Astigmatism is a common vision problem caused by an error in the shape of the cornea. Symptoms can differ from person to person but may include blurry vision and difficulty seeing at night.

What is Astigmatism?

Astigmatism is a common type of refractive error that happens when the eye is slightly monstrous. Hypermetropia( diplopia) and vision( presbyopia) are the other two refractive crimes.  The clear subcaste in front of your pupil is called the cornea. A normal cornea is unevenly rounded like a clunk pong ball, but an presbyopic cornea resembles the top of an egg — still rounded, but a little pointed. This causes blurred vision at both near and far distances. This condition is nearly noway a cause for concern but is simply a treatable vexation.

What are the symptoms of astigmatism?

The most common symptoms of astigmatism are:

1. Blurry vision
2. Needing to squint to see clearly
3. Headaches
4. Eye strain
5. Trouble seeing at night

If you have mild astigmatism, you might not notice any symptoms. That’s why it’s important to get regular eye exams — your eye doctor can help you make sure you’re seeing as clearly as possible. This is especially true for children, who may be less likely to realize that their vision isn’t normal.

What are the Causes of astigmatism?

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

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

In a perfectly shaped eye, each of these elements has a round curvature, like the surface of a smooth ball. A cornea or lens with such curvature bends (refracts) all incoming light equally to make a sharply focused image directly on the retina at the back of the eye.

A refractive error

If either the cornea or the lens is egg-shaped with two mismatched curves, light rays aren't bent the same, which means that two different images form. These two images overlap or combine and result in blurred vision. Astigmatism is a type of refractive error.

Astigmatism occurs when the cornea or lens is curved more steeply in one direction than in another. You have corneal astigmatism if your cornea has mismatched curves. You have lenticular astigmatism if your lens has mismatched curves.

Either type of astigmatism can cause blurred vision. Blurred vision may occur more in one direction: horizontally, vertically or diagonally.

Astigmatism may be present from birth, or it may develop after an eye injury, disease or surgery. Astigmatism isn't caused or made worse by reading in poor light, sitting too close to the television or squinting.

Other refractive errors

Astigmatism may occur in combination with other refractive errors, which include:

Nearsightedness (myopia). This occurs when the cornea is curved too much or the eye is longer than usual. Instead of being focused precisely on the retina, light is focused in front of the retina, making distant objects seem blurry.

Farsightedness (hyperopia). This occurs when the cornea is curved too little or the eye is shorter than usual. The effect is the opposite of nearsightedness. When the eye is in a relaxed state, light never comes to a focus at the back of the eye, making nearby objects seem blurry.

How is astigmatism diagnosed?

An eye care specialist will diagnose astigmatism with an eye exam. They’ll look at your eyes (including inside them).

Your eye care specialist might use a few tests to diagnose astigmatism, including:

• Visual acuity test: A visual acuity test is a test that checks your vision. You’ve had a visual acuity test if you’ve ever looked at a wall chart of letters or symbols during an eye exam.
• Refraction test: Your eye care specialist will measure how much light focuses and is bent as it enters your eye.
• Keratometry: Keratometry measures your cornea’s curve.
• Slit lamp exam: A slit lamp is a special microscope with a bright light that your eye care specialist shines into your eye.

They’ll adjust the brightness and thickness of the light’s beam to see the different layers and parts of your eye.

What are astigmatism prescription measurements?

Astigmatism is measured in diopters, which is the optical power of a lens. If your eye doesn’t have astigmatism, you have a diopter of 0. If you have one, though, you’ll likely have a diopter greater than 0.5. Treatment isn’t usually necessary for a slight astigmatism, but you might need contacts or glasses for a diopter measurement of 1.5 or higher.

The only part of an optical prescription associated with astigmatism are the cylinder and axis. The cylinder part of the prescription measures the degree or extent of the irregularity. Doctors use the axis measurements to determine the location of an eye astigmatism on the cornea.