Diffractive-refractive Intraocular Lenses Research Articles

Light scattering from a diffractive-refractive intraocular lens: a goniometer-based approach for individual zone assessment.

We proposed and tested a method to measure light scattering from the diffractive lens profile in an echelle element featuring 9 zones. Measurements were performed using a goniometer-based setup up to 7.5°. The proportion of scattered light was calculated to derive the loss of light. Material scattering was minimal (∼1 deg2/sr); however, each echelle zone acted as a scattering source. A nearly gradual straylight increase was found with the zone number showing peak intensity between 3° and 3.75°. An estimated 6.2% ± 0.1% was lost due to scattering, which ought to be considered when reporting an IOL's light loss.

Update on the Use of Premium Intraocular Lenses in Glaucoma

In this report, we review the latest evidence for and against the use of premium intraocular lenses (IOL) in patients with glaucoma. Visual outcomes from clinical studies of newer Extend Depth of Focus (EDF) IOLs and low add apodized diffractive-refractive IOLs are significantly better than prior generations of multifocal (MF) IOLs. Clinical studies show that EDF and monofocal IOLs have similar contrast sensitivities in photopic conditions independent of spatial frequency. Premium IOLs restore uncorrected visual function, but intolerable visual disturbances and contrast impairment are uncommon side effects. Awareness of issues unique to glaucoma is critical for appropriate patient selection. Combined procedures with sizable shifts in IOP may have better refractive outcomes when staged. Toric and accommodating IOLs are reasonable options for most stages of glaucoma without fixation loss. EDF and newer MF IOLs can be appropriate options for stable pre-perimetric and early perimetric conditions.

Diffractive-Refractive Intraocular Lenses with Binary Structures

The paper presents a brief analytical review of papers dealing with the use of simple binaryphase diffractive structures in multifocal artificial eye lenses (intraocular lenses) to increase the focal region. The results of theoretical studies of the influence of spherical aberrations of the eye, the optical power of the diaphragm (pupil diameter), and the duty cycle of the structure on the depth of focus (limits of clear vision) are given. The intensity distribution in diffraction orders (foci) in the simplest binary diffractive-refractive intraocular lenses is analyzed.

Remote clinical results of implantation of the multifocal diffractive-refractive intraocular lens MIOL-Record-3

Remote clinical results of implantation of the multifocal diffractive-refractive intraocular lens MIOL-Record-3

Visual Performance With Bifocal and Trifocal Diffractive Intraocular Lenses: A Prospective Three-Armed Randomized Multicenter Clinical Trial

To evaluate and compare quality of vision and reading performance outcomes after implantation of bifocal refractive-diffractive, bifocal apodized diffractive, or trifocal diffractive-refractive intraocular lenses (IOLs). This randomized, prospective, three-armed multicenter (Spain, Germany, and France) trial included 104 eyes of 52 patients (mean age: 63.2 ± 7.7 years). Patients underwent cataract surgery with bilateral implantation of either AT LISA 809M (Carl Zeiss Meditec, Jena, Germany: AT LISA group, 38 eyes), AT LISA tri 839MP (Carl Zeiss Meditec: AT LISA tri group, 32 eyes), or ReSTOR SN6AD1 (Alcon Laboratories, Inc., Fort Worth, TX: ReSTOR group, 34 eyes) IOLs. Visual and refractive outcomes, depth of focus, and reading performance were evaluated at 1, 6, and 12 months postoperatively. The AT LISA tri group showed significantly better 12-month uncorrected (UIVA) and binocular distance-corrected (DCIVA) intermediate visual acuity (P ≤ .016) than the AT LISA group. The AT LISA tri group showed a significantly better 3-month UIVA compared to the ReSTOR group (P = .042). Binocular uncorrected and corrected distance visual acuities were not significantly different among groups (P ≥ .092) at the 12-month follow-up. A total of 85.3%, 90.0%, and 78.1% of eyes had a spherical equivalent within ±0.50 D in the AT LISA, AT LISA tri, and ReSTOR groups, respectively, at 12 months (P = .038). No statistically significant differences between the trifocal and bifocal groups were detected for reading performance (P ≥ .055). The trifocal diffractive-refractive IOL provides enhanced intermediate visual restoration compared to bifocal diffractive-refractive or apodized diffractive IOLs. The addition of an intermediate focal point did not deteriorate far or near vision. A comparable reading performance was maintained with the trifocal lens. [J Refract Surg. 2017;33(10):655-662.].

