Extrapolation from international figures suggests that more than 2,000 people in Ireland suffer from keratoconus. This non-inflammatory disease of the cornea causes a central thinning of the corneal tissue until the thinnest part of the cornea begins to bulge forward, becoming cone-shaped. The condition is estimated to affect one in every 2,000 people, although this varies according to the population. For example, the incidence of the condition is approximately 7 per cent in Down’s syndrome.

Aetiology

As if yet there is no known cause of the disease but it does have an association with certain medical conditions such as asthma, atopic eczema and systemic disease.

The role of inheritance has not been clearly defined but most patients do not have a positive family history. However, some studies have shown that keratoconus corneas lack important anchoring fibrils which structurally stabilize the anterior cornea.

Eye rubbing has also been proposed as a possible cause while others believe the onset of the disease during puberty may point towards an endocrine component.

Other studies indicate an abnormal elimination process of superoxide radicals in keratoconus corneas, since affected corneas lack the ability to self-repair routine damage.

Diagnosis

Keratoconus is generally first diagnosed in the teenage years and early signs include slightly blurred or distorted vision and increased sensitivity to light. Other symptoms include halos or ghosting especially at night, difficulty driving at night, eye strain, headaches and eye pain, eye irritation and excessive eye rubbing. Often the first sign is a need for frequent changes in eyeglasses prescription or blurred vision that cannot be corrected with glasses.

However, the symptoms can also be caused by several other eye conditions, which make the diagnosis of keratoconus in its early stages somewhat difficult.

Slit lamp examination can identify corneal thinning, Fleischer’s ring (iron coloured ring around the cones), Vogt’s striae (stress lines caused by corneal thinning) and atypical scarring (at the apex of the cone).

Management

There is still no medical treatment for keratoconus. Once the cornea begins thinning, the process cannot be reversed.

Current treatment options focus on correcting the distorted vision caused by the thinning and bulging cornea.

Glasses or soft contact lenses may be used to correct the mild myopia or astigmatism caused by the keratoconus in its earliest stage. However, as the condition progresses, rigid gas permeable contact lenses will be required. The rigid material allows the lens to lie across the distorted cornea, forcing the irregular shape into a smooth uniform refracting surface. Patients should be educated and reminded regularly about the need to properly clean and store contact lenses.

In recent years, the US FDA has approved Intacs for the treatment of keratoconus. These thin, plastic, semi-circular rings are inserted into the mid layer of the cornea, changing the shape and location of the cone.

Unfortunately, for 15 to 20 per cent of keratoconus patients, a corneal transplant will ultimately be required due to scarring, extreme thinning or contact lens intolerance. Most corneal transplant surgeries are performed on an out-patient basis. To prevent rejection of the new cornea, steroid eye drops are used for several months after the operation and, in some cases, may be required indefinitely.

In the post-operative period, particular attention should be paid to any redness, sensitivity to light, vision loss or pain. Flashing lights, floaters and loss of peripheral vision also warrant investigation.

New horizons

A new ground-breaking procedure has emerged in recent years which can arrest the progression of keratoconus and prevent the need for corneal transplantation. Corneal cross-linking increases the collagen cross-links within the cornea, strengthening the cornea and preventing it from bulging outwards.

The procedure involves gently peeling back the corneal epithelium and dropping riboflavin drops onto the cornea for approximately 20 minutes until the cornea is saturated. Once saturation is achieved, the riboflavin is activated using focussed ultraviolet light on the cornea for exactly 30 minutes.

Mr Arthur Cummings, from the Wellington Eye Clinic in Dublin, was the first ophthalmologist in Ireland to use the corneal cross-linking technique and has carried out almost 100 procedures to date.

According to Mr Cummings, a slowdown in disease progression has been observed in all of these cases following surgery. In more than 95 per cent of the patients, the keratoconus has been "stopped in its tracks", and 70 per cent of patients have experienced a reversal of the keratoconus, with topography maps actually improving.
Cross-linking is not a cure for keratoconus. The aim of the treatment is to halt the progression of the disease, thereby preventing the need for corneal transplantation.
Glasses or contact lenses will still be needed following surgery, although a change in prescription may be required.

The US FDA is currently conducting a trial into corneal cross-linking and the initial results reflect the European and international experience. In some European studies, patients have been followed for up to eight years already and the effects of the procedure appear to be long-term.

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