Scientific Design of the AcrySof IQ IOL
Details from the inventors of this aspheric IOL.
The AcrySof IQ IOL (Alcon Laboratories, Inc., Fort Worth, TX) (Figure 1) is designed to restore youthful vision to patients with cataracts. With its advanced biocompatible material and innovative design, this IOL not only reduces spherical and total higher-order aberrations, but it also increases mesopic contrast sensitivity and improves functional vision.1
A GOLDEN OPPORTUNITY
Many inventions are successful because they address needs and solve problems; this is the case with the AcrySof IQ IOL. The issue of higher-order aberrations and their effect on human vision has been extensively studied. Higher-order aberrations may provide some benefits, such as a natural defense against ocular chromatic aberrations2 and mitigation of image deterioration by myopic defocus.3 However, higher-order aberrations also degrade optical image quality.4,5 Due to its high refractive power, the cornea is a known primary contributor to higher-order aberrations.5,6 For instance, given a typical 6-mm pupillary diameter, the cornea contributes about +0.28 µm of spherical aberration,7 a larger portion than that of any other contributor. Through innovative IOL design and by capitalizing upon the proven platform of the AcrySof Natural Lens (Alcon Laboratories, Inc.), we had a golden opportunity to restore the spherical aberration found in a typical youthful eye to patients with cataracts.
PROVEN MATERIAL AND DESIGN
The single-piece AcrySof IQ IOL is composed of a high-refractive-index, soft, foldable, hydrophobic acrylic material. This acclaimed, highly successful material is biocompatible, has been used in IOLs for many years, and is appreciated for its foldability and low rate of posterior capsular opacification.8,9 Clinical studies assessing tilt and decentration have confirmed the stability of the single-piece platform.10,11 The AcrySof IQ IOL has ultraviolet and blue-light–filtering chromophores to reduce retinal exposure to blue light. Studies show that these properties do not adversely affect normal color vision.1,8 The supporting haptics of the AcrySof IQ IOL have a stable force modified-L design.1
RETURNING JUST THE RIGHT AMOUNT OF SPHERICAL ABERRATION
Based on our analysis of human corneal characteristics, we created a design that provides improved image quality. In the young eye, the cornea contributes positive spherical aberration, the crystalline lens contributes negative spherical aberration, and the overall spherical aberration of the eye is slightly positive. With age, physiologic changes occur in the crystalline lens that cause the overall spherical aberration of the eye to become more positive. When removing a cataract and implanting an IOL, there is an opportunity to provide an IOL that returns just the right amount of negative spherical aberration—an amount that is similar to that of a young, natural crystalline lens (Figure 2).
Many clinical studies that include young subjects have reported a modest amount of positive spherical aberration for the overall eye.7,12-14 The design of the AcrySof IQ IOL was based on spherical aberration measurements from multiple important clinical studies.6,7,13,15 Taken together, these studies revealed that the typical young human eye has an internal lens spherical aberration of -0.18 µm and that the crystalline lens is the primary contributor of negative spherical aberration. Thus, the AcrySof IQ IOL was designed with an IOL spherical aberration of -0.2 µm, providing implanted patients with a modest amount of residual spherical aberration (ie, ~ +0.1 µm at a 6-mm entrance pupil). This amount of spherical aberration is consistent with that found in young eyes at their peak visual performance,16 in US Navy pilots,17 and in a visual performance study that included young subjects.18
Providing just the right amount of spherical aberration is critical for successful patient outcomes. Our analysis of published spherical aberration measures and comparative computations indicate that the AcrySof IQ IOL provides 96% of patients (within ±2.00 standard deviation) with the spherical aberration typical of young eyes, whereas other aspheric IOLs can achieve this in only 85% (Tecnis [Advanced Medical Optics, Inc., Santa Ana, CA]) or 52% (SofPort AO [Bausch & Lomb, Rochester, NY]) of patients.
