Keratoconus: Symptoms, Progression, Cross-Linking and Lenses

The cornea is the clear, dome-shaped window at the front of the eye. It does most of the eye's focusing, so even small changes in its shape affect how sharply you see. In keratoconus, the cornea gradually becomes thinner and weaker and begins to bulge forward into a cone. The irregular surface scatters light, producing blur, distortion and glare that ordinary glasses increasingly struggle to correct.

Keratoconus usually begins in the teenage years or early twenties and can progress for a decade or more before stabilising. The good news is that care has changed dramatically: a treatment called corneal cross-linking can stop progression in most patients, and specialist contact lenses give many people excellent vision. This guide explains the condition, its warning signs, why eye rubbing matters so much, and the treatment options from glasses to corneal transplant.

What is keratoconus?

The name comes from the Greek words for cornea (kerato) and cone (konos). The cornea is made of hundreds of layers of collagen fibres arranged in a precise lattice that gives it strength and transparency. In keratoconus, this structure weakens, the bonds between collagen fibres loosen and the cornea thins, usually most in an area just below the centre. Normal pressure inside the eye then pushes the weakened area outwards.

The result is an irregular, steep cornea. Unlike ordinary astigmatism, where the cornea is curved more like a rugby ball but still smooth and regular, keratoconus produces irregular astigmatism and higher-order aberrations that glasses cannot fully correct. Our guide to refractive errors explains these focusing problems in more detail.

Keratoconus usually affects both eyes, although often unevenly: one eye may be much more advanced than the other. It is not an inflammatory condition and it does not cause total blindness, but untreated advanced disease can seriously reduce vision and quality of life, particularly because it affects people during school, university and early working years.

How common is it and who gets it?

Older estimates suggested keratoconus affected around 1 in 2,000 people, but modern corneal imaging detects milder cases and studies now report higher figures, varying considerably by country and ethnicity. It appears to be more common in some populations in the Middle East and South Asia. The exact cause is not fully understood; it is thought to result from a combination of genetic predisposition and environmental factors.

Risk factors

• Eye rubbing. Frequent, vigorous rubbing is one of the most consistently reported risk factors and is thought to contribute to both onset and progression.
• Allergies and atopy. Hay fever, allergic conjunctivitis, asthma and eczema are linked to keratoconus, partly because itchy eyes lead to rubbing. See our eye allergies guide.
• Family history. Having a parent or sibling with keratoconus increases your risk; relatives are often advised to have corneal imaging.
• Age. Onset is typically around puberty, with the fastest progression in teenagers and young adults.
• Certain conditions. Keratoconus is more common in people with Down syndrome, some connective tissue disorders and Leber congenital amaurosis.
• Sleep apnoea and eye-down sleeping positions have been associated with keratoconus in some studies, though the evidence is less certain.

Symptoms and early signs

Early keratoconus can be hard to spot because it looks like ordinary short-sightedness or astigmatism. Clues that should prompt a closer look include:

• Blurred or distorted vision that keeps worsening, with frequent changes in glasses prescription, particularly increasing astigmatism.
• Ghosting or multiple images, often seen as shadows around letters or several moons at night.
• Glare, halos and starbursts around lights, making night driving difficult.
• Sensitivity to light and eye strain or headaches from struggling to focus.
• Glasses that never seem to give truly sharp vision, even when freshly prescribed.
• Difficulty wearing ordinary soft contact lenses.

In advanced cases a sudden painful, watery, cloudy eye can occur when a small tear in the inner layer of the cornea lets fluid flood in. This is called acute hydrops. It is alarming but usually settles over weeks to months with treatment, often leaving a scar.

How keratoconus is diagnosed

Diagnosis is made by an ophthalmologist or optometrist using several tests:

• Corneal topography and tomography map the shape, curvature and thickness of the whole cornea. These are the key tests for detecting early disease and tracking progression.
• Pachymetry measures corneal thickness.
• Slit-lamp examination can reveal later signs such as thinning, fine stress lines (Vogt striae) and a brownish ring of iron deposits (Fleischer ring).
• Refraction and visual acuity show how vision and astigmatism are changing.

Progression is usually confirmed by comparing scans taken several months apart. Because timing matters so much, young people with suspected keratoconus should be monitored closely, often every three to six months at first. Our guide to eye examinations describes what to expect.

