US Patent 8132916 High precision contrast ratio display for visual stimulus

Embodiments of the present invention include approaches for controlling light valve devices to improve the range and precision of the contrast ratio and the grayscale levels of a display used for visual field tests. In one embodiment, two or more illumination devices are used to enable the display device to display a wide range of contrast stimuli at precise illumination intensities over a fixed background illumination level. In another embodiment, the gamma curves of the display elements are adjusted to allow greater variations in the brightness of the display.