Calculation of Nott dynamic retinoscopy

The accommodation that the eye uses to focus at a certain distance does not correspond exactly with the value of the accommodative stimulus. Such accommodation matches the diopter value of what is called the accommodative response. The Nott method is used in the optometric examination to measure the accommodative response at 40 cm by dynamic retinoscopy. The test is performed with the eye compensated by its neutralizing lens (PNL), obtained from binocular subjective examination. In the literature one can find a measurement procedure in which an accommodative test is situated at a distance of 40 cm, starting from that distance, the optometrist without moving the test, shifts the retinoscope until he finds the point of neutralization. The value of the lead or lag of accommodation is usually obtained by subtracting at 2.50D the inverse of the distance to the point of neutralization (in meters). The value of 2.50D is considered accommodative stimulus at 40 cm. The normal value of the accommodative response, considered for the test at 40 cm, is +0'50 or +0.25 D with a standard deviation of ± 0'25D

Memoria del croma en sujetos tricrómatas normales y anómalos

Póster presentado en la VIII Reunión Nacional de Óptica, Alicante, Septiembre 2006.Los observadores tricrómatas anómalos más numerosos son los que presentan defecto rojo-verde en la visión del color protanómalos y deuteránomalos). Se caracterizan por ser normales en lo que respecta a la agudeza visual, pero con discriminación cromática reducida en el eje rojo-verde, igualación metamérica anormal, y tiempos de respuesta mayores que los que precisan los observadores tricrómatas normales. El objetivo de este trabajo es obtener con 7 tests de color y para tres grupos de observadores tricrómatas (uno con visión cromática normal y dos con anomalía rojo-verde), las correspondientes diferencias CIELAB de croma media, ΔC*ab, utilizando los métodos de igualación cromática simultánea y por memoria (con tiempos de retraso de 15 s, 15 min y 24 hrs), buscando analizar las diferencias significativas obtenidas entre aquellos

Software for simulating dichromatic perception of video streams

We have designed a configurable stand-alone Matlab-based software to simulate dichromatic perception of video streams. The algorithm used is an extension for video streams of the “corresponding pair algorithm” by Capilla and coworkers for simulation of dichromatic perception of images. The software allows the user to upload a video sequence and to process it using different dichromatic color vision models and viewing conditions. The output video may be generated in different spatial and temporal resolutions and file formats. The functions for Matlab environment and a stand-alone application may be downloaded from the Repository of the University of Alicante

Validation of Digital Applications for Evaluation of Visual Parameters: A Narrative Review

The current review aimed to collect and critically analyze the scientific peer-reviewed literature that is available about the use of digital applications for evaluation of visual parameters in electronic devices (tablets and smartphones), confirming if there are studies calibrating and validating each of these applications. Three bibliographic search engines (using the search equation described in the paper) and the Mendeley reference manager search engine were used to complete the analysis. Only articles written in English and that are evaluating the use of tests in healthy patients to measure or characterize any visual function aspects using tablets or smartphones were included. Articles using electronic visual tests to assess the results of surgical procedures or are conducted in pathological conditions were excluded. A total of 19 articles meeting these inclusion and exclusion criteria were finally analyzed. One critical point of all these studies is that there was no mention of the characterization (spatial and/or colorimetrical) of screens and the stimuli used in most of them. Only two studies described some level of calibration of the digital device before the beginning of the study. Most revised articles described non-controlled comparatives studies (73.7%), reporting some level of scientific evidence on the validation of tools, although more consistent studies are needed.The author David P. Piñero has been supported by the Ministry of Economy, Industry and Competitiveness of Spain within the program Ramón y Cajal, RYC-2016-20471

