Keratoconus is an eye disease characterised by progressive thinning of the cornea and a resultant bulging of the weakened tissue. The cornea is the transparent dome at the front of the eye, largely responsible for bending (refracting) light through its surface to provide clear vision. Normally, the cornea is uniformly round, like half a soccer ball. As the cornea thins and bulges outward during keratoconus, it may take on more of a cone shape, which is where the name “keratoconus” is derived from. The distortion of this tissue during keratoconus results in impaired vision.
Keratoconus is found at a prevalence of about 1 in 2000. Usually, the condition is present in both eyes but it is not uncommon for it to be more advanced in one eye compared to the other. This can lead to differences in the potential to improve vision between the eyes by conventional means, and one eye may require corneal surgery while the other can still be corrected with optical aids like a contact lens.
Most cases of keratoconus are first detected between the ages of 10 and 25 years old but there are some patients who may go undiagnosed for longer.
Symptoms of keratoconus can often be dismissed for something else but a thorough eye exam by an optometrist or ophthalmologist can help to diagnose the condition. Typical symptoms include:
- Blurred or distorted vision: this is a result of the distorted cornea.
- Glare sensitivity: as light passing through the cornea is distorted, light sources such as oncoming car headlights or traffic lights may appear flared or in a starburst pattern, making them uncomfortable to view.
- Ghosting or double vision: the irregularity of the cornea can result in the appearance of a second image of the one object.
- Frequent changes to your contact lens or glasses prescription: this will typically involve increasing degrees of astigmatism.
Though keratoconus is not typically associated with pain, advanced keratoconus cases may involve a sudden influx of fluid into the cornea, known as hydrops. This situation can be painful and cause an abrupt drop in vision.
While these symptoms may be nonspecific to keratoconus, an eye care professional can perform tests to identify keratoconus as the underlying condition. These tests include:
- Pachymetry: a measurement of the thickness of the cornea will determine if it is thinner than average. Multiple measurements over time will detect progressive thinning.
- Corneal topography or keratometry: similar to geographical topography, a corneal topographer maps the surface curvature of the cornea, noting any uneven areas. Keratometry is similar but much more simplified and only measures a small area.
- Refraction: multiple measurements of your prescription over time can monitor increasing levels of astigmatism as well as keep track of your best corrected visual acuity.
What is Keratoconus Caused By?
The question what is keratoconus caused by is not currently fully understood. Experts believe there to be a combination of both genetic and environmental factors. Studies suggest that around 20% of people with keratoconus also have at least one relative with the condition. There are also known genetic diseases that are often associated with keratoconus, such as Down’s syndrome, Ehlers-Danlos syndrome, retinitis pigmentosa, and Marfan’s syndrome. It is also possible that there is some genetic predisposition for corneal weakness, as some studies indicate keratoconic corneas lack stable structural fibres or have an impaired ability at repairing oxidative damage to their cells.
A history of allergic disease, known as atopy, is a known risk factor for the development of keratoconus. Atopy encompasses conditions such as asthma, eczema, and hayfever. Related to this is another known risk factor for keratoconus – eye rubbing. It is thought that vigorous eye rubbing triggers the corneal fibres to break down further and has been implicated as contributing to keratoconus in those with a genetic predisposition.
In the early stages of keratoconus it is possible to improve vision with normal glasses or soft contact lenses. However, as the disease progresses, the potential to improve vision with these options becomes less likely and you may need to be fitted with hard contact lenses, known as rigid gas permeable (RGP) lenses. Some cases are suitable for a procedure known as corneal cross-linking, which utilises UV light to strengthen the corneal fibres. In advanced disease, even RGP lenses may be insufficient at improving your vision and your ophthalmologist may recommend corneal surgery. A corneal graft can be performed by an eye specialist experienced in corneal surgery, and may be the only option for successfully restoring sight to a functional level.
If you need further information on what is keratoconus or suspect that you or a family member may have the condition, speak to your eyecare professional.