Eye conditions & symptoms 2 min read

Astigmatism vs Myopia: What's the Difference?

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There are a number of eye conditions that can affect your vision, which are often grouped together as refractive errors. Typically refractive errors occur due to an irregularity in the eye, including the cornea, lens and general shape of the eye. It can often be confusing separating the different refractive errors, especially as they can typically come hand-in-hand. Two of the most common eye conditions include astigmatism and myopia. Both of these refractive errors are different in some ways and similar in others.

What is astigmatism?

Astigmatism is a very common defect that affects the curvature of the cornea or lens. Typically your cornea or lens will be symmetrical, but astigmatism can affect this. A regular cornea is shaped like a football, but if you have astigmatism then it's more likely to resemble a rugby ball.

There is both corneal astigmatism and lenticular astigmatism, depending on whether the condition affects your cornea or lens. There is also regular astigmatism and irregular astigmatism. Regular astigmatism occurs when the cornea curves more in one direction, while the irregular type occurs when the cornea curves in a number of directions.

diagram showing the difference between normal and astigmatic eye

 

How does astigmatism differ from myopia?

Astigmatism is typically present from birth, while myopia usually appears in school-age children. Myopia will usually get worse until it stabilises in early adulthood. While astigmatism is usually down to the natural shape of your eye, myopia is closely linked to genetics and environmental factors. For example, if one or both parents are myopic, it's more likely the child will be. However, myopia can also happen if the eyes grow slightly too long.

Astigmatism and myopia often come hand-in-hand, so if you have astigmatism it's more likely that you are also short-sighted. It's also linked with hypermetropia or long-sightedness. In this sense, both refractive errors affect the way the light enters your eyes.

The signs of astigmatism and myopia can be similar in that they will both result in blurry or distorted vision. However, myopia occurs when objects far away appear blurred, while astigmatism will also make it more difficult to distinguish certain shapes. In both cases, you might experience headaches or eye strain if it goes untreated.

Diagram showing difference between normal and myopic eye

Can either myopia or astigmatism be treated?

Both refractive errors are diagnosed during a routine eye examination, and usually, both can be treated with corrective lenses. However, irregular astigmatism can only be corrected with the use of contact lenses. 

There are ways to slow down the progression of myopia through special lenses known as orthokeratology, which helps to improve the curvature of the eye while you sleep. This means you may not have to wear corrective lenses throughout the day.

Your lens prescription

Astigmatism and myopia are recorded separately on your prescription. If you see a minus sign under the 'Sphere' column, this means you have a degree of myopia. The number after the minus sign can range from 0.25 to 6.00. The higher the number, the stronger your prescription is.

The 'Cylinder' column indicates astigmatism. If there is nothing here, your eyes are perfectly round. A higher number, such as 3.00, means your eyes are quite oval. The 'Axis' section of your prescription will help the lab to position your lenses correctly, according to the direction of astigmatism, which is measured in degrees.

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