Publications by authors named "Pablo Artal"

179 Publications

Adaptation to the eye's chromatic aberration measured with an adaptive optics visual simulator.

Opt Express 2020 Dec;28(25):37450-37458

Some aspects of vision after correcting the longitudinal chromatic aberration (LCA) of the eye are not yet completely understood. For instance, correcting the LCA notably alters the through focus visual acuity (VA) curve, but it does not improve the best VA obtained for the natural case. In this work, vision with corrected LCA is further investigated by using an adaptive optics visual simulator (AOVS). VA was measured continuously during 20 minutes in 5 subjects under both natural and corrected LCA conditions to explore possible adaptation effects. Low contrast VA as a function of time exhibited a consistent and significant boost of 0.19 in decimal scale after an average time of 10.9 minutes of continuous testing. For high contrast, only one subject showed a similar increase in VA. These results suggest that some LCA neural adaptation may exist, particularly for low contrast. This adaptation impacts the performance of vision under corrected LCA, and possibly prevents measurement for immediate visual benefit. The results have practical implications for the design and visual testing of optical aids, especially those correcting, or altering, the LCA.
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http://dx.doi.org/10.1364/OE.404296DOI Listing
December 2020

The Role of Thermal Accumulation on the Fabrication of Diffraction Gratings in Ophthalmic PHEMA by Ultrashort Laser Direct Writing.

Polymers (Basel) 2020 Dec 11;12(12). Epub 2020 Dec 11.

Laboratorio de Óptica, Centro de Investigación en Óptica y Nanofísica, Campus Espinardo, Universidad de Murcia, 30100 Murcia, Spain.

The fabrication of diffraction gratings by ultrashort direct laser writing in poly-hydroxyethyl-methacrylate (PHEMA) polymers used as soft contact lenses is reported. Diffraction gratings were inscribed by focusing laser radiation 100 µm underneath the surface of the samples. Low- and high-repetition rate Ti:sapphire lasers with 120 fs pulsewidth working at 1 kHz and 80 MHz respectively were used to assess the role of thermal accumulation on microstructural and optical characteristics. Periodic patterns were produced for different values of repetition rate, pulse energy, laser wavelength, distance between tracks, and scanning speed. Compositional and structural modifications of the processed areas were studied by micro-Raman spectroscopy showing that under certain parameters, thermal accumulation may result in local densification. Far-field diffraction patterns were recorded for the produced gratings to assess the refractive index change induced in the processed areas.
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http://dx.doi.org/10.3390/polym12122965DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7763622PMC
December 2020

Straylight in Different Types of Intraocular Lenses.

Transl Vis Sci Technol 2020 11 9;9(12):16. Epub 2020 Nov 9.

Laboratorio de Óptica, Universidad de Murcia, Campus de Espinardo, Murcia, Spain.

Purpose: To show the importance of measuring the angular distribution of straylight as an in vitro test for intraocular lenses (IOLs).

Methods: The optical integration method was implemented to measure the point spread function, up to 5.1°, of IOLs immersed in a wet cell. The straylight parameter was calculated as the product of the point spread function by the squared angle. The effect of the scattered light is shown in extended images of a target surrounded by headlamps as glare sources. Three different IOLs were tested: (1) AcrySof IQ SN60WF, monofocal, (2) AcrySof IQ PanOptix, trifocal, and (3) Tecnis Symfony ZRX00, bifocal with extended depth of focus. Measurements were compared to previously reported clinical studies where the same IOL models were implanted.

Results: The mean amount of scattered light, between 1.0° and 5.1°, generated by each IOLs were, in degsr units: (1) 1.2, (2) 12.1, and (3) 33.4. Lens (3) present a high amount of straylight related to a halo of an approximate diameter of 2°.

Conclusions: In vitro measurements of the angular distribution of the point spread function of different types of IOLs showed important aspects related to their manufacturing quality. These results are in line with previous clinical findings where glare sensitivity was tested in the same angular range.

Translational Relevance: In vitro measurement of angular dependence of straylight in IOLs, regardless their design, provides a valuable feedback to improve their optical quality. The minimization of the amounts of straylight positively impacts the recurrence of photic phenomena.
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http://dx.doi.org/10.1167/tvst.9.12.16DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7671868PMC
November 2020

Portable device for presbyopia correction with optoelectronic lenses driven by pupil response.

Sci Rep 2020 11 20;10(1):20293. Epub 2020 Nov 20.

Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo, 30100, Murcia, Spain.

A novel portable device has been developed and built to dynamically, and automatically, correct presbyopia by means of a couple of opto-electronics lenses driven by pupil tracking. The system is completely portable providing with a high range of defocus correction up to 10 D. The glasses are controlled and powered by a smartphone. To achieve a truly real-time response, image processing algorithms have been implemented in OpenCL and ran on the GPU of the smartphone. To validate the system, different visual experiments were carried out in presbyopic subjects. Visual acuity was maintained nearly constant for a range of distances from 5 m to 20 cm.
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http://dx.doi.org/10.1038/s41598-020-77465-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7680150PMC
November 2020

Phase-only modulation with two vertical aligned liquid crystal devices.

