Correcting near vision with an intraocular lens is one of the toughest challenges in refractive cataract surgery. While multifocal IOLs are often an excellent solution, they come with limitations such as reduced contrast sensitivity and night vision problems. For many cataract patients, an accommodating IOL is a promising alternative. As a monofocal lens, it focuses all available light to a single point, thereby addressing the issues seen with multifocal IOLs, while still providing improved near power. This is especially advantageous when any ocular pathology that affects vision is present, such as significant ocular surface disease, corneal dystrophies such as EBMD, macular pathologies or glaucoma.
And these lenses provide at least some accommodation, unlike standard IOLs. Due to anatomical differences, patients will experience varying amounts of accommodation: some may experience over two diopters of accommodation, but most will experience around 1.00D to 1.50D. In rare cases, a patient will experience little to none.
Crystalens (Bausch + Lomb)—the only accommodating IOL marketed in the US—has been available since 2003 and has seen several design updates. It’s a silicone elastomer-based plate haptic lens. Two hinged haptics allow the optic to vault with accommodation of the ciliary muscle, creating an accommodative effect on the visual system.
Implantation & Post-op Care
Surgical implantation of Crystalens is slightly different than a traditional IOL because of its design and larger size. A different injector is used to implant the lens through a slightly larger corneal incision. Although the rotational orientation of the Crystalens inside the eye does not matter, there is a toric version of the lens, Trulign (Bausch + Lomb), that requires on-axis rotation for astigmatism correction. In addition, the surgeon will typically spend extra time polishing the posterior capsular surface to prevent early postoperative capsular opacification. The lens will end up sitting in the capsular back, with the optic posterior to the two hinged plate haptics.
|A Crystalens in place. Its hinged plate haptics bend in response to ciliary contraction, mimicking accommodation.|
The accommodative effects of the lens are often not realized for several weeks to months after implantation, and patients should be counseled accordingly. The targeted refraction should be realized immediately, and postoperative management for the first several weeks is no different than a standard IOL.
There are some unique concerns with Crystalens that become significant several weeks post-op. These involve capsular contraction and opacification and can affect vision in several different ways. Any amount of capsular contraction can limit the movement of the lens and push it slightly anteriorly. This can result in limited accommodation and a slight myopic refractive shift. Both of these issues will resolve with capsular tension release provided by a YAG capsulotomy.
If the contraction is excessive or asymmetric, one of the bendable plate haptics can fold forward, leaving the lens tilted in the capsular bag. With one haptic folded anteriorly and one posteriorly, the lens will look like the letter Z in the bag, known as Z syndrome. Your first sign of this will be a refractive change and decreased uncorrected visual acuity several weeks after surgery. Refractive errors will often mimic crossed cylinder effects and give you hyperopic refractions with roughly double the amount of cylinder. This complication should be addressed in a timely manner and, again, is often alleviated with a simple YAG capsulotomy. Z syndromes are rare, but do need to be ruled out for any Crystalens patient who has a refractive shift.Because capsular contraction can occur in the peripheral part of the capsular bag, it is important to dilate any Crystalens patient who is not achieving expected results. Dilation can be considered as soon as several weeks post-op, but is usually not necessary for at least a month. Luckily, most Crystalens complications are temporary and easily alleviated with a YAG capsulotomy. Think YAG early and often to keep these patients happy.