Common Causes Of Myopia
There are several known causes of myopia, better known as nearsightedness. Myopia occurs when the eye, which is nearly spherical, becomes elongated in shape and begins to appear more egg-shaped than spherical. This elongation of the eye is the direct cause of myopia. However, some of the factors leading up to this elongation of the eyeball are not fully understood.
Distance From Lens To Retina The Key - In years past we had to focus slide projectors to get a clear image on the screen, or focus the camera to get a sharp image on the film. The way the eye in constructed, there is seldom a need for focusing, as the lens in a normal, healthy eye focuses the light rays entering the eye so that they fall on the retina in a manner which produces a clear, sharp image. If something should happen to the shape of the eye such that the distance from the lens to the retina is changed, the image will become less distinct, or blurry. If the eye becomes elongated, the light rays will converge at a distance slightly in front of the retina rather than on the retina itself, and distant images will become blurred. Viewed form another perspective, the distance between lens and retina must be exact and extremely precise.
Myopia is generally incurable though it is treatable. It is generally incurable because there are no medications or mechanical devices that can reshape the eye so the light rays converge on the retina. Myopia is treatable thanks to eyeglasses, contact lenses or lens implants, which can refocus the light rays so they converge on the retina. That's what eyeglasses do.
Corneal Curvature - The term generally incurable is used because there is an exception. One of the causes of myopia, which does not necessarily involve a lengthening of the eye, is that when the curvature of the cornea, the outer surface of the eye, changes. A change in the curvature of the cornea can effectively cause the lens to be either slightly distorted or moved to the extent the light rays fail to converge on the retina. Curvature of the cornea can often be cured through the use of laser surgery. Surgery to correct myopia due to corneal curvature is seldom performed on children as their eyes are still growing, and even if the surgery were effective it would quite likely have to be repeated later.
Axial Length Myopia - Myopia most often occurs during childhood, when the eyes are still growing. For some children it is a congenital condition as the eye is not perfectly formed when the child is in the womb. In other words, myopia can be a congenital condition. Genetics can play a role as the eye may grow too rapidly, either in utero before birth, or in the months following birth. This condition, one of the causes of myopia, is known as axial length myopia, where the eye grows too long as a result of genetics. Children whose parents have myopia have a higher risk of becoming nearsighted, although one or both parents having myopia does not necessarily mean the child will suffer the same fate.
Glaucoma Is A Cause - Another of the causes of myopia is glaucoma, a condition in which the fluids inside the eye are subjected to higher than normal pressures. Glaucoma can cause many more problems than nearsightedness; in fact it is one of the leading causes of blindness, as the retina may become damaged or detached. Myopia will result if the pressure inside the eye causes the eyeball to stretch. Once the pressure is relieved the eye often returns to normal and the myopia disappears.
Cataracts Can Cause Myopia - Cataracts are also one of the causes of myopia. The removal of the cataracts however does not in itself cause the eye to return to normal, as the lens must be replaced following or as part of the procedure. With a lens implant, a fairly straightforward procedure, long distance vision usually returns to normal if there are no other eye diseases present, and the formerly nearsighted person can again see distant objects clearly, without the need for eyeglasses or contact lenses.
Diet and close work are also factors which can affect vision. While neither is regarded as being one of the causes of myopia, both are considered to be contributing factors.