Keratoconus is a rare eye condition which alters the structure of the cornea, changing its gradual curve into a thinner and more conical shape. These changes affect the clarity of your vision and can deteriorate over time, usually starting in adolescence.
Research suggests that it affects between 1 in 1000 and 1 in 3000 people – although there is difficulty pinning down the exact rate of occurrence because symptoms can overlap with other similar conditions.
Signs & Symptoms
Symptoms of keratoconus can include:
- Slight blurring of vision.
- Poor vision in low lit conditions, or when you are tired.
- A halo or ‘ghost’ effect when looking at bright lights.
- Sensitivity to light.
- Eye strain.
Many of these symptoms are common among different eye conditions, so it is essential to be evaluated by a specialist in order to diagnosis keratoconus or other complaints.
What Causes Keratoconus?
There is no scientific consensus on what causes keratoconus, the fact that it occurs more frequently in certain ethnic groups – such as people from Asia – suggests the causes are genetic. Existing evidence would imply that there is less than a 10% chance of a family member of someone with keratoconus also being a sufferer. Considering the condition is also quite rare you are unlikely to have a family member who is affected.
There are also hypotheses that environmental factors can aggravate or bring on the condition – particularly vigorous rubbing of the eyes. Many sufferers also have allergies such as hay fever, asthma, or eczema – it may be this is what stimulates the need to rub the eyes or there may be another causal factor. Although these theories remain unproven, it is recommended that people with keratoconus or those who suspect they have it, avoid persistent rubbing of their eyes.
How Your Eye Works: The Basics
The eye is made of four main components that work together in order to function:
The Cornea and Lens – These are at the front of the eye, helping to focus light directly onto the retina in a similar way to a camera lens.
The Retina – This is a layer of cells at the back of the eye that work by sensing light and colour before converting them to electrical signals.
The Optic Nerve – The nerve that transmits electric impulses to the brain where they are interpreted.
The cornea is the transparent part of the eye that sits at the front, along with the lens it refracts light and drives the majority of the focusing power of the eye. It is made up of many layers and is one of the most sensitive tissues in the body as it is so densely packed with nerve fibres.
When you have keratoconus, the shape of the cornea changes, becoming thinner and distorting how images are processed. Given how crucial the cornea is, conditions that affect it can have a large influence on the quality of your vision.
How is Keratoconus Diagnosed?
Keratoconus is very difficult to diagnose – partly because it is very rare – and partly because the symptoms are similar to a variety of other eye conditions. If the symptoms match those that we detailed in the first section – blurred vision, halo effects, light-sensitivity – then you should certainly see an eye doctor and be referred for an eye test. Even if keratoconus is not the source of the problem, the cause could potentially be another chronic eye condition.
A doctor will observe your symptoms and eyes, but may also confirm the condition with direct measurement in two ways:
- Slit-lamp examination - a combination of microscope and a thin beam of light allows a specialist to examine the front of your eyes looking for tell-tale signs of damage, such as corneal thinning or scarring.
- Keratometry or Corneal topography – two ways of mapping the curvature of the cornea, looking for signs of thinning.
Adults should have their eyes routinely tested every two years, unless they have been told otherwise. These normally last up to half an hour with an optician, and involves having your eye health examined as well as your vision.
An optometrist will get your medical history and ask about any symptoms you may be showing, how severe they are and how long you have had them. They may also ask general questions about your lifestyle, health, and any medication you are taking.
After having your eye health checked, you will normally have a vision test. This involves examining your distance vision, near vision, and intermediate vision, as well your visual acuity - you often read from a Snellen chart (each line of letters becomes smaller). If you wear glasses or contact lenses, you may be tested with and without them.
How do you treat Keratoconus?
There are various treatments for keratoconus depending on the severity, none of them can reverse the effects of the condition, but they can help correct distorted vision. In extreme cases surgery may be required.
- Spectacles/contact lenses. Initially these may be used to correct astigmatism or myopiacaused by keratoconus, usually in the early stages when damage is limited.
- Rigid Gas Permeable (RGP) Contact Lenses. These form a rigid material over the lens which replaces the distorted cone shape of the cornea with a smooth refracting surface.
- Intrastromal corneal ring segments also known as ‘INTACS’. These are small plastic rings that are inserted into the middle of the cornea’s many layers. They force the conical shape of the cornea to transform, flattening it out into its original, gradual curve.
- Corneal Crosslinking (CXL) is a relatively new treatment, the point of which is to increase rigidity of the cornea – it is only useful in stopping the deterioration of the cornea, once it becomes too thin CXL is no longer useful.
- Corneal Transplant. In a minority of cases keratoconus may become so severe that glasses or contact lenses cannot correct the distorted vision. A surgeon will graft a donor cornea to the existing eye tissue of the patient. Recovery takes around 1-2 months and according to the National Keratoconus Foundation the success rate of surgery is 95% or greater when performed on an otherwise healthy eye.