Effect of Correcting Peripheral Refractive Errors on Retinal Sensitivity in Younger and Older Healthy Adults.

SIGNIFICANCE: Retinal sensitivity decreases with age and age-related eye diseases. Peripheral retinal sensitivity may also be compromised if the refractive correction is not optimized for peripheral vision. PURPOSE: This study aimed to determine the impact of using a peripheral refractive correction on perimetric thresholds and the influence of age and spherical equivalent on this impact. METHODS: We measured, in 10 younger (20 to 30 years) and 10 older (58 to 72 years) healthy subjects, perimetric thresholds for Goldmann size III stimulus in several test locations along the horizontal meridian of the visual field (eccentricity, 0, ±10, and ±25°), with default central refractive correction and with peripheral refractive corrections as measured with a Hartmann-Shack wavefront sensor. We used analysis of variance to determine the effect of age and spherical equivalent (between-subject variables) and eccentricity and correction method (central vs. eccentricity specific; within-subject variables) on retinal sensitivity. RESULTS: Retinal sensitivity was higher if the eyes were optimally corrected for the concerning test location (P = .008), and the effect of this peripheral correction differed between the younger and older subjects (interaction term between group and correction method: P = .02), primarily because of more myopia in the younger group (P = .003). The average improvement by applying peripheral corrections was 1.4 dB in the older subjects and 0.3 dB in the younger subjects. CONCLUSIONS: Peripheral optical correction has a variable impact on retinal sensitivity, and therefore, assessment of retinal sensitivity may be more accurate if peripheral defocus and astigmatism are corrected.

Rostock Glare Perimeter: a distinctive method for quantification of glare.

PURPOSE: Disability glare induced by headlights of oncoming cars has been associated with reduced quality of vision. This study aimed at developing the Rostock Glare Perimeter to quantify dysphotopsia effects under simulated realistic conditions. METHODS: Sixty phakic subjects of different ages were dazzled by a bright light source centered at a projection screen 3.30 m away from the subject's eye. Using a projected marker moving outward from the screen center with angular steps of 0.25° in 12 directions, the area where the subject cannot distinguish the white spot from the glare effects of the light source was determined. A corresponding mean radius in a field angle relative to the subject's eye was defined as a measure for disability glare. Monocular and binocular measurements were performed, and a separate repeatability and reproducibility study was executed to determine the precision of the Rostock Glare Perimeter. RESULTS: A significant mean positive correlation of disability glare with age (r = 0.534, p < 0.001) was found. The disability glare ranged from 0.33° to 1.8°, and a strong (r = 0.93, p < 0.0002) binocular summation effect was found. The repeatability and reproducibility limit of the Rostock Glare Perimeter method is 0.14° for 95% confidence interval. CONCLUSIONS: The Rostock Glare Perimeter method is sensitive to detect age-related disability glare differences and to find binocular summation for disability glare in a healthy population for small field angles with high angular resolution. These findings suggest that the Rostock Glare Perimeter method is a helpful device to quantify symptoms of glare.

Effect of Violet Light-Filtering and Manufacturing Improvements in an Extended Depth-of-Focus Intraocular Lens on Visual Performance.

Purpose: To assess the experimental visual performance and dysphotopsia characteristics of the new Tecnis Symfony OptiBlue extended-depth-of-focus with violet light-filtering (ZXR00V) intraocular lens (IOL) compared with the colorless Tecnis Symfony (ZXR00) IOL. Methods: Range of vision was assessed with simulated visual acuity defocus curves, predicted by white light through focus modulation transfer function (MTF) measurements. The clinical visual acuity defocus curve of the ZXR00 IOL was used to validate the predicted range of vision. Image quality was compared by measuring white light MTF at a spatial frequency of 15 cycles per degree (c/deg) for 3 mm and 5 mm pupil diameters with optical powers of 5 D, 20 D, and 34 D using the average corneal eye (ACE) model with the average spherical and chromatic aberration of the cataract population. Effects on dysphotopsias were predicted by measurement and computer simulation of light scatter (straylight parameter) and subsequent determination of retinal veiling luminance (RVL) in vitro. Contrast enhancement under challenging light conditions was calculated based on the effects in RVL. Results: The simulated visual acuity defocus curves and image quality outcomes were comparable between the ZXR00V and ZXR00 IOLs. The area under the straylight curve for the straylight parameter showed a 19% improvement in halo performance with ZXR00V versus ZXR00. A 12% to 17% reduction in RVL was achieved in favor of ZXR00V over ZXR00, which enhanced contrast vision by 9% to 13% under challenging light conditions. Conclusion: The violet light-filtering technology and improved manufacturing of ZXR00V delivers a comparable range of vision and tolerance to refractive error to ZXR00 while mitigating dysphotopsias and enhancing contrast vision.

Visualization of the retinal image in an eye model with spherical and aspheric, diffractive, and refractive multifocal intraocular lenses.