INNOVATIVE DESIGN OVERCOMES SURGICAL VARIABILITY
Design features of the AcrySof IQ IOL address surgical challenges such as achieving refractive predictability19 while minimizing the induction of astigmatism and higher-order aberrations. By reducing the variation of the effective lens position between lens powers, the AcrySof IQ IOL improves refractive predictability.19 With moderate surface asphericity, the AcrySof IQ IOL mitigates optical degradation caused by surgical misalignments such as lens decentration and lens tilt. Because of its central lens thickness of only about 0.6 mm for midpower lenses, the AcrySof IQ IOL can be delivered via small incisions, without altering the magnitude of corneal higher-order aberrations.20 In addition, the low rate of posterior capsular opacification of AcrySof IOLs has also been attributed to the AcrySof material and square-edge design.8,9
Numerous clinical studies have confirmed the benefits of the AcrySof IQ IOL's correction of spherical aberration. Compared with a spherical IOL, the AcrySof IQ IOL has demonstrated superior contrast sensitivity in mesopic conditions.21-23 The AcrySof IQ IOL has also shown a significantly superior reduction of spherical and total higher-order aberrations as well as significantly superior results with mesopic contrast sensitivity at 6 cpd with and without glare, compared with a spherical-control IOL 90 to 120 days after surgery.1 As part of this study, a subset of subjects underwent night-driving simulation testing and FACT contrast sensitivity testing. Those implanted with the AcrySof IQ IOL had significantly better functional outcomes under most conditions than those with spherical control IOLs.1 Beiko reported that targeting a residual spherical aberration of +0.1 µm following cataract surgery resulted in superior vision compared with targeting 0 µm.24 Eyes targeted for +0.1 µm spherical aberration had significantly better contrast sensitivity at 6 cpd and 12 cpd in both photopic (85 cd/m²) and mesopic (3 cd/m²) conditions.24 In another study, eyes implanted with AcrySof IQ IOLs achieved significantly higher contrast sensitivity results compared with eyes implanted with Tecnis or SofPort AO IOLs.25
PREFERRED BY PHYSICIANS AND PATIENTS
The proven material, innovative design, and asphericity of the AcrySof IQ IOL have become the preference of leading physicians9 and will be enjoyed by patients who want crisp, reliable vision. Since the introduction of the AcrySof IQ IOL in 2005, nearly 7.4 million of these lenses have been implanted worldwide.
The AcrySof IQ lens combines a proven design platform with aspheric properties to restore the spherical aberration of youthful eyes to cataract patients. Based on reduced spherical aberration, increased contrast sensitivity, and improved functional vision compared with traditional spherical designs, the AcrySof IQ lens is an excellent choice for cataract surgeons and their patients.
Xin Hong, PhD, is Manager, Optical Design, at Alcon Laboratories, Inc, Fort Worth, Texas. Dr. Hong may be reached at (817) 615-2589; Xin.Hong@AlconLabs.com.
Stephen J. Van Noy is Senior Director of Surgical Intraocular Lens Development at Alcon Laboratories, Inc, Fort Worth, Texas. Mr. Van Noy may be reached at (817) 568-6451; Steve.VanNoy@AlconLabs.com.
Dan Stanley is Associate Director, Product Development, Alcon Laboratories, Inc, Fort Worth, Texas. Mr. Stanley may be reached at (817) 568-6432; Daniel.Stanley@AlconLabs.com.
Xiaoxiao Zhang, PhD, is Director, Optics Research, Alcon Laboratories, Inc, Fort Worth, Texas. Dr. Zhang may be reached at (817) 615-2604; Xiaoxiao.Zhang@AlconLabs.com.
Mutlu Karakelle, PhD, is Vice President, Surgical Devices Research, Alcon Research Limited, Fort Worth, Texas. Dr. Karakelle may be reached at (817) 568-6457; Mutlu.Karakelle@AlconLabs.com.
The authors thank Jeannette Tomanka for her scientific writing assistance and Diane Houtman for her critical review and clinical expertise.
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