As many cataract surgery experts contend, the success of micro phaco will depend on the development of an intraocular lens that can be placed through a 1.5-mm incision. The ThinLens from ThinOptx (Abingdon, Va.), which is currently available in Europe and most of Asia, is one of the newer lenses that's allowing surgeons to make strides toward this goal. The lens could eventually come to the United States in about two years, according to the company. Here is an update.
The ThinLens is an acrylic lens that is between 350 and 500-µm thick at the optic (between half and a third of the thickness of a conventional IOL) and 100-µm thick at the haptic. This thin profile allows it to be rolled tightly into an injector and put through an incision of around 1.5 mm. The surgeon inserts the lens into the anterior chamber, where it unrolls. Then, he floats it down into the bag.
|The lens is inserted in the anterior chamber, then situated in the bag.|
Alicante, Spain's Jorge Alio, MD, PhD, has implanted about 200 of the lenses in his micro-incision cataract surgery (MICS) procedure. "The quality of vision [with the lens] is comparable to the Alcon AcrySof lens, which is considered one of the best in terms of quality of vision," he says. However, he says there's also a benefit to using MICS, which the lens allows. "I think regular phaco induces vectorial changes in astigmatism that are significantly larger than in MICS. Second, I've consistently found that MICS reduces the total phaco power and effective phaco time that I use in cataract surgery, so it's more efficient. Using a lens that can go through a 1.5 or even 1.2-mm incision means you don't have to enlarge the incision to implant the lens."
The main complications in a small, 50-patient study of Dr. Alio's earlier cases are inverted implantations (4 percent) and posterior capsular opacification (4 percent). The incidence of these complications has decreased as he's become more proficient with the lens, he says.
"The lens is ultra-thin, and looks very similar if it's upside down or normal," says Dr. Alio. "So, it's possible to invert it. If it's upside down, halos, glare and visual disability occur. To make sure you're implanting it correctly, you have to look at the tiny holes at the ends of the haptics and make sure they're oriented properly. Second, you have to make sure no viscoelastic is left behind the lens. To enable this, it's necessary to make a larger capsulorhexis than is usually used in cataract surgery, 6 mm if possible. Then, the lens enters the bag and is controlled in a much better way during the maneuvers you use to take out the viscoelastic." Finally, the surgeon also has to assure the haptic tips aren't folded incorrectly behind the lens, which can lead to malpositioning.
"As the lens goes into the posterior capsule, it curls, and that curling effect sizes the lens in the capsule," explains Wayne Callahan, ThinOptx president. "Some of the doctors have found that curling to be a little difficult to accomplish, but when they do it properly, the lens works well. So, we're going to introduce a model of the lens with a little bit different haptic configuration that will allow it to stretch out in the capsule without the surgeon having to worry about it."