Processes for manufacturing multifocal diffractive-refractive intraocular lenses

Manufacturing methods and design features of modern diffractive-refractive intraocular lenses are discussed. The implantation of multifocal intraocular lenses is the most optimal method of restoring the accommodative ability of the eye after removal of the natural lens. Diffractive-refractive intraocular lenses are the most widely used implantable multifocal lenses worldwide. Existing methods for manufacturing such lenses implement various design solutions to provide the best vision function after surgery. The wide variety of available diffractive-refractive intraocular lens designs reflects the demand for this method of vision correction in clinical practice and the importance of further applied research and development of new technologies for designing improved lens models.

Spatial-energy characteristics of the focal areas of bifocal diffractive-refractive intraocular lenses

Computer simulation was performed for the measurement process of the parameters of MIOL-Akkord bifocal diffractive-refractive lenses in which the central area of the diffractive element is reduced and spherical aberrations of the eye are compensated. The spatial-energy characteristics of an ideal diffractive lens are preliminarily calculated using existing formulas. The simulation of the process of controlling the intraocular lens parameters has shown that the intensity distribution along the optical axis does not characterize the diffraction efficiency, which is the total (integrated) intensity in the beam cross section at the focus. It has been found that due to the mutual influence of diffraction orders, it is difficult to measure the absolute diffraction efficiency and it is better to evaluate only the relative efficiency.

Effect of Decentration on the Optical Quality of Two Intraocular Lenses.

To analyze the effect of decentration on the optical quality of two diffractive-refractive intraocular lenses, a bifocal and a trifocal, when displaced laterally (horizontal direction) from the center. The AT LISA 809M IOL (+3.75 D add) with two main foci and the AT LISA tri 839MP intraocular lens with three main foci (Carl Zeiss Meditec AG, Jena, Germany) were analyzed. The optical quality of the intraocular lenses was measured with the PMTF (power and modulation transfer function [MTF] measurement for refractive and diffractive intraocular lenses) optical bench (Lambda-X, Nivelles, Belgium). The optical quality of the lenses was evaluated by the MTF at different object vergences, the average modulation in the range of frequencies from 0 to 100 cycles/mm, and the through-focus MTF curves. All measures were recorded when the intraocular lenses were centered and decentered for 3.0- and 4.5-mm apertures. The Strehl ratio and the percentage of energy allocated at each focus at the centered position were also obtained. Our results showed a lower optical quality with increasing decentration. The MTFs for the diffractive-refractive intraocular lenses decreased when the intraocular lenses were decentered. Also, the relative percentages of light energy allocated at each object vergence, for both intraocular lenses, agreed well with theoretical specifications and were consistent with the overall design of each lens. The optical quality of these diffractive-refractive multifocal intraocular lenses was slightly reduced when the induced decentration was less than 0.4 mm. For a decentration of 0.4 mm, the maximum difference in average modulation values was about 18% compared to the centered position.

LIGA technology for the synthesis of diffractive refractive intraocular lenses

The manufacturing of test diffractive refractive intraocular lenses is illustrated by means of LIGA (deep X-ray LIthography and GAlvanoplastics and polymer forming). Dynamic X-ray lithography used while rotating the substrate versus an X-ray mask fixed in a beam of synchrotron radiation (SR) yields smooth optical 3D surfaces with roughnesses of 10–30 nm rms in polymethylmethacrylate (PMMA) layers. The axisymmetric diffractive refractive profile of a lens is predetermined by the radial angular function of the X-ray mask topology. The quality of the optical surface is reproduced for the nickel master form, which is electroplated onto a gold layer atop the PMMA relief. The optical quality also remains high for replicated lenses synthesized in this manner during silicon polymerization.

