Keratoconus

What is Keratoconus?

Keratoconus is an eye condition where the normal, round-shaped cornea (the transparent front layer of the eye) becomes thin and bulges outward to form a cone shape (i.e: changing from the shape of an orange to more like the shape of a lemon). 

The abnormal curvature in the cornea can prevent the eye from focusing light accurately on the retina resulting in blurred vision.

Keratoconus usually affects both eyes, but it may affect one eye more than the other initially. 

Who Does Keratoconus Affect?

Keratoconus can manifest at different ages, from childhood up to the age of about 40 years. 

Symptoms of Keratoconus

Keratoconus usually progresses slowly over several years, but it can also worsen suddenly. 

The signs and symptoms of keratoconus vary with the progression of the disease.

Early symptoms include:

• The blurring of vision
• Distorted or double vision
• Halos or rings seen around lights
• Night vision problems and glare

A patient with keratoconus may notice frequent changes in their spectacle prescription especially the degree of astigmatism. 

Rarely, patients may experience sudden clouding of vision (hydrops). 

What are the Causes of Keratoconus?

The exact cause of keratoconus is not clearly understood. 

Keratoconus has an inherent genetic component, meaning it can be passed on from one generation to the next. 

It is thought to be due to the weakening of collagen fibres, which maintain the shape of the cornea. 

There is a strong association between keratoconus and excessive eye rubbing, and hence people with allergic eye disease are strongly advised to stop eye rubbing. 

Also, keratoconus is more commonly seen in patients with certain medical conditions, such as Down’s syndrome, Ehlers-Danlos syndrome and atopic dermatitis. 

Keratoconus assessment

When a patient experiences any of the above symptoms, you should consult a corneal specialist (an ophthalmologist with subspecialty interest in corneal diseases). Your ophthalmologist will 

• Review your medical history 
• Conduct a thorough eye examination
• Order a few diagnostic tests to measure the corneal curve to evaluate the projection and shape of your eyes 

It is essential to recognise that the treatment of keratoconus should be personalised for the individual patient. 

Your ophthalmologist should be able to suggest appropriate treatment options based on the severity and progression of your condition, your work and your lifestyle. 

How is Keratoconus Treated?

The current treatment for keratoconus is focused on stabilising the disease and improving vision. 

For visual improvement, glasses and soft contact lenses should be prescribed in the first instance. Specialised contact lenses (rigid gas permeable or semi-scleral contact lenses) may be needed in more severe cases to neutralise the irregular corneal astigmatism.

Corneal Collagen Crosslinking Therapy 

In recent years, corneal collagen cross-linking has been utilised to halt the progression of the disease by stiffening the collagen fibres within the cornea. 

In addition, this procedure may help to improve patients’ vision, although this beneficial effect is not always predictable. 

The primary aim of this procedure is to allow eye drops that are rich in vitamin B2 (riboflavin) to diffuse into the cornea. After adequate absorption of the eye drops, the patient is:

• Positioned with the UV light at a short distance from the cornea for 30 minutes
• A bandage contact lens is inserted
• The eye will be patched for 24 hours.

The full effect of corneal collagen cross-linking may not be apparent for six months or more. 

Not all patients with keratoconus are suitable to undergo this procedure. 

Surgical Treatments for Keratoconus

A corneal transplant may be required in extreme or end-stage keratoconus.

Penetrating Keratoplasty (PK)

Traditionally, a Penetrating Keratoplasty (PK) was performed in which the full thickness of the patient’s cornea will be replaced by a donor corneal graft. Although the success rate of PK is very high, the postoperative recovery time is relatively long and sometimes it may take years to achieve the functional vision in the operated eye. 

Also, there is a higher risk of graft rejection compared with other types of corneal transplantation. 

Deep Anterior Lamellar Keratoplasty (DALK)

The latest surgical treatment of choice for keratoconus is Deep Anterior Lamellar Keratoplasty (DALK), a partial thickness corneal graft. The bottom two layers (Descemet’s membrane and endothelium) of the patient’s cornea are preserved as these layers are not affected by the disease process. This technique has a quick recovery time and less risk of graft rejection.