Keratoconus is the most frequent axial corneal ectasia of non-inflammatory origin. The central or lower paracentral area of the cornea becomes thinner, becoming progressively more cone shaped and resulting in myopia, irregular astigmatism and cone apex protrusion.
Keratoconus is the primary cause of corneal transplant in young patients.
Its aetiology is not 100 % known and is probably due to many different factors. A positive family history has been described in 6 % - 8 % of the cases, although it's likely that, if we carried out corneal topography on the relatives of those patients affected by keratoconus, this percentage would be higher. In the rest of the cases it sporadically appears to be related to complex hereditary patterns that are still being studied.
There are also cases related to eye allergies and chronic eye rubbing.
It typically appears in puberty and progresses over the next ten to twenty years. The rate of progression is usually faster the younger the patient.
In its initial stages, patients may have good visual acuity even without correction and the only sign we find is difficulty in establishing a patient's refractive index.
In intermediate stages patients have reduced vision and a sudden increase in astigmatism which cannot be completely corrected with glasses and improves by placing a rigid or gas permeable contact lens in the eye. Due to the progression of the astigmatism, patients require frequent changes in glasses and contact lenses.
When keratoconus is very advanced, visual acuity is altered both with glasses and contact lenses due to irregular astigmatism, an increase in high order aberrations and corneal scarring.
Unlike myopia and hypermetropia, astigmatism does not usually evolve naturally with age. It's therefore important, when there's a sudden increase in astigmatism in children or young patients, to consult an ophthalmologist to rule out keratoconus.
It's very important to diagnose these patients in the initial stages because, with the application of treatments to stop its progression, the prognosis of keratoconus has changed greatly and the need for corneal transplants has fallen.
There are different types of treatment possible depending on the progression of the keratoconus.
Some cases of keratoconus are sufficiently slight, at least for a period of time, to allow sight to be duly corrected with glasses. However, rigid or gas permeable contact lenses are more useful in all cases except in very slight disorders.
In those cases where the keratoconus is seen to progress and evolve, corneal cross-linking has been proven to be highly effective in delaying its progression.
Intrastromal corneal ring segments regularise the cornea, correcting the deformity produced by keratoconus.
In the most advanced cases, when vision has been significantly reduced or there is central corneal scarring, the treatment is a corneal transplant, which can currently be carried out by selectively replacing only the affected layers of the cornea. This is known as lamellar keratoplasty.