In Hess-Lancaster testing, which setup correctly describes the relation between the patient's flashlight color and the examiner's projection?

• A. The patient uses a red flashlight and the examiner projects a green light
• B. The patient uses a green flashlight and the examiner projects a red light
• C. The patient uses a blue flashlight and the examiner projects a red light
• D. The patient uses a yellow flashlight and the examiner projects a blue light

Answer: (B)

Hess-Lancaster uses red-green color separation to isolate each eye’s target. The two eyes are presented with two distinct colors so that each eye sees only its own stimulus through its corresponding filter. In the described setup, the eye that carries the red filter will see the red projection, while the eye with the green filter will see the green light from the flashlight. This opposite pairing—green flashlight for the patient and a red projection from the examiner—ensures each eye receives a separate target, allowing the clinician to map the alignment of each eye independently on the screen. Colors like blue or yellow aren’t part of the standard red-green separation, so they don’t provide the same clean isolation, which is why those options aren’t used.