As mentioned elsewhere on the site, image formation in the eye mainly occurs by means of the cornea and the crystalline lens. Due to the improvement in crystalline lens replacement techniques, this surgical option is becoming increasingly popular among the international ophthalmologic community.
Lens replacement surgery implies the surgical removal of the crystalline lens, replacing it with an artificial intra-ocular lens of specific design and power to correct the refractive error which resulted from the wrong power of the original natural lens. This procedure is therefore significantly different from placing a phakic lens into the eye. Phakic lens surgery implies the placement of an additional lens into the eye with preservation of the natural lens.
The lens replacement procedure is well proven over a number of decades, as it is essentially identical to a cataract operation – a procedure familiar to the public. In the case of cataract surgery, the diseased cataractous (opaque) crystalline lens is replaced through the same technique.
The principle disadvantage of the natural lens replacement technique is the loss of natural accommodation (the ability to adjust focus). It is therefore mainly employed in cases where patients have already lost their accommodation in a natural fashion, i.e. the presbyopic group of patients.
However, with the advent and continuous development of modern intra-ocular lenses, the final frontier in refractive surgery, presbyopia, is quickly coming within reach. The procedure, coined PRELEX (presbyopic lens exchange) by Dr Charles Clauoe in 1997, is well established over the past number of years. Here, the intra-ocular lens implanted following crystalline lens removal has multifocal properties.
The indications for this treatment modality correspond to that of phakic lenses, i.e. patients with extreme pathological refractive errors. The advantage of this method, however, is that it is much cheaper as opposed to the former technique.