Correction and control of ocular aberrations with adaptive optics : effects on human vision

El objetivo de esta tesis doctoral es la comprensión de la relación entre la óptica de la imagen que se proyecta en la retina (en particular, la degradación impuesta por las aberraciones ópticas de alto orden) y la calidad visual. Se ha llevado a cabo el desarrollo de un nuevo sistema de Óptica Adaptativa, que incluye un sensor de frente de onda tipo Hartmann-Shack y un espejo deformable, implementando vías de psicofísica para la medida de la función visual y percepción neuronal bajo control de las aberraciones oculares mediante el espejo deformable. En esta tesis, se presenta una serie de estudios psicofísicos desarrollados para investigar el efecto de la aberraciones sobre la visión humana y la adaptación neuronal a las aberraciones oculares y también para demostrar la correlación entre la codificación interna del emborronamiento y el emborronamiento impuesto por las aberraciones de alto orden en términos de magnitud y orientació

Influence of adaptive-optics ocular aberration correction on visual acuity at different luminances and contrast polarities

12 pages, 10 figures.We evaluated the visual benefit of correcting astigmatism and high-order aberrations with adaptive optics (AO) on visual acuity (VA) measured at 7 different luminances (ranging from 0.8 to 50 cd/m2) and two contrast polarities (black letters on white background, BoW, and white letters on black background, WoB) on 7 subjects. For the BoW condition, VA increased with background luminance in both natural and AO-corrected conditions, and there was a benefit of AO correction at all luminances (by a factor of 1.29 on average across luminances). For WoB VA increased with foreground luminance but decreased for the highest luminances. In this reversed polarity condition AO correction increased VA by a factor of 1.13 on average and did not produce a visual benefit at high luminances. The improvement of VA (averaged across conditions) was significantly correlated (p = 0.04) with the amount of corrected aberrations (in terms of Strehl ratio). The improved performance with WoB targets with respect to BoW targets is decreased when correcting aberrations, suggesting a role of ocular aberrations in the differences in visual performance between contrast polarities.MEyC FIS2005-04382, MCeI FIS 2008-02065, and EURYI award to SM; MEyC FPI Predoctoral Fellowship to LS; CSIC I3P Predoctoral Fellowship to EG.Peer reviewe

Change in arteriole diameter of retina with visual simulation

poster abstractNeural activity and blood flow in the brain are tightly coupled. This coupling allows the brain to respond to periods of increased neural activity with increased blood flow. This coupling is known as neurovascular coupling. Many vascular based imaging techniques such as Functional MRI scans provide maps of signals of brain activity but they are limited by the resolution of fMRI to a few mm. The fMRI signal is indirect because the scanner is not tracking the neural activity directly but are measuring the changes in the blood oxygen levels. Since the retina and optic tract are part of the central nerves system and they can be measured optically it should be possible to make precise measurements of the retinal vasculature of the human retina and its response to changing stimulation levels. In this study we used an adaptive optics scanning laser ophthalmoscope (AOSLO) with multiply scattered light to measure the change in arteriolar diameter when the retina was stimulated with flickering light. We hypothesized that we could use this technique to measure both arterial dilation and time course. We used information from the reflectance of the vessel to Change in arteriole diameter of retina with visual simulation measure total vessel diameter. Images were acquired at approximately 30 Hz and averaged over 3.3 second periods. Retinal arteries were measured in five observers before, during, and after presentation of a large flickering stimulus. There was a 6-10% dilation of the blood vessels during the flicker. The Vascular dilation occurred within seconds of flickering onset and constricted again following the end of flicker stimulation. This work shows that with modern retinal imaging methods it is possible to make precise measures of vascular constriction and its time course in response to changing tissue demand

Tunable lenses: Dynamic characterization and fine-tuned control for high-speed applications

Tunable lenses are becoming ubiquitous, in applications including microscopy, optical coherence tomography, computer vision, quality control, and presbyopic corrections. Many applications require an accurate control of the optical power of the lens in response to a time-dependent input waveform. We present a fast focimeter (3.8 KHz) to characterize the dynamic response of tunable lenses, which was demonstrated on different lens models. We found that the temporal response is repetitive and linear, which allowed the development of a robust compensation strategy based on the optimization of the input wave, using a linear time-invariant model. To our knowledge, this work presents the first procedure for a direct characterization of the transient response of tunable lenses and for compensation of their temporal distortions, and broadens the potential of tunable lenses also in high-speed applicationsVA and EL acknowledge financial support from Comunidad de Madrid and Marie Curie Action of the European Union FP7/2007-2013 COFUND 291820; XB from Comunidad de Madrid Doctorado Industrial IND2017/BMD-7670; EL from Spanish Government Ramon y Cajal Program RyC-2016-21125; EG from Spanish Government Torres-Quevedo Program PTQ-15-07432; LS from EU H2020 SME Innovation Associate GA-739882; EG from EIT Health; SM from ERC Grant Agreement ERC-2011-AdC 294099 and Spanish Government Grants FIS2014-56643-R; SM and CD from Spanish Government Grant FIS2017-84753-R; and CD from DTS16-0012

Visual Optics and Biophotonics Lab, Institute of Optics (CSIC): recent achievements, lines of research and future directions

