Len Zheleznyak

Objective evaluation of through-focus optical performance of presbyopia-correcting intraocular lenses using an optical bench system

PURPOSE: TO evaluate spherical aberration and through‐focus optical performances of 5 presbyopia‐correcting and 2 monofocal intraocular lenses (IOLs). SETTING: Flaum Eye Institute, University of Rochester, Rochester, New York, USA. DESIGN: Experimental study. METHODS: Five presbyopia‐correcting IOLs (Restor +4D SN6AD3, Restor +3D SN6AD1, Rezoom NXG1, Tecnis multifocal ZM900, Crystalens HD500) were tested using an optical bench system consisting of a model eye, a high‐resolution Hartmann‐Shack wavefront sensor, and an image‐capturing device. Two monofocal IOLs (Sofport AO LI60AOV, Acrysof SN60AT) were measured for comparison. No accommodation was simulated. The spherical aberration profiles of each IOL were measured using the wavefront sensor. Through‐focus performance was evaluated by calculating cross‐correlation coefficients and comparing the likenesses of captured images of a resolution target and a perfect reference image. RESULTS: With a 5.0 mm entrance pupil, the SN6AD3, SN6AD1, ZM900, NXG1, and HD500 IOLs had spherical aberration of −0.18 μm, −0.14 μm, −0.15 μm, −0.07 μm, and −0.01 μm, respectively. Distance image quality was poorer with multifocal and accommodating IOLs than with monofocal IOLs. All multifocal IOLs had effective distance and near image quality but had a loss in intermediate image quality. The HD 500 accommodating IOL had decreased distance image quality and slightly increased depth of focus compared with the monofocal IOLs because of the bispheric design. CONCLUSIONS: The presbyopia‐correcting IOLs had different optical characteristics, including spherical aberration profile and through‐focus performance. An accurate understanding of the optical characteristics of individual IOLs is essential to selecting the best presbyopia‐correcting IOL and thus improving cataract surgery outcomes. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Binocular visual performance and summation after correcting higher order aberrations

Although the ocular higher order aberrations degrade the retinal image substantially, most studies have investigated their effect on vision only under monocular conditions. Here, we have investigated the impact of binocular higher order aberration correction on visual performance and binocular summation by constructing a binocular adaptive optics (AO) vision simulator. Binocular monochromatic aberration correction using AO improved visual acuity and contrast sensitivity significantly. The improvement however, differed from that achieved under monocular viewing. At high spatial frequency (24 c/deg), the monocular benefit in contrast sensitivity was significantly larger than the benefit achieved binocularly. In addition, binocular summation for higher spatial frequencies was the largest in the presence of subject’s native higher order aberrations and was reduced when these aberrations were corrected. This study thus demonstrates the vast potential of binocular AO vision testing in understanding the impact of ocular optics on habitual binocular vision.

Impact of corneal aberrations on through-focus image quality of presbyopia-correcting intraocular lenses using an adaptive optics bench system

PURPOSE: To measure the impact of corneal aberrations on the through‐focus image quality of presbyopia‐correcting intraocular lenses (IOLs) using an adaptive optics IOL metrology system. SETTING: Flaum Eye Institute, University of Rochester, Rochester, New York, USA. DESIGN: Experimental study. METHODS: An adaptive optics IOL metrology system comprising a model eye, wavefront sensor, deformable mirror, and an image‐capturing device acquired through‐focus images of a letter chart with 3.0 mm and 5.0 mm pupil diameters. The system was used to induce corneal astigmatism and higher‐order aberrations (HOAs) in previously measured pseudophakic presbyopic eyes. A single‐optic accommodating IOL (Crystalens HD (HD500), an apodized (Restor +3.0 diopter [D] SN6AD1) and full‐aperture (Tecnis ZM900) diffractive multifocal IOL, and a monofocal IOL (Acrysof SN60AT) were evaluated. Image quality was quantified using the correlation‐coefficient image‐quality metric. RESULTS: The single‐optic accommodating IOL and monofocal IOL performed similarly; however, with a 3.0 mm pupil, the former had better intermediate (1.50 D) image quality. The multifocal IOLs had bimodal through‐focus image quality trends. Corneal astigmatism reduced through‐focus image quality and depth of focus with all IOLs; however, the multifocal IOLs had the most severe decline in depth of focus. Ocular spherical aberration had the strongest impact on image quality when typical pseudophakic corneal HOAs were present. CONCLUSIONS: The uncorrected corneal astigmatism and HOAs in pseudophakic eyes significantly affected through‐focus performance of presbyopia‐correcting IOLs. Although multifocal IOLs significantly increased depth of focus, this benefit diminished when more than 0.75 D astigmatism remained uncorrected. Residual ocular spherical aberration had a significant effect on image quality in the presence of other corneal HOAs. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Optical and neural anisotropy in peripheral vision

