Astigmatism Tests

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What is Astigmatism?

If you have astigmatism, you suffer from a type of refractive error. A refractive error refers to when your eye is unable to refract (or bend) light properly onto the retina. 

diagram showing eye with normal vision vs astigmatism

In this case, astigmatism occurs when the curvature of the cornea or lens is not regular. The curvature may appear in the shape of a football or egg. Because of this incorrect formation of the eye, you can find viewing objects difficult. 

In general, astigmatism is present at birth or can develop after an eye injury, surgery, or disease. If you have astigmatism, you may also have myopia (nearsightedness) or hyperopia (farsightedness). These conditions tend to co-exist. 

Fortunately, treatment options, including refractive surgery, are available for astigmatism.  

Symptoms of Astigmatism

In more severe cases of astigmatism, you may have symptoms that include:

  • Blurry vision 
  • Eyestrain (tiredness in the eyes)
  • Headaches
  • Dry eyes
  • Squinting
  • Eye discomfort
  • Glare
  • Light sensitivity

Some people can confuse astigmatism with amblyopia (often referred to as a “lazy eye”). These eye conditions are not the same. However, severe astigmatism can contribute to amblyopia. 

Causes of Astigmatism

Astigmatisms happen when your cornea or lens has a steeper curvature in one direction or the other. There are two different types of astigmatism:

  • Corneal astigmatism. There are mismatched curves in the cornea. 
  • Lenticular astigmatism.  There are mismatched curves in the lens. 

Eye doctors do not know why the curvature of the eye varies from one person to the next. However, the likelihood of astigmatism is higher in people with a family history of the condition. 

It is important to remember that astigmatism does not occur because of:

  • Reading in poor light
  • Watching TV up close
  • Squinting

Again, astigmatism is often present at birth. It can also develop after you have an eye injury, surgery, or disease.

This particular refractive error happens in approximately 1 in 3 people in the United States. 

Different Levels of Astigmatism

You may find that ophthalmologists and optometrists use various measurement approaches for astigmatism. Although the prescriptions may seem different, your optical shop should have no problem understanding what your eye specialist prescribed. 

In general, though, your ophthalmologist or optometrist will measure astigmatisms in diopters. A perfect eye with no astigmatism will have 0 diopters. However, many people will have between 0.5 to 0.75 diopters of astigmatism. 

When you have a measurement of 1.5 or more diopters, you most likely will need contacts, eyeglasses, or even corrective surgery to enjoy improved vision. 

With eye prescriptions, there are two areas or numbers that refer to astigmatism:

  • Cylinder. The number here reflects how steep or irregular the curvature of your cornea is. 
  • Axis. In degrees, this value shows where the astigmatism is on the cornea. Axis numbers will range from 0 to 180. 

People who are 60 years old and up have a higher chance of hyperopia (farsightedness) and/or astigmatism than younger people. 

How to Test for Astigmatism

Professional Eye Exams

To test for astigmatism, you will undergo a comprehensive eye exam. In this check-up, your eye doctor will examine your visual acuity (your ability to discern the shapes and details of objects you see). You may be asked to read letters on an eye chart. 

You may also undergo other exams with several different devices. 

How They Work

Your eye doctor may use the following tools during your eye exam:

  • A phoropter. This device helps the eye doctor to determine the correction needed to improve your vision. You will look through different lenses, so your eye doctor can see which one is the most suitable for your vision.
  • An autorefractor. This device gives the eye doctor a starting point from which to refine your prescription. It shines light into the eye and measures how it changes when it returns from the back of the eye.
  • A keratometer. This device helps measure the curve of your cornea. Your eye doctor may also include a corneal topography to learn more about the corneal surface and its shape. 

Online Astigmatism Tests

Another option to help determine if you have astigmatism is online testing. Multiple online tests are available and can serve as an initial means to identifying a vision problem. 

How They Work

The tests are simple. You will look at a display of shapes and lines while standing a certain distance away from the monitor. You will have to cover your left and right eyes, alternating between both during this test. 

Are Online Astigmatism Tests Reliable?

While online tests are helpful, they are not conclusive. These tests rely on your judgement, and accuracy is not precise.

In other words, to have a confirmed diagnosis of astigmatism, you should follow up with an eye care professional. You will be able to undergo all the relevant tests and have results that shed light on your eye health. 

Treatment Options for Astigmatism

Treatment for astigmatism may include:

Astigmatism Glasses

Eyeglasses for people with astigmatism have a special cylindrical lens prescription. This means that specific parts of the lens boast additional power. In many cases, a single-vision lens may work to provide clear vision at any distance. Although, if you’re over the age of 40 and have presbyopia (poorer near vision due to aging), you may need a bifocal or progressive addition lens. 

Contact Lenses

People with severe astigmatism may need to use rigid gas permeable lenses.

However, if you do not have severe astigmatism, you may be eligible for soft lenses called toric contact lenses. 

It is essential to visit your optometry clinic and speak with a specialist to determine which eyewear option suits your needs. 

LASIK Eye Surgery

An eye doctor may recommend this type of laser surgery to treat astigmatism. LASIK stands for laser in situ keratomileusis.

The LASIK procedure is a basic procedure that consists of the following steps:

  1. A topical (eye drop) anesthetic is squeezed into the eye before surgery 
  2. Using a femtosecond laser to form a small flap in the cornea’s epithelium (the outer protective barrier), a LASIK surgeon then loosens the tissue and folds back the thin flap to one side
  3. The surgeon then directs laser energy to the area for a few seconds to a minute to change the shape of the corneal tissue underneath the flap
  4. Once done, the flap is put back into its original place for natural healing

If you have astigmatism and decide to undergo LASIK surgery, you can enjoy many of the advantages, including:

  • Speed and safety. LASIK surgery is done on an outpatient basis. This means that you do not need to stay overnight, and surgery could last approximately 20 minutes. Although the time may be short, the laser is safe. There is an automatic shut-down function that works when your eye makes any sudden movement. 
  • Earlier results. You can have clear vision soon after LASIK eye surgery. Within a few hours after surgery, many people who undergo the laser procedure may notice a positive difference in visual acuity. 

Improved vision for more extended periods. A primary concern about corrective eye surgery is duration. However, with LASIK surgery, you may be able to make the most of the stronger vision for long, if not permanent, periods. This means that you may be able to hold off on wearing eyeglasses or contacts to participate in regular activities. 

Resources
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Astigmatism. (2019, September 04). Retrieved March 30, 2021, from https://www.mayoclinic.org/diseases-conditions/astigmatism/symptoms-causes/syc-20353835

Astigmatism. (n.d.). Retrieved March 30, 2021, from https://www.aoa.org/healthy-eyes/eye-and-vision-conditions/astigmatism?sso=y

Astigmatism. (n.d.). Retrieved March 30, 2021, from https://www.health.harvard.edu/a_to_z/astigmatism-a-to-z

Boyd, K. (2021, February 23). What is astigmatism? Retrieved March 30, 2021, from https://www.aao.org/eye-health/diseases/what-is-astigmatism

Vimont, C. (2021, February 22). What do astigmatism measurements mean? Retrieved March 30, 2021, from https://www.aao.org/eye-health/diseases/what-do-astigmatism-measurements-mean

Vitale, Susan et al. “Prevalence of refractive error in the United States, 1999-2004.” Archives of ophthalmology (Chicago, Ill. : 1960) vol. 126,8 (2008): 1111-9. doi:10.1001/archopht.126.8.1111. https://jamanetwork.com/journals/jamaophthalmology/fullarticle/420707#:~:text=We%20found%20that%20refractive%20error,and%20of%20astigmatism%2C%2036%25.

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