Eye rubbing: the habit to break

If there is one lifestyle change that matters in keratoconus, it is stopping eye rubbing. Rubbing raises pressure on the cornea, may weaken its collagen and is closely associated with progression. Many patients rub without realising it, especially on waking, when tired, or when allergies flare.

• Treat itch at its source: ask about antihistamine or mast-cell stabiliser drops for allergies and lubricating drops for dryness.
• Use a cool compress instead of rubbing when eyes itch.
• Keep nails short and notice triggers such as screens late at night or dusty rooms.
• Parents can gently remind children and teenagers, who are at the highest risk of progression.

Corneal cross-linking: stopping progression

Corneal collagen cross-linking (CXL) is the only widely established treatment that halts keratoconus progression. Riboflavin (vitamin B2) drops are applied to the cornea and then activated with controlled ultraviolet-A light. The reaction creates new chemical bonds between collagen fibres, stiffening the cornea.

What it involves

In the standard epithelium-off technique, the thin surface layer of the cornea is gently removed after numbing drops, riboflavin is applied, and UV light is shone on the eye for a set time. A bandage contact lens is placed while the surface heals over several days. Pain, light sensitivity and blurred vision are common in the first days, and vision may fluctuate for weeks or months. Faster protocols and epithelium-on techniques exist; they are more comfortable, but their effectiveness relative to the standard method is still being studied.

What to expect

Large studies and long-term follow-up show that cross-linking stops progression in the great majority of treated eyes, and some eyes flatten slightly with a modest improvement in vision. However, its main purpose is to preserve existing vision, not to restore it. That is why the best time to cross-link is early, as soon as progression is documented, especially in young people. National bodies such as the UK's NICE recognise cross-linking as an effective treatment for progressive keratoconus. Possible complications are uncommon but include infection, corneal haze and, rarely, scarring.

Seeing clearly: glasses and contact lenses

Cross-linking strengthens the cornea, but most people still need optical correction to see well. The choice depends on disease stage.

Rigid lenses work because the tear film fills the space between the irregular cornea and the smooth lens, effectively replacing the distorted surface with a regular one. Scleral lenses have transformed care for many people with advanced keratoconus, often postponing or avoiding transplant. Fitting these lenses takes skill and several visits, so look for an optometrist or contact lens practitioner experienced in keratoconus. Strict hygiene matters: see our guide to contact lenses.

Other procedures

• Intracorneal ring segments. Small arcs of plastic inserted into the cornea can flatten and regularise its shape, improving lens tolerance or vision in selected patients. They do not stop progression on their own.
• Topography-guided surface laser combined with cross-linking is offered in some centres to smooth the cornea. It is used selectively and is not standard everywhere.
• Phakic intraocular lenses can correct remaining short-sightedness in stable eyes in carefully chosen cases.

Corneal transplant

When the cornea becomes too thin, scarred or irregular for lenses to give useful vision, a corneal transplant (keratoplasty) is considered. Thanks to cross-linking and scleral lenses, this is needed far less often than in the past, but keratoconus remains one of the common reasons for transplantation in young people.

Two main techniques are used. In penetrating keratoplasty, the full thickness of the central cornea is replaced with donor tissue. In deep anterior lamellar keratoplasty (DALK), only the front layers are replaced and the patient's own inner layer (endothelium) is kept, which reduces the risk of rejection. Recovery is long, often a year or more before final vision, stitches may be adjusted or removed over time, and many people still need glasses or contact lenses afterwards. Long-term success rates for keratoconus grafts are generally good. Read more in our guide to corneal transplant and eye donation.

Living with keratoconus

Most people with keratoconus finish school, drive, work in a wide range of careers and live full lives. Practical points that help:

• Keep regular follow-up appointments, particularly in your teens and twenties.
• Do not rub your eyes, and keep allergies under control.
• Protect your eyes from UV and glare with good sunglasses.
• Tell your eye doctor promptly if vision changes, lenses become uncomfortable or a lens no longer fits well.
• Check driving vision standards in your country and make sure your corrected vision meets them.

When to see a doctor

See an optometrist or ophthalmologist if your vision keeps getting worse, your glasses prescription keeps changing, you notice ghosting or distortion, or someone in your family has keratoconus. Teenagers with allergies who rub their eyes and need frequent new glasses deserve particular attention.