Negative still rules
Negative still rules
The Tecnis aspheric lens Source: Abbott Medical Optics
The AcrySof aspheric lens Source: Alcon
The ReSTOR lens Source: Alcon
Aspheric IOLs remain popular choice among physicians
Despite the loss of the NTIOL (new technology IOL) Medicare reimbursement, negative aspheric IOLs are still a valuable offering in refractive cataract practices.
"I think it became the conventional wisdom at a certain point that aspheric lenses are superior, you get better image quality and better patient satisfaction, so especially for multifocal lenses, I think they made a huge improvement in results with the ReSTOR [Alcon, Fort Worth, Texas] in particular," said Mark Packer, M.D., clinical associate professor of ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland. He continued: "I think the market stayed there, but the prices fell in response to the loss of the new technology status. It may be that they didn't fall for hospital outpatient departments; they never got anything anyway. It's only surgery centers, but surgery centers are about two-thirds of the market for cataract surgery. I imagine that companies renegotiated because no one is going to take a loss on that."
Warren E. Hill, M.D., East Valley Ophthalmology, Mesa, Ariz., explained why negative spherical IOLs continue to be popular. The human cornea has positive spherical aberration, while normally, the natural lens has negative spherical aberration, and the two come close to cancelling each other out, he said. So when the natural lens is removed, the human optical system in the aphakic state has positive spherical aberration. If a spherical lens that also has positive spherical aberration is implanted, the magnitude of the zernike coefficient is increased and you lose contrast sensitivity, he said.
In small pupils like 3 mm it doesn't matter all that much, Dr. Hill said, but in a younger patient with larger pupils, if the spherical aberration is increased, you decrease the contrast and decrease visual quality. That's one instance where having an aspheric IOL that has negative spherical aberration is a real value, he said.
Another instance in which negative aspheric IOLs are valuable is if a patient has had a radial keratotomy or myopic LASIK; what that procedure does is flatten the central cornea, Dr. Hill said. The consequence of flattening the central cornea is that spherical aberration is increased. Again, if you put in a spherical IOL that further increases spherical aberration, you decrease visual quality because that zernike coefficient is going up, he explained.
"I proposed to some manufacturers that they create a special type of lens that has a high value for negative spherical aberration to help these patients who have had LASIK and radial keratotomy have a little better quality. If the spherical aberration is high, the visual quality is going to go down, and that's why a lot of people who've had RK [radial keratotomy] and LASIK have difficulties at night—the high spherical aberration value in addition to other things like coma, astigmatism, and trefoil. It really does have value," he said.
Li Wang, M.D., assistant professor of ophthalmology, Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, agreed. "Optically, the smaller the aberrations, the clearer the image, especially in those eyes with prior myopic LASIK or PRK [photorefractive keratectomy]; their corneas have more positive spherical aberration induced by the myopic LASIK or PRK procedures. In those eyes, the negative amount of asphericity in lenses is helpful to compensate for that higher amount of astigmatism," she said.
The proof is in night driving
Perhaps the best evidence of the superiority of aspheric lenses can be seen in the night driving simulation studies, Dr. Packer said. Following FDA clinical trials for the Tecnis aspheric lens (Abbott Medical Optics, AMO, Santa Ana, Calif.), it says specifically on the labeling that it makes the roads safer for patients who receive these lenses and for whom they share the road with—a pretty broad recommendation, Dr. Packer said.
More recently, in another night driving simulation conducted by Alcon at the University of Iowa, Iowa City, with the AcrySof aspheric, using the AcrySof spherical as a control, the former outperformed the latter and showed significant improvement in vision, Dr. Packer said.
"Contrast sensitivity testing generally correlates with those types of studies, but it's still a test that's performed in an exam room, it's not the real world. People don't look at contrast sensitivity gradings. In the real world, they're doing things like driving; if you can show that driving performance is enhanced by the use of an aspheric lens, that's the strongest argument by far to me."
