In normal sight, light rays passing into the eye are focused exactly on the retina, giving a small, sharp image, which is upside down and is reversed by the brain. It is amazing that emmetropia or normal sight is normal, given that 1/25 in (1 mm) variation is enough to distort the image. However, several common types of vision problems can usually be rectified by glasses or contact lenses.
Healthy young eyes have a tremendous focusing range, from long distance down to a few inches. This focusing range alters and reduces with age, and the change is particularly noticeable after the age of about forty. Don’t worry about this; it is absolutely normal, so much so that if change of focus does not occur within a few years of the expected time you should have your eyes tested. Some people actually find that the change in focusing noticeably improves their sight.
Common Types of Vision Problems: Myopia
Myopia or short sight ranks high in the list of common types of vision problems. It occurs when the lens is too rounded and thick, or the eyeball is too long from front to back. The light rays are then refracted in front of the retina, making the image blurred. Glasses or contact lenses must be concave to correct the focus.
Common Types of Vision Problems: Hypermetropia
Hypermetropia or long sight occurs when the lens is too long and thin, or the eyeball is too short from front to back, so that the focus falls behind the retina again making a blurred image. Many people become mildly long-sighted as they get older. Convex lenses correct the focus for reading for close work.
Common Types of Vision Problems: Astigmatism
Astigmatism occurs when the cornea is unevenly curved, so that the refractive power of the eye varies, and it cannot focus on vertical and horizontal objects at the same time – for example, in letters such as E, F or T. Corrective lenses compensate by affecting the light rays on only one plane.
Common Types of Vision Problems: Strabismus
Strabismus or squint occurs when the eye muscles fail to hold the eye in place – hence the term ‘lazy eye’. It is a common condition in children, who often outgrow it. Most people who have a ‘cross eye’ know that it becomes more pronounced when they are tired. Conventional treatment is to build up the eye muscles by covering the strong eye with a patch and making the week one do the work. Acute cases can be corrected by surgery.
Common Types of Vision Problems: Night Blindness
Night blindness is a condition when the eye fails to focus in semi-darkness – is often due to a dietary deficiency in Vitamin A, and commonly improves with the regular intake of foods containing this vitamin, such as eggs, milk, carrots, liver and kidneys.
Common Types of Vision Problems: Color Blindness
Color blindness, as it is commonly called, though it is really color-defective vision, occurs in approximately 8 per cent of men and in less than 1 per cent of women, though some surveys have shown a slight increase in color blindness among women who take the Pill. Total color blindness or mono-chromatic vision, when only shades of black and white can be seen, is extremely rare. The most common form of color-defective vision is the failure to distinguish between red and green.
Millions of people all over the world have problems with sight. Often problems manifest as vision blurred, dark spots or strange changes in what is seen. But many of the vision problems do not produce any symptoms as long as things get worse. So be careful. Some of the common types of vision problems can cause permanent loss of sight. Even they can lead to complete blindness.