Opt Express 2020 Nov;28(23):34180-34189

Spatial Light Modulators (SLMs) are widely used in several fields of optics such as adaptive optics. SLMs based on Liquid Crystal (LC) devices allow a dynamic and easy representation of two-dimensional phase maps. A drawback of these devices is their elevated cost, preventing a massive use of the technology. We present a more affordable approach based on the serial arrangement of vertical aligned LC devices, with characteristics of phase modulation similar to a widely used parallel aligned LC device. We discuss the peculiarities of the approach, the performance and some potential areas of applications.
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http://dx.doi.org/10.1364/OE.410429DOI Listing
November 2020

Vision with pulsed infrared light is mediated by nonlinear optical processes.

Biomed Opt Express 2020 Oct 15;11(10):5603-5617. Epub 2020 Sep 15.

Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Edificio 34), E-30100 Murcia, Spain.

When the eye is exposed to pulsed infrared (IR) light, it is perceived as visible of the corresponding half wavelength. Previous studies have reported evidence that this is due to a non-linear two-photon absorption process. We have carried out a study which provides additional support to this nonlinear hypothesis. To this end, we have measured the spectral sensitivity at 2 different pulse repetition rates and have developed a theoretical model to account for the experimental observations. This model predicts a ratio between the minimum powers needed to detect the visual stimulus at the 2 pulse repetition rates employed of 0.45 if the stimulus were detected through a nonlinear effect and 1 if it were caused by a linear effect as in normal vision. The value experimentally found was 0.52 ± 0.07, which supports the hypothesis of a nonlinear origin of the two-photon vision phenomena.
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http://dx.doi.org/10.1364/BOE.403695DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7587254PMC
October 2020

In vivo SS-OCT imaging of crystalline lens sutures.

Biomed Opt Express 2020 Oct 2;11(10):5388-5400. Epub 2020 Sep 2.

Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, ul. Grudziądzka 5, 87-100 Toruń, Poland.

We demonstrate three-dimensional (3-D) visualization of crystalline lens sutures in healthy eyes using swept source optical coherence tomography (SS-OCT). Volumetric data sets of the crystalline lenses were acquired and processed to obtain enhanced contrast projection images and to extract suture patterns in both anterior and posterior lens. The results presented different types of the sutures including Y-sutures, simple and complex star sutures. Age-related changes in suture arrangement were characterized quantitatively. Crystalline lens suture imaging with SS-OCT might be a useful tool in fundamental studies on development and ageing of human lens.
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http://dx.doi.org/10.1364/BOE.401254DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7587285PMC
October 2020

Two-dimensional peripheral refraction and retinal image quality in orthokeratology lens wearers.

Biomed Opt Express 2020 Jul 4;11(7):3523-3533. Epub 2020 Jun 4.

Aier School of Ophthalmology, Central South University, Changsha, China.

Orthokeratology (O-K) is a common procedure that uses rigid contact lenses to reshape the cornea while worn overnight. Beyond the correction of refractive error, it has been suggested that this approach can also be used to reduce myopia progression, possibly because it induces changes in peripheral optics. As this hypothesis remains unproven, the aim of the present study was to explore changes in peripheral retinal optical quality in a group of myopic children following O-K treatment. We provide a comprehensive description of optical characteristics in a group of myopes before and after achieving stable corneal reshaping using overnight O-K lenses. These characteristics extended across the central visual field (60° horizontal x 36° vertical) as measured with a custom Hartmman-Shack wavefront sensor. After corneal reshaping, peripheral refraction was found to be asymmetrically distributed, with a myopic relative refraction of approximately 3D in the temporal retina. Astigmatism and higher order aberrations also increased in the temporal side. Based on corneal topography following treatment, subjects were divided into two groups: Centred Treatment (CT, decentration ∈ [-0.5 + 0.5] mm) and Slightly Decentred Treatment (subjects with more decentred lenses). The process was also modelled by ray-tracing simulation. The results indicate that increased myopia in the temporal retina is caused by the decentration of lenses towards the temporal side. Peripheral optics differ significantly following O-K lens treatment, but further research is required to determine whether this is likely to affect myopia progression.
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http://dx.doi.org/10.1364/BOE.397077DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7510915PMC
July 2020

Fluorescent bicolour sensor for low-background neutrinoless double β decay experiments.

Nature 2020 07 22;583(7814):48-54. Epub 2020 Jun 22.

Donostia International Physics Center (DIPC), San Sebastián/Donostia, Spain.

