Astigmatism – Understanding the Basics of a Common Eye Condition

Astigmatism refers to a common eye condition leading to blurriness in your vision due to irregular shape of the cornea (the clear covering at the front of the eye), or because of the curvature of the lens within the eye.

Light cannot focus appropriately on the retina (the lining at the back of the eye, comprising of light sensitive tissues) when you have an irregularly shaped cornea or lens. This causes blurriness in your vision, which can lead to eye discomfort and headaches.

Astigmatism exists in many people to some degree, but usually no treatment is required for that, because it doesn’t affect vision.

Eye conditions like myopia (nearsightedness) and hyperopia (farsightedness) are also a frequent cause of astigmatism, referred collectively as ‘refractive errors’, as they affect the way light is refracted or bent by the eyes.

Are There Different Types of Astigmatism?

Yes, there are different types of astigmatism, classified into three major categories:

Myopic Astigmatism:

A scenario where there is nearsightedness in one or both principal meridians of the eye. (Nearsightedness in both meridians means they are myopic in differing degree.)

Hyperopic Astigmatism:

A scenario where there is farsightedness in one or both principal meridians of the eye. (Farsightedness in both meridians means they are hyperopic in differing degree.)

Mixed Astigmatism:

A scenario where there is nearsightedness in one principal meridian and farsightedness in the other one.

There is another way of astigmatism classification, i.e. ‘Regular Astigmatism’ and ‘Irregular Astigmatism’. Let’s have a look at them as well:

Regular Astigmatism

The type of astigmatism where the principal meridians are at angle of 90 degrees with each other (perpendicular to each other).

Irregular Astigmatism

As you may have concluded, a scenario where the principal meridians are not perpendicular to each other.

Most cases of astigmatism are considered to be ‘Regular Corneal Astigmatism’, a condition due to which the front surface of the eye gets an oval shape.

What Causes Astigmatism?

For your vision to work correctly, the curvature of the cornea and the lens need to bend the light entering in the eye in a specific manner, so that it can focus precisely on the retina. In case of astigmatism, the curvature of the cornea or lens is somewhat different.

This makes your cornea’s surface more like a football rather than that of a basketball (which is needed for a correctly functioning vision), hampering the eye’s ability to focus light rays precisely on a single point. So, your vision loses focus for any distance.

Moreover, any changes in the curvature of the lens inside the eye can lead to an increase or decrease in the severity of astigmatism. This change is more likely to gain momentum in adulthood and can also become a cause of naturally occurring cataracts.

Astigmatism may also result from an eye injury or eye surgery or even a relatively rare condition known as ‘Keratoconus’, which not only thins down the cornea, but also turns it into cone-shape. This leads to a higher degree of astigmatism, causing poor vision not completely correctable with eyeglasses, eventually needing a corneal transplant in many cases.

How is Astigmatism Diagnosed?

For many children born with the disease, knowing about it is not possible until having an eye exam. Undiagnosed astigmatism can affect a child’s reading and concentrating abilities in school, so regular examination of eyes is much imperative.

The tools most likely to be used by an eye specialist for examining the eye include:

Visual Acuity Test

Where you need to read letters on a specially designed chart, comprising of letters becoming progressively smaller line after line.

Astigmatic Dial

Comprises of a chart displaying a series of lines making up a semicircle whose lines are clearly visible to people with perfect vision.

Keratometer or Ophthalmometer:

A device used to measure the light that reflects from the surface of the cornea. It can assess the degree of abnormal curvature by measuring the radius of the cornea’s curvature.

Corneal Topography:

A process aimed at getting more information about the shape and curve of the cornea.

Astigmatism Symptoms

Some most common signs and symptoms of astigmatism include: