Person:
Alonso Fernández, José

First Name

José

Last Name

Alonso Fernández

URI

https://hdl.handle.net/20.500.14352/79966

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Óptica y Optometría

Department

Óptica

Area

Optica

Identifiers

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Now showing 1 - 10 of 41

Generalized grating imaging using an extended monochromatic light source
(Journal of the Optical Society of America A-Optics Image Science And Vision, 2000) Crespo Vázquez, Daniel; Alonso Fernández, José; Bernabeu Martínez, Eusebio
It is a well-known fact that one grating can act as an imaging element for another grating when the first is illuminated with an extended monochromatic light source. The conditions for image formation in such a system are studied when the finite size and position of the broad light source are considered. From the presented analysis, expressions for the location and the depth of focus of such images can be derived.
Generation of optical reference signals robust to diffractive effects
(Ieee Photonics Technology Letters, 2007) Saez Landete, José; Salcedo Sanz, Sancho; Rosa Zurera, Manuel; Alonso Fernández, José; Bernabeu Martínez, Eusebio
In grating measurement systems, a reference signal is needed to achieve an absolute measurement of the position. The zero reference signals are normally obtained illuminating two identical superimposed zero reference codes (ZRCs) and registering the transmitted light by means of a photodiode. As one ZRC moves with respect to the other, the two codes overlap and the signal registered is the autocorrelation of the ZRC transmittance. In high resolution systems, the diffraction effects degrade the geometrical shadow of the first ZRC as it propagates to the second one. As a result, the autocorrelation is also degraded and the amplitude of the reference signal is greatly reduced. In this letter, we present a method for designing ZRCs with minimum diffractive effects. The method is based on the optimization of ZRCs by means of a genetic algorithm.
Importance of Lid Hygiene Before Ocular Surgery: Qualitative and Quantitative Analysis of Eyelid and Conjunctiva Microbiota
(Eye & Contact Lens: Science & Clinical Practice, 2016) Peral Cerda, María Asunción; Alonso Fernández, José; García García, María De La Concepción; Niño Rueda, Cristina; Calvo del Bosque, Patricia
Objective: To evaluate the efficacy of a cleansing eyelid wipe in reducing the microbiota present on the ocular surface before cataract surgery. Methods: A single-center, prospective, single-blind phase IV study was conducted at the University Complutense of Madrid. Forty-five adult patients who were scheduled for ocular surgery after treatment with commercially available eyelid wipes were consecutively enrolled. The study lasted 5 days and the patients were examined at day 0 (D0), day 3 (D3), and day 5 (D5). They received instructions to apply the eyelid wipe only to the eye subject to surgery, using the other eye as a control with no treatment. Lid and conjunctival swabs were taken on each day and microbes identified. Ocular surface microbiota was estimated by measuring the area of the agar plate occupied by the grown colonies with respect to the total available area. Results: Measurements at D3 and D5 showed a percent reduction of 58% and 63%, respectively, in the microbial load on the eyelid in the treated eyes (P=0.0011). There was also a reduction, although nonsignificant, in the microbiota of the conjunctiva of 72% and 69% on D3 and D5, respectively. Conclusions: The degree of microbiota reduction was comparable with that obtained after topical application of antibiotics in other studies. The results suggest the use of these eyelid wipes as a complementary prophylactic method before any ocular surgery.
Effect of illuminating wavelength on the contrast of meibography images
(OSA Continuum, 2018) Peral Cerda, María Asunción; Alonso Fernández, José; Gómez Pedrero, José Antonio
Evaluation of the Meibomian glands morphology is becoming a popular assessment for dry eye. This evaluation is usually done by imaging the glands on the everted lids while they are illuminated with infrared light. Nowadays techniques to determine gland condition and dropout are based on grading scales with which meibography images are subjectively evaluated. In this work, we have measured the contrast of Meibomian gland images from ten subjects and for a range of wavelengths of the monochromatic illuminating light. We have used a xenon lamp and a monochromator as a light source, and a semi-automatic image processing technique for measuring the image contrast from 600 nm to 1050 nm. Contrast values inside glands are from 0.025 to 0.015 and between glands from 0.06 to 0.04. The greater values of contrast are obtained when Meibomian glands are illuminated with a wavelength close to 600 nm.
Zero reference signal for displacement measuring systems by use of speckle
(Applied Optics, 2003) Pérez Quintián, Fernando; Alonso Fernández, José; Atencia Carrizo, Jesús; Bernabeu Martínez, Eusebio
An optical method for generating a reference signal for an incremental displacement measurement system is proposed. We achieved this zero reference signal by comparing two speckle patterns arriving from two symmetric diffusers, which are used as natural random codes that are identical only when the reading head is located equidistantly between the diffusers. The comparison of the speckles is obtained either by interference, as in a Michelson interferometer, or by intensity correlations.
Incremental PCA algorithm for fringe pattern demodulation
(Optics express, 2022) Gómez Pedrero, José Antonio; Estrada, Julio César; Alonso Fernández, José; Quiroga Mellado, Juan Antonio; Vargas Balbuena, Javier
