Nick Mamalis
Modern cataract surgery has evolved tremendously over the past 40 years. Through the advent of small incision phacoemulsification with foldable intraocular lenses (IOLs), we are now able to provide excellent refractive results. Further progress includes the expansion of different premium IOLs that attempt to provide adequate near and intermediate vision following cataract surgery; these lenses were first developed in different varieties of multifocal designs to solve the problem of accommodation. There have also been various extended depth of focus lenses, designed to minimize the visual side effects associated with multifocal lenses, such as glare and dysphotopsias. Alternatively, other lenses have tried to change the anterior curvature of the IOL to provide an extended depth of focus. The definitive issue with current lenses, however, is the persistent lack of accommodation and clear near vision with standard IOLs.
The holy grail of cataract surgery is a lens that provides true accommodation. Such a lens would allow focus at distance, intermediate, and near, without the potential visual issues noted with multifocal type lenses. Our initial attempts at accommodative lenses were done using a dual optic system, which had an anterior lens optic, with a high positive power, and a posterior optic with a variable negative power connected with thin struts. Alongside ciliary muscle contraction, there would be a forward displacement of the anterior optic that could allow for clear near vision. “Could” is an important word in this case, but with relaxation of the ciliary muscle, the two lenses would – in theory – come closer together and provide distance vision. However, these types of lenses are no longer available on the market.
A different way of trying to provide accommodation is with a lens that has a large optic component with a liquid material inside, as well as communication with the haptic elements. The ciliary muscle exerts accommodative forces through the zonules to the capsular bag, altering the curvature of the front surface of the lens and thereby changing its optic power. This process involves fluid moving from the haptics to the optic unit of the lens, adjusting the curvature of the anterior optic component to achieve true accommodation. To date, there have been several different variations of a fluid driven IOL using different materials that flow from the haptics into the optic to change the anterior optic curvature. Many of these lenses are still in the early design phases or early evaluation in animal models, but a number of them have progressed to clinical studies in humans.
In addition to a single-piece accommodating IOL, research is also being conducted on a modular or adjustable accommodating lens. Various studies have even explored lenses featuring a fluid-filled accommodating base with a secondary optic unit clipped to the base. The advantage of this approach is that the power of the IOL can be adjusted postoperatively by removing the optic component and replacing it with a different lens. This then allows for the exchanging of the IOL optic component without disturbing the base unit, which would be well-fixated within the capsular bag. Moreover, these lenses would also have the advantage of providing accommodation, along with the idea of a modular or adjustable IOL.
One example of such a lens is the Juvene modular fluid optic IOL, which functions similarly to the natural crystalline lens in the human eye. As the ciliary muscle contracts, the zonules relax and allow the capsule to move inward. This, in turn, changes the curvature of the fluid lens optic and brings increased power with accommodation. When the ciliary muscle relaxes and the zonules tighten, the fluid lens optic will then flatten out on the surface to bring clearer distant vision. This lens has been studied in the “Grail Study,” which involves placement of the accommodating lens into the eyes of human patients with follow up for the six months after cataract surgery. The study was able to document significant intermediate and near vision in these patients with defocus curves. In addition, there were no significant complications related to the lens and there was a pristine posterior capsule with no sign of posterior capsule opacification in any of these lenses.
Who knows which of these technologies will be first past the post, but I can say with certainty that a truly accommodating IOL – one that provides clear distance, intermediate and near vision without visual aberrations – would be a fantastic addition to the cataract surgeon’s armamentarium and a clear win for the patient.
