Astigmatism vs. Keratoconus: What Are the Differences?

If you have either keratoconus or astigmatism, your vision may be blurry due to eye irregularities. You may wonder which is causing the problem. While these two conditions may be confused initially, there are definite differences.

In keratoconus, the cornea (the clear dome at the front of the eye) bulges into a cone shape and gets progressively steeper. In astigmatism, the cornea has an irregular shape and doesn't focus light sharply on the retina, the light-sensing layer at the back of the eye.

You should contact an eye doctor (ophthalmologist or optometrist) for a diagnosis and to receive optimal treatment for either condition. Astigmatism can be readily corrected with glasses, while keratoconus cannot. What's more, with progressive thinning of the cornea, keratoconus gets considerably worse with time.

This article will explore symptoms, causes, diagnosis, treatment, and preventive measures for keratoconus and astigmatism.

Symptoms

Blurry vision is a symptom of both keratoconus and astigmatism. Other symptoms are associated with each condition.

In the early stages of keratoconus, you may experience a slight blurring of vision, which continues to get worse. Your glasses or contact lenses seem not to fully help improve your vision.

You may also have difficulty seeing at night and have other night vision problems, such as glare and halos around lights. Other keratoconus symptoms may include headaches, eye pain, and light sensitivity.

Symptoms of astigmatism may include blurry vision and visual distortion. You may also experience headaches and feel that you are straining your eyes. Corrective lenses help much more than they do for keratoconus.

Causes

While both keratoconus and astigmatism can usually be associated with an uneven cornea, the cause of that unevenness can be entirely different in each condition. Here's what to know about the causes of each.

Keratoconus

With keratoconus, vision problems are associated with a progressive thinning of the cornea, which can become misshapen as a result. The middle part of the cornea is composed of collagen, which is a connective tissue protein and water. Collagen gives structure to the eye and helps maintain its smooth, round shape.

When the cornea is shaped as it should be, it can effectively focus rays on the light-sensitive retina. In keratoconus, some collagen may be lost, and the thinning cornea may protrude into a cone shape. This usually begins at puberty and continues into your mid-30s.

While it's unclear why the collagen thins, people with keratoconus may be born with a predisposition for the condition. A family history may indicate an increased risk as well.

Astigmatism

With astigmatism, an imperfection in your eye's cornea or lens also can be present at birth. While the cause is unknown, you may have a genetic predisposition for astigmatism. You can also develop an imperfection after an eye injury or procedure. It can also result from an eye disease such as keratoconus.

Diagnosis

To determine what may be affecting your vision, make an appointment with an eyecare provider for a routine eye exam with refraction testing. Both astigmatism and keratoconus can be distinguished with this process. If keratoconus is suspected, other testing such as keratometry and/or corneal topography will also be done.

During an eye exam, an ophthalmologist or optometrist will test to see how sharp your vision is using an eye chart and a phoropter, a device that measures the refractor error in your eye as you test different lenses.

The amount of astigmatism in your eye will then be measured using an autorefractor or retinoscope. A machine will shine a beam of light into the eye to measure any changes as it hits the back of the eye and travels back out again.

The curve of the cornea will be measured with a keratometer. You may also undergo a corneal topography scan to identify any corneal imperfections. This detailed imaging will help to show if there is astigmatism on the corneal surface and if there is a steep cone present.

Treatment

Identifying which condition you have is essential for proper treatment. Each condition is treated very differently from the other.

Keratoconus

With keratoconus, treatment varies depending on the stage you are in. Early in the disease, it may be sufficient to correct vision problems with glasses or soft contact lenses.

As keratoconus progresses, you may need to wear hard, gas-permeable lenses that can smooth out any irregularities in the cornea (such as an emerging cone or scleral lens). In some cases, the hard lens may not be comfortable, so a soft contact lens may be worn underneath a hard lens. This is called piggybacking.

Also, scleral lenses may be considered. This is a hard, gas-permeable lens that creates a vault over all of the corneal surface (so there is space between the lens and the cornea) and rests on the sclera (the white of the eye).

In cases in which the keratoconus has progressed further, your eye doctor can implant small crescent-shaped segments in the eye that can help flatten the cornea. These are called intrastromal corneal ring segments (ICRS). A brand name is Intacs.

Another possible approach to strengthen the cornea and halt the progression of corneal thinning is a technique known as collagen cross-linking. This uses riboflavin drops activated by ultraviolet light, causing the collagen to form stronger bonds and become firmer.

If these approaches are not sufficient, there's also the possibility of undergoing a corneal transplant. With this, the diseased cornea is removed and replaced by healthy corneal tissue from a donor.

Astigmatism

If you have astigmatism, you can be treated with traditional visual correction such as the following:

• Glasses
• Contact lenses
• Laser refractive surgery such as laser-assisted in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) to reshape the cornea so that it is more spherical, allowing light to properly travel through the eye

Prevention

Unfortunately, there's no proven way to keep either of these conditions from occurring. With keratoconus, avoiding eye rubbing may help. Anything that you can do to reduce itchy eyes may be helpful.

Summary

Astigmatism or keratoconus may cause blurry vision. While initially similar, they have different underlying causes and treatments.

You can be born with astigmatism, or it can result from an eye injury or surgery, or from an eye condition like keratoconus. Keratoconus occurs because the cornea thins due to a decrease of collagen. This allows a cone of tissue to protrude on the cornea.

Both conditions can be diagnosed during a regular eye exam. Treatment for keratoconus will depend on the stage and will vary from rigid gas-permeable lenses to corneal transplantation. Astigmatism can be corrected with glasses or contacts.

A Word From Verywell

If you are seeking a diagnosis for what you think may be either astigmatism or keratoconus, keep in mind that both conditions are treatable. Astigmatism is easier to correct. Keratoconus can be effectively treated with measures that depend on the stage. Treatment will allow you to see clearly once again.