Observation of the neutrinoless double β decay is the only practical way to establish that neutrinos are their own antiparticles. Because of the small masses of neutrinos, the lifetime of neutrinoless double β decay is expected to be at least ten orders of magnitude greater than the typical lifetimes of natural radioactive chains, which can mimic the experimental signature of neutrinoless double β decay. The most robust identification of neutrinoless double β decay requires the definition of a signature signal-such as the observation of the daughter atom in the decay-that cannot be generated by radioactive backgrounds, as well as excellent energy resolution. In particular, the neutrinoless double β decay of Xe could be established by detecting the daughter atom, Ba, in its doubly ionized state. Here we demonstrate an important step towards a 'barium-tagging' experiment, which identifies double β decay through the detection of a single Ba ion. We propose a fluorescent bicolour indicator as the core of a sensor that can detect single Ba ions in a high-pressure xenon gas detector. In a sensor made of a monolayer of such indicators, the Ba dication would be captured by one of the molecules and generate a Ba-coordinated species with distinct photophysical properties. The presence of such a single Ba-coordinated indicator would be revealed by its response to repeated interrogation with a laser system, enabling the development of a sensor able to detect single Ba ions in high-pressure xenon gas detectors for barium-tagging experiments.
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http://dx.doi.org/10.1038/s41586-020-2431-5DOI Listing
July 2020

Two-Dimensional, High-Resolution Peripheral Refraction in Adults with Isomyopia and Anisomyopia.

Invest Ophthalmol Vis Sci 2020 06;61(6):16

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Purpose: The purpose of this study was to investigate the two-dimensional peripheral refraction in fellow eyes of patients with isomyopia and anisomyopia.

Methods: Sixty-eight young adults were recruited, including 25 isomyopes with interocular differences (IODs) of foveal refraction < 1.00 D and 43 anisomyopes with IOD > 1.50 D. Peripheral refraction across an area of the visual field of 60° × 36° with a resolution of 1° was measured using a custom-made Hartmann-Shack wavefront sensor. The retinal area was divided into 3 × 3 zones for comparison between the fellow eyes.

Results: There was no difference of refraction in all corresponding zones between the fellow eyes in the isomyopic group (all P > 0.05). The IODs between more myopic (MM) eyes and less myopic (LM) eyes in the anisomyopic group ranged from -1.40 to approximately -2.46 D (all P <0.001), which was flagged in the center and attenuated in peripheral zones by varied magnitudes. In the stratification analysis for different levels of anisomyopia, the nasal retina first presented significant relative hyperopic shifts compared to the center, followed by the temporal retina. In contrast, the superior and inferior periphery only differed from the center when the central IOD was greater than 3.00 D.

Conclusions: The two-dimensional peripheral refraction patterns showed a mirror symmetry between the fellow eyes of a patient with isomyopia. However, in the anisomyopic group, peripheral refraction showed significantly relative hyperopic shift when compared with the center and developed with a varied rate in different areas. These findings may indicate an asymmetrical variation in the peripheral refraction patterns during myopia progression.
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http://dx.doi.org/10.1167/iovs.61.6.16DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7415287PMC
June 2020

Inheritance of Refractive Error in Millennials.

Sci Rep 2020 05 18;10(1):8173. Epub 2020 May 18.

Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Ed. 34), 30100, Murcia, Spain.

Over the last decades, the prevalence of myopia has suddenly increased, and at this rate, half of the world's population will be myopic by the year 2050. Contemporary behavioural and lifestyle circumstances, along with emergent technology, are thought to be responsible for this increase. Twin studies mostly reported a high heritability of refractive error across ethnicities. However, heritability is a population statistic and could vary as a result of changing environmental conditions. We studied the variance of refractive error in millennials with 100 twin pairs of university students in southeast Spain. The study population presented a high prevalence of myopia (77%). Statistical analysis showed the variance of refractive error in this group of young twins was mainly driven by the shared environment and, to a lesser extent, by additive genetic factors. We found an increase in myopia prevalence accompanied by a decrease in heritability in this sample of millennials in contrast with results from a previous generation group from the same ethnic origin.
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http://dx.doi.org/10.1038/s41598-020-65130-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7235039PMC
May 2020

Peripheral image quality in pseudophakic eyes.

Biomed Opt Express 2020 Apr 11;11(4):1892-1900. Epub 2020 Mar 11.

Department of Research, Athens Eye Hospital, Leof. Vouliagmenis 45, Glifada 166 75, Greece.

