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 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)

Pràctica 4. Astigmatisme

El document forma part dels materials docents programats mitjançant l'ajut del Servei de Política Lingüística de la Universitat de ValènciaGuió de la quarta pràctica de l'assignatura d'Òptica Fisiològica del Grau d'Òptica i Optometria de la Universitat de ValènciaScript of the fourth practice of Physiological Optics subject of the Optics and Optometry Degree of the University of Valenci

Examining the utility of pinhole-type screens for lightfield display

The use of microlens arrays for lightfield display has the drawback of providing images with strong chromatic aliasing. To overcome this problem, pinhole-type lightfield monitors are proposed. This paper is devoted to evaluating the capability for such lightfield monitors to offer the user a convincing 3D experience with images with enough brightness and continuous aspect. Thus, we have designed a psychophysical test specifically adapted for lightfield monitors, which allowed us to confirm the usability of pinhole-type monitors

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

Evaluation of Intraocular Pressure and Other Biomechanical Parameters to Distinguish between Subclinical Keratoconus and Healthy Corneas

Purpose: To assess the main corneal response differences between normal and subclinical keratoconus (SCKC) with a Corvis® ST device. (2) Material and Methods: We selected 183 eyes of normal patients, of a mean age of 33 ± 9 years and 16 eyes of patients with SCKC of a similar mean age. We measured best corrected visual acuity (BCVA) and corneal topography with a Pentacam HD device to select the SCKC group. Biomechanical measurements were performed using the Corvis® ST device. We carried out a non-parametric analysis of the data with SPSS software (Wilcoxon signed rank-test). (3) Results: We found statistically significant differences between the control and SCKC groups in some corneal biomechanical parameters: first and second applanation time (p = 0.05 and p = 0.02), maximum deformation amplitude (p = 0.016), highest concavity radius (p = 0.007), and second applanation length and corneal velocity ((p = 0.039 and p = 0.016). (4) Conclusions: Our results show that the use of normalised biomechanical parameters provided by noncontact tonometry, combined with a discriminant function theory, is a useful tool for detecting subclinical keratoconus.Cátedra FISABIO-Alcon-Universidad de ValenciaMedicin

Umbrales de discriminación cromática y su aplicación a un algoritmo de filtraje de imágenes digitales

Memoria del Máster en Optometría Avanzada y Ciencias de la Visión.Este estudio trata de conseguir un algoritmo de filtraje de imágenes digitales utilizando la interpolación de los umbrales de discriminación cromática experimentales del sistema visual humano, teniendo en cuenta, en particular, el cambio en la sensibilidad que se produce cuando se antepone un filtro coloreado. Se trabaja con un soporte informático para la caracterización de las imágenes que se presentan al observador, con lo que las conclusiones deben ser interpretadas para este tipo de representaciones. Para ello, realizaremos la medida de una serie de elipses de discriminación cromática, distribuidas uniformemente dentro del diagrama cromático, valiéndonos del software Colour Cambridge Test. A continuación el algoritmo del modelo de visión nos proporcionará el rellenado del resto del diagrama cromático mediante un proceso de empaquetamiento de elipses. Por último, haremos actuar estos umbrales de discriminación sobre una serie de imágenes digitales con el fin de simular el efecto de los umbrales del sistema visual humano y reconocer las zonas de colores que, aunque con diferente especificación colorimétrica en la imagen original, tienen la misma apariencia para el observador