The cheiroscope is a good instrument to determine the visual performance of the brain. 

The ocular is designed in a way, that allows one eye to see an image through a mirror, while the other eye only looks at the blank background, where you can place a piece of paper. The patient has to draw the image, using his brain to transfer the visual information onto the other eye. Hand-eye-coordination is also optimized. This is a good tool to change between monocularity and binocularity.