While keratoconus typically develops in both eyes, it can be asymmetrical, which means it can be much worse in one eye. It’s typically treated with eyeglasses or special contact lenses.

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Keratoconus is an eye condition that affects the cornea, the part of the eye that lets in light. The cornea is normally dome-shaped, but in keratoconus, it becomes thinner and cone-shaped, distorting your vision.

Keratoconus typically affects both eyes. In some cases, it can be worse in one eye. Over time, the eye with milder keratoconus can get worse.

Read on to learn more about unilateral keratoconus.

Unilateral keratoconus refers to keratoconus that affects only one of your eyes.

It’s generally accepted by experts that there’s no true unilateral keratoconus. Instead, it’s considered to be asymmetrical.

This means that while one eye has detectable keratoconus, the other eye may have an early or milder form of the condition that will develop into detectable keratoconus over time.

However, there have been reports of unilateral keratoconus that have remained stable over many years.

Your cornea is important for helping to focus the light that enters your eye. The changes in shape that happen due to keratoconus affect the cornea’s ability to focus light.

You might notice vision changes like:

As keratoconus progresses, you might also experience:

It’s not exactly clear why some people develop keratoconus while others don’t.

Experts think genetics may play a role. According to the American Academy of Ophthalmology, about 1 in 10 people with keratoconus have a biological parent who also has it.

Additional factors believed to contribute to keratoconus include:

A 2024 study stated that some experts think that it’s possible for unilateral keratoconus to occur due to stress from repeated rubbing of an eye already predisposed to the condition.

An earlier 2017 case report detailed a person with unilateral keratoconus seemingly caused by eye rubbing.

Keratoconus is generally considered to be a bilateral condition. That means that it affects both eyes instead of just one.

As mentioned earlier, keratoconus can be asymmetrical. This means that the severity of the condition may be notably more severe in one eye.

If you have mild keratoconus in one eye, the vision changes can be very subtle. A small 2019 study found that in people with unilateral keratoconus, the seemingly unaffected eyes had cornea changes. This may indicate that their vision would get worse with time.

There are several ways to manage keratoconus, and the treatment your doctor recommends will depend on how much it has progressed.

For example, if your case is mild, you may just need eyeglasses or contact lenses. If it’s slightly more advanced, you might need hard contact lenses, a special type of lens that reshapes the surface of your cornea.

Various procedures can also be used to treat keratoconus. These include:

  • Corneal cross-linking: This is where an ophthalmologist uses riboflavin and a specialized type of UV light to strengthen your cornea and prevent it from deforming further.
  • Intracorneal ring segments: Also called INTACS, these are small curved inserts that help to flatten out and strengthen your cornea.
  • Corneal transplant: During this procedure, an ophthalmologist replaces some or all of your cornea with tissue from a healthy donor.

Overall, early detection is important for keratoconus outlook. This is because treating the condition right away can help to slow or stop progression, reducing the need for more invasive procedures later on.

If you have unilateral keratoconus, your doctor will also want to monitor your other eye for signs of keratoconus.

In addition to using a standard eye exam, your doctor can use an imaging test called corneal topography to check for keratoconus. This test creates a 3D image of your cornea that can allow a doctor to evaluate its shape and thickness.

Your doctor can also use corneal tomography to monitor the progression of your existing keratoconus.

While people with stable unilateral keratoconus have been identified, it’s generally accepted that keratoconus is bilateral. This means that it impacts both eyes instead of only one.

Sometimes, keratoconus may be asymmetrical, meaning that one eye is affected more severely than the other.

The outlook for keratoconus is best when it’s found and treated early on. Because of this, be sure to see your eye doctor if you notice symptoms like blurry or distorted vision, sensitivity to light, or poor night vision.