Analysis of the calculation of the amplitude of accommodation

The push-up method is routinely used to measure the amplitude of accommodation. In this method the diopter value corresponding to the nearest point that the eye can focus is determined, wearing his neutralizing lens, but not the value of the maximum diopter variation that makes the eye. The aim of this paper is to review the calculation described in the push-up method taking into account the real position of the near point of the eye. In the subjective push-up method, it is calculated the reciprocal of the distance from the lens until the test object at this position of first, slight, sustained blur. We calculated the differences between this value and the ocular amplitude of accommodation, taking into account that the eye is really looking at the image of first blur through the neutralizing lens. Experimental measurements were also taken to determine whether they were similar to theoretical values. The results obtained by the two calculation methods compared were in general significantly different and the difference was greater for young people with high ametropy. The theoretical results were in agreement with the experimental ones. According to the optometric information required must select the appropriate calculation method, since the values obtained in each of them are not comparable

Optopad

Se ha llevado a cabo la implementación de una batería de tests (Optopad) que permite la medida de la discriminación cromática (Optopad-Color) y la sensibilidad al contraste (Optopad-CSF) del sistema visual de una persona, utilizando un iPad como dispositivo de visualización. El diseño colorimétrico para el test de color se fundamenta en la pérdida de discriminación cromática a lo largo de direcciones específicas del espacio de color, en función de la anomalía del paciente. Los sujetos con cualquiera de los tres tipos de discromatopsias congénitas: protan, deutan y tritan, pierden discriminación a lo largo de las llamadas líneas de confusión. Los sujetos con alteraciones de la visión del color adquiridas pierden discriminación a lo largo de las direcciones cardinales del espacio de modulaciones oponentes de Derrington-Krauskopf-Lennie. El diseño para el test de sensibilidad se fundamenta en la respuesta del sistema visual a redes sinusoidales, con variaciones acromáticas, rojo-verde y azul-amarillo. Se ha implementado un software para Matlab 2016a o superior, que fabrica estímulos acromáticos y cromáticos que se ajustan a las características de las células de los mecanismos del sistema visual humano. Para poder fabricar los estímulos, el usuario debe disponer de la tabla 3DLUT de caracterización colorimétrica del dispositivo con el que trabaja. El software incluye también un análisis de los resultados obtenidos con un paciente en comparación con una base de datos de sujetos normales

Diseño y testeo de un campímetro de umbral incremental por proyección

In the present study, we have designed and tested a perimeter for the detection of damage in the chromatic mechanisms using a video projector. To this purpose, we have characterized pixel to pixel a video projector, to account for the inhomogeneities in the projection. We have measured the tristimulus values of the projector primaries as a function of digital level, at 49 locations of the projection screen and, from them, we have arrived to a characterization model which reduces the color differences between predicted and reproduced color, in comparison with the traditional method, which generalizes the characterization of the screen center to all the screen. With the perimeter, we measured the detection thresholds of stimuli favouring the response of the red-green and blue-yellow chromatic mechanisms of the human visual system. Stimulus size could either be constant or change with eccentricity with the size of the receptive fields of the neurons in the visual cortex. The psychophysical method of measurement used is the MOBS (Modified Binary Search). We have studied the factors that can distort the measurements, as well as the repeatability, the specificity and the sensitivity of the device, with good results. A database has been created for the configuration of constant size stimulus. The trends shown by the data are consistent with the literature. When comparing both size configurations, the peripheral sensitivity is increased and repeatability is better with the stimulus size adapted to the eccentricity.En el presente estudio se ha diseñado y testeado un campímetro de detección de anomalías en la percepción cromática utilizando un proyector de vídeo (Multicampímetro). Para ello se ha caracterizado colorimétricamente un proyector de vídeo, píxel a píxel, intentando modelizar las inhomogeneidades de la proyección. Se han determinado los valores triestímulo de los primarios del proyector, en función del nivel digital, en 49 localizaciones de la superficie de proyección y, a partir de ellas, se ha llegado a un modelo de caracterización del dispositivo que minimiza las diferencias de color entre el color predicho y el reproducido, en comparación con el método tradicional, que generaliza la caracterización del centro a toda la pantalla. Con este perímetro, hemos medido los umbrales de detección de estímulos que favorecen la respuesta de los mecanismos cromáticos (rojo-verde y azul-amarillo) del sistema visual humano, utilizando dos configuraciones de tamaño: tamaño constante y tamaño variable con la excentricidad y adaptado a los campos receptivos del córtex visual. El método psicofísico de medida utilizado es el MOBS (Modified Binary Search).Se han estudiado los parámetros que pueden influir en la distorsión de la medida, así como la repetitividad, la especificidad y la sensibilidad del dispositivo, resultando favorables estos tres últimos parámetros. Se ha creado una base de datos para la configuración de estímulo a tamaño constante y se ha comprobado que los resultados de la sensibilidad de ambos mecanismos reproducen las características ya descritas en la bibliografía. Al comparar ambas configuraciones de tamaño, se encuentra mayor sensibilidad periférica y mejor repetitividad con el estímulo de tamaño adaptado a la excentricidad

