Dr. Pedro M. Serra Profile

Dr. Pedro M. Serra

Assistant Professor at Univ of Beira Interior

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Proceedings Article | 3 October 2019 Paper

Influence of pupil function in pseudophakia

Elsa S. Fonseca, Paulo Fiadeiro, Renato Gomes, Angel Sanchez Trancon, António M. Baptista, Pedro Serra

Proceedings Volume 11207, 112071N (2019) https://doi.org/10.1117/12.2527412

KEYWORDS: Eye models, Eye, Visualization, Data modeling, Visual process modeling, Image quality, Spherical lenses, Statistical modeling, Modulation transfer functions, Surgery

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In pseudophakia, the eye is unable accommodate so proximal objects can be properly focused. Achieving functional vision levels relies on individual anatomical features, notably, the pupil size. This study measured the range of pupil sizes found in a population of pseudophakes, for an object placed at different distances, and modeled the optical quality associated to pupil variation. The pupil size of 58 pseudophakic eyes (age mean ± standard deviation: 70.5 ± 11.3 years) was measured using a binocular eye-tracker. The participants observed on a monitor a circular white patch subtending 5° with a cross on its center. The object was placed at 3.0, 1.0, 0.66, 0.5, 0.4, 0.33 m. The pupil size variation as a function of object distance was modelled using a linear mixed effects model. The mean and 95% confidence interval (CI) were calculated for a far object and the slope of the function, indicative of the proximal myosis. The effect of object distance on the image quality was modeled using a pseudophakic model eye for the pupil size data. The mean distance pupil sizes were 4.45 (95%CI: 2.74, 6.17) mm and the mean proximal myosis was -0.23 (95%CI: -0.53, -0.08) mm/D. The VA estimation for a distance object ranged from -0.1 logMAR for the smallest pupil to 0.08 logMAR and the near VA when mean myosis was considered ranged from 0.28 logMAR to 0.65 logMAR. These results support the importance of distance pupil size measurement for the prediction of visual performance in pseudophakia, while suggesting that myosis has a negligible impact in VA variability.

Proceedings Article | 22 August 2014 Paper

Revisiting grating orientation effects on visual contrast sensitivity using optical interferometry

P. Serra, L. Santos, J. Corte-Real, P. Fiadeiro

Proceedings Volume 9286, 92864E (2014) https://doi.org/10.1117/12.2063728

KEYWORDS: Contrast sensitivity, Spatial frequencies, Eye, Visualization, Fringe analysis, Interferometers, Visual optics, Phase modulation, Visual system, Retina

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Sinusoidal gratings of equal spatial frequency but different orientation require different levels of contrast to be detected by the human visual system. This phenomenon defined as oblique effect has a neuronal origin. The purpose of this work was to determine the neuronal magnitude of this effect, by isolating it from the optics of the eye. A visual interferometer was assembled to generate and project on the retina an interference pattern consisting of sinusoidal gratings with variable orientation (0º to 165º, 15º step). Adding background light to the interference pattern of 12 cycles/degree (cpd), different contrast levels were generated while the retinal illuminance was kept unaltered. A 2º circular stimulus was presented (during 500 ms) on the fovea producing a retinal illuminance of 134 Td (trolands). The contrast sensitivity threshold of four observers (ages 23, 33, 33, 52 years old) was determined using a Yes-No psychophysical method, and the 50% odds of correct response determined by a Weibull cumulative function. The four observers showed different contrast sensitivity thresholds dependent on the grating orientation. Oblique gratings (≈45º/≈135º) required more contrast to be detected than horizontal and vertical gratings. The maximum differences in contrast sensitivity between orientations ranged from 0.15 to 0.31 log units. The mean contrast threshold across all orientations was then calculated to investigate the effect of age on the contrast sensitivity. It was found a 0.046 log units decrease per decade (r=0.94). Oblique effect is an evident neuronal phenomenon with considerable inter-subject variability, making grating orientation important information in contrast sensitivity evaluation.

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