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Keratoconus is a progressive eye disease that starts near the collagen fibres, i.e. the cornea, causing the normally round cornea to thin and change from a spherical to a cone-like shape.
What is keratoconus?
The cornea is the transparent front part of the eye that refracts light. A normal cornea is shaped like a perfectly round ball and consists of collagen fibres which give the cornea its structure and firmness.
Keratoconus is a progressive eye disease that starts near these collagen fibres, i.e. the cornea, causing the normally round cornea to thin and change from a spherical to a cone-like shape.
This progressive thinning of the cornea leads to a bulging with irregular astigmatism (oval eye) and worsening myopia (short-sightedness). In most cases (80-90 %), both eyes are affected, but a difference in severity between both eyes is common (bilateral asymmetric disorder). Keratoconus usually develops from puberty up to the age of about 45 and is more common in men than in women.
What are the symptoms of Keratoconus?
Keratoconus is difficult to diagnose because it develops slowly. Possible symptoms are:
Causes of keratoconus
The true cause of keratoconus is unknown. Probably several factors play a role: hereditary (10 %) and environmental.
Other possible causes could be:
How do we treat keratoconus?
Initially, keratoconus can be treated with corrective lenses or (semi) hard contact lenses, but, as time goes by, patients can develop a progressive intolerance to lenses. Corneal transplant used to be the treatment of choice if the condition degenerated but the risk of subsequent complications was high.
Recently, a new technology was developed that halts the corneal thinning process – Ultraviolet Cross-linking, and a method to normalise the shape of the cornea, i.e. intracorneal ring segments.
Keratoconus is characterised by reduced cross-links between the collagen fibres which ultimately reduces corneal strength.
Ultraviolet Crosslink is a new technique. The objective of this treatment is to strengthen the collagen structures in the central part of the cornea by creating new connections between the collagen fibres. This increases the strength and stability of the cornea and flattens the central, weaker, thinner area. Short-sightedness and astigmatism will improve as a result. This treatment is not suitable for patients with advanced keratoconus.
A photosensitive fluid (riboflavin) is administered to the cornea which penetrates into the deeper layers of the cornea. The cornea is then irradiated with ultraviolet-A light, creating extra connections between the collagen fibres and thickening the collagen fibres. The collagen fibres become three times stronger and this process stabilises after 6 months. As the cornea flattens out and becomes less pointed, vision can improve. This treatment can halt the progression of keratoconus during the progressive phase.
While this treatment used to take over an hour (30 minutes for the eye drops, 30 minutes for UV), the AVEDRO technology has reduced it to a maximum of 20 minutes for the eye drops and to just 4 minutes for UV radiation. This is mainly due to a change in the eye drops and the higher energy of the UV source.
An additional advantage is that therapy can now be performed via the transepithelial route, so patients do not experience any post-operative pain.
Refractive abnormalities (myopia, irregular astigmatism) are treated beforehand with lasers (the topo-guided excimer laser) or afterwards by phaco with toric intraocular lenses.
When is this treatment indicated?
To prevent the development of keratoconus
- To treat progressive keratoconus
- To treat corneal ectasia (bulging)
- To address corneal instability after radial keratotomy (i.e. incisions into the eye to correct short-sightedness)
- In the case of chronic corneal oedema (swelling) and a resistant cornea ulcer (sore)
- For recurrent keratoconus after corneal transplant surgery
Possible risks associated with this procedure are slow wound healing, abnormal wound healing (this risk is lower with AVEDRO technology) and post-operative infections.
Who is not eligible?
In patients with a corneal thickness of < 325 µm, with epithelial healing disorders, herpes keratitis and during pregnancy.
Intracorneal ring segments (Intacts)
Intracorneal ring segments (corneal implants) can be used when people cannot tolerate contact lenses or to postpone corneal transplant surgery. This outpatient treatment involves placing 1 or 2 semi-circular rings into the outer edges of the cornea under local anaesthetic. These cause the central, thinner part of the cornea to flatten out again, significantly reducing myopia and astigmatism. The rings also support the weaker, bulging part of the cornea.
This technique, which has been used for more than 15 years, recently gained momentum once again when the corneal tunnel incision that was previously carried out by means of surgical blades can now be performed with more precision using a laser device (Ziemer). The irregular shape of the cornea is corrected, markedly enhancing the patient’s quality of life.
In about 10 % of cases the intracorneal ring segments need to be adjusted.
Possible complications include ring displacement and post-operative infections; however, these are easily treated if detected at an early stage. After surgery, some patients may experience short-term irritation, light halos and photophobia.
When the above treatments are no longer viable, corneal transplantation will be considered. If, as keratoconus progresses, patients can no longer tolerate contact lenses, a corneal transplantation can provide relief. Approximately 20 % of keratoconus patients will eventually reach this stage.
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