The purpose of this work was to evaluate peripheral image quality in the pseudophakic eye using computational, physical, and psychophysical methods. We designed and constructed a physical model of the pseudophakic human eye with realistic dimensions using a corneal phantom and a board-only camera that was pivoted around an axis that matched the anatomical center of a human retina, assuming a radius of curvature of 12 mm, while it was submersed in a 23.4 mm long water filled chamber to emulate human ocular axial length. We used this optical setup to perform direct recording of the point spread function (PSF) and the associated retinal images for a commercial intraocular lens (IOL). Additionally, psychophysical tests were carried out to investigate the impact of the off-axis astigmatism in peripheral visual performance, where spectacle-induced astigmatism simulated the pseudophakic conditions in healthy subjects. Our findings using the physical eye model confirm the existence of large amounts of astigmatism in the periphery of the pseudophakic eye. The psychophysical tests revealed a significant reduction of detection sensitivity in the peripheral visual field. The latter suggests that off-axis astigmatism in patients implanted with IOLs may have performance and safety implications for activities requiring efficient peripheral vision.
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http://dx.doi.org/10.1364/BOE.387254DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7173905PMC
April 2020

33 International Pupil Colloquium, Murcia, Universidad de Murcia (Spain); 2 -4 October 2019.

Ophthalmic Physiol Opt 2020 05;40(3):376

Laboratorio de Optica, Universidad de Murcia, Murcia, Spain.

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http://dx.doi.org/10.1111/opo.12688DOI Listing
May 2020

Spherical Aberration Customization to Extend the Depth of Focus With a Clinical Adaptive Optics Visual Simulator.

J Refract Surg 2020 Apr;36(4):223-229

Purpose: To evaluate the use of the VAO adaptive optics visual simulator (Voptica SL, Murcia, Spain) for customization of spherical aberration to increase depth of focus.

Methods: Through-focus visual acuity with both high- and low-contrast letters from +1.00 to -3.00 diopters (D) was measured in 17 dilated eyes with three different induced amounts of spherical aberration for a 4.5-mm pupil diameter: control (0 µm), -0.15 µm, and -0.30 µm.

Results: The defocus curves followed the same behavior with both values of contrast, but the visual acuity was 0.2 logMAR lower with low contrast. The mean values of high-contrast logMAR visual acuity at far, intermediate (67 cm), and near (40 cm) were -0.10, 0.11, and 0.37 for control, 0.04, 0.00, and 0.15 for -0.15 µm, and 0.23, 0.00, and 0.06 for -0.30 µm conditions. The 95% confidence interval ranged from ±0.14 to ±0.45 logMAR and the middle 50% of the distribution was approximately 0.2 logMAR.

Conclusions: Negative values of spherical aberration extend the depth of focus in different ways depending on each patient. The VAO is a new instrument that allows the visual customization of spherical aberration to enhance depth of focus. [J Refract Surg. 2020;36(4):223-229.].
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http://dx.doi.org/10.3928/1081597X-20200212-02DOI Listing
April 2020

Impact of longitudinal chromatic aberration on through-focus visual acuity.

Opt Express 2019 Nov;27(24):35935-35947

An enhanced adaptive optics visual simulator (AOVS) was used to study the impact of chromatic aberration on vision. In particular, through-focus visual acuity (VA) was measured in four subjects under three longitudinal chromatic aberration (LCA) conditions: natural LCA, compensated LCA and doubled LCA. Ray-tracing simulations using a chromatic eye model were also performed for a better understanding of experimental results. Simulations predicted the optical quality of the retinal images and VA by applying a semi-empirical formula. Experimental and ray tracing results showed a significant agreement in the natural LCA case (R = 0.92). Modifying the LCA caused an impairment in the predictability of the results, with decreasing correlations between experiment and simulations (compensated LCA, R = 0.84; doubled LCA, R = 0.59). VA under modified LCA was systematically overestimated by the model around the best focus position. The results provided useful information on how LCA manipulation affects the depth of focus. Decreased capability of the model to predict VA in modified LCA conditions suggests that neural adaptation may play a role.
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http://dx.doi.org/10.1364/OE.27.035935DOI Listing
November 2019

2-D Peripheral image quality metrics with different types of multifocal contact lenses.

Sci Rep 2019 12 6;9(1):18487. Epub 2019 Dec 6.

Eberhard Karls University Tuebingen, Institute for Ophthalmic Research, Tuebingen, 72076, Germany.

To evaluate the impact of multifocal contact lens wear on the image quality metrics across the visual field in the context of eye growth and myopia control. Two-dimensional cross-correlation coefficients were estimated by comparing a reference image against the computed retinal images for every location. Retinal images were simulated based on the measured optical aberrations of the naked eye and a set of multifocal contact lenses (centre-near and centre-distance designs), and images were spatially filtered to match the resolution limit at each eccentricity. Value maps showing the reduction in the quality of the image through each optical condition were obtained by subtracting the optical image quality from the theoretical physiological limits. Results indicate that multifocal contact lenses degrade the image quality independently from their optical design, though this result depends on the type of analysis conducted. Analysis of the image quality across the visual field should not be oversimplified to a single number but split into regional and groups because it provides more insightful information and can avoid misinterpretation of the results. The decay of the image quality caused by the multifocal contacts alone, cannot explain the translation of peripheral defocus towards protection on myopia progression, and a different explanation needs to be found.
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http://dx.doi.org/10.1038/s41598-019-54783-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6898319PMC
December 2019

One-year follow-up of changes in refraction and aberrations induced by corneal incision.

