When most patients experience blurred vision, it is due to a change in the refractive state of the eyes. These refractive errors are generally a result of normal growth changes in the eye, and are probably caused by family genetics. The four most common refractive errors are shown below along with a normal emmetropic eye.
A condition where light is focused at a point behind the retina. The eye is spherical in shape but somewhat smaller and shorter in size, such as a ping-pong ball. When you are farsighted the eye must focus all the time to see clearly. It must focus to see distance objects clearly, and it has to focus even more to read. Usually, these patients complain of reading problems or they have no complaints at all.
A condition where light is focused at a point in front of the retina. This condition allows a person to see up close but distance vision is blurred. The eye is spherical in shape but the eye is larger or longer in size, such as a tennis ball.
EMMETROPIA (Normal Eye)
A condition where light is focused at a point on the retina. This eye does not have hyperopia or myopia because it has a spherical shape and correct size and length. A golf ball would be a good comparison for an emmetropic or normal eye.
A condition that exists when an eye has an out of round shape. Chicken eggs are not spherical in shape but oval, and are similar in shape to eyes that have astigmatism. Eyes with severe astigmatism can be thought of as football shaped eyes. Astigmatic eyes do not focus the light at a single point but at many points. Astigmatism can cause blurred vision, headaches, or eyestrain. Many times it is found in association with myopia or hyperopia.
A condition where distant objects are focused clearly on the retina, but near objects are not because the focusing ability of the eye has diminished due to the aging process. This focusing ability is called accommodation. Loss of accommodation starts in our early teens and slowly becomes less and less each year. It is brought on by a hardening of the crystalline lens inside the eye. Most people will experience problems seeing objects up close clearly around age forty. Some people have near focus problems by age thirty-five while others do not experience problems until age forty-five.