Astigmatism is a common, mild and generally easily treatable imperfection in the curvature of the eye. The defect can cause blurred vision and unclear sight. Astigmatism occurs when the front surface of the eye (cornea) or the lens, inside the eye, has a slightly different surface curvature in one direction from the other. Instead of being even and smooth in all directions, the surface may have some areas that are flatter or steeper.
Astigmatism blurs the vision at all distances. Astigmatism is often present at birth and may occur in combination with nearsightedness or farsightedness. It is often not necessary to undergo a corrective action. In more severe cases, the treatment options include corrective lenses and surgery.
Signs and symptoms of astigmatism may include:
- Blurred or distorted vision,
Two parts that focus images in the eye are the cornea and the lens. In a perfectly shaped eye, each of these focusing elements has a perfectly smooth curvature, like the surface of a smooth ball. A cornea or lens with such a surface curvature bends (refracts) all incoming light the same way and makes a sharply focused image on the back of the eye (retina).
In case when the cornea or lens is not evenly and smoothly curved, the light rays are unevenly focused. This causes a refractive error. In fact astigmatism is a type of refractive error.
In astigmatism, the cornea or lens is curved more steeply in one direction than in another. Corneal astigmatism occurs if the cornea has a distorted shape, whereas enticular astigmatism occurs when the lens is distorted.
Either type of astigmatism can cause blurred vision and may occur more in one direction, either horizontally, vertically or diagonally.
Astigmatism may occur in combination with other refractive errors, which like nearsightedness (myopia) and farsightedness (hyperopia).
Astigmatism may be present from birth, or develop after an eye injury, disease or surgery. Astigmatism isn't caused or made worse by reading in poor light, sitting too close to the television or squinting.
A small amount of astigmatism is very common and the tendency to develop astigmatism is inherited. A larger amount of astigmatism can be associated with diseases such as keratoconus.
If a person only has astigmatism in one eye, and does not correct it, this may cause the development of amblyopia (a lazy eye).
The common types of astigmatism cannot be prevented. Attention to eye safety can decrease the incidence of astigmatism due to trauma to the cornea.