Accommodative IOLs: Feasible?
Accommodation of the human eye is a complex mechanism based on multiple anatomical and physiological variables. The anatomy concerns the ciliary body, zonular fibres, lens capsule and, finally, crystalline lens content. Also, anatomical changes that happen in the anterior segment of the eye over time play a sure role in the changes that happen in the human eye over our lives.
The loss of accommodation, presbyopia, is one of the holy grails in ophthalmology. Although most of the problems concerning the correction of myopia, hyperopia, astigmatism and even irregular corneas are being overcome by refractive surgery, presbyopia remains a challenge. Presbyopia is today compensated for by monovision, intracorneal inlays (less successful now), multifocal intraocular lenses (IOLs) and pseudophakia, and new phakic IOL designs have recently been announced [Ideally, a reference would be included]. All these methods should be considered as compensation for presbyopia rather than treatment, as none restores accommodation.
This is the moment when accommodative IOLs appear. It is clear that the crystalline lens is mainly responsible for presbyopia, so the treatment of presbyopia should be based on the restoration of the function of the lens concerning variable focusing capabilities. Accommodating IOL have been tried in the past with negative results.
Very controversial reports, which are still ongoing, suggest that some models (e.g., Crystalens) are being used as accommodative IOLs, while many other reports and clinical evidence demonstrate that the changes in the focusing capabilities related to the ciliary body action are minimal or even absent. Accommodation is a change in the optical power of the eye related to ciliary body action. This excludes pseudoaccommodation related to changes in the aberrometry profile of any optical element of the eye and multifocality. Therefore, any accommodative lens has to demonstrate that it changes the power of the eye according to ciliary body action.
The failures of the past accommodative IOL have been based on their intrasacular use.
The implantation in the capsular bag has been demonstrated by our group not to offer a reliable place for an accommodative lens as, 6 months after the implantation of a measuring device inside the capsular bag, this is completely blocked. By contrast, sulcus implantation of an accommodative lens could work, as has been investigated by the Nulens project and, more recently, the Akkolens Lumina project. Recent evidence has demonstrated real changes in the optical power of the eye related to ciliary body action variable distances of focusing with the Lumina. In the last report the comparison with a young control group of 30 years of age demonstrates that accommodation is accomplished partially but effectively.
This lens is at present being implanted multicentrically in Europe and very soon in other countries in order to obtain the final proof that accommodation can be restored with a sulcus implanted IOL. The Lumina lens, based on the Alvarez principle, is unique in its design and
its anatomic location. The surgery is practically the same as that of a normal lens and safety issues have been cleared with over 10 years of observation of the initial control group.
The studies demonstrate that accomadative IOLs are feasible and that the design works, although long-term multicentric studies are necessary to validate its clinical indication and use.
The future of accommodative IOLs is positive. In particular, the Lumina lens still survives out of the many that have been proposed, and will hopefully benefit patients in the near future.
