IRIS CLAW LENS

José Güell MD, Barcelona, Spain has chosen as the topic of his Ridley lecture a long-term assessment of the iris claw lens, the brainchild of the late Prof Jan Worst.

" It seems fitting to devote a lecture named after the first IOL designer to honour another who followed in the same pioneering tradition so admirably. I first became acquainted with Prof Worst’s fantastic idea of an iris claw IOL when it first became commercially available in 1987. I was still in my residency around that time I met with Prof Worst and we discussed a lot of fabulous projects. Since then I've been involved in the clinical evolution of this particular way of fixating the lens in several different projects.

The original PMMA lenses are still in use, but there have been many new versions of the lens for different indications, and composed of different materials and additional optical designs. In my lecture, I shall be reviewing the results achieved with these lenses in large international trials and also in my own extensive experience with the implants. Originally the iris claw implant was designed for use in aphakia and I began to use it for that purpose, especially in paediatric patients. That was because the lens had the advantage of needing only standard biometry for lens power calculation. It was also not necessary to calculate the angle-to-angle or the sulcus-to-sulcus diameters for the lens.

Because of its particular means of fixation to the peripheral iris, the lens can be implanted in any eye with sufficient iris to support it. In addition, the iris claw lenses tend to fare much better than angle-supported phakic lenses in terms of endothelial cell loss. Their location in the anterior chamber is almost on the same plane as the iris, which means there is a much greater distance between the optic and the endothelium.

These advantages have lent themselves well to other indications for iris claw lenses, with new optic designs and materials. Most especially there are the toric and non-toric myopic and hyperopic Artisan/Verisyse models for phakic ametropes. There are also flexible versions of the toric and non-toric lenses, called the Artiflex. There is also a multifocal version of the Artisan, although it is not in great demand due to shallower anterior chambers of presbyopes and the much shorter interval between implantation of the lens and cataract onset compared to the younger ametrope, although it might be an excellent option as a secondary explant for those who like multifocality in previous monofocal pseudophakes.

The edge of the myopic lens is thicker than that of the hyperopic model, but that is generally balanced by the larger anterior chambers of myopic eyes. Conversely, some of the advantage of the thinner edge of the hyperopic implant is lost through the shallower anterior chambers of hyperopic eyes. Moreover, in the aphakic eye, many surgeons are now implanting the iris claw lenses on the underside of the iris to enhance endothelial safety. Whichever implant you're using and however you’re implanting it, you should obtain accurate measurements of the anterior chamber anatomy with the modern imaging instruments, to judge whether there will be a safe distance between the endothelium and the lens. When you implant this kind of lens you should always advise your patients that they will require postoperative controls for the rest of their lives.

The anterior chamber in phakic eyes tends to gradually collapse as people age, bringing the lens closer to the endothelium than it was initially. Therefore, every one-to-three years they should undergo endothelial cell counts and optical coherence tomography anterior segment imagining. Over the years, iris claw lens design has proved very versatile and can provide a good option in some unusual and difficult situations. The aphakic lens can be useful as a primary procedure in eyes with congenital or post-traumatic subluxation, where capsular fixation is not possible. The phakic lenses can also be effective in paediatric patients with significant anisometropia, and in patients who for one reason or another cannot wear contact lenses.

One exciting possibility to emerge in recent years is using these these kind of implants in the management of a keratoconic eye after intracorneal ring implantation and/or collagen crosslinking. Also very promising is the recent development of iris claw lenses with optics composed of an acrylic material, which are likely to become commercially available late in 2016 or early in 2017. There will be both phakic and aphakic versions of the lens with the new material, so for the first time we will be able to implant the lens in paediatric and adult aphakes using a conventional small incision."

José Güell: guell@imo.es