Optical blur in the peripheral retina is known to be highly anisotropic due to nonrotationally symmetric wavefront aberrations such as astigmatism and coma. At the neural level, the visual system exhibits anisotropies in orientation sensitivity across the visual field. In the fovea, the visual system shows higher sensitivity for cardinal over diagonal orientations, which is referred to as the oblique effect. However, in the peripheral retina, the neural visual system becomes more sensitive to radially-oriented signals, a phenomenon known as the meridional effect. Here, we examined the relative contributions of optics and neural processing to the meridional effect in 10 participants at 0°, 10°, and 20° in the temporal retina. Optical anisotropy was quantified by measuring the eyes habitual wavefront aberrations. Alternatively, neural anisotropy was evaluated by measuring contrast sensitivity (at 2 and 4 cyc/deg) while correcting the eyes aberrations with an adaptive optics vision simulator, thus bypassing any optical factors. As eccentricity increased, optical and neural anisotropy increased in magnitude. The average ratio of horizontal to vertical optical MTF (at 2 and 4 cyc/deg) at 0°, 10°, and 20° was 0.96 ± 0.14, 1.41 ± 0.54 and 2.15 ± 1.38, respectively. Similarly, the average ratio of horizontal to vertical contrast sensitivity with full optical correction at 0°, 10°, and 20° was 0.99 ± 0.15, 1.28 ± 0.28 and 1.75 ± 0.80, respectively. These results indicate that the neural systems orientation sensitivity coincides with habitual blur orientation. These findings support the neural origin of the meridional effect and raise important questions regarding the role of peripheral anisotropic optical quality in developing the meridional effect and emmetropization.

Impact of pupil transmission apodization on presbyopic through-focus visual performance with spherical aberration.

PURPOSE To investigate the impact on through-focus retinal image quality and visual performance of apodizing the pupils transmission function in combination with extended depth of focus presbyopic corrections, such as spherical aberration (SA). METHODS Through-focus retinal image quality was determined theoretically for various magnitudes of pupil transmission apodization and Zernike primary SA (-0.5 to +0.5 μm) for a 4-mm pupil. The impact of pupil transmission apodization was also assessed psychophysically with a vision simulator equipped with a liquid crystal spatial light modulator for controlling pupil transmission. Through-focus visual acuity (VA) was measured with and without apodization in three cyclopleged subjects from distance to near with monochromatic light (550 nm) under two multifocal aberration conditions. Phase plates induced +0.2 and -0.2 μm of SA over a 4-mm artificial pupil. A baseline condition of zero SA was also included for comparison. RESULTS The theoretical investigation showed that pupil transmission apodization significantly improved distance image quality in the presence of positive and negative SA. Retinal image quality at all target vergences for negative SA conditions was improved by apodization. Pupil transmission apodization improved through-focus VA by 0.1 to 0.2 logMAR at intermediate and near object distances for the zero and negative SA conditions. In the positive SA condition, apodization degraded VA by approximately 0.1 logMAR at intermediate object distances. CONCLUSIONS Pupil transmission apodization had a significant impact on though-focus visual performance. Pupil transmission apodization affects through-focus retinal image quality by diminishing the relative contribution to the retinal image from the peripheral region of the wavefront aberration. Through-focus visual performance in presbyopic eyes with negative SA was improved due to pupil transmission apodization.

