Multifocal intraocular lenses (IOLs) have grown in popularity among patients and surgeons. The technology has improved the quality of life for many pseudophakic patients by reducing or eliminating the need for spectacles.1–3 The AcrySof ReSTOR (Alcon Laboratories) and ReZoom (Advanced Medical Optics) are 2 multifocal IOLs that were recently approved by the U.S. Food and Drug Administration. The 2 IOLs use different modes of action to achieve multifocality.
The ReSTOR (model SA60D3) is an apodized diffractive IOL. It has a central 3.6 mm apodized diffractive optic region in which 12 concentric diffractive zones on the anterior surface of the lens divide light into 2 diffractive orders. Unlike the step heights of full-optic diffractive IOLs, which are the same, the ReSTOR IOL has step heights that decrease with increasing distance from the center of the lens to the edge of the diffractive region. This process, apodization, greatly increases the proportion of energy directed to the distance focus for larger pupil diameters. The addition (add) power of the IOL is 4.0 diopters (D) at the lens, which provides approximately 3.2 D of add power at the spectacle plane (J.A. Davison, M.J. Simpson, “How Does the ReSTOR Lens Work?” Review of Ophthalmology supplement, October 2004, pages 18–20).
The ReZoom (model NXG1) is a zonal-progressive IOL that incorporates a continuous range of foci. The multifocal area is contained within the full 6.0 mm optic and consists of 5 zones: 1, 3, and 5 are distance dominant, and 2 and 4 are near dominant. The aspherical transitions between the zones provide balanced intermediate vision. Compared with its predecessor, the Array IOL (American Medical Optics), the distance and near zone areas of the ReZoom IOL decrease unwanted halos under low light conditions without affecting good distance through near vision.4 The add power of the IOL is 3.5 D at the lens, resulting in 2.6 D of add power at the spectacle plane.
Bilateral implantation of simultaneous IOLs is associated with better visual outcomes,1,5–7 and the photic symptoms tend to improve with time after IOL implantation.5,8,9 The aim of this study was to investigate the 6-month postoperative visual outcomes and subjective symptoms in patients who had bilateral cataract surgery and implantation of ReSTOR or ReZoom multifocal IOLs.
PATIENTS AND METHODS
Patients who expressed a wish to increase spectacle independence after bilateral cataract surgery were randomly selected to have bilateral ReSTOR or ReZoom IOL implantation after cataract surgery. Patients who had uneventful sequential bilateral cataract extraction and multifocal IOL implantation from May 2005 to June 2006 were included in this study. Exclusion criteria were ocular pathology other than cataract, corneal astigmatism greater than 1.0 D, and intraoperative complications (eg, posterior capsule tear). The target refraction was emmetropia, and the Holladay 2 formula was used for IOL power calculation. To compare the true potential of the multifocal IOLs, patients with a postoperative spherical equivalent greater than ±0.75 D from the targeted refraction and a cylinder refraction of more than +0.75 D were excluded. All patients had the same type of IOL implanted in both eyes. The second eye was operated on within 6 to 8 weeks after the first eye. Fifty consecutive patients who satisfied the inclusion criteria were recruited in each arm of the study.
All operations were performed by 1 of 3 experienced surgeons (H.E.K., R.K.A., N.K.). A 2.7 mm clear corneal incision was placed at the steepest meridian. A standard phacoemulsification technique was used. The IOLs were injected into the capsular bag.
Postoperative binocular visual acuity results were obtained 6 months after implantation of the second multifocal IOL. The primary outcome measures were binocular uncorrected distance and intermediate (24 to 32 inches) visual acuities using the Snellen chart and uncorrected near (12 to 16 inches) visual acuity using the Jaeger chart. Patients were allowed to read the near and intermediate charts at best distance within the specified limitations. The results obtained at other distances than those intended for the chart used were converted to reflect the change in apparent letter size. Patients were asked in a survey to grade associated visual symptoms, visual satisfaction, and spectacle independence. They completed the surveys at home and returned them at a later date to reduce the effect of examiner presence.