Not suitable for everyone
While many can benefit from negative aspheric IOLs, they're not the best treatment for everyone. Y. Ralph Chu, M.D., clinical professor of ophthalmology, John A. Moran Eye Center, University of Utah, Salt Lake City, and medical director, Chu Vision Institute, Bloomington, Minn., said, "We learned in the past with the Tecnis lens that patients who've had hyperopic laser vision correction on their cornea of greater than +2 D, whether it's LASIK or PRK, are already inducing some negative spherical aberrations with that laser vision correction treatment. Those patients would probably do better with a non-aspheric lens."
Dr. Hill explained that hyperopic LASIK steepens the central cornea, and when the central cornea is steepened, the naturally occurring positive spherical aberration of the eye, which is about 0.27 microns, is reduced. Sometimes, with enough steepening of the central cornea, one can start out with the negative spherical aberration number and by adding a lens like the AcrySof IQ or the Tecnis that already has negative spherical aberration, you'll be doing the same thing as with a spherical IOL in the normal eye except in the opposite direction. Whether the spherical aberration number is positive or negative, if you have a lot of it, visual quality suffers, he said.
Other patients who wouldn't benefit from this lens are those who have naturally occurring very steep corneas as seen in high hyperopia and unusual corneas as in keratoconus, Dr. Hill said.
In addition, there've been some studies showing that if there's a chance that the lens will be significantly tilted or decentered by more than 1 mm or more than 14 degrees of tilt, perhaps a non-aspheric lens should be chosen, Dr. Chu said. However, those situations are pretty rare with modern cataract surgery, he added.
Dr. Hill said, "I implant lenses in commercial airline pilots, people who do a lot of flying, and there's no question in my mind that this is the lens that I would put in pilots."
Editors' note: Drs. Chu and Packer have financial interests with AMO. Dr. Hill has financial interests with Alcon. Dr. Wang has no financial interests related to this article.
Contact information
Chu: 612-232-2020, yrchu@chuvision.com
Hill: 480-981-6111, k7wx@earthlink.net
Packer: 541-687-2110, mpacker@finemd.com
Wang: 713-798-7946, liw@bcm.tmc.edu
by Enette Ngoei EyeWorld Contributing Editor
The Tecnis aspheric lens Source: Abbott Medical Optics
The AcrySof aspheric lens Source: Alcon
The ReSTOR lens Source: Alcon
Aspheric IOLs remain popular choice among physicians
Despite the loss of the NTIOL (new technology IOL) Medicare reimbursement, negative aspheric IOLs are still a valuable offering in refractive cataract practices.
"I think it became the conventional wisdom at a certain point that aspheric lenses are superior, you get better image quality and better patient satisfaction, so especially for multifocal lenses, I think they made a huge improvement in results with the ReSTOR [Alcon, Fort Worth, Texas] in particular," said Mark Packer, M.D., clinical associate professor of ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland. He continued: "I think the market stayed there, but the prices fell in response to the loss of the new technology status. It may be that they didn't fall for hospital outpatient departments; they never got anything anyway. It's only surgery centers, but surgery centers are about two-thirds of the market for cataract surgery. I imagine that companies renegotiated because no one is going to take a loss on that."
Warren E. Hill, M.D., East Valley Ophthalmology, Mesa, Ariz., explained why negative spherical IOLs continue to be popular. The human cornea has positive spherical aberration, while normally, the natural lens has negative spherical aberration, and the two come close to cancelling each other out, he said. So when the natural lens is removed, the human optical system in the aphakic state has positive spherical aberration. If a spherical lens that also has positive spherical aberration is implanted, the magnitude of the zernike coefficient is increased and you lose contrast sensitivity, he said.
In small pupils like 3 mm it doesn't matter all that much, Dr. Hill said, but in a younger patient with larger pupils, if the spherical aberration is increased, you decrease the contrast and decrease visual quality. That's one instance where having an aspheric IOL that has negative spherical aberration is a real value, he said.
Another instance in which negative aspheric IOLs are valuable is if a patient has had a radial keratotomy or myopic LASIK; what that procedure does is flatten the central cornea, Dr. Hill said. The consequence of flattening the central cornea is that spherical aberration is increased. Again, if you put in a spherical IOL that further increases spherical aberration, you decrease visual quality because that zernike coefficient is going up, he explained.
