Central anti-suppression check. The word FUSE is only seen by one eye, the word TEXT is seen by the other eye, and the word THIS is seen by both eyes.
Fixation disparity check. Small hash mark on the left of the outer ring on one card, and on the right of the ring on the opposite card to help improve accurate alignment and help reduce fixation disparity.
Convergence and divergence training when red/green glasses are used. Ex. If the green card is on the right and the green filter is over the left, divergence is done when fusing the two images.
This product is available in clear plastic.