When any of the brush sizes reaches a certain limit the edges failed to display and you can't see the complete circle of the brush. This occurred after I checked to allow Open GL Drawing in the preferences but after I unchecked it the problem persisted. I updated my driver (NVidia GForce 6800) to no avail. The brushes have been displaying fine for the last year with the same driver. Any ideas would be appreciated.
That sounds like an old nVidia display driver bug.
Is there any possibility you took a Windows Update or something that ''updated'' your display driver to an older WHQL version?
Perhaps completely removing the driver and getting the very latest one from nVidia.com might be in order.
P.S., keep in mind that you have to close and restart Photoshop in order for OpenGL Drawing settings changes to completely take effect.
Thanks Noel - you were right. I managed to locate a Nvidia driver update online that was more recent than I had previously used. As soon as I updated the Nvidia driver, the brush problem resolved, even using Open GL drawing.