IOL selection can affect retinal visualization
The modified optical curvatures of aspheric IOLs may help improve retinal imaging.
by Robert M . Kershner , MD , MS , FACS
Special to Ocular Surgery News
Some cataract patients, those with age-related macular degeneration, diabetes and high myopia, ultimately end up in the hands of the retinal surgeon. Diabetics who require panretinal photocoagulation therapy, high myopes who are at an increased risk of retinal detachment, those with posterior vitreous separation who develop retinal tear and those with AMD should be carefully screened for the type of IOL used. High-risk retinal patients will be better served if the style of the lens implant does not impede subsequent visualization of the fundus or prevent successful retinal surgery. What if the IOL actually improved retinal imaging?
Retinal surgeons used to be disturbed with the results of cataract surgery because of the possibility of interference with visualization of the fundus. Cataract surgeons have finally mastered the ability to minimize posterior capsular opacification (or more appropriately, intercapsular opacification or ICO, as referred to by David Apple, MD). Hydrodissection and capsular irrigation techniques have reduced the incidence of ICO. To further enhance our ability to deliver a post-cataract eye with clear vision and a clear capsule, IOL manufacturers have addressed lens materials, reconstructed the optic-haptic junction and adjusted optic design to reduce the incidence of ICO. Recent results have reflected the good outcomes achieved while maintaining capsule clarity with these new lens designs. Patients see out through these news lenses better than ever before, but what about our ability to see in?
Most of our retinal colleagues won't find fault with the results of today's cataract surgery. However, if we could go beyond today's retinal visualization standard and improve upon imaging within the eye, shouldn't we? When we first learned to visualize the retina with an indirect ophthalmoscope, we were told to select an aspheric 20 D handheld lens that would enhance imaging of the peripheral retina without the distortion that would come from a spherical lens. But for almost 50 years we have never applied the same logic to the lens replacement we chose for the cataract patient. Why have we consistently been using spherical IOLs to correct aspheric eyes?
Ophthalmic surgeons do a terrific job of improving upon visual acuity with lens implant surgery. Only recently, however, have we discovered that that may not be enough. There has been a lot of interest lately in developing IOLs with modified optical curvatures that would negate the spherical aberration contributed by the cornea. There are at least three IOLs with advanced optic designs to do that the AcrySof aspheric optic SN50WF higher-order aberrations IOL (Alcon Surgical), the aberration-free aspheric SofPort AO IOL (Bausch & Lomb) and a modified prolate anterior surface IOL designed to neutralize 100% of corneal spherical aberration in over 96% of the population with a nonmodified average corneal curvature, the Tecnis (Advanced Medical Optics).
The acrylate methacrylate copolymer AcrySof aspheric IOL with blue-light filtering material offers a posterior aspheric surface to reduce spherical aberration. The silicone SofPort AO IOL offers an aspheric anterior and posterior surface, as well as uniform power from the center to the edge of the optic. This IOL is aberration-free, which the manufacturer states may provide improved vision for patients who have limited positive spherical aberration in their eyes due to natural causes or as the result of previous hyperopic refractive correction procedures. If the aberration-free SofPort AO is decentered in the eye, it is designed not to induce coma or astigmatism, which could occur with other aspheric IOLs if they are decentered after implantation. The measurement of the asphericity of the average cornea (Q-value) is –0.26 (a perfect sphere with no spherical aberration would be –0.52). Using this as the eye model, the AcrySof IOL is expected to reduce the corneal spherical aberration in an average eye about 50% and the SofPort AO about 10%. These results are based upon studies of the modulation transfer function (MTF) over a series of spatial frequencies for each of the IOLs. The SofPort AO IOL demonstrates an MTF curve comparable to the 911A IOL (AMO), a similarly designed IOL to the Tecnis but without the modified prolate optic. Further clinical studies are necessary to see how the optics of these new IOLs may affect visual quality for the patient.
In clinical studies that I performed comparing the Tecnis IOL with conventional spherical silicone and acrylic IOLs, the Tecnis was shown to have significantly better uncorrected visual acuity and improved functional vision during the day, daytime with glare and particularly at night when one would expect a dilated pupil to degrade night driving performance. It is this latter finding that raises an interesting issue. In fact, the FDA just awarded the Tecnis IOL NTIOL status. Not only does this allow increased reimbursement for using this IOL, but the FDA ruling solidifies the body of data that demonstrates superior performance and increased functional vision. If we can alter the optics of the human eye to improve visual acuity, especially in the dark, why don't we do the same to improve retinal imaging?
In my study, I compared the digital retinal images taken through the cataract preoperatively and at 1 month postoperatively after IOL implantation. The Tecnis lens provided significant improvement in retinal image contrast compared to the other IOLs. The luminosity profile of the retinal images, similar to the improved contrast perception seen by the patients, was improved by 38.5%. Our ability to look into, visualize and record the retina was superior after implantation of the Tecnis IOL in every case. There has never been a single study published that demonstrates improved retinal imaging with IOL implantation alone.
In patients who are about to undergo treatments such as photodynamic therapy with verteporfin (Visudyne, Novartis Pharmaceuticals), intravitreal injection of pegaptanib sodium (Macugen, Pfizer/OSI) or triamcinolone acetonide, the need for providing better retinal imaging cannot be overstated.
For Your Information:
Robert M. Kershner, MD, MS, FACS , is president of Eye Laser Consulting in Boston and clinical professor of ophthalmology at the John A. Moran Eye Center of the University of Utah School of Medicine, Salt Lake City. He can be reached at firstname.lastname@example.org. Dr. Kershner has no proprietary or financial interest in any of the devices or techniques described in this article.
n Advanced Medical Optics, maker of the Tecnis IOL , can be reached at 1700 E. St. Andrew Place, Santa Ana, CA 92799; 714-247-8200; Web site: www.amo-inc.com. Alcon, maker of the AcrySof IOL , can be reached at 6201 South Freeway, Fort Worth, TX 76134; 817-293-0450; fax: 817-568-6142; Web site: www.alconlabs.com. Bausch & Lomb, maker of the SofPort AO IOL , can be reached at 180 Via Verde, San Dimas, CA 91773; 909-971-5100; fax: 800-362-7006; Web site: www.bausch.com.
Kershner RM. Retinal image contrast and functional visual performance with aspheric, silicone, and acrylic intraocular lenses. Prospective evaluation. J Cataract Refract Surg . 2003;29(9):1684-1694.
Kershner RM. Should retinal surgeons influence the selection of intraocular lens implants? Retinal Physician . 2005;2(3):58-60.
Chu, I. Ralph, Studies A comparison the modulation transfer function of each of three aspheric IOLs (in review-unpublished results)