PLoS One 2019 18;14(11):e0224823. Epub 2019 Nov 18.

Laboratorio de Óptica, Universidad de Murcia, Murcia, Spain.

Purpose: To evaluate the surgically induced changes in refraction (sphere and astigmatism) and higher order aberrations by corneal incision for one year.

Setting: University Hospital "Virgen de la Arrixaca", Murcia, Spain.

Design: Retrospective interventional case series.

Methods: Corneal power, astigmatism and higher order aberrations (HOA) were calculated from corneal topography measured in 27 eyes prior to surgery and at 2 weeks, 1, 2, 3 and 6 months and 1 year following cataract surgery with 3.2-mm corneal incision. At every stage, optical changes were calculated as the difference between pre- and post-surgery data (in each follow-up) using the formulas of obliquely crossed cylinders for the refraction and Zernikes coefficients for HOA.

Results: At 2 weeks after surgery the mean corneal values of induced sphere, cylinder and the root mean square (RMS) of HOA were +0.54±0.27 D, -0.77±0.32 D and 0.15 microns respectively. These parameters decreased significantly (p-values between 0 and 0.01) at 3 months to +0.33±0.27 D sphere, -0.50±0.24 D cylinder and 0.10±0.05 microns HOA and were stable at the next follow-ups. Induced spherical equivalent was around zero at all visits. The changes in HOA were mainly due to trefoil aberration.

Conclusions: Linear corneal incisions do not change the spherical power but can induce significant values of astigmatism and trefoil aberration in the cornea. However, these changes revert fully or partially to preoperative values by the third month after surgery and remain stable with time.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0224823PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6860439PMC
March 2020

Two-dimensional Peripheral Refraction and Retinal Image Quality in Emmetropic Children.

Sci Rep 2019 11 7;9(1):16203. Epub 2019 Nov 7.

Aier School of Ophthalmology, Central South University, 410000, Changsha, China.

The relationship between the optical properties of the eye in the periphery and myopia development is still under debate. To further clarify this issue, we provide here baseline data of two-dimensional peripheral optics results in a group of emmetropic Chinese children. Peripheral aberrations were measured under cycloplegia by using an open-view Hartmann-Shack wavefront sensor (VPR, Voptica SL, Spain). This instrument allows to measure fast in the horizontal visual field from temporal 30° to nasal 30° every 1°. Two-dimensional (2D) maps were retrieved from a series of horizonal scans taken every 4° from 20° superior to 16° inferior covering a visual field of 60 × 36°. A relatively homogeneous pattern of the 2D relative peripheral refraction was found across all these emmetropic subjects. Using cluster analysis followed by manual visual refinement, the 2D maps were identified to fit into four categories. More than 70% of the subjects showed a nearly flat horizontal refraction with a slightly myopic shift in the superior retina. Peripheral astigmatism was quite constant across subjects and similar to that expected theoretically. Peripheral aberrations were also similar to those in the fovea for a large retinal area. These baseline data would offer an important reference to compare with the future evolution with time, as well as with other refractive or age groups of subjects, to better understand the role of peripheral optical properties in myopia development.
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http://dx.doi.org/10.1038/s41598-019-52533-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6838170PMC
November 2019

Objective method for measuring the macular pigment optical density in the eye.

Biomed Opt Express 2019 Jul 24;10(7):3572-3583. Epub 2019 Jun 24.

Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo, E-30100 Murcia, Spain.

Macular pigment is a yellowish pigment of purely dietary origin, which is thought to have a protective role in the retina. Recently, it was linked to age-related macular degeneration and improved visual function. In this work, we present a method and a corresponding optical instrument for the rapid measurement of its optical density. The method is based on fundus reflectometry and features a photodetector for the measurement of reflectance at different wavelengths and retinal locations. The method has been tested against a commercially available instrument on a group of healthy volunteers and has shown good correlation. The proposed instrument can serve as a rapid, non-midriatic, low-cost tool for the measurement of macular pigment optical density.
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http://dx.doi.org/10.1364/BOE.10.003572DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6706042PMC
July 2019

Single-pixel imaging of the retina through scattering media.

Biomed Opt Express 2019 Aug 19;10(8):4159-4167. Epub 2019 Jul 19.

Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Edificio 34), E-30100, Murcia, Spain.

