Aspheric Multifocal Intraocular Lens

Abstract

Although many studies have demonstrated that the AcrySof ReSTOR SN6AD1 intraocular lenses (IOLs) with a near add of +3.00 diopter (D) can yield a full range of visual outcomes, especially intermediate visual outcomes,1Kohnen T. Nuijts R. Levy P. et al.Visual function after bilateral implantation of apodized diffractive aspheric multifocal intraocular lenses with a +3.0 D addition.J Cataract Refract Surg. 2009; 35: 2062-2069Abstract Full Text Full Text PDF PubMed Scopus (116) Google Scholar it is still of interest to evaluate visual function and possible adverse effects of the +3D IOL. Thus, we sought to investigate the optical quality of eyes implanted with the +3D IOL compared with a standard aspheric monofocal IOL, and analyzed specific indicators of optical quality—intraocular straylight, wavefront aberration, and contrast sensitivity (CS). This prospective pilot study enrolled 44 eyes of 22 patients who underwent phacoemulsification and bilateral implantation of the AcrySof ReSTOR SN6AD1 IOLs (the multifocal IOL group), and 44 eyes of 22 patients implanted with the AcrySof IQ SN60WF IOLs (the monofocal IOL group) (both IOLs, Alcon Inc). The protocol was approved by the institutional review board. Patients characteristics were evaluated preoperatively and postoperatively (Table 1, available at http://aaojournal.org). Uncorrected and distance-corrected intermediate visual acuity (UIVA and DCIVA), intraocular straylight (C-Quant straylight meter, Oculus, Germany), wavefront aberrations for 5.0 and 6.0 mm pupils (OPD-Scan, NIDEK, Japan), CS under photopic and mesopic conditions, and visual function index-14 (VF-14) without spectacles was performed at 6-month follow-up intervals. Continuous variables were calculated using the Mann-Whitney U test. The +3D IOL group showed significantly better binocular and monocular UIVA and DCIVA at 50 and 60 cm, compared with the IQ IOL group (P<0.05) (Table 2, available at http://aaojournal.org). Intraocular straylight was significantly higher for the +3D IOL group (1.26±0.21) than that for the IQ group (1.14±0.25) at 6-month follow-up (P = 0.011). There were no significant differences in total, higher-order, spherical, and coma aberrations for 5.0 and 6.0 mm pupils (P>0.10) (Figure 1, Figure 2, available at http://aaojournal.org). Contrast sensitivity at 1.5 and 3 cycles per degree (cpd) under photopic conditions were significantly different between the 2 groups; no differences were found under mesopic conditions (Figure 3, Figure 4, available at http://aaojournal.org). VF-14 was significantly higher for the +3D IOL than that for the IQ IOL (89.52±4.87 vs 86.63±7.60, P = 0.014). The AcrySof ReSTOR SN6AD1 IOL was designed to increase the range of focus, and thus to provide sufficient intermediate visual acuities. However, due to imperfections of the optical media, intraocular straylight results in dispersion of light entering the eyes to places other than the focal spot in the retina, thus decreasing the visual quality. This phenomenon may be associated with blindness at night, especially glare or halos, and correspond to disability glare.2Elliott D.B. Bullimore M.A. Assessing the reliability, discriminative ability, and validity of disability glare tests.Invest Ophthalmol Vis Sci. 1993; 34: 108-119PubMed Google Scholar The +3D IOL divides the amount of light energy over bifocal points simultaneously to yield focused images of near and far objects, rather than to 1 of the 2 focal points. Thus, intraocular straylight is expected to be higher with refractive-diffractive multifocal IOLs. Apodization could provide a smooth transition of the distribution of light energy to distance-dominant vision and perform as an aspheric surface to progressively decrease the height of the diffractive steps from the center to the periphery, thus, in our study, compared with the AcrySof IQ IOL, the AcrySof ReSTOR SN6AD1 IOL showed similar total aberrations, higher-order aberrations (HOAs), and spherical aberration with 5.0 and 6.0 mm pupils. Under photopic conditions, lower CS at 1.5 and 3 cpd could be interpreted to mean that CS at low spatial frequencies is influenced by light scatter, however, CS at high spatial frequencies is mainly related to optical blur (defocus and aberrations);3Montes-Mico R. Charman W.N. Choice of spatial frequency for contrast sensitivity evaluation after corneal refractive surgery.J Refract Surg. 2001; 17: 646-651PubMed Google Scholar while under mesopic conditions, as the pupil enlarges, 84% of the light focuses to the distance power,4Davison J. Simpson M. History and development