Astigmatism

Dr Ben Wild

Overview

As our bodies develop from birth until adulthood, our eyes have to change in lock-step. This process is called emmetropization (where the growth of the eye matches the change in focusing power). Most of the focusing power of the eye comes from the cornea, the clear tissue in front of the colored iris, and the intra-ocular lens, a clear tissue located through the pupil.

A sagittal view of an eye focusing a dot of light on the retina.

Astigmatism occurs when the cornea and/or lens start to grow into the shape of a cylinder and not a sphere. This means that the eye requires a corrective lens that is equally shaped as a cylinder but pointed in the opposite direction. The technical definition of astigmatism is the inability to focus a dot of light into a dot of light. Instead, the light is focused as a line of light.

A sagittal view of an eye focusing a dot of light on the retina as a line of light (top) and an eye with a cylindrical glass lens refocusing the light as a dot of light on the retina (bottom).

Astigmatism isn't caused by doing anything wrong but has been associated with large amounts of reading and near work. It can sometimes be seen at birth.

Signs and Symptoms

Signs

Squinting.

Symptoms

Eyestrain, headaches, blurry near and distance vision, dots of light (headlights) look like lines of light.

Causes and Risk Factors

Causes

Usually, astigmatism originates from the cornea developing into the shape of a cylinder instead of a sphere. Occasionally the intra-ocular lens can be in the shape of a cylinder.

Risk Factors

Genetics, corneal ectasia (like keratoconus), eye infections or scarring, excessive near work.

Prevention and Treatment

Prevention

There are no preventative measures.

Treatments

· Glasses.

· Contact lenses (soft and hard).

· Laser eye surgery.

Prognosis

Astigmatism does not usually progress past teenage years and does not cause any eye disease like myopia. There are some eye conditions that can cause astigmatism, such as corneal ectasias, scarring, and more, but generally it is due to the development of the eye. Glasses, contact lenses and laser eye surgery can be very well utilized for clear vision. If high amounts of astigmatism go uncorrected for too long as a child, the visual cortex of the brain may never fully develop and vision, even with the best glasses prescription, may never reach 20/20. This is called amblyopia. It is important to correct astigmatism in youth.