Imaging the retina of cataractous patients is useful to detect pathologies before the cataract surgery is performed. However, for conventional ophthalmoscopes, opacifications convert the lens into a scattering medium that may greatly deteriorate the retinal image. In this paper we show, as a proof of concept, that it is possible to surpass the limitations imposed by scattering applying to both, a model and a healthy eye, a newly developed ophthalmoscope based on single-pixel imaging. To this end, an instrument was built that incorporates two imaging modalities: conventional flood illumination and single-pixel based. Images of the retina were acquired firstly in an artificial eye and later in healthy living eyes with different elements which replicate the scattering produced by cataractous lenses. Comparison between both types of imaging modalities shows that, under high levels of scattering, the single-pixel ophthalmoscope outperforms standard imaging methods.
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http://dx.doi.org/10.1364/BOE.10.004159DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6701540PMC
August 2019

In vivo two-photon microscopy of the human eye.

Sci Rep 2019 07 12;9(1):10121. Epub 2019 Jul 12.

Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo (Ed. 34), 30100, Murcia, Spain.

Two-photon (2P) microscopy is a powerful tool for imaging and exploring label-free biological tissues at high resolution. Although this type of microscopy has been demonstrated in ex vivo ocular tissues of both humans and animal models, imaging the human eye in vivo has always been challenging. This work presents a novel compact 2P microscope for non-contact imaging of the anterior part of the living human eye. The performance of the instrument was tested and the maximum permissible exposure to protect ocular tissues established. To the best of our knowledge, 2P images of the in vivo human cornea, the sclera and the trabecular meshwork are shown for the very first time. Acquired images are of enough quality to visualize collagen arrangement and morphological features of clinical interest. Future implementations of this technique may constitute a potential tool for early diagnosis of ocular diseases at submicron scale.
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http://dx.doi.org/10.1038/s41598-019-46568-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6626016PMC
July 2019

Quantitative Discrimination of Healthy and Diseased Corneas With Second Harmonic Generation Microscopy.

Transl Vis Sci Technol 2019 May 27;8(3):51. Epub 2019 Jun 27.

Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Murcia, Spain.

Purpose: To analyze the spatial organization of pathological corneas with second harmonic generation (SHG) imaging and to provide a proof of concept to objectively distinguish these from the healthy corneas.

Methods: A custom-built SHG microscope was used to image the anterior stroma of ex vivo corneas, both control and affected by some representative pathologies. The structure tensor (ST) was employed as a metric to explore and quantify the alterations in the spatial distribution of the collagen lamellae.

Results: The collagen arrangement differed between healthy and pathological samples. The former showed a regular distribution and a low structural dispersion (SD < 40°) within the stroma with a well-defined dominant orientation. This regular arrangement drastically turns into a disorganized pattern in pathological corneas (SD > 40°).

Conclusions: The combination of SHG imaging and the ST allows obtaining quantitative information to differentiate the stromal collagen organization in healthy and diseased corneas. This approach represents a feasible and powerful technique with potential applications in clinical corneal diagnoses.

Translational Relevance: The ST applied to SHG microscopy images of the corneal stroma provides an experimental objective score to differentiate control from pathological or damaged corneas. Future implementations of this technique in clinical environments might might be a promising tool in Ophthalmology, not only to diagnose and monitor corneal diseases, but also to follow-up surgical outcome.
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http://dx.doi.org/10.1167/tvst.8.3.51DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6601709PMC
May 2019

Comparing the performance of a femto fiber-based laser and a Ti:sapphire used for multiphoton microscopy applications.

Appl Opt 2019 May;58(14):3830-3835

Ti:sapphire laser systems are the more extended excitation sources in multiphoton (MP) microscopy. Although tunable, the cost, size, and lack of portability often limit their use in some research fields. Femtosecond fiber-based lasers represent an attractive alternative since they are portable, compact, and affordable. Most MP applications using these devices employ wavelengths beyond 1000 nm. This work evaluates the performance of a mode-locked fiber-based laser emitting at 780 nm (within the spectral region often used with Ti:sapphire devices) for use in MP imaging microscopy. MP images acquired with this laser system have been compared with those obtained with a "regular" solid-state source. Results herein show that the images recorded with both laser sources were similar, independently of the depth location of the imaged plane. The structural information contained in the images hardly differed. Moreover, the images of deeper layers improved by means of adaptive optics were also similar. These ultrafast laser sources are expected to enhance the impact of MP microscopy in basic research, as well as in biomedical environments.
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http://dx.doi.org/10.1364/AO.58.003830DOI Listing
May 2019

Simultaneous aberration and aperture control using a single spatial light modulator.