This work proposes a new algorithm for demodulating fringe patterns using principal component analysis (PCA). The algorithm is based on the incremental implantation of the singular value decomposition (SVD) technique for computing the principal values associated with a set of fringe patterns. Instead of processing an entire set of interferograms, the proposed algorithm proceeds in an incremental way, processing sequentially one (as minimum) interferogram at a given time. The advantages of this procedure are twofold. Firstly, it is not necessary to store the whole set of images in memory, and, secondly, by computing a phase quality parameter, it is possible to determine the minimum number of images necessary to accurately demodulate a given set of interferograms. The proposed algorithm has been tested for synthetic and experimental in ter ferograms showing a good performance. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
Optical method for the surface topographic characterization of Fresnel lenses
(Optical Fabrication, Testing and Metrology IV, 2011) Martínez Antón, Juan Carlos; Gómez Pedrero, José Antonio; Alonso Fernández, José; Quiroga Mellado, Juan Antonio
Fresnel lenses and other faceted or micro-optic devices are increasingly used in multiple applications like solar light concentrators and illumination devices. As applications are more exigent this characterization is of increasing importance. We present a technique to characterize the surface topography of optical surfaces. It is especially well adapted to Fresnel lenses where abrupt surface slopes are usually difficult to handle in conventional techniques. The method is based on a new photometric strategy able to codify the height information in terms of optical absorption in a liquid. A detailed topographic map is simple to acquire by capturing images of the surface. Some experimental results are presented. A single pixel height resolution of similar to 0.1 mu m is achieved for a height range of similar to 50 mu m. A surface slope analysis is also made achieving a resolution of similar to +/- 0.15 degrees.
Improved Analytical Theory of Ophthalmic Lens Design
(Applied Sciences, 2021) Pascual, Eduardo; Gómez Pedrero, José Antonio; Alonso Fernández, José
A revisited form of the classic third-order ophthalmic lens design theory that provides a more precise and meaningful use of aspheric surfaces and a generalization of the standard oblique errors is presented. The classical third-order theory follows from the application of the Coddington equations to a ray trace through the lens and the expansion of the incidence angles and the surface sagittas appearing on them up to order two of the radial coordinate. In this work we show that the approximations for surface sagittas and angles can be decoupled, and the lens oblique powers predicted by the proposed theory provides a better fit to the numerical results obtained by exact raytracing and multi-parametric optimization than the classical third-order theory does. Modern ophthalmic lens design uses numerical optimization and exact ray tracing, but the methods presented in this paper provide a deeper understanding of the problem and its limitations. This knowledge and the more general merit functions that are also presented may help guide the numerical approaches.
Theoretical performance of progressive addition lenses with poorly measured individual parameters
(Ophthalmic and Physiological Optics, 2023) Pascual, Eduardo; Gómez Pedrero, José Antonio; Alonso Fernández, José
Purpose: The aim of this paper was to present a theoretical study of how poorly measured individual parameters affect the optical performance of progressive addition lenses (PALs). Modern progressive lenses can be prescribed based on parameters such as vertex distance, pantoscopic and wrap angles. These parameters can be measured from the lens wearer using specific devices; however, not all of them can be measured with the same precision, and the impact of measurement errors on the lens performance is still unknown. Methods: Data from 1900 patients were used to simulate the performance of four PAL designs with different degrees of complexity: perfect individual design, individual design with induced errors in the individual parameters, optimised design and conventional/basic design. For each patient and design, a quality metric was calculated to describe the optical performance of the lens. Results: The design having the best performance was the perfect individual design, followed by the individual design with induced errors, the optimised design and finally the conventional/basic design. Conclusions: Individual designs with measurement errors have better optical performance than lenses with less complexity, such as the optimised or conventional designs. This knowledge is useful for the eye care professional to make informed choices when dispensing these lenses.
Phenomenological model of visual acuity
(Journal of Biomedical Optics, 2016) Gómez Pedrero, José Antonio; Alonso Fernández, José
We propose in this work a model for describing visual acuity (VV) as a function of defocus and pupil diameter. Although the model is mainly based on geometrical optics, it also incorporates nongeometrical effects phenomenologically. Compared to similar visual acuity models, the proposed one considers the effect of astigmatism and the variability of best corrected VV among individuals; it also takes into account the accommodation and the “tolerance to defocus,” the latter through a phenomenological parameter. We have fitted the model to the VV data provided in the works of Holladay et al. and Peters, showing the ability of this model to accurately describe the variation of VV against blur and pupil diameter. We have also performed a comparison between the proposed model and others previously published in the literature. The model is mainly intended for use in the design of ophthalmic compensations, but it can also be useful in other fields such as visual ergonomics, design of visual tests, and optical instrumentation.