Can an Aspheric IOL Improve Visual Performance?

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In 2002, the FDA approved the Tecnis Z-9000 lens (Pfizer Inc., New York, NY), which features an anterior, modified prolate, aspheric surface. The aim of the IOL's design is to restore the balance between the positive spherical aberration of the cornea and the negative spherical aberration of the youthful crystalline lens that is lost upon the development of a cataract. At the ASCRS annual meeting in San Francisco in April 2003, I presented the results of my study to determine whether the aspheric optic of the Tecnis lens can improve retinal image contrast and functional visual performance.1

METHODOLOGY
For the prospective study, 221 eyes of 156 patients were randomized to receive either the STAAR AA4207-VF silicone IOL (STAAR Surgical Company, Monrovia, CA), an Alcon SA60AT acrylic IOL (Alcon Laboratories, Inc., Fort Worth, TX), or a three-piece Tecnis IOL. I performed all of the lens extractions and IOL implantations. Observers and I collected data while blinded as to IOL identity, and we followed subjects for 6 months. We measured patients' visual acuity preoperatively and at 1 day, 1 week, 3 weeks, 1 month, 3 months, and 6 months postoperatively. We performed fundus photography and functional acuity contrast testing under photopic and mesopic conditions preoperatively and at 3 months postoperatively. I analyzed the photographs via Adobe Photoshop 7.0 image software (Adobe Systems Incorporated, San Jose, CA) using the L*a*b color model,2 an international standard for color measurement designed to be consistent no matter which device is used to produce the image.

RESULTS

No surgical or postoperative complications occurred during the course of this study. Thirty-one patients (7%) experienced a rise in postoperative IOP (>24 mm Hg) that was unassociated with lens style. The increase in pressure resolved with the release of aqueous and the application of one drop of 0.5% Timolol (Merck and Co., Inc., West Point, PA) to achieve IOPs below 18 mm Hg. The YAG capsulotomy rate at 6 months was 0.9% for the silicone group and 0% for the aspheric and acrylic groups.

I found no statistically significant difference between subject groups in spherical, astigmatic refractive error or BCVA, pre- and postoperatively. Patients who received the aspheric IOL, however, achieved the best UCVA during the first postoperative month. Under photopic conditions, they demonstrated a 38% to 47% increase in contrast sensitivity, whereas I found little difference in contrast sensitivity under these lighting conditions between the preoperative cataract, silicone, and acrylic IOL groups. The aspheric IOL also performed best under mesopic conditions (an improvement of 9% to 100% vs 25% to 50% in the acrylic group and 0% in the silicone group) (Figure 1). Subjects who received the spherical silicone IOL experienced no increase in contrast sensitivity as compared with preoperative cataract levels. My digital analysis of retinal imaging showed an increase in threshold luminance levels in the aspheric group, as well as in image contrast, when compared with the preoperative cataract, silicone, and acrylic groups (Figure 2).

At the 1-month visit, the UCVA of subjects who received acrylic IOLs matched that of those who received the aspheric IOL. A statistically significant difference in UCVA continued after the 3- to 6-month visits, however, between the aspheric group (20/25 ±2) and the silicone (20/36 ±1) and acrylic (20/30 ±1) groups (results at 6 months). This difference could not be explained on the basis of pre-existing or postoperative refractive error.

CONCLUSIONS
All three IOLs improved patients' UCVA after cataract surgery, but the greatest improvement occurred in the aspheric group during the first month. Patients who received the silicone IOL did not demonstrate improved contrast testing despite an improvement in visual acuity. The acrylic IOL improved patients' contrast testing under some lighting levels when compared with preoperative levels, but the increased values were significantly less than those experienced by subjects who received aspheric IOLs. Although the clarity of the retinal imaging improved in all subject groups when compared with the preoperative images, the retinal image contrast markedly improved in the patients who received aspheric IOLs as compared with those who received either silicone or acrylic IOLs (Figure 3).

These data demonstrate that implanting the aspheric IOL significantly enhances patients' objective retinal image contrast and functional visual performance. This lens technology may represent a new standard in IOL visual quality.

Robert M. Kershner, MD, FACS, is Director of the Eye Laser Center in Tucson, Arizona, and Clinical Professor of Ophthalmology at the Moran Eye Center, University of Utah School of Medicine, Salt Lake City. He has no proprietary or financial interest in the products described herein . Dr. Kershner may be reached at (520) 797-2020; kershner@eyelasercenter.com.
1. Kershner RM. A prospective evaluation of aspheric (Tecnis), silicone, and acrylic IOLs on retinal image contrast and functional visual performance. J Cataract Refract Surg. In press.
2. Adobe Systems Incorporated. Adobe Photoshop Users Manual. San Jose, CA; 2002.