An Introduction to Astigmatism


Story at-a-glance

  • If you have a refractive error, it means that your eyes are not able to properly focus light on the retina. This may occur because of two reasons: Either there are abnormalities in the shape of the eyeball or aging has affected the focusing mechanisms of the eye
  • Astigmatism is one of these refractive errors, along with hypermetropia, myopia and presbyopia. It happens when the cornea found at the front of the eye is curved instead of being perfectly rounded

Do you experience symptoms such as blurry or fluctuating vision, headaches and eye strain, which usually manifest after reading a book, staring at a computer screen or looking at far-off distances?1,2 It’s possible that you have astigmatism, a type of refractive error.

Don’t be frightened, however; astigmatism is fairly common and is not a dangerous disorder. But to truly understand why astigmatism occurs, you must first learn how the human eye works.

Here’s How Your Vision Works

When you look at a particular object, light rays from the object need to pass through the eyes so that it can reach the retina. This then triggers nerve messages to be sent from the retina cells down to the optic nerve and then to the brain’s vision centers. The information received is then processed by the brain, which then allows us to see.

Light rays can come off from an object in all directions. This is because they come from many light sources around us, such as sunlight, moonlight and artificial light (from light bulbs and lamps), which then bounce back from that specific object. However, the part of this bounced light that enters the eye from an object must be focused on a small part of the retina. If this fails to happen, then the object you’re staring at will be blurred.

The task of focusing light falls on your cornea and lens. The cornea is mainly responsible for this, as it refracts or bends the rays of light, which then pass through the lens. The lens then finely adjusts the focusing, by changing its thickness. This is known as “accommodation,” as the lens is actually elastic, and can shift from being rounded or flatter. If the lens is more rounded, the light rays can be better bent inwards.

The lens’ shape varies depending on the small muscles in the ciliary body. Suspensory ligaments, which are small string-like structures, are attached at one end to the lens, connecting it to the ciliary body. Think of its structure as a trampoline: The lens acts as the bouncy center, the suspensory ligaments are the springs and the ciliary muscles act as the rim around the edge of the bouncy center.

When the muscles in the ciliary body tighten, it causes the ligaments to slacken, making the lens fatter. This is what happens when you’re looking at objects that are near. For objects that are far away, the ciliary muscle becomes relaxed, causing the ligaments to tighten. The lens then thins out. For nearby objects, more refraction of the light rays is necessary to allow better focus. However, less bending is needed if the object is far away.3

So How Does Astigmatism Occur?

Again, refraction is the method by which the eye – specifically the cornea – bends light. If you have a refractive error, it means that your eyes are not able to properly focus light on the retina. This may occur because of two reasons: Either there are abnormalities in the shape of the eyeball or aging has affected the focusing mechanisms of the eye.

Astigmatism is one of these refractive errors, along with hypermetropia, myopia and presbyopia. It happens when the cornea found at the front of the eye is curved instead of being perfectly rounded. Think of it as a mini rugby ball. If curved in the wrong direction or if the curve is too great, that’s when astigmatism happens.

This is because the light rays that enter the cornea and lens are not focused on a particular spot on the retina, and instead is spread. Because there’s a lack of point focus, the images transmitted to the brain are blurred.4

Discover More About Astigmatism by Reading These Pages

Astigmatism is fairly common, but don’t fret: It’s not an eye disease, and it can be easily addressed. Read these pages to learn everything you need to know about astigmatism and how you can prevent it from interfering with your daily activities.

MORE ABOUT ASTIGMATISM

Astigmatism: Introduction

What Is Astigmatism?

Astigmatism Symptoms

Astigmatism Causes

Astigmatism Test

Types of Astigmatism

Astigmatism Treatment

Contact Lenses For Astigmatism

Astigmatism Prevention

Astigmatism FAQ



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What Is Astigmatism?

[+]Sources and References [-]Sources and References

  • 1 EMedicineHealth, Astigmatism Symptoms, July 5, 2016
  • 2 EyeHealthWeb, Astigmatism — Symptoms, Causes, and Treatment, October 2015
  • 3, 4 Patient, Astigmatism, November 2, 2016