Cause of astigmatism can be hereditary and is usually present from birth. It can change as a child grows and may decrease or worsen over time.
What causes Astigmatism?
Astigmatism occurs due to the irregular shape of the cornea or the lens inside the eye. The cornea and lens are primarily responsible for properly focusing light entering the eyes allowing us to see things clearly.
Causes of astigmatism can be hereditary and is often present at birth. It can also due to pressure from the eyelids on the cornea, incorrect posture or an increased use of the eyes for close work can cause this unwanted pressure.
The curvature of the cornea and lens causes light entering the eye to bend in order to focus it precisely on the retina at the back of the eye. In astigmatism, the surface of the cornea or lens has a somewhat different curvature in one direction than another. In the case of the cornea, instead of having a round shape like a basketball, the surface of the cornea is more like a football. As a result, the eye is unable to focus light rays to a single point causing vision to be out of focus at any distance.
Sometimes astigmatism may develop following an eye injury or eye surgery. There is also a relatively rare condition called keratoconus, where the cornea becomes progressively thinner and cone shaped. This results in a large amount of astigmatism resulting in poor vision that cannot be clearly correct with spectacles. Keratoconus usually requires contact lenses for clear vision, and it may eventually progress to a point where a corneal transplant is necessary.