PURPOSE: To present a method that visually demonstrates how spherical, aspheric, diffractive, and refractive multifocal intraocular lenses (IOLs) process light received from the cornea. METHODS: Monochromatic green light was projected through an Average Cornea Eye (ACE) Model with a cornea in front of the IOL. The model simulates a human cornea with average spherical aberration and visualizes the converging bundle of light leaving the IOL. Additionally, a US Air Force target was projected through the model, and the projected (retinal) image was captured. Various IOLs of differing designs were evaluated using this test setup. Multifocal IOLs included the aspheric diffractive Tecnis ZM900 and ZMA00 lenses; the refractive ReZoom NXG1 lens; the spherical AcrySof ReSTOR SA60D3 apodized diffractive lens; and the spherical diffractive CeeOn 811E lens. Monofocal IOLs included the spherical CeeOnEdge 911A IOL and the aspheric SofPort LI61AO, AcrySof IQ SN60WF, and Tecnis Z9000 and ZA9003 IOLs. RESULTS: The light paths of the different diffractive and refractive multifocal IOLs showed the variations in the processing of incoming light, illustrating the functional differences of IOL concepts. The US Air Force target projections in the ACE Model gave an impression of the functional optical quality of the different lenses. The value of this visualization method was demonstrated by comparing the results with modulation transfer function measurements. CONCLUSIONS: This visualization technique furthers the understanding of the working principles and quality of the retinal images produced by different mono- and multifocal IOLs.

Degradation of Visual Performance With Increasing Levels of Retinal Stray Light.

PURPOSE: To quantify the effect of induced stray light on halo size, luminance threshold, and contrast sensitivity. METHODS: Retinal stray light was induced in five healthy subjects using different photographic filters. The stray light induced ranged from levels observed in intraocular lenses (IOLs) with glistenings (low) to cataract level (high). The visual impact was measured for halo size, luminance detection threshold, and contrast sensitivity with and without a glare source. RESULTS: The amount of retinal stray light induced by the different filters was similar when measured using the psychophysical method and the optical bench method. Low amounts of induced stray light cause the halo size to increase by 21%, the luminance detection threshold to increase by 156%, and contrast sensitivity to decrease by 10% to 21% dependent on spatial frequency and presence of a glare source. The visual impact percentages for high amounts of induced stray light were, respectively, 76%, 2130%, and 30% to 49%. In the presence of a glare source, contrast sensitivity losses were larger and shifted to lower spatial frequencies. CONCLUSIONS: Low levels of retinal stray light can cause significant increases in halo sizes, elevations in luminance detection thresholds, and reductions in contrast sensitivity whether or not a glare source is present.

Explanted multifocal intraocular lenses.

UNLABELLED: We report 2 cases in which single-piece multifocal acrylic intraocular lenses (IOLs) were explanted because of complications related to the presence of glistenings in the bulk of the IOL optic. In both cases, the patients complained about blurry or hazy vision. In vivo slitlamp examinations prior to IOL explantation confirmed the presence of severe glistenings in the IOL optic in 1 case and moderate glistenings in the second case. In the first case, the symptoms resolved and both corrected and uncorrected distance visual acuities improved by 4 lines following IOL exchange with a monofocal IOL. In the second case, the visual symptoms persisted with a hard contact lens. Symptoms resolved following an exchange with a monofocal IOL that was free of glistenings. These findings indicate that straylight caused by IOLs with glistenings may be clinically significant in cases in which multifocal IOLs are implanted and patients require optimized retinal sensitivity. FINANCIAL DISCLOSURE: Mr. van der Mooren, Ms. Langeslag, and Dr. Piers are employees of Abbott Medical Optics, Inc. Drs. Steinert and Tyson are consultants to Abbott Medical Optics Inc.

Effect of the equivalent refractive index on intraocular lens power prediction with ray tracing after myopic laser in situ keratomileusis.

PURPOSE: To determine the impact of the equivalent refractive index (ERI) on intraocular lens (IOL) power prediction for eyes with previous myopic laser in situ keratomileusis (LASIK) using custom ray tracing. SETTING: AMO B.V., Groningen, the Netherlands, and the Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA. DESIGN: Retrospective data analysis. METHODS: The ERI was calculated individually from the post-LASIK total corneal power. Two methods to account for the posterior corneal surface were tested; that is, calculation from pre-LASIK data or from post-LASIK data only. Four IOL power predictions were generated using a computer-based ray-tracing technique, including individual ERI results from both calculation methods, a mean ERI over the whole population, and the ERI for normal patients. For each patient, IOL power results calculated from the four predictions as well as those obtained with the Haigis-L were compared with the optimum IOL power calculated after cataract surgery. RESULTS: The study evaluated 25 patients. The mean and range of ERI values determined using post-LASIK data were similar to those determined from pre-LASIK data. Introducing individual or an average ERI in the ray-tracing IOL power calculation procedure resulted in mean IOL power errors that were not significantly different from zero. The ray-tracing procedure that includes an average ERI gave a greater percentage of eyes with an IOL power prediction error within ±0.5 diopter than the Haigis-L (84% versus 52%). CONCLUSION: For IOL power determination in post-LASIK patients, custom ray tracing including a modified ERI was an accurate procedure that exceeded the current standards for normal eyes.

A new intraocular lens design to reduce spherical aberration of pseudophakic eyes.

