As you know, a number of factors affect a surgeon's choice of intraocular lens (IOL), including biocompatibility, glare, ease of insertion, centration, safety during the insertion process and reactivity if other procedures are performed later. Thanks to a good track record in most of these areas, acrylic IOLs have steadily increased in popularity.

At the same time, IOL preference is usually a trade-off: tolerating disadvantages in one area in order to gain advantages in another. Like silicone lenses, acrylic lenses aren't perfect. But new developments and refinements are addressing some of the concerns surgeons have had regarding these lenses.

To bring you up to date on some of the latest thinking about acrylic IOLs and insertion techniques, we interviewed three surgeons who work with the latest acrylic lenses: Stephen Lane, M.D., of Stillwater, Minn., Richard J. Mackool, M.D., who practices in Astoria, N.Y., and Harry Grabow, M.D., of Sarasota, Fla.

In search of a smaller incision�����������

All three surgeons were drawn to acrylic lenses because of some notable advantages of the material, especially in the area of biocompatibility. At the same time, the most notable disadvantages of acrylic lenses -- the need to enlarge the wound for insertion of the IOL following phaco, and problems with glare -- are slowly being addressed.

"The downside of acrylic IOLs is the need to enlarge the incision slightly for insertion, as compared to a silicone lens of the same optic diameter," explains Dr. Lane. "This means taking an extra step to enlarge the wound after you've performed the lens removal. I don't think this induces much more astigmatism, but for some surgeons, that extra step is a nuisance."

Three factors that may help to resolve this problem came up during the interviews:

�       Improvements in technology. Some of the latest injector system innovations from manufacturers are making it possible to use a smaller incision. "Allergan has gotten pretty close," observes Dr. Lane. "They've done an excellent job with their Sapphire delivery system for their new Sensar lens. It allows you to get a 6-mm lens through a 3.2- or 3.3-mm incision. But even so, you're going to have to open the wound up a little bit."

�       Choosing a larger optic. Despite the advantages of a 5.5-mm lens, including insertion through a smaller wound, Dr. Grabow doesn't believe this is a good trade-off. "Smaller lenses have some limitations as far as edge phenomena, especially when compared to a 6.0-mm lens. There are glare issues, and in cases of late decentration due to fibrosis of the capsule, the small optic will come into play, producing more symptoms than the larger optics."

�       Changes in technique. Dr. Mackool currently favors the new Alcon one-piece SA30AL AcrySof foldable IOL. Because both the optic and the haptics are made of acrylic, the haptics unfold much more slowly and uniformly than haptics made of polymethylmethacrylate (PMMA).
This makes it possible for Dr. Mackool to use a different insertion technique that permits a smaller incision. "When inserting other multi-piece acrylic lenses, you end up with a haptic headed in one direction and an optic headed in another. You have to have the tip of the cartridge all the way inside the eye to control the direction of the leading haptic.
"Because the new SA30 is a single-piece lens, it tends to exit from the cartridge in a single plane/uniplanar direction. As a result, only the leading edge of the cartridge needs to clear the internal incision to deliver the lens. So the incision can be 2 to 3 tenths of a millimeter smaller on the internal side."
Dr. Mackool concedes that this doesn't eliminate the extra step of altering the wound. "Because the cartridge still must go part of the way in, you do have to enlarge the external part of the incision slightly. I normally inject the SA30 through an external incision of about 3.2 or 3.3 mm. However, the internal incision remains small -- about 2.9 to 3.0 mm."
Dr. Mackool widens the external part of the wound using the same instrument that he uses to make the phaco incision -- a disposable metal keratome. "I use the tip to extend each side of the external incision a slight amount," he explains.
"I don't think you lose any sealing capacity when you enlarge the external incision in this manner," he adds. "It's the internal incision that's most important to wound sealing. And I don't think this has any effect on astigmatism."

Haptics, zonules and centration

All three surgeons spoke favorably about the new one-piece SA30AL lens, in part because of the malleability of the haptics. "The haptics, as they go in, provoke virtually no tension or trauma upon the zonule," says Dr. Mackool. "They also make it possible to position the lens in the recess of the capsular fornix, away from the incision. You can easily remove viscoelastic from behind it with any I/A tip; you can put the tip right behind the lens very easily because the lens is on the other side of the eye.

"When you're done removing the viscoelastic from the eye, you can gently massage the top of the lens and maneuver the optic into a central location. And despite the soft haptics, I've found these lenses to remain centered perfectly," he adds.

Dr. Grabow is also impressed by the SA30's softer haptics, although he doesn't consider the SA30 his IOL of choice. "I still reserve use of the SA30 for pseudo-exfoliation cases and eyes with a history of pars-plana vitrectomy or trauma -- in other words, any eye that has a weak zonule. It's also good if you've inadvertently created a tear in the posterior capsule when removing the cataract. It's a very safe lens to use.

"However, at the present time my standard lens is the AMO Sensar (AR40). The AMO Sapphire injector system is excellent, and I've had excellent results with the Sensar lens."

The end of glare?

Dr. Lane's experience with the SA30 was also positive. "The new one-piece lens is very malleable, very forgiving," he observes. "It's also eliminated some of the problems previous acrylic lenses have had with glare and reflections off the anterior surface of the lens because it's more of a true bi-convex optic, and it has a new satin-like finish on the haptic and optic edge. In more than 500 cases I've performed with this lens, no one has complained of glare."

Dr. Mackool agrees. "I haven't seen any glare or unwanted photic phenomena with this lens. That's been a welcome improvement in acrylic lens performance."

Dr. Grabow believes that the reduction in glare is at least partly the result of the way the edges of the optic are truncated, which may also reduce the posterior capsule opacification rate. "The edges of the optic aren't truncated at 90 degrees like some other lens optics are. The posterior edge of the optic is sharp and can act as a barrier to lens cell migration. However, the anterior edge appears somewhat rounded. The side view of the lens looks like a trapezoid. And the haptics have the same edge design as the optic.

"This should be a good thing," he concludes. "It should produce much less glare, and also act as a barrier, blocking the migration of lens epithelial cells."

Into the future

What does the future hold? "Right now, I think technology is moving in the direction of the acrylic lens," says Dr. Grabow. "However, I think this is just another step in our evolution toward better materials and better surgery. We may end up with something completely different.

"We're still looking at ways to completely retard epithelial cell growth. We're also looking at ways to inject the capsular bag with something that will not only retard epithelial cells, but will also accommodate, like the natural lens does in youth. This will make it possible to completely restore the eye to its full form and function.

"Of course, we're at the very beginning of that type of research. There's a lot more work to be done."

Haptics . . . and Macular Edema?

Dr. Richard Mackool's experience with the one-piece SA30AL acrylic lens from Alcon has led him to develop a theory about a possible connection between the impact of haptics and the occurrence of macular edema.

"I've been suspicious for a long time that some patients develop macular edema after surgery because of stiff haptics. Even though the haptics are within the capsule, they can push the capsule right up against the ciliary processes. This has been demonstrated in autopsy eyes.

"I think that in some eyes this compression can cause chronic low-grade inflammation of the ciliary body and macular edema.

"It may be that the SA30 lens, because of the softness of the haptics, eliminates the possibility of any pressure or compression on the ciliary processes through the capsular sac. We may see a significantly lower incidence of macular edema, all because the ciliary body doesn't know that this lens is in there."