Changes in contrast sensitivity for aged users of tinted sunglasses

Hoy en día es cada vez más habitual el uso de filtros solares coloreados en un gran número de actividades, tanto de ocio como en el trabajo, al aire libre o en ambientes cerrados. Nos hemos planteado si es recomendable el uso de lentes con cromaticidades diferentes y si esa recomendación sería dependiente del grupo de edad del sujeto.Tinted lenses are increasingly used in many activities, both during leisure time and for work, out in the open and indoors. Our aim is to test if any tinted lens is more advisable than another, and if the choice of colour depends on the age group.Esta investigación se ha llevado a cabo en el marco del proyecto de la Generalitat Valenciana GV06/185

Chromatic-achromatic perimetry in four clinic cases: Glaucoma and diabetes

Background: Some diseases that affect the visual system may show loss of chromatic-achromatic sensitivity before obvious physical signs appear in the usual examination of the eye's posterior segment. A perimetric study has been conducted with four typical patients with glaucoma and diabetes, at different stages of the disease. Materials and Methods: In addition to the standard white-on-white (standard automated perimetry [SAP]), a test battery has been used to study patient's contrast sensitivity, using stimuli with different chromatic, spatial, and temporal content (multichannel perimetry). The choice of stimuli tries to maximize the response of different visual mechanisms: Achromatic (parvocellular and magnocellular origin); chromatic red-green (parvocellular origin); and chromatic blue-yellow (koniocellular origin). Results: The results seem to indicate losses in the achromatic-parvocellular perimetry and both chromatic perimetry tests, undetected by conventional SAP. Conclusions: Our results illustrate that our patients without visible retinal alterations show signs of suspicion in multichannel perimetry.The ATD multichannel perimeter was built thanks to the support of the Spanish Ministery for Science and Technology Grants DPI2000-0116-P4-02 and PTR 1995-0909-OP, in collaboration with INDUSTRIAS DE OPTICA SA (San Cugat del Vallés, Spain)

Visual function alterations in essential tremor: A case report

Our purpose is to report alterations in contrast sensitivity function (CSF) and in the magno, parvo and koniocellular visual pathways by means of a multichannel perimeter in case of an essential tremor (ET). A complete evaluation of the visual function was performed in a 69-year old patient, including the analysis of the chromatic discrimination by the Fansworth–Munsell 100 hue test, the measurement of the CSF by the CSV-1000E test, and the detection of potential alteration patterns in the magno, parvo and koniocellular visual pathways by means of a multichannel perimeter. Visual acuity and intraocular pressure (IOP) were within the ranges of normality in both eyes. No abnormalities were detected in the fundoscopic examination and in the optical coherence tomography (OCT) exam. The results of the color vision examination were also within the ranges of normality. A significant decrease in the achromatic CSFs for right eye (RE) and left eye (LE) was detected for all spatial frequencies. The statistical global values provided by the multichannel perimeter confirms that there were significant absolute sensitivity losses compared to the normal pattern in RE. In the LE, only a statistically significant decrease in sensitivity was detected for the blue-yellow (BY) channel. The pattern standard deviation (PSD) values obtained in our patient indicated that there were significant localized losses compared to the normality pattern in the achromatic channel of the RE and in the red-green (RG) channel of the LE. Some color vision alterations may be present in ET that cannot be detected with conventional color vision tests, such as the FM 100 Hue