In vitro optical performance of nonrotational symmetric and refractive–diffractive aspheric multifocal intraocular lenses: Impact of tilt and decentration

To evaluate the optical quality of Acrysof Restor SN6AD1 refractive-diffractive +3.00 D and Lentis Mplus LS-312 nonrotational symmetric +3.00 D aspheric multifocal intraocular lenses (IOLs) and analyze the effect of tilt and decentration. University of Valencia, Valencia, and University of Murcia, Murcia, Spain. Experimental study. An artificial model eye was used to measure wavefront aberrations of both IOL models. The modulation transfer function (MTF) and point-spread function (PSF) were calculated for a 5.0 mm pupil and under 5 situations: centered, 0.2 mm and 0.4 mm decentered, and 2 degrees and 4 degrees tilted. The refractive-diffractive IOL had the highest MTF values at all spatial frequencies. Similarly, the PSF was worse for the refractive-diffractive IOL. The MTFs for the refractive-diffractive IOL decreased when the IOL was decentered or tilted, being more robust for tilting than decentration. The MTFs for the nonrotational symmetric IOL were similar under all testing conditions. Cutoff frequencies for the refractive-diffractive IOL were stable over the range of tilting studied and comparable with the cutoff when the IOL was centered (approximately 50 cycles per degree [cpd]). When the IOL was decentered, the cutoff frequency decreased by approximately 40 cpd. The nonrotational symmetric IOL cutoff frequencies for misalignment and tilt were low (approximately 30 cpd) and similar under all conditions. The refractive-diffractive IOL provided better optical quality than the nonrotational symmetric IOL. Tilt and decentration had a significant impact on optical quality with both IOLs, being more severe with the nonrotational symmetric IOL.

Effect of the eye pupil diameter and the phase shift in the diffraction structure on bifocal properties of diffractive-refractive intraocular lenses

As the eye pupil decreases, the bifocal properties of the intraocular lens (IOL), which is an artificial eye lens, can be violated. To avoid it, a phase shift is introduced into the structure of the IOL diffractive component. Results of an analytical study of the light intensity distribution on the axis of a bifocal IOL for different values of the eye pupil and phase shift in the diffractive component with a focal power of 4.2 D (diopters) are presented. Because of broadening and asymmetry of the intensity distribution function arising at small pupil diameters, the foci of orders 0 (far vision) and +1 (near vision) of the bifocal IOL are demonstrated to affect each other: they come closer or farther, become separated or overlapped. The total intensity distribution may be continuous or have a dip whose magnitude depends on the pupil diameter and phase shift. It is noted that the optimal phase shift at which separation of the foci (bifocality) begins from the pupil diameter of ∼0.9 mm and is not violated with further pupil expansion is 180° (π radian).

Chromatic aberrations of diffractive-refractive intraocular lenses in an eye model

Results of analyzing chromatic aberrations of an eye model with different designs of intraocular lenses (IOLs), that is, artificial crystalline lenses (refractive, diffractive-refractive, diffractive, and harmonic, i.e., multiorder lenses) are represented. Investigations were carried out sequentially for elements of the model, namely, for a cornea, refractive and diffractive components, and IOL, and as a whole, for a cornea + IOL. It is shown that diffractive-refractive IOLs in which the diffractive components produce a positive additional focal power possess the best chromatic characteristics. Chromatic aberration of the eye model with such IOLs is 2 times less than that of a model with a refractive IOL, whereas with other IOL designs it is 2 times greater and even more.

Methods for investigating optical characteristics of bifocal diffractive-refractive intraocular lenses

Peculiarities of designing and determining the refraction (lens power) and the diffraction efficiency of bifocal hybrid (diffractive-refractive) intraocular lenses (IOL)—implants—are considered. Methods for designing the refractive IOL for near and far vision are analyzed and compared by means of measuring the focal lengths in the air and medium. It is shown that in investigating the hybrid lenses it is more convenient to estimate the conformity of the profile height with the designed value from the relationship of intensities of the 1st and 2d diffraction orders in the air and of the zero and 1st orders in the medium. Admissible errors of measurements and deviations of the hybrid IOL parameters are determined and used for calculating the refraction and diffraction efficiency.