Astigmatism – Back to Basics

Astigmatism

We have been talking about refractive errors this week. Having discussed myopia and hyperopia, we move on to another type of refractive error: Astigmatism. Astigmatism is a term that a lot of people are familiar with, yet are uncertain as to what it actually means.

What is Astigmatism and how is it caused?

Astigmatism differs from Myopia and Hyperopia as it does not occur as a result of the length of the eye. Rather it is due to an imperfection in the curvature of the cornea, or lens of the eye. the degree of astigmatism does not refer to the length of the eye, rather it refers to the curvature of the cornea or the shape of the lens inside the eye. In a normal eye both the cornea and the lens are smooth and curved equally in all directions, like that of a geometric sphere.

Astigmatism can be further categorised depending on where the irregularity is found: If the cornea has an irregular shape, it is called corneal astigmatism. When the shape of the lens is irregular or distorted, it is called lenticular astigmatism. Lenticular astigmatism is less common than corneal astigmatism. Regardless of the type of astigmatism you have, vision for both near and far objects appears blurry or distorted because the images focus both in front and beyond the retina. See below:

Astigmatism can also be caused as part of an eye condition, such as Keratoconus.  It can also occur due to an injury to the eye or following surgery to the eye.

What are the symptoms of Astigmatism?

Symptoms of refractive error have a common theme, those suffering from uncorrected Astigmatism may experience:

• blurry vision
• areas of distorted vision
• headaches
• eyestrain
• squinting of eyes in an effort to clear vision

*It is important to note that if you are experiencing any of these symptoms, you may not necessarily have astigmatism. Any of the above symptoms would indicate the need for a comprehensive eye examination with your ophthalmologist.

Astigmatism is either predominantly vertical or horizontal in nature, depending on the axis of the cornea that is irregular; be it steeper or flatter than normal.

Astigmatism in children

Because astigmatism can be present from birth, it is important to have your child’s eyes checked by an ophthalmologist to ensure there are no concerns about visual development.

How is Astigmatism diagnosed?

In addition to a standard vision test, the process for diagnosing astigmatism is much the same as for detecting other types of refractive errors. Your ophthalmologist will sometimes take measurements of your corneal curvature using different pieces of equipment, all of which are non invasive and painless. The results of these tests in addition to a refraction, will allow your ophthalmologist to determine the power of glasses or contact lenses required to provide clear vision. He or she will then discuss the best treatment options for you.

How is Astigmatism treated?

Mild to moderate astigmatism can usually be corrected with glasses or contact lenses. Years ago, contact lens options to treat astigmatism was limited to hard or rigid contact lenses. Now, soft contact lenses called Toric contact lenses can correct astigmatism. If you require a high degree of astigmatism correction, glasses or rigid contact lenses may be more suitable. This is something your ophthalmologist will discuss with you. As with all types of refractive errors, some people with astigmatism may be suitable for refractive surgery.

Glasses use curved lenses to refocus light rays onto the cornea

Contact Lenses correct vision in the same way as glasses, only they are placed directly onto the eye.

Refractive Surgery changes the shape of the cornea, by ‘ablating’ or removing corneal tissue to correct astigmatism. There are different types of surgery but the most common are LASIK and PRK.

 

References:

https://www.aao.org, https://nei.nih.gov, https://www.healthdirect.gov.au/astigmatism