Contrast (vision)

About: Contrast (vision) is a research topic. Over the lifetime, 10379 publications have been published within this topic receiving 221480 citations.

Spatial Contrast Sensitivity Deficits in Monkeys Produced by Optically Induced Anisometropia

Abstract: An anisometropia was simulated in infant rhesus monkeys by securing a high-powered minus lens (—10 D) in front of one eye. The anisometropia rearing procedure was initiated at 30 days of age and was continued for durations of 30, 60, or 90 days. Behavioral measurements of spatial contrast sensitivity obtained when the animals were 9 months of age indicated that the monkeys treated for 30 days had equal or nearly equal contrast sensitivities and cut-off spatial frequencies in the two eyes. The 30-day monkeys also demonstrated normal binocular summation for threshold stimuli. In contrast, the monkeys treated for either 60 or 90 days showed a significant reduction in contrast sensitivity in the defocused eyes for spatial frequencies greater than 1.0 cycles/deg and failed to show an improvement in contrast sensitivity under binocular viewing conditions. The cut-off spatial frequencies obtained at moderate luminance levels for the defocused eyes of the 60- and 90-day monkeys were slightly more than 1.0 octave lower than the cut-offs for the nondeprived eyes and, like humans with anisometropic amblyopia, the deficits in the spatial resolving capacity of the defocused eyes were observed over a large range of background luminances. The results indicate that the lens-reared monkey is a promising model for anisometropic amblyopia in humans. Invest Ophthalmol Vis Sci 26:330-342, 1985 Functional amblyopia is a reduction in visual acuity that occurs in the absence of any ophthalmoscopically detectable anomalies of the eye, and in appropriate cases, is remediated by therapeutic measures. The three most common etiologies of functional amblyopia are anisometropia, strabismus, and sensory deprivation. 1 Although all three of these forms of amblyopia are characterized by decreased visual acuity, recent psychophysical investigations 2 " 7 have revealed substantial differences in the visual characteristics of humans with these three types of amblyopia. The different patterns of visual deficits observed in human amblyopes suggest that these three forms of functional amblyopia may be associated with different neural abnormalities. Since a thorough understanding of the neural basis of amblyopia is essential for the development of optimal clinical treatment and management procedures, investigators have worked to develop animal models of amblyopia that could be used in anatomic

Microbubbles as a scattering contrast agent for grating-based x-ray dark-field imaging.

Abstract: In clinically established-absorption-based-biomedical x-ray imaging, contrast agents with high atomic numbers (e.g. iodine) are commonly used for contrast enhancement. The development of novel x-ray contrast modalities such as phase contrast and dark-field contrast opens up the possible use of alternative contrast media in x-ray imaging. We investigate using ultrasound contrast agents, which unlike iodine-based contrast agents can also be administered to patients with renal impairment and thyroid dysfunction, for application with a recently developed novel x-ray dark-field imaging modality. To produce contrast from these microbubble-based contrast agents, our method exploits ultra-small-angle coherent x-ray scattering. Such scattering dark-field x-ray images can be obtained with a grating-based x-ray imaging setup, together with refraction-based differential phase-contrast and the conventional attenuation contrast images. In this work we specifically show that ultrasound contrast agents based on microbubbles can be used to produce strongly enhanced dark-field contrast, with superior contrast-to-noise ratio compared to the attenuation signal. We also demonstrate that this method works well with an x-ray tube-based setup and that the relative contrast gain even increases when the pixel size is increased from tenths of microns to clinically compatible detector resolutions about up to a millimetre.