PURPOSE: The aim of this study was to design and evaluate in the laboratory a new intraocular lens (IOL) intended to provide superior ocular optical quality by reducing spherical aberration. METHODS: Corneal topography measurements were performed on 71 cataract patients using an Orbscan I. The measured corneal surface shapes were used to determine the wavefront aberration of each cornea. A model cornea was then designed to reproduce the measured average spherical aberration. This model cornea was used to design IOLs having a fixed amount of negative spherical aberration that partially compensates for the average positive spherical aberration of the cornea. Theoretical and physical eye models were used to assess the expected improvement in optical quality of an eye implanted with this lens. RESULTS: Measurements of optical quality provided evidence that if this modified prolate IOL was centered within 0.4 mm and tilted less than 7 degrees, it would exceed the optical performance of a conventional spherical IOL. This improvement occurred without an apparent loss in depth of focus. CONCLUSION: A new IOL with a prolate anterior surface, designed to partially compensate for the average spherical aberration of the cornea, is intended to improve the ocular optical quality of pseudophakic patients.

Impact of intraocular lens material and design on light scatter: In vitro study.

PURPOSE: To determine the typical in vitro straylight levels for intraocular lenses (IOLs) of different materials and designs. SETTING: Abbott Medical Optics, Inc., Groningen, the Netherlands. DESIGN: Experimental study. METHODS: Two optical bench setups were used to determine baseline straylight levels of IOLs placed in a saline-filled cuvette: one for forward scatter positions between 0.6 and 3.0 degrees and one for positions up to 22.0 degrees. Line-spread functions were measured using the small-angle setup, and scattered light intensity was measured using the wide-angle setup. From these measurements, the angular dependent straylight parameter was calculated. Ten IOLs of different materials (hydrophobic and hydrophilic) and designs (monofocal or diffractive multifocal and spheric or aspheric) were studied, and their measured straylight levels were compared with the levels in a 20-year-old and a 70-year-old healthy noncataractous human crystalline lens. RESULTS: Irrespective of the material or design, monofocal IOLs had straylight levels below or close to those of a 20-year-old human crystalline lens. Diffractive multifocal IOLs had straylight levels higher than those of monofocal IOLs but less than those of a 70-year-old human crystalline lens. With increasing angle, hydrophobic IOLs showed a gradual decrease in straylight level. After an initial decrease, hydrophilic IOLs showed an increase in straylight level for larger angles. CONCLUSIONS: The baseline straylight levels of IOLs were design and material dependent (hydrophobic < hydrophilic; monofocal < diffractive multifocal). Most monofocal IOLs had straylight levels below the levels in a 20-year-old human crystalline lens.

Effects of glistenings in intraocular lenses.

Glistenings consist of multiple microvacuoles in intraocular lenses (IOLs) that cause retinal stray light and may affect quality of vision. For four IOL types, the microvacuole particle size distribution and particle volume density was measured using confocal light microscopy and dark field microscopy, and the corresponding extinction coefficient γ was determined. The light scatter contribution induced by microvacuoles was measured as function of both angle and extinction, and was verified by calculations using Mie theory. Two IOL types possessed significant glistenings having stray light levels higher than that of a healthy 20 year old crystalline lens corresponding to γ ≥ 0.08 mm(-1).

Combining in vitro test methods for measuring light scatter in intraocular lenses.

Intraocular lenses (IOLs) are designed for implantation for vision correction following cataract removal. The IOL typically replaces a cataractous natural lens that exhibits very high levels of light scattering. The amount of scattering is significantly reduced with an IOL, though it is rarely quantified and both the surface and the bulk of the intraocular lens may contribute to light scatter at some level, and in some cases potentially affecting patients' post-operative quality of vision. The purpose of this paper is to describe two complementary in-vitro quantitative methods for measuring light scatter caused by IOLs. The first method directly measures light scatter from the lens in one plane for angles larger than two degrees. The second method measures light scatter in an eye model including the focal point out to three degrees in the image plane. The measured amount of light scatter from an IOL is typically lower than that found in healthy donor crystalline lenses of various ages that are used as a basis for comparison.

Model eyes for evaluation of intraocular lenses.

In accordance with the present international standard for intraocular lenses (IOLs), their imaging performance should be measured in a model eye having an aberration-free cornea. This was an acceptable setup when IOLs had all surfaces spherical and hence the measured result reflected the spherical aberration of the IOL. With newer IOLs designed to compensate for the spherical aberration of the cornea there is a need for a model eye with a physiological level of spherical aberration in the cornea. A literature review of recent studies indicated a fairly high amount of spherical aberration in human corneas. Two model eyes are proposed. One is a modification of the present ISO standard, replacing the current achromat doublet with an aspheric singlet cut in poly(methyl methacrylate) (PMMA). The other also has an aspheric singlet cut in PMMA, but the dimensions of it and the entire model eye are close to the physiological dimensions of the eye. They give equivalent results when the object is at infinity, but for finite object distances only the latter is correct. The two models are analyzed by calculation assuming IOLs with different degrees of asphericity to elucidate their sensitivity to variation and propose tolerances. Measured results in a variant of the modified ISO model eye are presented.