the optic nerve joins the eye, and it contains neither rods nor cones. The cord of nerve fibers that carries messages to the brain is the optic nerve. The process by which the brain puts these different images together is called stereoscopic vision. Peripheral vision is the process of seeing objects at the sides of your eyes.

Healthy vision requires three basic processes: formation of an image on the retina (refraction), stimulation of rods and cones, and conduction of nerve impulses to the brain. Malfunction of any of these processes can disrupt this chain of processes, producing a visual disorder.

Here are some tips to protect your eyes. When you work in an area in which the eyes need protection, be sure to wear protective safety glasses to keep the eyes from harm. This will protect your eyes from chemicals, light, and heat. If you are participating in sports, you will also need the proper helmets or goggles to prevent injury. When working near moving particles where there is a great deal of blowing sand or dust or even smoke, don't forget to wear goggles. These are common for many industrial workers, but some work around the home also makes their use necessary.

Many rays injure the eyes. The cutting flame of the acetylene torch produces rays highly injurious to the conjunctive. Bright light from glowing blocks of metals and arc lamps also affects the conjunctive and may produce blurred vision. Infra-red rays from glowing glass have long been known to produce "glass blower's cataracts." Infra-red rays are also responsible for a condition known as snow blindness, which is not caused by snow but from the rays reflected from the snow. Permanent or serious damage to the eye can result from any of these rays, and the use of protective devices, goggles, or sunglasses is necessary.

There can be many wounds made by penetration of the eye that cause loss of sight or even permanent damage. Children playing with sharp-pointed toys, scissors, darts, etc., can be very dangerous. The use of wooden sticks is dangerous, too, because these can become broken and then form sharp, jagged ends. Prevention is important, so it is wise to discard toys that can damage and be very careful about buying new toys that may cause harm, especially to small children.

When you do very close reading, it is a good idea to practice good eye hygiene and to prevent eye injuries. Reading can be complex and is usually done without any thought or attention to injuries. You use the external muscles of your eyeball to shift from line to line; at the same time, your ciliary muscles keep your eyes focused on the same point. The amount of light admitted by the pupil is controlled by the muscles of the iris. You have to sometimes re-read the same line of print if your vision is in poor muscular condition. Try not to read in a car or on a moving bus, train, or airplane because your eye muscles are subjected to the strain of continually refocusing the words read. Reading while lying down or propped on one elbow will cause eyestrain. Have a good source of light if you plan to read in bed and assume a normal position for reading with your back propped with a pillow.

Wearing the proper corrective lenses is very essential. Choosing whether to wear either contact lenses or eyeglasses depends on several factors, such as the kind of eye problems, activities of the person, and personal preferences. If you choose to wear eyeglasses, there are many lenses or frames from which to choose. You may want to choose a pair of eyeglasses that best suit your lifestyle. These glasses come in all different colors and shapes. You can also get prescription sunglasses or glasses with darkened lenses for prevention of too much glare. Be sure to discuss the choices fully with your vision specialist before making a decision.

Contact lenses sometimes can provide a wider field of vision than eyeglasses because they tend to increase peripheral vision. As the years go by, more and more improvements are being made with contact lenses. There are some made of hard, inflexible materials, which can be worn for only a short length of time because the hard lens can scratch the cornea. Some lenses can also irritate the eye by depriving it of oxygen. Now newer materials for contact lenses enable one to wear them for long periods of time. There are even ones that are disposable on the market today.

If you have contact lenses, there must be much care given to them. First of all, be sure your hands are washed before touching contact lenses because you can introduce bacteria into the eye. You won't want to wear the lenses to bed unless you have purchased extended-wear lenses; wearing lenses to bed causes irritated corneas and interferes with fluid circulation in your eyes. Sloppy cleaning techniques can lead to serious eye infections or even permanent eye problems. If your contact lenses are not working well, get your eyes retested by a vision specialist because your eye acuity may have changed. If your eyes are continually irritated or become painful, it is certainly time for a visit. If you are a woman, you need to insert your lenses before you put on makeup or mascara, and be careful with spraying hair spray around your eyes if you are wearing your contact lenses. Carry a spare pair of glasses with you in case you lose a contact lens.

If you experience any of the following symptoms please have your eyes checked by an optometrist or ophthalmologist: difficulty focusing or seeing close or distant objects, dryness, itch or burning in the eyes, black spots or flashes of light or excessively watery eyes. Watch for blurred or double vision, spots, or ghost-like images, vertical lines looking wavy or distorted, difficulty adjusting to darkened rooms or halos (colored rings around lights). Using the familiar big "E" chart, the examiner will determine if you can see clearly. A rating of 20/20 is normal. A visual acuity of 20/30 means that what a normal person can see at 30 feet, you can see only at 20 feet. The most common vision defects are nearsightedness, farsightedness, and astigmatism.