Statistical analysis of the results was performed with Prism 3.03 (GraphPad Software, Inc.). Results were expressed as means and medians. The unpaired t test was used to compare the patient's age and postoperative refraction. Comparisons between visual acuities were performed using the Mann-Whitney test. Categorical variables were compared using the chi-square test. A P value less than 0.05 was considered statistically significant.
Table 1 shows the preoperative characteristics of patients by IOL group. There was no significant difference in the sex ratio between groups.
Six months after the second eye was operated on, the mean spherical equivalent was +0.20 ± 0.25 D in the ReSTOR group and +0.13 ± 0.35 D in the ReZoom group (P = .13). One patient in the ReZoom group was excluded due to a refractive surprise of +2.0 D sphere in the second eye. The next consecutive patient with bilateral ReZoom IOL implantation was recruited to replace the patient.
The mean binocular uncorrected near visual acuity was 20/26 (J1.22) in the ReSTOR group and 20/34 (J2.34) in the ReZoom group (P<.0001) (Table 2). Binocular uncorrected near acuity of 20/20 (J1+) or better was achieved in 20% of ReSTOR patients and 4% of ReZoom patients; of 20/25 (J1) or better in 66% and 20%, respectively; of 20/32 (J2) or better in 88% and 44%, respectively; and of 20/40 (J3) or better in 96% and 84%, respectively. All patients had an uncorrected near acuity of 20/50 (J5) or better.
The mean binocular uncorrected intermediate visual acuity was 20/42 in the ReSTOR group and 20/34 in the ReZoom group (P = .003) (Table 3). Binocular uncorrected intermediate acuity of 20/25 or better was achieved in 4% of ReSTOR patients and 18% of ReZoom patients; of 20/32 or better in 24% and 50%, respectively; of 20/40 or better in 50% and 74%, respectively; and of 20/50 or better in 88% and 96%, respectively. No patients had an uncorrected intermediate acuity worse than 20/63.
The mean binocular uncorrected distance visual acuity was 20/23 in the ReSTOR group and 20/21 in the ReZoom group (P = .091) (Table 4). Binocular uncorrected distance acuity of 20/20 or better was achieved in 46% patients in the ReSTOR group and 60% in the ReZoom group and of 20/25 or better in 83% and 88%, respectively. All patients had binocular uncorrected distance acuity of 20/32 or better. Binocular best corrected distance acuity of 20/20 or better was achieved in 82% in the ReSTOR group and 86% in the ReZoom group (P = .14).
On the survey, 86% of ReSTOR patients and 70% of ReZoom patients said they did not wear spectacles for daily activities (Table 5); there was no statistically significant difference between groups (P = .29). The rest of the patients in both groups required spectacles occasionally; none wore them full time. All patients in the ReZoom group who required spectacles occasionally needed them for reading. Two of 7 patients in the ReSTOR group who required spectacles occasionally wore them for reading only. The remaining patients needed spectacles for intermediate visual tasks (eg, working on the computer, reading music notes). The ReSTOR group had higher spectacle independence for near vision and the ReZoom group, for intermediate vision (P = .001, Fischer exact test).
Moderate glare was reported by 20% of ReSTOR patients and 30% of ReZoom patients. Moderate halos were reported by 14% and 28%, respectively. There was no significant difference between groups in photic phenomena (Table 5). No patient in either group reported severe glare, although a few mentioned some degree of symptoms in the first few weeks after surgery.
The survey showed no statistically significant difference between groups in satisfaction with near vision (P = .08). Twenty-four percent of patients in the ReSTOR group said they had to get used to the closer reading distance and would have preferred it to be slightly farther. No patient in the ReZoom group mentioned this. More ReZoom patients than ReSTOR patients seemed to be satisfied with intermediate vision (P = .04). The between-group difference in overall satisfaction with vision was not statistically significant (Table 5).
