What Is Astigmatism? - Definition, Symptoms & Causes

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Do you wear glasses or contact lenses? One of the problems with eyesight includes astigmatism. Read this lesson to find out what astigmatism is, what causes it to develop, and what the symptoms are.

What Is Astigmatism?

You're probably no stranger to the idea of corrective lenses, either in the form of glasses or contact lenses. One specific problem of the eyes is astigmatism. This occurs when the cornea or lens is abnormally shaped and curved improperly. A normal eye is round, and an eye with astigmatism is oblong in one direction. As a result, light fails to enter the eye correctly, meaning it does not hit the retina from the proper angle, distorting the image the person sees. In fact, the light is broken up and hits the retina in more than one place, so there is never just a single version of the object being formed. Astigmatism comes in a variety of types, with some being minor and non-problematic and others being severe, leading to both blurred vision and headaches.

In this diagram, the cornea (front layer of the eye) is curved, causing light to refract off the retina in multiple places instead of one. This causes the resulting image to be blurry and out of focus.

Causes of Astigmatism

What causes parts of the eye to be abnormally shaped? Unfortunately, there is no direct cause. It's a hereditary condition that is usually inherited at birth. For example, both of my parents are nearsighted and have slight astigmatism. As such, both my sibling and I have compromised vision and require pretty strong corrective lenses, and we both have severe astigmatism. The shape of our eyes is not perfectly round, causing light to bend differently when it passes through the eye.

Astigmatism Symptoms

We already know that blurry vision is the primary symptom. Because of the improper refraction of light leading into the eye and retina, the image the brain interprets will always be blurry or fuzzy. With severe cases, headaches, fatigue, and nausea may also occur.

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