Any time we can reduce optical aberrations during cataract surgery, it benefits the quality of vision we can offer the patient. Standard IOLs, however, add positive spherical aberration to the positive spherical aberration already found on the cornea and thereby decrease optical quality. Hence, it makes sense to choose an aspheric design with negative asphericity to minimize the total amount of spherical aberration of the eye. On the other hand, some surgeons raise the concern that aspheric IOLs may negatively impact a patient's depth of focus, therefore impairing intermediate or near UCVA.1,2 In this article, we discuss results of recent clinical studies and demonstrate that implanting an IOL with negative asphericity enhances postoperative quality of vision without impairing a patient's depth of focus.
Aspheric IOL designs have been shown to effectively reduce spherical aberration and significantly improve contrast sensitivity.3-5 Additionally, Bellucci et al3 found that BCVA was better in eyes implanted with an aspheric versus a conventional IOL with positive spherical aberration. We also have had positive results with aspheric IOLs. Previously, we compared the Tecnis Z9000 aspheric IOL (Advanced Medical Optics, Inc., Santa Ana, California) with the AcrySof SA60AT spherical IOL (Alcon Laboratories, Inc., Fort Worth, Texas).6 Across 52 patients, contrast sensitivity at 3 months was better at photopic and mesopic luminance levels with the aspheric IOL. Additionally, glare was not an issue at the mesopic level. Because the defocus curves of both IOLs were the same, there was no evidence to suggest that aspheric IOLs impair depth of focus (Figure 1).
More recently, we evaluated the Tecnis 1-Piece, which now features a one-piece design that increases the ease of implantation, to evaluate its aspheric design and how it correlates to patient benefits. The Tecnis 1-Piece meets the latest surgical requirements with the advantage of hydrophobic acrylic material suitable for small-incision implantation with an injector system, three-point fixation for stable centration, a 360¼ square-edge continuous barrier, and a frosted edge design for glare reduction. Most important, the aspheric design of the IOL aims to completely correct the total spherical aberration of the eye.
In this prospective study, 102 patients received the Tecnis 1-Piece. Because the benefit provided by an aspheric IOL may be more important under dim lighting,4 all results were measured at various pupil diameters. By measuring total spherical aberration and lower-order aberrations at the 3-, 4-, 5-, and 6-mm optical zones, we were able to determine that total spherical aberration was virtually zero in all patients at all optical zones (median, 0 ±0.02, 0 ±0.03, 0 ±0.06, and 0 ±0.08, respectively). We also evaluated contrast sensitivity and depth of focus with 3- and 5-mm pinholes, comparing the effect of different pupil sizes on spherical aberration and its effect on clinical performance. In both photopic and mesopic conditions, results were the same as we saw with the Tecnis Z9000. Contrast sensitivity values with the 3- and 5-mm pinholes were similar (Figure 2), and depth of focus remained the same in both groups. We also discovered that despite the myopic shift that tends to occur with implantation of a spherical IOL,4 no shift occurred when we implanted the Tecnis 1-Piece.
Improving optical quality is always important to the patient; however, it is probably most beneficial under low-light conditions. Because we are now treating younger patients who have higher demands and lead more active lifestyles, it is important to use an IOL with superior optical quality, especially under dim light conditions.
My goal with every surgery is to satisfy the patient; however, correcting sphere and cylinder is only half the battle. Optimizing asphericity, for both mesopic and photopic conditions, also contributes to optimal visual quality.
In addition to the excellent BCVA and contrast sensitivity provided by the aspheric profile of the Tecnis 1-Piece, this IOL also avoids the myopic shift at larger pupil diameters noticed after implantation of spherical IOL models. Therefore, I find the Tecnis 1-Piece an adequate choice for my patients. It provides them with good depth of focus and good visual quality in all lighting conditions.
Peter Szurman, MD, PhD, is the Vice Chairman of the University Eye Hospital, Center of Ophthalmology, Eberhard-Karls University, Tuebingen, Germany. Dr. Szurman states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +49 7071 29 84915; fax: +49 7071 29 4674; e-mail: Peter.Szurman@med.uni-tuebingen.de.
Katrin Petermeier, MD, practices with the University Eye Hospital, Eberhard-Karls University, Tuebingen, Germany.
- Bühren J, Kohnen T. Application of wavefront analysis in clinical and scientific settings. From irregular astigmatism to aberrations of a higher orer—part 1: basic principles. Ophthalmology. 2007;104:909-923.
- Rocha KN, Soriano ES, Chamon W, Chalita MR, Nosé W. Spherical aberration and depth of focus in eyes implanted with aspheric and spherical intraocular lenses: a prospective randomized study. Ophthalmology. 2007;114:2050-2054.
- Bellucci R, Scialdone A, Buratto L, et al. Visual acuity and contrast sensitivity comparison between Technis and AcrySof SA60AT intraocular lenses: A multicenter randomized study. J Cataract Refract Surg. 2005;31:712-717.
- Bellucci R, Morselli S, Piers P. Comparison of wavefront aberrations and optical quality of eyes implanted with five different intraocular lenses. J Refract Surg. 2004;20:297-306.
- Mester U, Dillinger P, Anterist N. Impact of a modified optic design on visual function: clinical comparitive study. J Cataract Refract Surg. 2003;29:652-660.
- Petermeier K, Szurman P. Comparison of visual acuity and contrast sensitivity between the Tecnis Z9000 and AcrySof SA60AT intraocular lenses. Paper presented at the: XXIII Congress of the ESCRS; September 8-13, 2006; London.