Bilateral multifocal IOL implantation is effective in achieving good near and distance vision.8–12 The ReSTOR and ReZoom multifocal IOLs use different technologies to achieve multifocality. In addition to distance, intermediate, and near visual acuities, it is essential that the performance of multifocal IOLs be established on the grounds of objective and subjective visual outcomes, which we sought to do in this study. To objectively compare the efficacy of the 2 IOL models, we included only patients with a postoperative spherical equivalent within ±0.75 D of the targeted refraction and cylinder refraction less than +0.75 D. We believe these figures allowed the IOLs to perform reasonably well while encompassing most, if not all, our patients. This was important to enable comparison of the intended vision (uncorrected acuity) after surgery as well as patient satisfaction.
The mean binocular uncorrected near visual acuity was significantly better in the ReSTOR group than in the ReZoom group. However, there was no statistically significant between-group difference in satisfaction with near vision. Conversely, the mean binocular uncorrected intermediate visual acuity was significantly better in the ReZoom group than in the ReSTOR group. This was supported by the fact that more ReZoom patients were satisfied with intermediate vision (P = .04).
Both groups had similarly good uncorrected distance visual acuity, which is consistent with results in other studies of multifocal IOLs.5,9–12 Some studies8,9,12 report that most patients experienced photic symptoms postoperatively. This seems to be a problem with multifocal IOLs. In a prospective study of the Array IOL, 34% of eyes had severe glare and approximately 20% of patients were very dissatisfied with their vision.12 Although not directly comparable, our study found a high level of satisfaction in both multifocal IOL groups despite most patients' experience of various degrees of halos and glare. Similar findings have been reported.2,13,14 This suggests the visual symptoms produced by ReSTOR and ReZoom IOLs are more tolerable. Another study of the ReSTOR IOL15 reports patients with halos and glare were not prepared to trade off the symptoms for the inability to read unaided. We did not find a statistically significant difference in the photic phenomena experienced or satisfaction with overall performance between the 2 IOL groups.
Depth of focus and contrast sensitivity were not addressed in our study. Better depth of focus has been reported with multifocal IOLs than with monofocal IOLs.16–18 The contrast sensitivity with ReSTOR IOLs has been shown to be similar to that with monofocal IOLs and does not decrease visual functionality.3,19 The main objective of multifocal IOLs is to reduce spectacle dependence. In our study, more patients in the ReSTOR group than in the ReZoom group remained spectacle independent; however, the difference between groups was not statistically significant. Previous studies11,15,20 report between 85% and 92% of patients with bilateral ReSTOR IOLs are spectacle independent. There was no peer-reviewed study of spectacle independence with bilateral ReZoom IOLs at the time this manuscript was written.
In our study, the ReSTOR group had better near visual acuity and greater spectacle independence for reading than the ReZoom group. The near add at the spectacle plane of the ReZoom IOL and ReSTOR IOL is 2.6 D and 3.2 D, respectively.4 Thus, the optimal reading distance is closer with the ReSTOR IOL. Approximately one fourth of ReSTOR patients mentioned, without being asked directly, that they preferred a farther reading distance. The lower add power of the ReZoom IOL seemed to provide sufficient power for good functional near vision and an opportunity for better intermediate vision than that of the ReSTOR IOL. However, the poorer intermediate vision in the ReSTOR group may be outweighed by good near and distance vision as the overall satisfaction was comparable between the 2 IOL groups. The ReZoom group had greater spectacle independence for intermediate vision. Patients who require good intermediate visual acuity (eg, computer work, reading music notes) may consider ReZoom IOL a better option than the ReSTOR IOL.
Further studies of the efficacy of combined ReSTOR–ReZoom IOL implantation is needed to assess whether these 2 types of multifocal IOLs can complement each other. Our study found that spectacle dependence was greatly reduced with both types of multifocal IOLs. The evolution of the multifocal design has played an important role in enhancing patient lifestyle as a result of this.
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