Phase-transfer function of the human eye and its influence on point-spread function and wave aberration.

The bidimensional phase-transfer function (PTF) of the human eye has been computed from aerial retinal images of a point test. These images were previously determined by using a recently developed hybrid optical-digital method. Actual PTF data have been obtained directly without linear variations with spatial frequency and have shown great variations among individual subjects. The influence of the PTF on the determination of the point-spread function and the wave-aberration function for emmetropized and slightly astigmatic subjects has been also evaluated. Finally, the effect of pupil size on the PTF was determined by computing these functions from the wave aberration. These results allow us to give a more thorough description of the optical image quality of the human eye and can be used as actual data in subsequent psychophysical studies.The authors thank M. Nieto-Vesperinas for his critical reading of the manuscript. This research was supported by the Comision Asesora de Investigaci6n Cientifica y T6cnica (grant 2520/83), Ministerio de Educaci6n y Ciencia, Spain.Peer Reviewe

Single-pixel imaging of the retina through scattering media

Imaging the retina of cataractous patients is useful to detect pathologies before the cataract surgery is performed. However, for conventional ophthalmoscopes, opacifications convert the lens into a scattering medium that may greatly deteriorate the retinal image. In this paper we show, as a proof of concept, that it is possible to surpass the limitations imposed by scattering applying to both, a model and a healthy eye, a newly developed ophthalmoscope based on single-pixel imaging. To this end, an instrument was built that incorporates two imaging modalities: conventional flood illumination and single-pixel based. Images of the retina were acquired firstly in an artificial eye and later in healthy living eyes with different elements which replicate the scattering produced by cataractous lenses. Comparison between both types of imaging modalities shows that, under high levels of scattering, the single-pixel ophthalmoscope outperforms standard imaging methods

Propuesta didáctica de sensibilización hacia la discapacidad visual desde el área de Educación Física

En el presente Trabajo Fin de Grado se muestra una unidad didáctica del área de Educación Física para fomentar la sensibilización hacia la discapacidad en las aulas de Educación Primaria, centrándose en la discapacidad visual. Entre los principales resultados, se destaca cómo a través de la presente propuesta se ha conseguido, mediante la inclusión, sensibilizar hacia la discapacidad visual a un grupo de alumnos de un colegio público de Educación Primaria de la provincia de Segovia. A la vez que se ha conseguido fomentar la empatía en ellos hacía las personas discapacitadas. Podemos concluir cómo la elaboración y puesta en práctica de esta propuesta didáctica busca también despertar el interés en los docentes sobre este tipo de temas, dando respuesta a los interrogantes de algunos maestros del área Educación Física que no tengan formación sobre la atención a la diversidad en alumnos con necesidades educativas especiales, en concreto por discapacidad sensorial visual.Grado en Educación Primari

Extended source pyramid wave-front sensor for the human eye.

We describe a new wave-front sensor based on the previously proposed pyramid sensor. This new sensor uses an extended source instead of a point-like source avoiding in this manner the oscillation of the pyramid. After an introductory background the sensor functioning is described. Among other possible optical testing uses, we apply the sensor to measure the wave-front aberration of the human eye. An experimental system built to test this specific application is described. Results obtained both in an articficial eye and in a real eye are presented. A discussion about the sensor characteristics, the experimental results and future work prospects is also included

Second Harmonic Generation Microscopy: A Tool for Quantitative Analysis of Tissues

Second harmonic generation (SHG) is a second‐order non‐linear optical process produced in birefringent crystals or in biological tissues with non‐centrosymmetric structure such as collagen or microtubules structures. SHG signal originates from two excitation photons which interact with the material and are “reconverted” to form a new emitted photon with half of wavelength. Although theoretically predicted by Maria Göpert‐Mayer in 1930s, the experimental SHG demonstration arrived with the invention of the laser in the 1960s. SHG was first obtained in ruby by using a high excitation oscillator. After that starting point, the harmonic generation reached an increasing interest and importance, based on its applications to characterize biological tissues using multiphoton microscopes. In particular, collagen has been one of the most often analyzed structures since it provides an efficient SHG signal. In late 1970s, it was discovered that SHG signal took place in three‐dimensional optical interaction at the focal point of a microscope objective with high numerical aperture. This finding allowed researchers to develop microscopes with 3D submicron resolution and an in depth analysis of biological specimens. Since SHG is a polarization‐sensitive non‐linear optical process, the implementation of polarization into multiphoton microscopes has allowed the study of both molecular architecture and fibrilar distribution of type‐I collagen fibers. The analysis of collagen‐based structures is particularly interesting since they represent 80% of the connective tissue of the human body. On the other hand, more recent techniques such as pulse compression of laser pulses or adaptive optics have been applied to SHG microscopy in order to improve the visualization of features. The combination of these techniques permit the reduction of the laser power required to produce efficient SHG signal and therefore photo‐toxicity and photo‐damage are avoided (critical parameters in biomedical applications). Some pathologies such as cancer or fibrosis are related to collagen disorders. These are thought to appear at molecular scale before the micrometric structure is affected. In this sense, SHG imaging has emerged as a powerful tool in biomedicine and it might serve as a non‐invasive early diagnosis technique

The Role of Thermal Accumulation on the Fabrication of Diffraction Gratings in Ophthalmic PHEMA by Ultrashort Laser Direct Writing

