What Is Astigmatism?

  • 1st Revision: Lidia Manconi

Overview

Have you ever heard of the term 'astigmatism'? It is a name for a frequent eye condition that alters how people perceive the outside surroundings.1 This can cause vision to become blurred at any distance, whether it is close or far. Continue reading this article to find out more about astigmatism, how it is treated, and how it is identified.

Astigmatism is, by definition, a condition where there are parallel rays of light passing from the cornea do not converge to a point of focus on the retina. While the cornea is the clear front covering the iris and pupil, the retina is the light-sensitive surface in the back of the eye receiving all the images and sending them as electric signals through the brain. As a result, just a portion of the object you are looking at is correctly focused by the light on the retina. This causes all objects, regardless of distance, to have a blurred definition.1,2,3

According to the World Health Organization (WHO), in the last report in 2019 on vision, uncorrected refractive errors, such as astigmatism were responsible for vision impairment or blindness in 123,7 million people worldwide.4,5 The prevalence of this condition is also related to factors like age, ethnicity, or gender, being more frequent in Caucasian and Asian populations.6

Types of astigmatism

Although these types of astigmatism are not mutually exclusive, it is nevertheless vital to define them in order to provide better care and a better tool for managing the symptoms. There are a number of things to take into account in order to comprehend this situation, such as:

  • The aetiology, or the origin of the astigmatism:
    • Corneal astigmatism is the most frequent type of astigmatism and is caused by an irregular corneal curve
    • Lenticular, also known as lenticonus, is the name for an abnormal corneal curvature where the eye's lens has a conical surface. It may occur as a result of the lens tilting or displacement due to a subluxation causing positional astigmatism or being referred as index astigmatism when it causes the various meridians' refractive indices to vary
    • Retinal is a condition in which the macula, the rounded centre of the retina, is positioned obliquely
  • The symmetry of the corneal or lens curvature, known as the regularity:
    • With the rule, anytime the two main meridians are at a right angle to one another, yet the vertical meridian is steeper than the horizontal. Due to the pressure of the eyelids, there is about 0.25 D more in the vertical meridian than the horizontal
    • Against the rule, despite being at a right angle to one another, in this instance the horizontal meridian has a more significant curvature than the vertical meridian
    • Oblique, when neither the vertical nor the horizontal of the two main meridians are angled to one another
    • Bioblique, in this situation the two principal meridians are not right-angled to each other2,5,7

The astigmatism can also be defined according to the relative position of the principal meridians, being myopic whenever the focus of the light rays is on the front of the retina or hypermetropic when the focus is behind the retina. If this focus is in one meridian, the astigmatism is designated as simple and complex or compound when the focus is in more than one meridian. There is also a mixed astigmatism when there is a combination of a myopic meridian with a  hypermetropic meridian.2,5

Causes of astigmatism

As mentioned above, astigmatism is caused when one of the cornea's and the retina's curves are different from the other's; rather than both being round, one of them has a distinct form that is more identical to an egg. People can born with it or acquire it during life, but whenever this occurs, it results in a particular sort of refractive error where light is not focused evenly on the retina by the eye due to a difference in the eye's optical strength for light coming from opposite directions.1,2,7,8

However, what causes this different curvature that characterise astigmatism? Usually, the reason behind astigmatism is genetic factors even though some other situations like keratoconus, eye injuries, complications after surgery or ocular diseases like pterygium or pinguecula can also cause it.1,3

Signs and symptoms of astigmatism

As was previously said, the primary symptom of astigmatism is blurred vision, regardless of the distance at which the affected person is gazing at an item.  But there are other symptoms that should also be taken into consideration like:

  • Headaches
  • Pain or heaviness in the eyes
  • Difficulty focusing
  • Transient blurring
  • Drowsiness.1,2

Astigmatism is a condition that can be managed, however when it is left uncorrected it can lead to an increased risk of falls, night-time driving difficulties,puttinged to do things like elongation of objects or put objects close to the eyes while reading. In most severe situations, astigmatism can lead to nausea.1,2

Management and treatment for astigmatism

When considering several treatment options for astigmatism, you should speak with their ophthalmologist. There are a number of ways to treat astigmatism symptoms, with the most popular being the use of corrective lenses or spectacles to improve vision and lessen other symptoms. While the lenses will improve vision at all distances, there are additional treatment alternatives available, such as orthokeratology, which reshapes the cornea using stiff lenses for brief periods of time each day.1,2,7

People with moderate astigmatism may occasionally be able to achieve clear vision, but not always and not without the hard lenses, as the astigmatism may revert to its initial state. Additionally, surgery to reshape the cornea is an option. The two most popular surgical techniques are laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK).2,4,7

