Foveal optical modulation transfer function of the human eye at various pupil sizes

Riemannian color difference metric for spatial sinusoidal color variations

Several studies report on the sensitivity of human vision to static spatial sinusoidal achromatic and chromatic contrast variations. However, a Riemannian color difference metric, which includes the spatial and colorimetric properties of sinusoidal gratings, is lacking. Such a metric is important for various applications. Here we report on the development of a new Riemannian metric, for the prediction of detection ellipsoids in color space, for spatial sinusoidal gratings as a function of the grating's size, spatial frequency, luminance and chromaticity. The metric is based on measurements and models of achromatic and isoluminous chromatic contrast sensitivity functions available in literature, and the Riemannian metric for split fields which we reported earlier. We find adequate agreement with various data sets of experimental achromatic and isoluminous chromatic contrast sensitivity functions and with experimentally determined threshold ellipses of isoluminous chromatic Gabor gratings.

Modulation transfer function formula for different age ranges

The modulation transfer function (MTF) is one of the most complete tools to study the optical performance of the eye. We present the average radial MTF profiles measured in 68 subjects grouped in six age ranges (from 20 to 80 years) and a general formula to estimate the radial profile of human MTF as a function of pupil size and age. The mean MTF for each age group was fitted to an analytical expression to compute two parameters related to aging. The proposed formula fitted reasonably well to experimental data available in previous works and predicted the average changes with aging of different optical quality parameters obtained from MTF.

Representing the observer in electro-optical target acquisition models

Electro-optical target acquisition models predict the probability that a human observer recognizes or identifies a target. To accurately model targeting performance, the impact of imager blur and noise on human vision must be quantified. In the most widely used target acquisition models, human vision is treated as a "black box" that is characterized by its signal transfer response and detection thresholds. This paper describes an engineering model of observer vision. Characteristics of the observer model are compared to psychophysical data. This paper also describes how to integrate the observer model into both reflected light and thermal sensor models.

Transparency of the bovine corneal stroma at physiological hydration and its dependence on concentration of the ambient anion

De-epithelialised and de-endothelialised bovine corneal stromas with a hydration of 3.2 equilibrated at 154 mM NaCl and buffered at pH 7.4 had their optical density (400-750 nm) measured. Stromas equilibrated against 10, 20, 30, 50 or 100 mM NaCl made isotonic to 154 mM NaCl by supplementing with sorbitol were progressively more transparent as NaCl increased. Hypertonic equilibration against 300, 600 or 1000 mM NaCl resulted in a progressive loss of transparency compared with 154 mM NaCl. Light scattering as a function of wavelength fitted a lambda(-3) function well for 10, 30, 50, 100 and 154 mM NaCl preparations between 450 and 650 nm, but not at higher wavelengths. However, hypertonic 300, 600 and 1000 mM NaCl preparations showed a lambda(-2) dependence in the 450-750 nm range. Experiments with 154 mM NaCl and either 0 or 300 mM sorbitol suggested that the changes in light scattering in hypertonic preparations are unlikely to be caused by osmotic alterations to the stromal keratocytes. Psychophysical studies of the optical transmission function of preparations indicated that corneal stromas dialysed against 154 mM NaCl had usable optical properties, but preparations dialysed against 10 mM NaCl were effectively unable to transmit an image. The results are related to the known increase of fixed negative charge in the corneal matrix when chloride ions are adsorbed onto the matrix. It is suggested that the ordering force between corneal collagen fibrils, generated in part by anion binding, may be crucial to the physiological functioning of the visual system.