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

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

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

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 Contrast Sensitivity Functions and Colour Discrimination in Smoker Patients

In this study, effects of smoking on colour vision with the Farnsworth–Munsell 100 Hue test (FM100h) and achromatic (A), red-green (RG), and blue-yellow (BY) contrast sensitivity functions were evaluated. In total, 50 non-smoker controls and 25 smokers, divided into two groups (group 1, less than 10 cigarettes per day, with 15 patients, and group 2, >10 cigarettes per day, with 10 patients) took part in the experiments. Best-corrected visual acuity (BCVA), FM100h, and A, RG, and BY contrast sensitivity functions were measured. Total and partial RG and BY error scores (TES and PTES) and colour axis index (CA) were used in the analysis. No differences between smoker and non-smoker groups were found in BCVA, CA and A and BY contrast sensitivity, but TES and PTES values and RG contrast sensitivity at 1 cpd were statistically different. Differences between smoker groups were not significant. Error scores in smokers were positively correlated with the number of cigarettes smoked per day, and in BY also with age. Tobacco caused discrimination losses in both chromatic mechanisms but affected the red-green pathway more than the blue-yellow, and therefore, a partial RG score of FM100h test seems to be a good predictor of smoker colour deficiencies

Visual fields in a chloroquine treatment

Purpose: In this study, we describe contrast sensitivity losses in the visual field of a patient affected by chloroquine toxicity, measured with stimuli favoring different visual mechanisms. We have compared these results with those of other, usual clinical tests. Methods: The vision of a patient who underwent ten years of chloroquine treatment was analyzed by a battery of clinical tests: visual acuity (VA), Amsler’s grid, Farnsworth–Munsell 100-hue test, spectral domain optical coherence tomography, multifocal electroretinogram (ERG), white-on-white and red-on-white Humphrey perimetries, chromatic and achromatic contrast sensitivity perimetry tests, and fluorescein angiography. Measurements were taken just before the cessation of the treatment, and 6 months later. Results: The subjective visual perception of the patient was worse (in comparison with the rest of the visual field at the time of the first visit) in the center of the visual field, and was impaired on the second visit. Although standard automated perimetry (SAP) was practically normal and ERG results did not worsen with time, VA, Amsler’s grid, and visual fields with stimuli favoring the magnocellular and chromatic pathways signalled progressive loss of visual function. Conclusions: Standard tests such as SAP or ERG may not detect visual field losses or progression of existing visual losses in a case of chloroquine toxicity, whereas tests evaluating contrast sensitivity with stimuli favoring different visual mechanisms may be more sensitive.The ATD multichannel perimeter was built thanks to the support of the Spanish Ministerio de Ciencia y Tecnología (Grants DPI2000-0116-P4-02 and PTR 1995-0909-OP), in collaboration with Industrius De Optica SA (San Cugat del Vallés, Spain)

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)

Reliability in perimetric multichannel contrast sensitivity measurements

Background: In this study, the reliability of perimetric contrast sensitivity measurements favouring the achromatic, the red-green and the blue-yellow post-receptorial mechanisms was analysed. Methods: A new technique, multichannel ATD perimetry, provides spatial and temporal stimuli favouring the detection by an achromatic mechanism (A), from a magno or parvocellular origin or by a red-green (RG) chromatic mechanism, with a parvocellular origin or a blue-yellow (BY) mechanism, with a koniocellular origin. The repeatability and reproducibility of contrast sensitivity measurements with these stimuli were studied in a group of 40 healthy subjects. The analysis was carried out on 21 testing points within a 60° by 40° fovea-centred region of the visual field. Results: The within-observer repeatability for the four mechanisms studied is either good or excellent when the intra-class correlation coefficient (ICC) can be calculated. For the remaining points, the Friedman's test finds that the measurements are repeatable. The between-observer reproducibility was either excellent or good in cases where the ICC was applied and according to the Friedman's test all results were reproducible. Conclusions: The results obtained showed good repeatability and reproducibility with A, RG and BY stimuli, although with BY stimuli repeatability is slightly worse. Future studies on the diagnostic validity of this device are based on the fact that changes of sensitivity can be compared by means of a visual single task, contrast sensitivity measurement and using a common metric.The ATD multichannel perimeter was built thanks to the support of the Spanish Ministerio de Ciencia y Tecnología Grants DPI2000-0116-P4-02 and PTR 1995-0909-OP, in collaboration with INDUSTRIAS DE OPTICA SA (San Cugat del Vallés, Spain)

Can Applications Designed to Evaluate Visual Function Be Used in Different iPads?

SIGNIFICANCE: Apple devices could be suitable for vision tests, provided that the test has been correctly adapted to the device, after considering the spatial and colorimetric characterization of the screen. PURPOSE: The majority of vision applications has not been developed by vision or colorimetry experts and suffers from conceptual and design errors that may lead average users to an erroneous assessment of their visual capabilities. The reliability of vision tests depends on the accurate generation of the necessary visual stimuli in a particular device. Our aim was to ascertain whether a given color test, designed for a colorimetrically characterized device, might be used in another similar device. METHODS: We evaluated color reproduction errors in three iPad tablets of different models with Retina screens, using their individual color characterization models and the model derived for another device. RESULTS: Our results showed, even with this small sample, the high degree of error caused when disregarding the fact that the colorimetric design valid for a given device may not be correct when displayed in another. CONCLUSIONS: The distortion of the chromatic content may lead to subjects with vision defects to pass as normal or vice versa, compromising diagnosis reliability

New iPAD-based test for the detection of color vision deficiencies

Purpose: To develop and validate a new iPad-based color vision test (Optopad). Methods: A total of 341 student eyes were enrolled in a first comparative study between Optopad and the Isihara tests. In a second comparative study, Optopad vs. the Farnworth-Munsell test (FM 100H), a total of 66 adult eyes were included. Besides the agreement between tests, the correlation between FM 100H and Optopad outcomes were investigated. Multiple regression analysis was used to predict the total error score (TES) from contrast thresholds measured with the Optopad test. Results: The Ishihara and Optopad tests detected the same anomalous patients. Concerning FM 100H vs. Optopad, 10 subjects were diagnosed as anomalous with both tests, 3 mild anomalous cases based on TES were classified as normal with Optopad, and 2 anomalous subjects based on Optopad test showed normal TES values. Statistically significant correlations of TES and partial error red-green (PTESRG) with thresholds measured with the red-green Optopad stimuli were found. A multiple quadratic regression model was obtained relating TES and chromatic contrast values from Optopad (R2 = 0.855), with only 13 cases showing residuals of ≥ 25 units. Conclusions: The design and implementation of a chromatic contrast discrimination test has been carried out, with promising clinical results. This test seems to provide comparable outcomes to those obtained with Ishihara and FM 100H tests