The amount of astigmatism you may have is probably determined genetically, inherited from your parents. Astigmatism is not caused by using your eyes "too much," sitting too close to the TV set or reading in poor lighting conditions.
Seeing With Astigmatism
Images produced by corneal astigmatism are never quite clear, either for objects viewed far away or nearby. Large degrees of astigmatism can result in considerable blurring of vision. Astigmatism may blur vertical lines more than horizontal lines or vice versa. Sometimes as person will try to "clear" the image by squinting. While this is not harmful to the eyes, it can result in headaches from the continuous muscular effort. Persons with a lot of astigmatism are so used to squinting that they may not be aware they are doing so!
How Is Astigmatism Treated?
Because it is an optical problem involving the corneal surface of the eye, astigmatism can be optically compensated for in most cases with appropriate eyeglasses or contact lenses. (A small amount of astigmatism does not need correction if it does not affect your vision or cause eyestrain.) Sometimes it may take a few weeks for the patient prescribed glasses for astigmatism to get used to them.
Hard, gas permeable contact lenses can also help to reduce the optical effects of astigmatism. Soft lenses generally are not helpful unless they are special "toric" lenses that are made to compensate specifically for the astigmatic shape of the cornea. Correct toric lens fitting requires considerable experience and skill on the part of the practitioner who is prescribing them for the patient.
The degree of astigmatism usually does not change rapidly, but gradual changes may occur as the patient ages. Regular eye examinations are the best way to determine any progression of astigmatism and the lens changes that may be necessary to correct for it. The amount of time you wear your lens correction does not effect your basic astigmatism or its progression.