Opt Express 2019 Apr;27(9):12399-12413

A method to simultaneously control aberrations and the aperture of an optical system using a single phase-only spatial light modulator was investigated. The experiment was performed using a liquid-crystal-on-silicon spatial light modulator (LCoS-SLM) within an adaptive optics system used for visual testing, although the method has broader applications in adaptive optics field. The performance of the technique was characterized through the estimation of the system's modulation transfer functions (MTFs) by using a random chart method. MTFs obtained from the phase modulation-based approach were compared with those from using a real aperture (diaphragm). The areas under the MTFs for the two conditions were similar up to 98%, confirming that the low-pass filter effect associated to the size of the entrance pupil was similar for the phase-modulated pupil and the physical pupil. As an example of application, both aberrations and pupil were controlled by a single phase-only modulator to study the through-focus visual performance in real subjects. Limitations and possible enhancements of the presented method were also discussed. The presented technique reduces complexity and cost of adaptive optics systems. It opens the door to new experiments by allowing dynamic modulation of aberrations and apertures of any shape.
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http://dx.doi.org/10.1364/OE.27.012399DOI Listing
April 2019

Wide-range adaptive optics visual simulator with a tunable lens.

J Opt Soc Am A Opt Image Sci Vis 2019 May;36(5):722-730

An adaptive optics visual simulator (AOVS) with an extended dioptric range was developed, allowing measuring and correcting aberrations in a majority of highly ametropic eyes. In the instrument, a tunable lens is used for defocus correction, while a liquid-crystal-on-silicon spatial light modulator is used for compensating or inducing any other aberration. The instrument incorporates a digital projector, which uses a micromirror array to display the stimuli. A motorized diaphragm enables operation for any physiological pupil size. A full description of the instrument and its calibration are provided, together with the results obtained in seven highly myopic subjects with refraction of -7.2±1.8   (mean±). Refraction obtained with the instrument was compared to the standard refraction prescribed by trial lenses. When using the refraction obtained by the AOVS, the visual acuity (VA) exhibited an average increase of 0.21 (decimal scale). The visual impact of correcting high-order aberrations is presented in three subjects, whose VAs slightly improved with the correction. High myopes are able to benefit from the improved refraction assessment. The new instrument creates a possibility for a wide number of new experiments, especially for eyes exhibiting large refractive errors, where previous AO instruments failed to operate.
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http://dx.doi.org/10.1364/JOSAA.36.000722DOI Listing
May 2019

Tear-film dynamics by combining double-pass images, pupil retro-illumination, and contrast sensitivity.

J Opt Soc Am A Opt Image Sci Vis 2019 Apr;36(4):B138-B142

Tear-film dynamics were analyzed by a synchronizing recording of double-pass (DP) and pupil retro-illumination (RI) images with contrast sensitivity (CS) measurements. Simultaneous DP and RI images were acquired in three subjects wearing contact lenses while keeping the eye open. Changes in contrast sensitivity for an 18 c/deg green grating were also estimated. From the DP retinal images, the effect of the tear film is described through the objective scattering index (OSI). This presented a negative correlation with the increase in CS during tear-film deterioration (as observed by RI imaging). These results show a relationship between visual outcome degradation due to tear-film breakup and the increase in intraocular scattering. This work shows a combined methodology for the evaluation of tear-film dynamics.
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http://dx.doi.org/10.1364/JOSAA.36.00B138DOI Listing
April 2019

Effect of Crystalline Lens Aberrations on Adaptive Optics Simulation of Intraocular Lenses.

J Refract Surg 2019 Feb;35(2):126-131

Purpose: To evaluate the impact of the lens aberrations on the adaptive optics visual simulation of pseudophakic intraocular lens (IOL) profiles.

Methods: In 20 right phakic eyes, lens higher order aberrations (HOAs) were calculated as the whole eye minus the corneal aberrations. Visual simulation using low and high contrast corrected distance visual acuity (CDVA) testing was carried out with the VAO instrument (Voptica, SL, Murcia, Spain), considering three optical conditions of the lens: removing HOA (no lens-HOA), removing spherical aberration (no lens-SA), and with lens HOA (natural condition). In addition, a through-focus visual simulation of a trifocal diffractive IOL profile with high contrast CDVA was also measured in two conditions: no lens-HOA and natural condition. Three different pupil sizes (3, 4.5, and 6 mm) were tested for all conditions.

Results: There were no significant intersubject differences between the three optical conditions and in the IOL simulation for all pupil sizes (P > .05). For 4.5- and 6-mm pupils, mean VA values of the no-lens SA and no lens-HOA conditions were similar and slightly worse than those of the natural condition. Individual differences between the no lens-HOA condition and the other two optical conditions, estimated as 95% limits of agreement, were acceptable for 3-mm pupil but worse as pupil diameter increased.

Conclusions: The effect of lens aberrations on visual simulation is imperceptible for a small pupil diameter of 3 mm. Although the increment of pupil size increases the probability of patients with significant visual impact of lens HOAs, the mean intersubject VA differences are negligible. [J Refract Surg. 2019;35(2):126-131.].
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http://dx.doi.org/10.3928/1081597X-20181212-02DOI Listing
February 2019

Initial Clinical Results With a Novel Monofocal-Type Intraocular Lens for Extended Macular Vision in Patients With Macular Degeneration.

