The lees screen test.

The Lees screen is a modification of the Hess screen. It is used to obtain the same information about incomitant strabismus, but using a different method of dissociation. Red and green complementary color dissociation is replaced with a double-sided mirror. The mirror prevents both eyes viewing the same screen simultaneously, although the patient perceives both images seen by the fovea of each eye as if they are projected straight ahead.