Astigmatism: Simplified Anatomy of Eye, Causes of Astigmatism (For CBSE, ICSE, IAS, NET, NRA 2022)

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  • Astigmatism is an optical defect which blurs the vision. Before learning what causes this defect, let us understand how the eye perceives light.
  • Normally, the cornea and lens are smooth and curved equally in all directions.
  • When light enters a perfectly spherical lens (spherical like a basketball) , it refracts or bends, evenly.
  • If the lens is not properly spherical, the light that enters the lens is refracted more in one direction than another.
  • Astigmatism is an imperfection in the curvature of your eye՚s cornea or lens.

Simplified Anatomy of Eye

Simplified Anatomy of Eye

Causes of Astigmatism

Our eye has two structures with curved surfaces that bend (refract) light onto the retina, which makes the images:

  • Cornea, the clear front surface of your eye along with the tear film
  • Lens, a clear structure inside your eye that changes shape to help focus on near objects

Astigmatism in Eyes

Astigmatism in Eyes
  • In a perfectly shaped eye, each of these elements has a perfectly round curvature, like the surface of a round ball.
  • A cornea and lens with such curvature bend or refract all incoming light equally to make a sharply focused image directly on the retina, at the back of your eye.
  • So, when light enters a person՚s eye which is naturally shaped like a sphere it creates a clear view of the object as the light is refracted evenly.
  • But in any case the eye of a person is curved but not completely spherical, like the back of a spoon
  • For this person, when light enters the eye it is refracted more in one direction than the other, allowing only part of the object to be in focus at one time, Which is called a refractive error Objects at any distance can appear blurry and wavy.
  • This defect in the eye or in a lens caused by a deviation from spherical curvature, which results in distorted images, as light rays are prevented from meeting at a common focus, is called Astigmatism.

Other Refractions

  • Nearsightedness (myopia) . It occurs when our cornea is curved too much or our eye is longer than normal. Instead of being focused precisely on our retina, light is focused in front of our retina, making distant objects seem blurry.
  • Farsightedness (hyperopia) . This occurs when our cornea is curved too little or our eye is shorter than normal. The effect is the opposite of nearsightedness. When our eye is in a relaxed state, light never comes to a focus on the back of our eye, making nearby objects seem blurry.

Types of Astigmatism

Corneal Astigmatism: The Eye Defect is Usually Caused by an Irregularly Shaped Cornea or Distorted Lens. When the Cornea Has an Irregular Shape, It is Called Corneal Astigmatism

Lenticular Astigmatism: When the Shape of the Lens is Distorted, You Have Lenticular Astigmatism

  • As a result of both type, your vision for both near and far objects appears blurry or distorted.

Regular Astigmatism: Principal Meridians Are Perpendicular to Each Other (90-Degree Separation)

  • Most astigmatism is regular corneal, which gives the front surface of the eye an irregularly curvy shape, like that of a spoon.

Irregular Astigmatism: In Irregular, the Principal Meridians Are Not Perpendicular to Each Other

  • Eye injuries that result in scars on the cornea can cause an irregular defect. Certain types of eye surgeries or a disease called keratoconus (gradual thinning of the cornea) can also cause an irregular defect
  • It՚s almost like looking into a funhouse mirror in which you appear too tall, too wide or too thin.
  • The steepest and flattest meridians of an eye with astigmatism are called the principal meridians.

Astigmatism Symptoms

  • Try to see clearly, or
  • Eye discomfort
  • Blurry vision or areas of distorted vision
  • Eyestrain
  • Headaches


  • Astigmatism is diagnosed by giving an eye exam to a doctor.
  • A complete eye exam involves a series of tests to check your eye health and a refraction, which determines how your eyes bend light.
  • The doctor uses these tests to examine different aspects of your eyes and vision and to determine the prescription needed to provide clear vision with eyeglasses or contact lenses.

Astigmatism Correction Options

Astigmatism can usually be corrected with

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