Francisco Pérez-Ocón

Corneal asphericity after refractive surgery when the Munnerlyn formula is applied

We deduce a mathematical equation for corneal asphericity after refractive surgery when the Munnerlyn formula is used. For this, an analytical least-squares procedure is used. The equation explains the discrepancies found by different authors when the Munnerlyn formula or its paraxial approximation is used. Equations for corneal asphericity deduced here may be of clinical relevance, for example, in studying quantitatively the role of different factors (decentration, type of laser, optical role of the flap, wound healing, biomechanical effects, technical procedures) during corneal ablation.

Correction factor for ablation algorithms used in corneal refractive surgery with gaussian-profile beams.

We provide a correction factor to be added in ablation algorithms when a Gaussian beam is used in photorefractive laser surgery. This factor, which quantifies the effect of pulse overlapping, depends on beam radius and spot size. We also deduce the expected post-surgical corneal radius and asphericity when considering this factor. Data on 141 eyes operated on LASIK (laser in situ keratomileusis) with a Gaussian profile show that the discrepancy between experimental and expected data on corneal power is significantly lower when using the correction factor. For an effective improvement of post-surgical visual quality, this factor should be applied in ablation algorithms that do not consider the effects of pulse overlapping with a Gaussian beam.

Associated Phoria in Relation to Stereopsis with Random-Dot Stereograms

In the present work, we use random-dot stereograms to test a possible relationship between associated phoria and stereopsis. We determined, using a modified constant-stimulus method, the disparity range that indicates the maximum range at which stereoscopic correspondence can be achieved. A total of 27 observers took part in the experiment. The value of the disparity range as a function of the associated phoria (measured with a Mallet unit) seems to indicate that greater associated phoria (fixation disparity) correlates with a deterioration in stereoscopic vision, reducing the disparity range and therefore the space region in which stereoscopic vision can be attained.

A simple method for designing efficient public lighting, based on new parameter relationships

Abstract New parameter relationships for public lighting design (i.e. average illuminance, luminaire spacing, and mounting height) were calculated from a large sample of data sets optimized with a multi-objective evolutionary algorithm. Optimization criteria included maximum energy efficiency and overall uniformity. The relations thus derived are a simple and elegant method for designing any type of public lighting installation without the need to use complex, expensive and/or unavailable software. It would therefore be desirable that manufacturers include such parameters in the product datasheet in order to make the calculation easier.

Impact of induced aniseikonia on stereopsis with random-dot stereogram.

In this work, we evaluate the impact of induced aniseikonia on stereopsis. For this, we determined the disparity range (maximum disparity), a parameter related to the size of the physical region that can be perceived stereoscopically. A significant decline in the disparity range was detected with aniseikonia induced by size lenses of 3% for five of the seven observers tested; 5% was necessary for the other two observers. The data indicate the influence of aniseikonia in stereopsis and the need to minimize such impact. These results may be useful in surgical processes such as the correction of pseudophakic patients and refractive surgery in which aniseikonia can be induced to alter the binocular function of the patient.

Fast single-mode characterization of optical fiber by finite-difference time-domain method

Usually, although not always, manufacturers producing optical fiber state that the functioning will be single mode in most cases without specifying the wavelengths to be worked with. A rapid method of light simulation within the optical fibers was developed for a single-mode characterization, which avoids errors and problems in transmitting the signals through the fiber. The method was validated with two optical fibers, in which the intensity patterns are well known in theory, and a rather good fit between the theoretic intensity curves at the endface of the fibers was achieved. In order to characterize the monomodal regime, the method was applied to two optical fibers with different refractive-index profiles, using the finite-difference time-domain (FDTD) for the body of revolution (BOR)

Retinal-Image Quality and Contrast-Sensitivity Function in Age-Related Macular Degeneration

Purpose: In this article, retinal-image quality and contrast sensitivity were measured in 25 patients with age-related macular degeneration (ARMD) and 15 patients with normal retinal health. Materials and Method: Retinal-image quality was evaluated with an objective device based on the double-pass technique, and for visual performance we measured the contrast-sensitivity function. Results: The results from double-pass device revealed the Strehl ratio to be significantly (p < 0.0001) lower for the ARMD group with a 54.3% reduction for 3 mm pupil size and a 46.9% reduction for 4 mm. Contrast-sensitivity function for ARMD subjects was also significantly lower than for the control group (p < 0.05) with a 38.6% reduction. Conclusions: Patients affected with ARMD showed poorer retinal-image quality and visual performance than normal subjects. The use of objective devices based on the double-pass technique could be useful for the accurate description of the retinal-image quality of ARMD eyes, in which retinal scattering is significantly increased.

A Continuous Liquid-Level Sensor for Fuel Tanks Based on Surface Plasmon Resonance

A standard problem in large tanks at oil refineries and petrol stations is that water and fuel usually occupy the same tank. This is undesirable and causes problems such as corrosion in the tanks. Normally, the water level in tanks is unknown, with the problems that this entails. We propose herein a method based on surface plasmon resonance (SPR) to detect in real time the interfaces in a tank which can simultaneously contain water, gasoline (or diesel) and air. The plasmonic sensor is composed of a hemispherical glass prism, a magnesium fluoride layer, and a gold layer. We have optimized the structural parameters of the sensor from the theoretical modeling of the reflectance curve. The sensor detects water-fuel and fuel-air interfaces and measures the level of each liquid in real time. This sensor is recommended for inflammable liquids because inside the tank there are no electrical or electronic signals which could cause explosions. The sensor proposed has a sensitivity of between 1.2 and 3.5 RIU−1 and a resolution of between 5.7 × 10−4 and 16.5 × 10−4 RIU.

FDTD analysis of the light propagation in the cones of the human retina : An approach to the Stiles-Crawford effect of the first kind

In this work, we analyse the propagation of light in the human retinal cones by the finite-difference time-domain method (FDTD) in cylindrical coordinates, for systems with axial symmetry or body of revolution (BOR). This work constitutes a preliminary approach to the study of the Stiles?Crawford effect of the first kind (SCE I), as a cone has been simulated, while the SCE I is a consequence of a large number of photoreceptors. The FDTD method enables a numerical resolution of Maxwells equations. With the computational implementation of these equations we have obtained, in the cone endface, the intensity patterns for different angles with which the light strikes the input side of the photoreceptor, and different wavelengths of incident light. In view of the results, the characteristics of fibre optics presented by the retinal cones remain valid, as does the goodness of the method and of the computational cone model that we have proposed. This work demonstrates, in short, the computational validity of our cone model as well as the power and versatility of the FDTD-BOR algorithm for the analysis and comprehension of the phenomenon of light propagation in retinal photoreceptors. It therefore offers broad possibilities in the field of research on visual processes, serving as support for analysis and interpretation of experimental measurements.

Exponential discretization of the Perfectly Matched Layer (PML) absorbing boundary condition simulation in FD-TD 3D

Summary We present the discretized equations of the 12 PML (perfectly matched layer) in the three-dimensional case using the Cartesian geometry. These equations can be used in different fields where Maxwell equations need to be solved.