The fabrication of diffraction gratings by ultrashort direct laser writing in poly-hydroxyethyl-methacrylate (PHEMA) polymers used as soft contact lenses is reported. Diffraction gratings were inscribed by focusing laser radiation 100 µm underneath the surface of the samples. Low- and high-repetition rate Ti:sapphire lasers with 120 fs pulsewidth working at 1 kHz and 80 MHz respectively were used to assess the role of thermal accumulation on microstructural and optical characteristics. Periodic patterns were produced for different values of repetition rate, pulse energy, laser wavelength, distance between tracks, and scanning speed. Compositional and structural modifications of the processed areas were studied by micro-Raman spectroscopy showing that under certain parameters, thermal accumulation may result in local densification. Far-field diffraction patterns were recorded for the produced gratings to assess the refractive index change induced in the processed areasThis research was funded by the PIT2 program of the University of Murcia’s own research plan. Fundación Seneca grant No 20647/JLI/18, Junta de Castilla y León (project SA287P18), MINECO (project FIS2017-87970-R) and European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie IF No 795630 are also acknowledged

The human eye is an example of robust optical design

In most eyes, in the fovea and at best focus, the resolution capabilities of the eye's optics and the retinal mosaic are remarkably well adapted. Although there is a large individual variability, the average magnitude of the high order aberrations is similar in groups of eyes with different refractive errors. This is surprising because these eyes are comparatively different in shape: Myopic eyes are longer whereas hyperopic eyes are shorter. In most young eyes, the amount of aberrations for the isolated cornea is larger than for the complete eye, indicating that the internal ocular optics (mainly the crystalline lens) play a signif icant role in compensating for the corneal aberrations, thereby producing an improved retinal image. In this paper, we show that this compensation is larger in the less optically centered eyes that mostly correspond to hyperopic eyes. This suggests a type of mechanism in the eye's design that is the most likely responsible for this compensation. Spherical aberration of the cornea is partially compensated by that of the lens in most eyes. Lateral coma is also compensated mainly in hyperopic eyes. We found that the distribution of aberrations between the cornea and lens appears to allow the optical properties of the eye to be relatively insensitive to variations arising from eye growth or exact centration and alignment of the eye's optics relative to the fovea. These results may suggest the presence of an auto-compensation mechanism that renders the eye's optics robust despite large variation in the ocular shape and geometry

Peripheral optical errors and their change with accommodation differ between emmetropic and myopic eyes

The progression of myopia is thought to be controlled by the retinal image quality, but its triggering factors are not yet well known. The differences between the peripheral optics in emmetropic and myopic eyes might explain why some eyes become myopic. The present study further investigates peripheral optical quality and how it is affected by accommodation. The refraction and aberrations of the right eyes of five emmetropes and five myopes were measured using a laboratory Hartmann-Shack wave front sensor, specially designed for peripheral measurements with an open field of view. The off-axis optical quality was assessed in steps of 10-out to T40-horizontally and T20-vertically for two different states of accommodation (targets at 0.5 D and 4.0 D). As expected, the emmetropes had a higher relative peripheral myopia, that is, more positive c 2 0 coefficient, than the myopes. The new results of this study are that this well-known difference was found to be asymmetric over the visual field and that it increased with accommodation. This increase was because the relative peripheral defocus profile of the myopes did not show a consistent change between far and near vision, whereas the emmetropes became relatively more myopic in the periphery with accommodation. These findings may indicate a difference between emmetropic and myopic eyes that could be an important clue to understand myopia progression

Unidad didáctica de 2º bachillerato: Nietzsche

En el siguiente trabajo de fin de máster (TFM de la modalidad A) voy a exponer la unidad didáctica (UD) que he desarrollado durante mi estancia como profesor de prácticas en el IES Clara Campoamor Rodríguez, situado en el zaragozano barrio Parque Goya II. El núcleo del trabajo, por tanto, será el desarrollo de los distintos aspectos que componen el diseño y la adecuación de un bloque de contenidos marcado por el currículo para su implantación en el aula. Antes de nada, me gustaría agradecer los conocimientos y consejos que he adquirido en la asignatura de diseño de actividades de aprendizaje de filosofía, impartida por Jorge Jiménez Portillo. Dado que una parte de esta asignatura consistía en el diseño de una unidad didáctica, he podido ir introduciendo y refinando las distintas partes que han de tenerse en cuenta a la hora de elaborar un trabajo de estas características. El enfoque del diseño de esta unidad didáctica estuvo en todo momento enfocado hacia el deseo de promover el pensamiento crítico y la autonomía del alumnado, siendo los dos valores clave que, a mi juicio, pueden y deben promoverse desde cualquier aula de filosofía.<br /

Intraocular Scattering, Blinking Rate, and Tear Film Osmolarity After Exposure to Environmental Stress

Purpose: Dry environments, such as those in offices or aircraft cabins, can potentially generate ocular discomfort and alter the tear film. We compare light scatter, blinking rate, and tear osmolarity in young and older subjects after exposure to low humidity using a controlled environmental chamber. Methods: Two groups of healthy subjects were recruited; younger (N = 13, 27 ± 6 years) and older (N = 23, 71 ± 7 years). Measurements were carried out before and after 90-minute exposure to low relative humidity (5%) and constant temperature (23 degrees). Ocular light scatter was measured using a double-pass instrument (OQAS, Visiometrics, Spain). Blinking rate was monitored using an infrared video camera. Tear osmolarity was measured using the TearLab system (Escondido, CA, USA). Results: Ocular light scatter increased by a factor of 10% after exposure to low humidity in the older group (P = 0.03) but did not change significantly in the younger group. Blinking rate increased significantly (40% more blinks) in both groups but there was no difference between the groups. No significant differences in osmolarity were shown between two age groups or as result of environmental stress. Conclusions: Exposure to dry environment increased light scatter in older subjects. Although more blinks were triggered in both younger and older groups to prevent corneal dehydration, there was no difference between the groups. Blink rate and osmolarity are not associated with the difference in light scatter. Translational Relevance: Our work approaches a clinical care problem using basic research methods (measuring ocular scatter and blink ratio)