J Refract Surg 2018 Nov;34(11):718-725

Purpose: To determine the feasibility of a novel intraocular lens (IOL) designed to improve retinal image quality at up to 10° of retinal eccentricity and optionally provide retinal magnification in patients with macular disease.

Methods: In this prospective, interventional pilot study, 8 eyes of 7 patients with bilateral dry age-related macular degeneration and 1+ or less cataract underwent phacoemulsification and capsular bag implantation of a single, injectable, hydrophobic acrylic IOL. Safety and efficacy were assessed by monitoring logMAR corrected distance and near visual acuity, intraocular pressure, specular microscopy, 80-point visual field testing, and anterior segment and macular optical coherence tomography at baseline and 1 week, 1 month, and 2 months postoperatively. Microperimetry was undertaken at baseline and 1 and/or 2 months postoperatively. Reading performance was assessed at baseline and 1 month postoperatively using the Minnesota low vision reading chart (MNREAD; Precision Vision, LaSalle, IL).

Results: Safety outcomes were equivalent to standard monofocal IOLs. Visual acuities improved in all patients. Mean corrected distance visual acuity improved from 0.93 ± 0.22 preoperatively to 0.59 ± 0.25 at 2 months postoperatively. Mean reading speed increased from 28 ± 19 to 44 ± 31 words per minute. Mean microperimetry threshold sensitivities increased from 8.2 ± 4.6 to 12 ± 5.6 dB. Mean percentage of fixation points within a 4° circle increased from 77% ± 17% to 91% ± 11% with evidence for progressive movement of preferred retinal loci away from areas of geographic atrophy.

Conclusions: Initial results indicate this novel IOL has a safety profile comparable with standard IOLs. Visual benefits may exceed those obtained with existing technologies in patients with macular disease. Further work is required to determine the full potential of extended macular vision technology. [J Refract Surg. 2018;34(11):718-725.].
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http://dx.doi.org/10.3928/1081597X-20180831-01DOI Listing
November 2018

Patient-specific determination of change in ocular spherical aberration to improve near and intermediate visual acuity of presbyopic eyes.

J Biophotonics 2019 Apr 9;12(4):e201800259. Epub 2018 Dec 9.

Imaging, Biomechanics and Mathematical Modeling Solutions Lab, Narayana Nethralaya Foundation, Bangalore, India.

The purpose was to determine the optimum negative spherical aberration induction required to improve near and intermediate visual acuity (VA) of presbyopic eyes. A total of 174 normal and diabetic (no retinopathy) presbyopic eyes (age ≥ 40 years) were measured with visual adaptive optics simulator (Voptica, Spain). First, baseline uncorrected VA and aberrations were measured. VA at 40 cm (near), 80 cm (intermediate) and distance was measured. Then, a negative spherical aberration (SA) was added to baseline ocular SA, and VA at all targets was reassessed after correction of distance refractive error. Clinically, baseline SA and root mean square of higher order aberrations were similar between the normal and diabetic presbyopic eyes. Baseline VA of the diabetic eyes at near and intermediate was better than the same of normal eyes (P = 0.001). After SA change, VA at near and intermediate of both normal and diabetic presbyopic eyes improved. However, fewer diabetic eyes needed higher SA change than normal eyes (P = 0.03). The corresponding trends with change in VA at near and intermediate were also similar between the normal and diabetic eyes. Patient-specific modulation of ocular SA to improve near and intermediate VA in a large cohort of eyes was successful in improving VA, sometimes even distance VA.
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http://dx.doi.org/10.1002/jbio.201800259DOI Listing
April 2019

Volumetric macro- and micro-scale assessment of crystalline lens opacities in cataract patients using long-depth-range swept source optical coherence tomography.

Biomed Opt Express 2018 Aug 24;9(8):3821-3833. Epub 2018 Jul 24.

Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Campus de Espinardo, E-30100 Murcia, Spain.

We demonstrate an optimized optical platform for the three-dimensional (3-D) visualization of crystalline lens opacities in vivo in the eyes of patients with different types and grades of cataracts. We developed a prototype long-depth-range swept source optical coherence tomography (SS-OCT) instrument operating at the speed of 50 kA-scans/second and at the central wavelength of 1 μm to perform high-resolution imaging of the whole anterior segment of the eye. Volumetric data sets of cataractous eyes were acquired and processed to obtain contrast-enhanced high-resolution images of lenticular structures and opacifications. The results showed lens micro- and macro-scale features related to possible cataract development such as cortical spokes, water clefts and enhanced scattering in the lens nucleus. The results demonstrate also the ability of this SS-OCT imaging to locate and characterize opacities quantitatively. The instrument might be a useful tool in the high-resolution preoperative evaluation of crystalline lens opacities in cataract patients.
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http://dx.doi.org/10.1364/BOE.9.003821DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6191641PMC
August 2018