VON GRAEFE TEST: The Von Graefe phoria test is a common clinical method to measure heterophoria (a latent eye turn) by using prisms to dissociate the eyes and have the patient align two separate images. HOW IT WORKS: Setup: The patient looks at a fixation target through a phoropter or trial frame at a specific distance (e.g., 6 meters for distance, 40 cm for near). Prism placement: A vertical prism (like a 12Δ base-up) is placed before one eye to vertically separate the images. A horizontal pris