Astigmatism

Most eyes are round like a ball.

Some eyes are shaped more like an egg. This can happen when you are born. It can also happen as you grow up.

An egg shape makes vision look blurry. It can make your eyes feel tired. You might even get a headache.

It can also make it hard to drive at night.

Doctors can test your eyes to see the shape. You can wear glasses to help you see. Contact lenses can work too. Some people even have a small surgery. This helps change the shape of the eye.

These tools help make things look clear again.

Most eyes are shaped like a round ball. This shape helps light focus clearly. But some eyes have a different shape. This is called astigmatism. In these eyes, the cornea or the lens is shaped like an egg.

Because the eye is not round, light does not focus in one spot. This can make vision look blurry or even double. It might cause eye strain or headaches. Some people find it hard to drive at night. Many people are born with this. It can also happen later in life. It might start after an eye injury or surgery.

Doctors use special tests to study the eye. They can measure how curved the eye is. There are three ways to fix it. The simplest way is to wear glasses. You can also wear contact lenses. These lenses can give you a wide view. Another way is refractive surgery. This is a way to change the eye shape forever. In Europe and Asia, many adults have this. It affects between 30% and 60% of them.

Astigmatism is a common way that eyes focus light. In most eyes, the cornea and the lens are nearly spherical. This means they are shaped like a round ball. When light enters a round eye, it focuses clearly on the retina.

However, an eye with astigmatism is not perfectly round. Instead, the cornea or the lens might be shaped more like an egg. This shape is called rotational asymmetry. Because the curves are uneven, light does not land on a single point. This can make vision look blurry or even double at any distance.

This condition works by changing how light rays travel through the eye. In a round eye, light bends evenly from all sides. In an astigmatic eye, there are different curves called principal meridians. One meridian might be very steep, while another is much flatter. We call the steepest part the steepest axis. If the vertical curve is steeper, it is called with-the-rule astigmatism. If the horizontal curve is steeper, it is called against-the-rule.

These different curves cause light to focus at different spots. Some light might focus in front of the retina, while other light focuses behind it. This mismatch is what causes the blurred vision.

People have been studying this eye shape for a long time. Thomas Young first reported on astigmatism in 1801. Since then, scientists have tried to find out why it happens. They believe it might be linked to genetics. Researchers use large studies called genome-wide association studies to look for clues. In 2011, a study on Asian populations found a link to the PDGFRA gene. Later, in 2018, a study by Shah and colleagues found more genes. They identified three new candidate genes called CLDN7, ACP2, and TNFAIP8L3.

There are many important facts about how many people have this. In Europe and Asia, between 30% and 60% of adults have astigmatism. It can be present at birth, or it can happen later. For example, a person might get it after a corneal injury. It can also happen after cataract surgery. Some people have a condition called keratoconus, where the cornea gets thinner and steeper. Doctors use an eye exam called autorefractor keratometry to see the eye's shape. They can also use a tool called a keratometer to measure the curves.

Luckily, there are three main ways to help people see better. The simplest way is to wear glasses. These glasses use special lenses to fix the light. Another option is to wear contact lenses. Some contact lenses, called toric lenses, are made specifically for this. Contact lenses can give a person a wider field of vision. The third option is refractive surgery. This surgery aims to change the shape of the eye permanently. This can help cure the astigmatism so the person does not need lenses.

Astigmatism is a type of refractive error caused by rotational asymmetry. This means the eye does not have a uniform shape. In a standard eye, the cornea and the lens are nearly spherical. They have a single radius of curvature, much like a round ball. This shape allows light to focus clearly on the retina. However, in an eye with astigmatism, these parts are slightly egg-shaped. One direction has a higher curvature than the other. This uneven shape results in distorted or blurred vision at all distances.

To understand the mechanism, we must look at the principal meridians. These are the steepest and flattest axes of the eye. In an astigmatic eye, light does not converge at a single point. Instead, it creates different focal lines. There are several ways this can be classified based on orientation. In regular astigmatism, the principal meridians are perpendicular to one another. This includes with-the-rule astigmatism, where the vertical meridian is steepest. It also includes against-the-rule astigmatism, where the horizontal meridian is steepest. There is also oblique astigmatism, where the steepest curve lies at specific angles.

Astigmatism can also be categorized by where the light focuses. This is known as the focal line position. Simple hyperopic astigmatism occurs when one focal line is on the retina and the second is behind it. Simple myopic astigmatism happens when the first line is in front of the retina and the second is on the retina. Compound astigmatism occurs when both focal lines are on the same side of the retina. This can be compound hyperopic or compound myopic. Finally, mixed astigmatism occurs when the focal lines straddle the retina, with one in front and one behind.

Researchers have studied the origins of this condition for centuries. Thomas Young first reported on astigmatism in 1801. While the exact cause remains unclear, scientists believe genetics play a role. Genome-wide association studies (GWAS) have helped identify potential genetic links. In 2011, researchers found a link to the PDGFRA gene in Asian populations. A 2018 study by Shah and colleagues replicated this finding. They also identified three new candidate genes: CLDN7, ACP2, and TNFAIP8L3. Other studies have looked at genes like VAX2, which helps develop the eye's axis.

Astigmatism is a very common condition across the globe. In Europe and Asia, it affects between 30% and 60% of adults. It can be present at birth, which is called congenital astigmatism. However, it can also be acquired later in life. An injury to the cornea can cause it. Surgery, such as cataract extraction, can also lead to it. In some cases, the scar from a wound causes the cornea to flatten in one direction. Another condition, keratoconus, causes the cornea to thin and steepen progressively.

Doctors use several specific tools to diagnose the condition. An eye examination might start with a Snellen chart to check visual acuity. An autorefractor or retinoscopy provides an objective estimate of the error. To measure the specific curvature of the cornea, doctors use a keratometer. They may also use corneal topography for a more detailed map of the eye's shape. To refine measurements, they might use Jackson cross cylinders in a phoropter. Some specialists even use a stenopaeic slit to check specific meridians in patients with high astigmatism.

There are three primary treatment options available today. The simplest and safest method is wearing eyeglasses. These lenses use a "cylinder" to compensate for the uneven light bending. Another option is wearing contact lenses. Some patients use toric lenses, which are designed for astigmatism. Contact lenses can provide a wider field of vision than glasses. The third option is refractive surgery. This aims to permanently change the eye's shape to cure the error. While surgery can eliminate the need for lenses, it carries more risk and expense than non-invasive options.