Keratoconus is a disorder of the cornea. The cornea is the front window of the eye, and is the most powerful focusing part of the eye. The underlying problem in keratoconus is a localized thinning of the cornea, with a subsequent ectasia or distortion of the cornea into a cone shape, rather than the normal regular sphere shape. The irregular conical shape means that the eye becomes short sighted and develops irregular astigmatism, causing difficulties whereby it is not possible to correct vision with glasses. The underlying mechanism for all of this is poorly understood.
Many people with Keratoconus are atopic, meaning that they suffer with allergic conditions such as hay fever, asthma and eczema. It has been suggested that the eye rubbing associated with these conditions may contribute to the corneal distortion.
Down’s syndrome is associated with keratoconus.
Slow painless loss of vision – this cannot be corrected with glasses. In some cases there may be an abrupt loss of vision associated with a red, painful and watery eye. This is a condition called hydrops, where the twisting and bending of the cornea is so severe that it becomes waterlogged with the aqueous fluid behind it. In these circumstances a corneal graft is required.
Sometimes a mild form of the disease may be picked up, which is minimally affecting vision and is not rapidly progressive. These cases can simply be observed and glasses may suffice.
The most common form of management is to use a rigid contact lens, which regularizes the front surface of the cornea and corrects the vision.
Collagen cross-linking is a treatment using a sensitizing agent (riboflavin) followed by Ultraviolet light. This strengthens the links between the layers of the cornea, slowing the distortion of the cornea. The results with this technique are promising in some patients where it has been helpful in slowing the progression of the disease.
Intacs – are plastic inserts that can be placed in the cornea in order to give it a rigid stabilizing framework.
Corneal grafting. When the problem becomes severe contact lenses may no longer sit comfortably and with stability. Additionally, there may be scarring; reducing the potential vision. Corneal grafting takes the corneal tissue from a deceased donor and involves sewing a patch of cornea onto the recipient. Great strides have been made with this form of surgery over the last decade. Grafts may be full thickness, involving the wholesale removal of a disc of cornea, or a partial thickness graft, which keeps the underlying layer and just replaces the front layer.
Corneal grafting is one of the most successful types of tissue grafts, since the cornea is relatively protected from rejection. This however is not always the case. The partial thickness grafts have less of a problem with rejection and a quicker rehabilitation time.
After corneal grafting, topical steroid drops will be required for up to a year. If a corneal stitch was placed, this will need to remain for around 18 months before removal. For full thickness grafts the rehabilitation to a stable outcome may take in excess of 18 months.
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On the left the cornea has become cloudy and waterlogged. Middle shows scarring lines. On the right there is a beautiful full thickness graft.