Attempt these options, not necessarily in order, to resolve the issue.
· Adjust the contrast and brightness knobs on the outside of your monitor to the highest settings. This may help you to see the more important details.
· Uninstall and then reinstall Riven. Go through the Setup Option, designed to assist you with adjusting your monitor's brightness and contrast.
· Contact the manufacturer of your video card to update its driver to the latest version.