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Correcting Keratoconus with Intracorneal Rings

By Richard Lindsay

Previous studies have demonstrated the efficacy of intrastromal corneal rings (INTACSTM, KeraVision) to correct low myopia (short-sightedness) by flattening the centre of the cornea. By reinforcing the cornea using an additive technique – in contrast to weakening its structure using incisions (e.g. astigmatic keratotomy) or ablation (e.g. LASIK) – INTACS is an interesting surgical alternative to delay or avoid corneal grafting in keratoconic patients who are unable to tolerate contact lens wear yet do not have an advanced form of the condition.INTACS work by an ‘arc-shortening’ effect of the corneal lamellae. Central corneal flattening occurs due to the longer path length of the lamellae from one side of the cornea to the other (that is, from limbus to limbus). Keratoconic corneal tissue has a thinner structure than normal tissue and can be flattened even more easily. Insertion of the intrastromal corneal rings does not violate (involve) the visual axis and is a reversible procedure.The results of studies in France and the USA using this technique on a small number of patients have been quite encouraging. Generally the use of INTACS inserts has led to an improvement in unaided vision, spectacle acuity and corneal topographical appearance, as well as a reduction in refractive error. The complication rate has been low with patients occasionally complaining of a foreign body sensation or haloes around lights at night. Note that the use of INTACS for the treatment of keratoconus has not yet been approved by the FDA in the USA. An FDA study is currently underway but obviously the long-term results with this procedure are still unknown. One of the major queries with this form of treatment would be to determine what effect it has, if any, on the progression of keratoconus.

The objective of using INTACS inserts for treating keratoconus is not to eliminate the corneal disease but to decrease the corneal abnormality associated with it and improve visual acuity – especially spectacle acuity - in affected patients to satisfactory levels. An important potential advantage of treating keratoconus with intrastromal corneal rings is to delay or eliminate the need for a corneal graft. At this stage, the keratoconic patient who would most benefit from this procedure is the one with reduced spectacle acuity who is also contact lens intolerant, yet only has a moderately advanced form whereby a corneal graft would not usually be considered. The aim of using the INTACS inserts in this situation would be to improve the spectacle acuity to a level such that the patient can function quite normally with a spectacle correction.