of the apodized diffractive intraocular lens.J Cataract Refract Surg. 2006; 32: 849-858Abstract Full Text Full Text PDF PubMed Scopus (235) Google Scholar therefore, the +3D IOL theoretically behaves similar as a monofocal IOL for distance vision, causing little loss in contrast sensitivity and minimal visual phenomena. Quality of life was evaluated by VF-14. Although glare and halos related to intraocular straylight typically are the main problems after implantation of multifocal IOLs, patient satisfaction of vision for the +3D IOL was high. In summary, bilateral implantation of apodized aspheric diffractive multifocal IOLs with +3D add power provided patients with greater visual function at intermediate distance without compromising wavefront aberrations, especially spherical aberrations, and CS in mesopic conditions, compared with a standard aspheric monofocal IOL. Increased intraocular straylight, and mildly decreased CS in photopic conditions were found. Considering the minimal adverse effects of the +3D IOL, it is likely that the IOL of aspheric apodization design and lower add power provide excellent daily-living visual function for patients. Table 1Patient CharacteristicsCharacteristicsMultifocal IOL GroupMonofocal IOL GroupP Value⁎Mann-Whiney U test, chi-square tests were used for categorical variables.No. of patients2222—No. of eyes (n)4444—Mean age (y)63.22 ± 7.2362.68 ± 10.790.925Sex (male/female)9/1310/220.879Mean IOL power (D)21.84 ± 3.0821.45 ± 4.480.764Mean axial length (mm)23.64 ± 2.7423.77 ± 2.950.854Mean sphere (D) Preoperative0.19 ± 1.46−0.15 ± 1.350.226 Postoperative−0.02 ± 0.23−0.07 ± 0.290.333Mean keratometric cylinder (D) Preoperative−0.45 ± 0.51−0.41 ± 0.580.835 Postoperative−0.33 ± 0.29−0.22 ± 0.260.052D = diopters; IOL = intraocular lens; SE = spherical equivalent.Data are mean ± standard deviation unless otherwise indicated. Mann-Whiney U test, chi-square tests were used for categorical variables. Open table in a new tab Table 2Postoperative Distance, Intermediate, and Near Visual AcuitiesParameterMean VA (LogMAR) ± SDP Value⁎Mann-Whiney U test.Multifocal IOL GroupMonofocal IOL GroupIntermediate (70 cm) Binocular UIVA0.19 ± 0.120.16 ± 0.100.511 Binocular DCIVA0.20 ± 0.110.19 ± 0.150.925 Monocular UIVA0.36 ± 0.160.34 ± 0.160.573 Monocular DCIVA0.37 ± 0.200.37 ± 0.140.683Intermediate (60 cm) Binocular UIVA0.16 ± 0.160.28 ± 0.140.017 Binocular DCIVA0.14 ± 0.100.24 ± 0.130.037 Monocular UIVA0.30 ± 0.150.48 ± 0.18<0.001 Monocular DCIVA0.27 ± 0.150.43 ± 0.16<0.001Intermediate (50 cm) Binocular UIVA0.11 ± 0.180.36 ± 0.11<0.001 Binocular DCIVA0.06 ± 0.120.35 ± 0.11<0.001 Monocular UIVA0.19 ± 0.100.56 ± 0.19<0.001 Monocular DCIVA0.13 ± 0.110.52 ± 0.20<0.001DCIVA = distance-corrected intermediate visual acuity; IOL = intraocular lens; LogMAR = logarithm of the minimum angle of resolution; SD = standard deviation; UIVA = uncorrected intermediate visual acuity; VA = visual acuity. Mann-Whiney U test. Open table in a new tab Figure 2Wavefront aberration analyzed for a 6.0 mm pupil diameter. Bars around data points correspond with standard deviations. There were no statistically significant differences between the 2 groups determined by the Mann-Whitney U test (P = 0.745, P = 0.346, P = 0.582, P = 0.894, respectively). HOAs = higher-order aberrations; IOL = intraocular lens.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 3Contrast sensitivity under photopic conditions. Bars around data points represent standard deviations. There were statistically significant differences at 1.5 and 3 cpd (P = 0.013, P = 0.026, respectively), and no statistically significant differences at 6, 12, and 18 cpd determined by the Mann-Whitney U test (P = 0.448, P = 0.284, P = 0.458, respectively). cpd = cycles per degree; IOL = intraocular lens.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 4Contrast sensitivity under mesopic conditions. Bars around data points represent standard deviations There were no statistically significant differences at 1.5, 3, 6, 12, and 18 cpd between the 2 groups determined by the Mann-Whitney U test (P = 0.409, P = 0.515, P = 0.156, P = 0.548, P = 0.499, respectively). cpd = cycles per degree; IOL = intraocular lens.View Large Image Figure ViewerDownload Hi-res image Download (PPT) D = diopters; IOL = intraocular lens; SE = spherical equivalent. Data are mean ± standard deviation unless otherwise indicated. DCIVA = distance-corrected intermediate visual acuity; IOL = intraocular lens; LogMAR = logarithm of the minimum angle of resolution; SD = standard deviation; UIVA = uncorrected intermediate visual acuity; VA = visual acuity.