Astigmatism is one of the most common refractory errors which can be corrected by wearing glasses, contact lenses or surgery. The condition is often misunderstood as eye disease, but it is not a disease. It is just a refractory error similar to nearsightedness or farsightedness.
In astigmatism the light which enters the eye is not focused at one point on the retina.
By and large everybody suffers from astigmatism of eye to some extent. However, a person may experience blurred vision only if there is severe astigmatism. Astigmatism is of two types, regular astigmatism and irregular astigmatism. The former is common and easy to correct. The later irregular astigmatism requires more advanced contact lenses and correction measures.
What Causes Irregular Astigmatism?
Astigmatism is a problem pertaining to the shape of cornea. In a normal eye the cornea is spherical in shape, or like the shape of a baseball.
However, in astigmatism the shape of cornea is irregular, it is like a football or inverted spoon. Thus light which enters through the cornea is not focused on one point on the cornea causing blurring and distortion of vision. The exact cause of astigmatism is not known, however, it may occur since birth, or an eye injury or infection or after eye surgery.
Difference Between Regular And Irregular Astigmatism
Once you understand astigmatism, it becomes easy to distinguish irregular and regular astigmatism. Irregular astigmatism is not as common as regular astigmatism. The surface of cornea in irregular astigmatism is not smooth, but rough with ups and downs like ridges and valley. As a result the light is not focused at one point on retina as it passes through the lens. A mild case of irregular astigmatism may cause slight blurring and distortion of vision. However, in severe irregular astigmatism, it may create many images of the same object leading to confusion and disorientation.
In regular astigmatism the corneal surface remains smooth, but the curvature is compromised. The angle for deviation of light may affect mild visual blurring.
The underlying reason for irregular astigmatism is not easy to detect. It may be due to genetic factor from birth, or appear later in life after eye surgery, infection. Aside from these causes, there is an important cause for irregular astigmatism, it is called keratoconus.
It is a disorder where the cornea becomes thin and is often present in persons who are in early twenties. In irregular astigmatism, both near and distant vision is affected. The person may have double vision. If one eye is closed, he may have temporary normal vision. Visual difficulty will lead to problems such headache, imbalance while walking etc.
How Is Irregular Astigmatism Corrected?
It is easy to correct regular astigmatism with regular glasses, contact lenses or laser eye treatment. However, it is difficult to correct irregular astigmatism. To correct this condition, some other type of lens is used, called rigid gas permeable lens. Because of being hard, it has to be used only when the person is awake. This type of contact lenses can be worn only for 20 years.
Nowadays laser surgery is also recommended by ophthalmologists to make the corneal surface smooth. In many cases the surgery may not always make the cornea perfect and smooth, but the patient to a great extent may see images clearly without any distortion.