Keratoconus

What happens in keratoconus

A normal cornea is dome-shaped and evenly curved, focusing light precisely. In keratoconus, collagen fibers in the cornea weaken, the cornea thins, usually in its lower central part, and pressure inside the eye pushes it forward into a cone. The irregular shape scatters light, causing irregular astigmatism that glasses cannot fully correct.

It affects about 1 in 400 to 1 in 2,000 people, and possibly more, as modern scans detect milder cases.

Causes and risk factors

The exact cause is not fully understood. It involves a mix of genetic susceptibility and mechanical and environmental factors:

• eye rubbing, one of the strongest risk factors
• allergies, eczema and asthma, which cause itching and rubbing
• family history: about 1 in 10 people with keratoconus have an affected relative
• Down syndrome
• connective tissue disorders: Ehlers-Danlos syndrome, Marfan syndrome, osteogenesis imperfecta
• floppy eyelid syndrome and sleep apnea
• Leber congenital amaurosis and some other eye conditions

Symptoms

• blurred vision that worsens over months to years
• distorted vision: straight lines look bent or wavy
• ghosting or double images in one eye
• glare and halos around lights, especially at night
• sensitivity to light
• frequent changes in glasses prescription, with increasing astigmatism and nearsightedness
• eye strain and headaches
• contact lenses that become uncomfortable or keep popping out

Symptoms often differ between eyes.

Corneal hydrops

In advanced keratoconus, the inner layer of the cornea can suddenly tear, letting fluid in. The cornea turns white and swollen with a sudden drop in vision, pain and watering. It usually settles over weeks to months but can leave a scar.

Diagnosis

• corneal topography and tomography: maps of the cornea's shape and thickness. These are the most sensitive tests and can detect early keratoconus
• slit-lamp examination: may show thinning, a cone, Vogt's striae (fine lines), or a Fleischer ring (iron deposit)
• refraction: increasing or irregular astigmatism
• pachymetry: measures corneal thickness

Screening is important before LASIK, because laser surgery on an undiagnosed keratoconic cornea can make it worse. Keratoconus is a contraindication to LASIK.

Treatment

Stopping progression: corneal cross-linking

Corneal cross-linking uses riboflavin (vitamin B2) drops activated by ultraviolet light to strengthen bonds between collagen fibers. It is FDA-approved and halts progression in most patients. It is ideally done early, before major vision loss, especially in teenagers, whose keratoconus tends to progress faster. Recovery takes several days of discomfort and weeks for vision to settle.

Improving vision

• Glasses or soft contact lenses for early, mild keratoconus.
• Rigid gas-permeable (RGP) lenses: create a smooth front surface over the irregular cornea and give much sharper vision.
• Hybrid lenses: rigid center with a soft skirt for comfort.
• Scleral lenses: large rigid lenses that vault over the cornea and rest on the white of the eye. Often the most comfortable and effective option for moderate to advanced disease.
• Intracorneal ring segments: small plastic implants that flatten the cone in selected patients.

Corneal transplant

When vision cannot be corrected with lenses, or there is significant scarring, a corneal transplant is performed. Deep anterior lamellar keratoplasty (replacing the front layers) or full-thickness penetrating keratoplasty are options. Success rates are high, but recovery takes many months and glasses or contact lenses are still often needed.

Stop eye rubbing

• treat allergies with antihistamine or mast cell stabilizer eye drops
• use cool compresses and lubricating drops instead of rubbing
• address habits such as rubbing on waking

Outlook

Keratoconus rarely causes blindness. With cross-linking, specialty lenses and, when needed, transplant, most people keep good functional vision. Regular monitoring with corneal scans is essential, especially in teens and young adults.

Frequently asked questions

What is keratoconus?

Keratoconus is a condition in which the cornea thins and bulges into a cone shape. This distorts light entering the eye, causing blurry, distorted vision and increasing astigmatism. It usually begins in the teens or twenties and can progress for years.

What causes keratoconus?

The cause involves genetic and environmental factors. Eye rubbing, allergies and eczema, family history, Down syndrome and connective tissue disorders such as Ehlers-Danlos syndrome increase the risk. The corneal collagen becomes weaker and less able to hold its shape.

Can keratoconus be stopped?

Yes, in most cases. Corneal cross-linking, which uses riboflavin drops and ultraviolet light, strengthens the cornea and halts progression in most patients. It works best when done early, before significant vision loss.

Can you wear contact lenses with keratoconus?

Yes. Specialty lenses are the main way to correct vision in keratoconus. Rigid gas-permeable, hybrid and scleral lenses create a smooth optical surface and usually give much better vision than glasses. Fitting by an experienced eye care professional is important.

Can you get LASIK if you have keratoconus?

No. LASIK removes corneal tissue and can make keratoconus worse. Screening scans before refractive surgery look for early keratoconus. Some people with stable, mild disease may be candidates for other procedures, such as cross-linking combined with surface treatments.