Astigmatism in Latin means absence of a focal point. This ailment comes as a result of an incorrect (non-spherical) shape of the cornea (rarely of the crystalline lens). In a normal state the cornea and the crystalline lens of a healthy eye have an even spherical surface. And astigmatism distorts it. The spherical surface displays uneven curvature in various directions. Accordingly, astigmatism introduces different refractive power in different meridians and the image is distorted when light pass through such a cornea. Some parts of the image may be focused on the retina, while others are focused either before or after the retina (there may be more complicated cases). The result is that instead of a normal image a person sees a distorted one in which some lines are sharp while other lines are blurred. One can get an idea of this by looking at the reflection in an oval-shaped teaspoon. A similar image distortion on retina occurs in case of astigmatism.

Specialists distinguish corneal astigmatism and lenticular astigmatism. The corneal type has greater impact on vision than the lenticular one since the cornea has greater refractive power. The difference in the refractive strength of the strongest and the weakest meridians defines the value of astigmatism in diopters. The direction of the meridians is defines by the astigmatism axis expressed in degrees.

Grades of astigmatism

Specialists identify three grades of astigmatism.

• light astigmatism – up to 3.0 D
• medium astigmatism – from 3.0 D to 6.0 D
• high astigmatism – over 6.0 D

Types of astigmatism

In terms of its nature, astigmatism is either congenital or acquired

• Congenital astigmatism of up to 0.5 D is found in most children and is identified as "functional", i.e. such astigmatism does not affect sharpness of sight and the development of binocular vision. However, if astigmatism exceeds 1.0 D and more, it reduces the vision substantially and requires treatment using glasses.
• Acquired astigmatism results from scars on the cornea due to injury or surgery.

Dangers of astigmatism

If astigmatism has not been taken care of, it may lead to strabismus and a acute regression of vision. Without proper correction astigmatism may cause headaches and eye gripes. For this reason it is important to visit an ophthalmologist regularly.