High-Tech IOLs
Lighting the way toward the perfect vision your cataract patients demand.
BY LOUIS PILLA

ILLUSTRATION: JOHN SCHREINER

Combining many functions into one device is an almost inevitable result of technology advances. Witness the office devices that combine a fax, scanner, copier and printer in one system, or the cell phone that also links to the Web.

The same equation holds true for IOLs. Originally designed to correct for aphakia, IOLs today are also asked to correct astigmatism, for instance, or retard or prevent posterior capsular opacification (PCO). "We're well past the era where we're just taking out a diseased lens and putting in something to take its place," says Paul Ernest, M.D., TLC Eye Care of Michigan, Jackson, Mich.

Many of the IOLs that are currently creating a buzz offer high-tech, specialty features in the way of edge design, asphericity, UV-blocking, ultra thinness, multifocality, and accommodation. They're all producing good results, in general use or in trials, but also may entail some quality-of-vision trade-offs. In this article, we'll look at where we are on the road to the perfect IOL.

Fine-Tuning Multifocals

The only FDA-approved multifocal IOL, the Array from AMO, has provided excellent results, says Eugene, Ore.-based I. Howard Fine, M.D. But this distance-dominant silicone lens can lead to trouble with night driving because of halos.

Also, it can reduce nighttime contrast sensitivity by as much as 40%, says Mark Packer, M.D., who practices with Dr. Fine. They tend to steer away from the lens in patients concerned with halos or glare and in those who are demanding in their vision requirements, such as engineers or artists. What's more, the lens is designed for bilateral use, they said.

Currently Pfizer (Pharmacia) is beginning U.S. clinical investigations of a diffractive multifocal version of the Tecnis modified prolate IOL. Also on the horizon sits a multifocal from Alcon that may outpace current results, says Louis D. "Skip" Nichamin, M.D., medical director, Laurel Eye Clinic, Brookville, Pa. The AcrySof ReSTOR has a combined diffractive/refractive optic that allows for pseudoaccommodation. It may provide fewer unwanted images, specifically glare and halo, he notes.

Torics Taking the Next Step

Advances in toric IOLs are also under way. Dr. Ernest says that surgeons are already able to significantly reduce astigmatism of three-quarters of a diopter and higher. He's pleased by the concept behind the STAAR Toric, but not so thrilled with its tendency to rotate.

He described a toric lens from Alcon that is now in clinical trials. The single-piece acrylic has haptics joined to the optic with a knee that's extremely flexible, he says. All the capsular forces are exerted on haptics distal to the knee, causing no rotational torsion on the optic itself.

The acrylic material also tends to be more adherent to the capsule. "Once this lens is in position, it's there," Dr. Ernest maintains.

Squaring Off with PCO

We now have several IOLs with square edges, and the evidence shows that a square-edge design on the posterior surface creates a capsule-bending angle that retards or prevents migration of lens epithelial cells onto the posterior capsule.

For example, one of the many PCO studies presented at the recent ASCRS meeting was performed by William Fishkind, M.D., of Tucson Ariz. Seventy-five eyes of 50 patients were implanted with AMO's Sensar with OptiEdge IOLs, and 39 eyes of 39 patients were implanted with Sensar lenses without OptiEdge. After 11 months, patients in both groups had similar visual acuities and spherical equivalents; however, in the OptiEdge group, PCO and YAG laser rates were lower.

Lenses with truncated and/or square-round edges are also available from CIBA Vision, Alcon and Bausch & Lomb.

While square-edged lenses are helping to prevent PCO, they're also associated with undesirable optical effects, such as arcs, rings, halos and streaks, called dysphotopsia.

In one theory, dysphotopsia comes from obliquely incident light striking the square edge; in another, it's from nearly direct incident light bouncing off the retina and onto the back surface of the front curve of the lens. Most agree that both factors are significant, says Samuel Masket, M.D., Advanced Vision Care, Los Angeles.

Modifications of a double-square-edge design seem to retain PCO-retarding benefits as well as reduce dysphotopsia. Dr. Masket points to one example, the OptiEdge-enhanced lenses. The posterior axis has a vertical square edge, which goes to a sloping portion and then a round portion on the anterior edge. Ray tracing, says Dr. Masket, shows less dysphotopsia with that design.

But a big unanswered question remains, he said: whether there's an acceptable degree of dysphotopsia with the OptiEdge clinically, as opposed to in the lab. Unfortunately, no clinical means exists for objectively exploring this question.

In the future, Dr. Masket expects that "we'll have chemical or thermal or other means for destroying the lens epithelial cells; it won't be necessary to rely upon lens implant design to retard PCO." In that case, the optics will simply have to provide the best quality of vision.

Keeping Up with Microphaco

Dysphotopsia does not appear to be an issue with the microincision Ultra Choice 1.0 thin IOL from ThinOptX. The plate-haptic acrylic lens with fresnel-like optics can be rolled into a tiny cylinder to go through a 1.4-mm incision. After more than 2,000 implants in Europe, it shows no dysphotopsias, says Kenneth J. Hoffer, M.D., St. Mary's Eye Center, Santa Monica, Calif., and clinical professor of ophthalmology at UCLA's Jules Stein Eye Institute. This lens, he says, forces peripheral images back onto the macula, instead of displacing and spreading out the focal image, thereby eliminating spherical aberration. FDA trials should start in July, he noted.