Neural adaptation to peripheral blur in myopes and emmetropes.

ABSTRACT In the presence of optical blur at the fovea, blur adaptation can improve visual acuity (VA) and perceived image quality over time. However, little is known regarding blur adaptation in the peripheral retina. Here, we examined neural adaptation to myopic defocus at the fovea and parafovea (10° temporal retina) in both emmetropes and myopes. During a 60‐min adaptation period, subjects (3 emmetropes and 3 myopes) watched movies with +2 diopters of defocus blur through a 6‐mm artificial pupil in two separate, counter‐balanced sessions for each retinal location. VA was measured at 10‐min intervals under full aberration‐corrected viewing using an adaptive optics (AO) vision simulator. By correcting subjects’ native optical aberrations with AO, we bypassed the influence of the individual subjects’ optical aberrations on visual performance. Overall, exhibited a small but significant improvement after the 60‐min of adaptation at both the fovea (mean ± SE VA improvement: −0.06 ± 0.04 logMAR) and parafovea (mean ± SE VA improvement: −0.07 ± 0.04 logMAR). Myopic subjects exhibited significantly greater improvement in parafoveal VA (mean ± SE VA improvement: 0.10 ± 0.02 logMAR), than that of emmetropic subjects (mean ± SE VA improvement: 0.04 ± 0.03 logMAR). In contrast, there was no significant difference in foveal VA between the two refractive‐error groups. In conclusion, our results reveal differences in peripheral blur adaptation between refractive‐error groups, with myopes displaying a greater degree of adaptation.

Optical quality of hydrogel ophthalmic devices created with femtosecond laser induced refractive index modification

The wavefront aberrations of hydrogel material were altered using a technique of femtosecond laser induced refractive index modification. Gradient-index Fresnel lenses ranging from −3.0 to +1.5 diopters (5.8 mm diameter) were written in contact lens material (Contaflex GM Advance 58). Optical quality was assessed in terms of wavefront aberrations, image contrast, and scatter. The spherical and cylindrical power writing errors were 0.05 D ± 0.07 D and 0.10 D ± 0.14 D respectively, and the lenses preserved almost all spatial frequency information relevant for human vision. The induced wavefronts were comprised of a mosaic of approximately 1400 stitched segments, leading to undesirable diffraction. This work demonstrates the capability of femtosecond laser induced refractive index modification to produce high quality optical devices for vision correction.

Manufacturing of Gradient Index Lenses for Ophthalmic Applications

Intra-Tissue Refractive Index Shaping (IRIS) is a scalable manufacturing process where a femtosecond laser can be used to photo-modify the refractive index of an ophthalmic material, including hydrogels for contact lenses and intra-ocular lenses, and native cornea.

Optical Bench Testing of IOLs

Optical bench testing of intraocular lenses (IOLs) enables visualization and quantification of through-focus retinal image quality. Combining adaptive optics with optical bench testing allows for the induction of corneal aberrations in a pseudophakic model eye. The adaptive optics bench system described in this study consisted of a model eye, artificial pupil, wavefront sensor deformable mirror, and an image-capturing device. This study measured the through-focus retinal image quality of 3 presbyopia-correcting IOLs and a monofocal control IOL with 3.0- and 5.0-mm pupils under various corneal aberration conditions. Uncorrected corneal astigmatism and higher order aberrations in pseudophakic eyes significantly affected through-focus image quality. Diffractive multifocal IOLs were especially vulnerable to degradations in image quality due to corneal aberrations.

Methods of Vision Correction

In this article, we review methods for correcting the eye’s optical aberrations, spanning from medieval looking-stones and spectacles to modern advances, such as surgical implants and laser refractive surgery. Whether it is sphero/cylindrical ametropia, or the subtler higher order and chromatic aberrations, all eyes suffer from some degree of optical error. Thus, the need for a robust, non-invasive means of providing clear vision persists. We will also explore promising future approaches to vision correction, such as corneal cross-linking and non-invasive laser induced refractive index modification.