Refractive lens Exchange
As mentioned elsewhere on the site, image formation in the eye occurs by means of the corneaThe cornea is the clear, transparent 'front window' of the eye through which light enters the eye. It handles about two-thirds of the focusing power of the eye and is critical for good vision. See Info on Eyes – Anatomy. and crystalline lensThe lens fulfils the same role as the lens in a camera. It handles about one-third of the focusing power of the eye and is critical for good vision.See Info on Eyes – Anatomy.. Due to the improvement in crystalline lens replacement techniques, this option is also available in selected cases of refractive correction.
Lens replacement surgery implies the surgical removal of the crystalline lens, and replacing it with an artificial intra-ocular lens of specific design and power to correct the refractive error which results from the deficient power of the original natural lens. This procedure is thus significantly different from the placing of 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 cataractA cataract forms when the natural lens in the eye is, or is starting to become, opaque. If not treated, it can lead to blindness, which in most cases can be treated. See Cataract Centre – Understanding Cataracts. operation - a procedure familiar to most people. In the case of cataract surgery, the diseased cataractous (opaque) crystalline lens is replaced through the same phacoemulsificationPhaco emulsification is the process used to liquify and extract an opacified natural lens (cataract) from the eye. The lens is then replaced with one of several types of artificial lenses. See Cataract Centre – About cataract surgery. technique.
The principal disadvantage of replacing the natural lens, is the resultant loss of natural accommodationAccommodation is the physiological process by which the eye changes focus. A ring of muscle around the lens, called the ciliary body, changes the shape of the lens, which allows the eye to focus at different distances. (the ability to adjust focus). It is therefore mainly employed in cases where patients have already lost their accommodation due to the natural ageing process, namely the presbyopic group of patients older than 40 years.
However, with the advent and continuous development of modern intra-ocular lensAn intra-ocular lens is an artificial lens that is implanted into the eye to either correct severe refractive errors, or to replace an opacified natural lens (cataract) during a cataract procedure. See Cataract Centre - Intra-ocular Lens Options.es, the final frontier in refractive surgery, presbyopiaPresbyopia is an age-related condition. As we age, the natural lenses in our eyes gradually become inelastic and lose their ability to focus on nearby objects and fine print. From the age of 40 it becomes increasingly noticeable and people often jokingly complain that their 'arms are getting too short'. See Info on Eyes – Optics and Refractive Errors - Presbyopia., is quickly coming within reach. A procedure coined PRELEX (presbyopic lens exchange) by Dr Charles Claoué in 1997, is well established over the past number of years. Here, the intra-ocular lens implanted following crystalline lens removal has multifocal properties or a truly accomodative ability. Dr Potgieter and colleagues are also working on a research project (of which he is the Principal Investigator) with the company PowerVisionPowerVision is a lens manufacturing company in the US that recently introduced a new and novel fluid-controlled intra-ocular lens. This lens has the potential to replace the natural lens of the eye that has become inelastic and thus renders the eye presbyopic. It has the ability to change shape and focus on near and distant objects, similar to the natural lens within the eye during the early years of life. from San Francisco in the US that aims at replacing the natural lens with an artificial lens, capable of maintaining the natural accommodation of the eye.
The indication for this treatment modality correspond to that of phakic lenses, namely patients with extreme pathological refractive errors. Should it be possible to exchange the natural lens with an artificial accomodative intra-ocular lens, this will be a significant breakthrough in the visual sciences, and will be the preferred treatment for presbyopia.
The advantages of PRELEX, is that it is much cheaper than a phakic lens placement, as well as the fact that the patient can never develop a cataract, since the natural lens (which forms the cataract) is replaced by an artificial lens. Since this procedure is identical to cataract surgery, please see Cataract Centre for further information.