The Visual Optics and Biophotonics Lab (Institute of Optics, CSIC) develops non-invasive optical techniques for the evaluation of the normal and pathological eye. We present experimental developments and recent results of applications in the fields of myopia and presbyopia and their correction techniques, as well as work in progress and future directions.El Laboratorio de Óptica Visual y Biofotónica del Instituto de Óptica del CSIC desarrolla técnicas ópticas no invasivas para la evaluación del ojo normal y patológico. Presentamos desarrollos experimentales y resultados recientes de aplicaciones en los campos de la miopía, presbicia y sus técnicas de corrección, así como trabajo en curso y direcciones futuras.La financiación reciente del grupo viene dada por dos proyectos del Ministerio de Educación y Ciencia (BFM2002-02638, FIS2005-04382), tres proyectos de la Comunidad Autónoma de Madrid (CAM08.7/0010.1/2000, CAM08.7/004.1/2003, GR/SAL/0387/2004), un Proyecto de Cooperación España-EEUU, una Acción Integrada, siete contratos de investigación con la industria, y un European Young Investigator Award. Además se han concedido a los distintos miembros del grupo becas y contratos postdoctorales I3P-CSIC, becas FPI, FPU, CSIC-Unidades Asociadas y de la Comunidad de Madrid.Peer reviewe

Accommodative lag and fluctuations when optical aberrations are manipulated

We evaluated the accommodative response to a stimulus moving from 0 to 6 D following a staircase function under natural, corrected, and induced optical aberrations, using an adaptive-optics (AO) electromagnetic deformable mirror. The accommodative response of the eye (through the mirror) and the change of aberrations were measured on 5 subjects using a Hartmann-Shack wavefront sensor operating at 12.8 Hz. Five conditions were tested: (1) natural aberrations, (2) AO correction of the unaccommodated state and induction (over 6-mm pupils) of (3) +1 2m and (4) j1 2m of spherical aberration and (5) j2 2m of vertical coma. Four subjects showed a better accommodative response with AO correction than with their natural aberrations. The induction of negative spherical aberration also produced a better accommodative response in the same subjects. Accommodative lag increased in all subjects when positive spherical aberration and coma were induced. Fluctuations of the accommodative response (computed during each 1-D period of steady accommodation) increased with accommodative response when high-order aberrations were induced. The largest fluctuations occurred for induced negative spherical aberration and the smallest for natural and corrected aberrations. The study demonstrates that aberrations influence accommodative lag and fluctuations of accommodation and that correcting aberrations improves rather than compromises the accommodative response

The organization of the cone photoreceptor mosaic measured in the living human retina

The cone photoreceptors represent the initial fundamental sampling step in the acquisition of visual information. While recent advances in adaptive optics have provided increasingly precise estimates of the packing density and spacing of the cone photoreceptors in the living human retina, little is known about the local cone arrangement beyond a tendency towards hexagonal packing. We analyzed the cone mosaic in data from 10 normal subjects. A technique was applied to calculate the local average cone mosaic structure which allowed us to determine the hexagonality, spacing and orientation of local regions. Using cone spacing estimates, we find the expected decrease in cone density with retinal eccentricity and higher densities along the horizontal meridians as opposed to the vertical meridians. Orientation analysis reveals an asymmetry in the local cone spacing of the hexagonal packing, with cones having a larger local spacing along the horizontal direction. This horizontal/vertical asymmetry is altered at eccentricities larger than 2 degrees in the superior meridian and 2.5 degrees in the inferior meridian. Analysis of hexagon orientations in the central 1.4° of the retina show a tendency for orientation to be locally coherent, with orientation patches consisting of between 35 and 240 cones

Visual performance with real-life tasks under Adaptive-Optics ocular aberration correction

We measured the effect of the correction of the natural aberrations of the eye by means of adaptive optics on the subject's performance on three different visual tasks: subjective sharpness assessment of natural images, familiar face recognition, and facial expression recognition. Images were presented through a dedicated psychophysical channel and viewed through an electromagnetic deformable mirror. Experiments were performed on 17 normal subjects. Ocular aberrations (astigmatism and higher order aberrations) were reduced on average from 0.366 ± 0.154 to 0.101 ± 0.055 μm for a 5-mm pupil diameter. On average, subjects considered to be sharper 84 ± 14% of the images viewed under AO correction, and there was a significant correlation between the amount of corrected aberrations and the percentage of images that the subject considered sharper when observed under AO-corrected aberrations. In all eyes (except one), AO correction improved familiar face recognition, by a factor of ×1.13 ± 0.12 on average. However, AO correction did not improve systematically facial expression recognition. © ARVO.MEyC FPI Predoctoral Fellowship to LS; CSIC I3P Predoctoral Fellowship to EG; MICINN FIS2008-02065 and PETRI PET-2006-0478, and EURYI-05-102-ES (EURHORCs-ESF) to SM.Peer Reviewe

Adaptive optics retinal imaging with automatic detection of the pupil and its boundary in real time using Shack-Hartmann images

Retinal imaging with an adaptive optics system usually requires that the eye be centered and stable relative to the exit pupil of the system. Aberrations are then typically corrected inside a fixed circular pupil. This approach can be restrictive when imaging some subjects since the pupil may not be round and maintaining a stable head position can be difficult. In this paper we present an automatic algorithm that relaxes these constraints. An image quality metric is computed for each spot of the Shack Hartmann image to detect the pupil and its boundary and the control algorithm is applied only to regions within the subject’s pupil. Images on a model eye as well as for five subjects were obtained to show that a system exit pupil larger than the subject’s eye pupil could be used for AO retinal imaging without a reduction in image quality. This algorithm automates the task of selecting pupil size. It also may relax constrains on centering the subject’s pupil and on the shape of the pupil