Targeting Higher-Order Aberrations

Spherical aberration is reduced by another lens as well, the Tecnis from Pfizer (Pharmacia), says Dr. Packer. Unpublished data, he explains, show a virtual elimination of spherical aberration and positive results from a nighttime driving study. "The Tecnis showed significant advantages under a series of different conditions during night driving simulation as compared to a spherical IOL," according to Packer. "Reducing spherical aberration really does seem to improve our ability to see particularly at night with large pupils under difficult conditions."

With the Tecnis, it's been proved that "an aspheric design substantially improves contrast sensitivity in low-light conditions," says Randall Olson, M.D., John Moran presidential professor, chair of ophthalmology, and director of the John Moran Eye Center at the University of Utah School of Medicine in Salt Lake City. "That information is pretty unassailable at this point."

Also, patients experience no loss in depth of focus with the Tecnis. The depth of focus "is identical to the depth of focus of a standard spherical IOL," says Dr. Packer.

That the lens was created based on an average cornea also isn't of concern, he thinks. "At worst it's going to be essentially the same as a spherical IOL." Eventually, more than one size Tecnis may be available, "but for now everyone will have an advantage from this lens."

However, decentration does present an issue. While it's true that the majority of lenses haven't decentered more than 0.4 mm, Dr. Olson says he's interested in the number, not the mean. What's important, he notes, is what percent of people in a series of 100 are decentered from the visual axis more than 0.5 mm and 1 mm. Decentration of 0.5 mm won't cause much of a vision problem, but 1 mm would, he says.

If the Tecnis decenters by a half millimeter or tilts by 7 degrees, the benefit is lost, says Dr. Hoffer. If the lens position exceeds those limits, the result could be worse than if a regular lens had been used, he points out.

As far as patient selection, the Tecnis has no particular advantage for patients with pupils of 2.5 mm or less, says Dr. Packer. With pupils of that size, quality of vision is limited by diffraction, so correction of higher-order aberrations won't make much difference.

Also, the Tecnis is a monofocal lens, so it's not suitable for a patient who wants to try to achieve pseudoaccommodation. If the goal is not to wear reading glasses, then a multifocal or accommodative IOL is a better choice.

Another consideration: As a silicone lens, the Tecnis isn't suited for an eye that might have silicone oil in the vitreous cavity, says Dr. Packer, such as in patients with active diabetic retinopathy.

Does Blue Light Matter?

Another special IOL feature being studied is the filtering of a greater range of blue light. With a yellow chromophore in a 0.04% concentration, Alcon's Acrysof Natural was designed to provide filtration without altering color perception. The human lens, says Dr. Ernest, filters between 20% and 80% of everything above 400 nanometers up to 500 nanometers. The Acrysof Natural mimics that filtration.

The lens does not appear to adversely affect night vision. Furthermore, investigators have found no difference between the current Acrysof lens and Acrysof Natural in contrast sensitivity under both photopic and mesopic conditions.

But no consensus exists on whether providing this filtration helps prevent macular degeneration. Dr. Olson, for example, believes that the current epidemiological information doesn't support the thesis that light causes macular degeneration.

But if the thesis stands up, and the yellow tint doesn't affect vision quality or color discrimination, this could represent an important breakthrough, says Dr. Nichamin. His biggest concern remains performance in low-light.

Accommodatives Coming Soon

It's likely that C&C Vision's AT-45 CrystaLens will be the first accommodative IOL approved in the United States, while the HumanOptics Akkommodative 1CU lens has been implanted more often in Europe than here. The literature reports about 1.0 to 1.5 diopters of accommodation with the HumanOptics lens, says Dr. Fine. As for the CrystaLens, 100% of his patients are 20/30 without correction and J3 near and intermediate.

Overall, results with these lenses indicate that most patients attain little to modest accommodation that seems to last for several years, says Dr. Nichamin.

Increasing the amplitude of accommodation remains the challenge in accommodative IOLs, according to Dr. Packer. Axial movement alone isn't sufficient.

Another challenge: Having lenses that are stable enough when used for distance but still respond when the patient goes to read or perform near work, says Dr. Ernest. "We need a material that remains pliable enough that it will alter the lens shape and provide accommodation," he says. "But the material also needs to be stable enough so that it doesn't change all the time and cause unwanted visual problems."

Nevertheless, Dr. Nichamin says he believes many surgeons would embrace some form of accommodating IOL instead of a multifocal design.

Adjustable IOLs

An entirely new approach is playing out in an investigative IOL from Calhoun Vision. Using lasers, the surgeon can create more positive or negative power or toricity to fine-tune the IOL after it's been implanted, says Dr. Fine. "You can impose wavefront technology and also correct for corneal higher-order aberrations with such systems." Such a technique, holds Dr. Olson, would offer a refractive precision better than anything done in the cornea.

Also being tested: Post-implantation adjustability by microfluidic control. A laser would excite small actuators within the implant to allow fluid to move and reshape the lens.

Putting it All Together

Don't be surprised to see more lenses combine various technologies and specialty features. Alcon, for instance, has plans to combine blue blocker, diffractive multifocal and toric abilities, says Dr. Nichamin.

Clinicians, says Dr. Fine, will move away from the cornea and "into the lens where we can treat every component of a patient's refractive error, including presbyopia."

Louis Pilla (louispilla@comcast.net) is a freelance healthcare journalist based near Philadelphia, Pa.