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.
Digital holography is a growing field that owes its success to the provided three-dimensional imaging representation. This is achieved by encoding the wave field transmitted or scattered by an object in the form of an interference pattern with a reference beam. While in conventional imaging systems it is usually impossible to recover the correct focused image from a defocused one, with digital holography the image can be numerically retrieved at any distance from the hologram. Digital holography also allows the reconstruction of multiple objects at different depths. In a previous study, the benchmark of the main available image coding standard solutions JPEG, JPEG-XT, JPEG 2000 and the HEVC intra mode was performed for digital holographic data represented on the object plane. The HEVC intra main coding profile outperforms the other standards while JPEG 2000 results in very similar compression performance. In the current work, a scheme based on the HEVC intra mode codec for holographic information compression on the object plane is proposed. In the base layer, a 2D version of the object (amplitude information on object plane) is coded with HEVC intra main coding profile. Previously was observed that the phase information requires much higher bit rates than the amplitude information, as standardized codecs are not adapted for the compression of this type of information. In this paper we propose a model where the amplitude information is encoded with the HEVC intra mode codec, while the phase is represented by encoding the real information and the signal of the imaginary information. The real information is also encoded using the HEVC intra mode as it already revealed appropriate for compression of this type of information. The imaginary information signal is encoded with JBIG. The advantage of this scheme is that the amplitude information provides a direct 2D representation of the hologram while the phase information can be considered as a 3D enhancement layer. The results show that the proposed scheme outperforms the state of the art in holography compression, while allowing compatibility with the current standards and direct 2D visualization.
The estimation of optical properties of highly turbid and opaque biological tissue is a difficult task since conventional
purely optical methods rapidly loose sensitivity as the mean photon path length decreases. Photothermal
methods, such as pulsed or frequency domain photothermal radiometry (FD-PTR), on the other hand, show
remarkable sensitivity in experimental conditions that produce very feeble optical signals. Photothermal Radiometry
is primarily sensitive to absorption coefficient yielding considerably higher estimation errors on scattering
coefficients. Conversely, purely optical methods such as Local Diffuse Reflectance (LDR) depend mainly on
the scattering coefficient and yield much better estimates of this parameter. Therefore, at moderate transport
albedos, the combination of photothermal and reflectance methods can improve considerably the sensitivity of detection of tissue optical properties. The authors have recently proposed a novel method that combines FD-PTR with LDR, aimed at improving
sensitivity on the determination of both optical properties. Signal analysis was performed by global fitting the
experimental data to forward models based on Monte-Carlo simulations. Although this approach is accurate, the
associated computational burden often limits its use as a forward model. Therefore, the application of analytical
models based on the diffusion approximation offers a faster alternative. In this work, we propose the calculation
of the diffuse reflectance and the fluence rate profiles under the δ-P<sub>1</sub> approximation. This approach is known
to approximate fluence rate expressions better close to collimated sources and boundaries than the standard
diffusion approximation (SDA). We extend this study to the calculation of the diffuse reflectance profiles. The
ability of the δ-P<sub>1</sub> based model to provide good estimates of the absorption, scattering and anisotropy coefficients
is tested against Monte-Carlo simulations over a wide range of scattering to absorption ratios. Experimental
validation of the proposed method is accomplished by a set of measurements on solid absorbing and scattering
A novel method for measuring the optical properties of highly absorbing and scattering biological media is described. The method combines frequency-domain photothermal radiometry (FD-PTR) with spatially resolved diffuse reflectance (SR-DR) techniques aimed at improving sensitivity on the determination of both scattering
and absorption coefficients. Simulation results with Monte-Carlo and Diffusion Theory approaches that assess the scope and feasibility of the method are presented. An optical fiber probe for SR-DR measurements was constructed for operations at small source-detector separations and an FD-PTR system was adapted for quasi-simultaneous
operation with the probe. Several experiments on epoxy phantoms that illustrate the validity and potential of the method are presented.
Lidar receivers perform time and/or space averaging to decrease the variance of the optical power estimates. In this paper we study an Avalanche PhotoDiode based receiver. The number samples to reach a given minimum variance depends on the receiver transfer function. Herein, we review the linear receiver and derive the number of samples for the logarithmic pre-amplifier. Comparing the two receivers, we show that the signal variance for the logarithmic case is degraded by a factor that vanishes as the receiver aperture increases. These results can be readily applied to the problem of estimating log-power returns in the context of Differential Absorption lidar systems. As an application example, we study two different log-power estimators and compare their performance.
This paper addresses the joint estimation of backscatter and extinction coefficients from range/time noisy data under a nonlinear stochastic filtering setup. This problem is representative of many remote sensing applications such as weather radar and elastic-backscatter lidar. A Bayesian perspective is adopted. Thus, in addition to the observation mechanism, relating in a probabilistic sense the observed data with the parameters to be estimated, a prior probability density function has to be specified. We adopt as prior a causal first order auto-regressive Gauss-Markov random field. By using a reduced order state-space representation of the prior, we derive a nonlinear stochastic filter that recursively computes the backscatter and extinction coefficients at each site. A set of experiments based on simulated data illustrates the potential of the proposed approach.