Keratoconus

The cornea, the eye’s clear front window, normally has a smooth, dome-like curvature that focuses light accurately onto the retina. In keratoconus this normally round cornea progressively thins and begins to bulge outward into a cone-like shape. The irregular shape prevents light from focusing correctly, leading to distorted and blurred vision.

Keratoconus typically begins in puberty or the late teens and can progress into the thirties or forties, although the rate and extent of progression vary widely between individuals. It usually affects both eyes, often one more severely than the other.

What causes the cornea to change shape

The exact cause is not fully understood, but it is believed to be a combination of genetic and environmental factors.

• Weakened corneal tissue. The condition involves a weakening of the collagen fibres within the cornea. Collagen provides strength and structure; when these fibres weaken, the cornea loses its ability to maintain its normal shape under the eye’s internal pressure, leading to the characteristic bulging.
• Genetics. A family history of keratoconus is present in a proportion of cases, suggesting a genetic predisposition.
• Eye rubbing. Chronic and vigorous eye rubbing is strongly associated with the development and progression of keratoconus. The mechanical stress further weakens an already susceptible cornea.
• Allergies and atopic conditions. Patients with asthma, eczema or hay fever often experience itchy eyes, leading to more frequent rubbing.
• Oxidative stress. An imbalance between free radicals and antioxidants in the cornea may also contribute to the weakening of corneal tissue.

Recognising the symptoms

Symptoms often start subtly and can include:

• Progressive blurring and distortion of vision
• Increased sensitivity to light and glare
• Frequent changes in spectacle prescription, with increasing astigmatism and short-sightedness that glasses can no longer fully correct
• Ghost images or multiple images
• Difficulty with night vision
• Eye strain or headaches
• Sudden clouding of vision and pain if acute corneal hydrops occurs — a rare complication where fluid enters the cornea through a break in Descemet’s membrane

Diagnosis

An ophthalmologist or optometrist can diagnose keratoconus during a comprehensive eye examination. Key diagnostic tools include:

• Slit-lamp examination — reveals characteristic signs such as corneal thinning, Vogt’s striae (fine stress lines in the cornea) or a Fleischer ring (an iron deposit around the base of the cone).
• Corneal topography — the most crucial diagnostic test. It creates a detailed, colour-coded map of the cornea’s surface curvature, clearly showing the irregular steepening and cone-like shape characteristic of keratoconus, even at very early stages.
• Pachymetry — measures corneal thickness, typically reduced in areas of conical protrusion.
• Refraction — to determine the degree of short-sightedness and astigmatism.

Treatment: from glasses to grafts

Treatment aims to provide clear vision and, importantly, to halt or slow progression. The approach depends on severity and rate of change.

Early stages

• Spectacles can correct mild short-sightedness and astigmatism.
• Soft contact lenses, custom-made, may work for some mild cases.

Moderate stages

• Rigid gas permeable (RGP) contact lenses are often the mainstay of treatment. They create a smooth refractive surface over the irregular cornea, providing much clearer vision than glasses.
• Scleral lenses — larger-diameter rigid lenses that vault over the entire cornea and rest on the sclera. They offer excellent comfort and vision for moderate to advanced keratoconus.
• Hybrid contact lenses combine a rigid centre with a soft outer skirt for comfort and clarity.

Slowing or halting progression

Corneal cross-linking (CXL) is designed to strengthen the corneal tissue and stop progression. Riboflavin (vitamin B2) drops are applied to the cornea and activated by ultraviolet-A light. The process creates new bonds between collagen fibres, making the cornea stiffer and more resistant to further bulging. CXL is most effective in earlier stages, before significant vision loss or scarring occurs.

Advanced stages

• ICRS (intracorneal ring segments) — small, clear, arc-shaped rings surgically inserted into the periphery of the cornea to flatten the cone and improve its shape. This can make contact lens wear easier or improve uncorrected vision.
• CAIRS (corneal allogenic intrastromal ring segments) — arc-shaped rings derived from allogenic donor stroma, acting as a spacer in ectatic corneas. They improve visual and topographic parameters while avoiding the risks associated with synthetic intrastromal ring segments.
• DALK — deep anterior lamellar keratoplasty is often the preferred transplant technique for keratoconus, because it preserves the patient’s own healthy endothelium and reduces the risk of graft rejection. It replaces the diseased anterior and stromal layers of the cornea.
• Penetrating keratoplasty — a full-thickness transplant may be required if DALK is not feasible or if there is significant scarring involving the deeper layers.

Living with keratoconus requires ongoing management and regular eye examinations. With the range of treatments now available — from specialised contact lenses and cross-linking to advanced surgical techniques — most patients can achieve good functional vision and maintain their quality of life. Early diagnosis and intervention, particularly with CXL, are key to preventing severe vision loss.