Understanding Keratoconus: Causes and How It Affects Vision

What Is Keratoconus?

The cornea is the front layer of the eye and acts as a lens, focusing incoming light so you can see clearly. A normal cornea has a smooth dome shape, much like a sphere. Sometimes the corneal structure is not strong enough to hold this rounded shape and bulges outward into a cone. This condition is called keratoconus.

What Causes Keratoconus?

There are several contributors to keratoconus; one of the most important is weakening of the small fibres in the eye known as collagen.

Collagen fibres help anchor the cornea in place and resist outward bulging. When these fibres weaken, they cannot hold the corneal shape, and the cornea gradually becomes cone-shaped.

The main reason collagen fibres in the eye weaken — and keratoconus develops — is a drop in protective antioxidants in the cornea. Corneal cells produce damaging by-products (oxidative free radicals), some of which arise from environmental exposures such as vehicle exhaust. Antioxidants normally clear these by-products and protect collagen fibres.

When antioxidant levels fall, collagen weakens, the cornea bulges forward into a cone, and keratoconus develops.

Who Is Affected by Keratoconus?

Keratoconus can run in families, so it is best to begin screening your children's eyes from age 10.

Progression tends to be faster in patients with certain medical conditions, including allergic disease — likely related to chronic eye rubbing.

Keratoconus typically appears in adolescence, though it can also begin in childhood and into the early thirties; presentations in the forties and beyond do occur but are less common. Corneal shape changes can happen quickly or unfold over many years. The reshaping leads to blurred vision, glare, and halos at night — particularly around streetlights.

Progression can stop at any time or continue for decades. There is no reliable way to predict the trajectory.

In most patients, both eyes are eventually affected, though usually not symmetrically — one eye typically progresses before the other.

In advanced disease, collagen fibres can stretch enough to cause a tear in the back layers of the cornea, leading to swelling as intraocular fluid enters the corneal tissue (acute corneal hydrops). This can substantially reduce vision and may take time to recover.

Can Keratoconus Cause Blindness?

One of the most common questions about keratoconus is whether vision can still be functional with the disease. The answer: changes in the cornea can make focusing impossible without glasses, rigid contact lenses, or intracorneal ring segments (ICRS). In very advanced cases, a corneal transplant may be needed to restore vision.

Complications of Surgery in Keratoconus

Why LASIK Is Risky in Keratoconus

Anyone with even subclinical keratoconus should not undergo LASIK. LASIK is dangerous in patients with keratoconus because it can further weaken the cornea and worsen vision.

You can discuss this with Dr. Shaarawy at your consultation, where a thorough corneal evaluation will rule out keratoconus before LASIK is considered.

How Is Keratoconus Diagnosed?

Keratoconus changes vision in two main ways:

Myopia

As the cornea shifts from a smooth dome to a cone, its surface becomes irregular — so-called irregular astigmatism. As the cornea steepens, the eye becomes more myopic. Myopia means near objects appear clearer than distant ones, which look blurry.

Symptoms of Keratoconus

During an eye examination, the ophthalmologist may notice signs of keratoconus, including:

• Reduced vision
• Double vision
• Distorted vision
• Halos around bright lights
• Ghost images
• Inability to drive due to blurred vision

How to Confirm a Keratoconus Diagnosis

Your doctor needs to measure the shape of your cornea. Several techniques exist; the most common are corneal topography and Pentacam imaging, which photograph and analyse the cornea in seconds. If you have keratoconus and have children, they should have a Pentacam each year starting at age 10 to catch any early signs of disease.

How Keratoconus Is Treated

Treatment for keratoconus often begins with new glasses, then progresses to rigid gas-permeable contact lenses if needed.

Glasses can improve vision in mild cases, though rigid contact lenses or intracorneal ring segments (ICRS) may be needed to flatten the cone and improve vision.

If vision improves with one of the above options, it is important to monitor with periodic Pentacam imaging. If progression appears, the next step is corneal cross-linking (CXL) — the so-called "corneal stabilisation" procedure — to halt further steepening. If glasses, contact lenses, and rings no longer provide stable, good-quality vision, deep anterior lamellar keratoplasty (DALK) can be performed.