"I proposed to some manufacturers that they create a special type of lens that has a high value for negative spherical aberration to help these patients who have had LASIK and radial keratotomy have a little better quality. If the spherical aberration is high, the visual quality is going to go down, and that's why a lot of people who've had RK [radial keratotomy] and LASIK have difficulties at night—the high spherical aberration value in addition to other things like coma, astigmatism, and trefoil. It really does have value," he said.
Li Wang, M.D., assistant professor of ophthalmology, Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, agreed. "Optically, the smaller the aberrations, the clearer the image, especially in those eyes with prior myopic LASIK or PRK [photorefractive keratectomy]; their corneas have more positive spherical aberration induced by the myopic LASIK or PRK procedures. In those eyes, the negative amount of asphericity in lenses is helpful to compensate for that higher amount of astigmatism," she said.
The proof is in night driving
Perhaps the best evidence of the superiority of aspheric lenses can be seen in the night driving simulation studies, Dr. Packer said. Following FDA clinical trials for the Tecnis aspheric lens (Abbott Medical Optics, AMO, Santa Ana, Calif.), it says specifically on the labeling that it makes the roads safer for patients who receive these lenses and for whom they share the road with—a pretty broad recommendation, Dr. Packer said.
More recently, in another night driving simulation conducted by Alcon at the University of Iowa, Iowa City, with the AcrySof aspheric, using the AcrySof spherical as a control, the former outperformed the latter and showed significant improvement in vision, Dr. Packer said.
"Contrast sensitivity testing generally correlates with those types of studies, but it's still a test that's performed in an exam room, it's not the real world. People don't look at contrast sensitivity gradings. In the real world, they're doing things like driving; if you can show that driving performance is enhanced by the use of an aspheric lens, that's the strongest argument by far to me."
Not suitable for everyone
While many can benefit from negative aspheric IOLs, they're not the best treatment for everyone. Y. Ralph Chu, M.D., clinical professor of ophthalmology, John A. Moran Eye Center, University of Utah, Salt Lake City, and medical director, Chu Vision Institute, Bloomington, Minn., said, "We learned in the past with the Tecnis lens that patients who've had hyperopic laser vision correction on their cornea of greater than +2 D, whether it's LASIK or PRK, are already inducing some negative spherical aberrations with that laser vision correction treatment. Those patients would probably do better with a non-aspheric lens."
Dr. Hill explained that hyperopic LASIK steepens the central cornea, and when the central cornea is steepened, the naturally occurring positive spherical aberration of the eye, which is about 0.27 microns, is reduced. Sometimes, with enough steepening of the central cornea, one can start out with the negative spherical aberration number and by adding a lens like the AcrySof IQ or the Tecnis that already has negative spherical aberration, you'll be doing the same thing as with a spherical IOL in the normal eye except in the opposite direction. Whether the spherical aberration number is positive or negative, if you have a lot of it, visual quality suffers, he said.
Other patients who wouldn't benefit from this lens are those who have naturally occurring very steep corneas as seen in high hyperopia and unusual corneas as in keratoconus, Dr. Hill said.
In addition, there've been some studies showing that if there's a chance that the lens will be significantly tilted or decentered by more than 1 mm or more than 14 degrees of tilt, perhaps a non-aspheric lens should be chosen, Dr. Chu said. However, those situations are pretty rare with modern cataract surgery, he added.
Dr. Hill said, "I implant lenses in commercial airline pilots, people who do a lot of flying, and there's no question in my mind that this is the lens that I would put in pilots."
Editors' note: Drs. Chu and Packer have financial interests with AMO. Dr. Hill has financial interests with Alcon. Dr. Wang has no financial interests related to this article.
Contact information
Chu: 612-232-2020, yrchu@chuvision.com
Hill: 480-981-6111, k7wx@earthlink.net
Packer: 541-687-2110, mpacker@finemd.com
Wang: 713-798-7946, liw@bcm.tmc.edu
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