Diagnosis of astigmatism

An eye exam conducted by either an optometrist or an ophthalmologist is required to identify astigmatism. The doctor will need to perform the following tests in addition to being able to focus light:

  • Visual Acuity test  by reading letters from a set distance, visual equity is assessed. The answer is typically expressed as a fraction, with the first number representing the reader's proximity to the letters and the second number representing the size of the letters.
  • Corneal topography or keratometry test – uses a device to evaluate the cornea's curvature, which is also crucial for the usage of contact lenses.
  • Refraction tests –  with the use of this test, doctors can examine how well their eyes can concentrate light, and by answering questions about their vision, it is possible to decide which lenses, if any, will help them see better in the future.2,9

FAQs

How can I prevent astigmatism

Unfortunately, astigmatism cannot be avoided. The exact cause of this refractive error of the eye problem is unknown to medical professionals. But there are other potential reasons, such as keratoconus, ocular traumas, or difficulties following surgery, in addition to genetic factors.

How common is astigmatism

According to the research the prevalence of astigmatism is estimated to be 40%, making it a fairly common refractive mistake that can affect anyone. Age, race, and gender are all associated with this condition's prevalence.6,7

Who are at risks of astigmatism

The people who are most at risk of developing astigmatism are those who have close relatives with this problem, who had eye traumas, or who have undergone eye surgery that has affected the cornea or lens.

When should I see a doctor

Whenever you experience vision problems, visit an optometrist or ophthalmologist. regularlyto have your eyesight examined on a regular basis, especially if you wear glasses or contact lenses.

Summary

Astigmatism is a refractive error that affects the way images are formed. It occurs when either the cornea or the lens has an irregular curvature, causing light rays to be refracted differently and hit the retina at different points. This results in blurred or distorted vision of both near and distant objects. Astigmatism can be congenital or acquired and can be related to genetic, traumatic, surgical, or ocular diseases. The most common treatment consists of wearing glasses or contact lenses that correct the refractive defect, but in some cases, laser eye surgery can be used to reshape the cornea. Astigmatism cannot be prevented but can be diagnosed with a full eye examination.

References

  1. Astigmatism [Internet]. [cited 2023 May 23]. Available from: https://www.aoa.org/healthy-eyes/eye-and-vision-conditions/astigmatism?sso=y
  2. Gurnani B, Kaur K. Astigmatism. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2023 May 23]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK582142/
  3. Astigmatism: Symptoms, Tests & Treatment [Internet]. Cleveland Clinic. [cited 2023 May 24]. Available from: https://my.clevelandclinic.org/health/diseases/8576-astigmatism
  4. World report on vision [Internet]. [cited 2023 May 24]. Available from: https://www.who.int/publications-detail-redirect/9789241516570
  5. Zhang J, Wu Y, Sharma B, Gupta R, Jawla S, Bullimore MA. Epidemiology and Burden of Astigmatism: A Systematic Literature Review. Optometry and Vision Science. 2023 Mar;100(3):218. Available from: https://journals.lww.com/optvissci/Fulltext/2023/03000/Epidemiology_and_Burden_of_Astigmatism__A.7.aspx
  6. Wajuihian SO. Characteristics of astigmatism in Black South African high school children. Afr Health Sci. 2017 Dec;17(4):1160–71. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5870290/
  7. Yang S, Jiang Y, Cui G, Li Y. Age- and gender-related characteristics of astigmatism in a myopic population. Frontiers in Medicine [Internet]. 2022 [cited 2023 May 23];9. Available from: https://www.frontiersin.org/articles/10.3389/fmed.2022.1011743
  8. Astigmatism - Symptoms and causes [Internet]. Mayo Clinic. [cited 2023 May 23]. Available from: https://www.mayoclinic.org/diseases-conditions/astigmatism/symptoms-causes/syc-20353835
  9. Astigmatism | National Eye Institute [Internet]. [cited 2023 May 23]. Available from: https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/astigmatism
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Inês Dias

Mestrado, Biologia Molecular e Genética, Faculdade de Ciências da Universidade de Lisboa

Inês is a scientist in the field of Biomedical Sciences, with a wealth of experience in various laboratory procedures. Her expertise is evident in her work as clinical analysis technician, performing puncture procedures for the collection of biological samples. She has also played a key role in COVID-19 sample processing in a laboratory setting. Recently obtained her master’s in Molecular Biology and Genetics from the Faculty of Sciences at the University of Lisbon.

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