Which statement about Hess-Lancaster testing is true?

• A. It uses only red filters
• B. It uses red and green filters to separate the two eyes
• C. It uses blue filters
• D. It uses incandescent lighting only

Answer: (B)

In this test, the key idea is separating what each eye sees so you can map how the eyes move independently. By giving one eye a red filter and the other eye a green filter, the two eyes view different projections of the light and grid. The examiner then traces where each eye would point on the grid across different directions of gaze, creating a color-separated map of eye movements. This dichoptic separation lets you see which eye is limited in which gaze position and helps identify paresies or incomitancies.

The other options don’t fit because the test relies on red and green separation to distinguish the eyes, not just red, blue, or incandescent lighting alone.