Understanding Keratoconus: Causes and How It Affects Vision

What Is Keratoconus?

The cornea is the front layer of the eye. It works like a lens, focusing incoming light so you can see clearly, and a healthy cornea holds a smooth dome shape, much like a sphere. Sometimes, though, the corneal structure isn't strong enough to keep that rounded shape, and it bulges outward into a cone. That condition is keratoconus.

What Causes Keratoconus?

Several factors contribute to keratoconus. One of the most important is weakening of the small fibres in the eye known as collagen.

Collagen fibres anchor the cornea in place and resist outward bulging. When they weaken, they can no longer hold the corneal shape, and the cornea gradually turns cone-shaped.

Why do those fibres weaken in the first place? The main reason keratoconus develops is a drop in protective antioxidants in the cornea. Corneal cells produce damaging by-products — oxidative free radicals — some of which come from environmental exposures such as vehicle exhaust. Antioxidants normally clear these by-products away and protect the collagen.

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

Who Is Affected by Keratoconus?

Keratoconus can run in families. If it runs in yours, start screening your children's eyes from age 10.

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

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

Progression can stop at any time, or it can continue for decades. There is no reliable way to predict which path a given eye will take.

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

In advanced disease, the collagen fibres can stretch enough to tear the back layers of the cornea. Intraocular fluid then enters the corneal tissue and the cornea swells (acute corneal hydrops). Vision can drop substantially, and recovery may take time.

Can Keratoconus Cause Blindness?

Can you still see well with keratoconus? It's one of the questions we hear most. The honest 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 these patients because it can further weaken the cornea and worsen vision.

This is worth discussing 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 — what doctors call irregular astigmatism. And as the cornea steepens, the eye becomes more myopic. With myopia, near objects look clearer than distant ones, which appear 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 every year starting at age 10 to catch any early signs of disease.

How Keratoconus Is Treated

Treatment for keratoconus often starts simply — new glasses — and moves on 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 these options, keep monitoring with periodic Pentacam imaging. Should progression appear, the next step is corneal cross-linking (CXL) — the so-called "corneal stabilisation" procedure — to halt further steepening. And if glasses, contact lenses, and rings no longer provide stable, good-quality vision, deep anterior lamellar keratoplasty (DALK) can be performed.