In a patient with a right homonymous hemianopsia due to stroke, the bases of the yoked prisms should be oriented toward which direction?

• A. Toward the left
• B. Toward the right
• C. Upward
• D. Downward

Answer: (B)

Yoked prisms displace the entire visual scene toward the direction of the prism bases. In a right homonymous hemianopsia, the right half of the visual field is lost in both eyes, so you want to shift the world toward the right to help detect right-field information and encourage scanning toward that side. Placing the bases to the right makes the perceived scene shift right, guiding the patient’s gaze and head toward the right and bringing more right-field stimuli into their usable area. Bases to the left would shift the scene the other way and wouldn’t address the right-field loss, and vertical prisms don’t target this horizontal field defect.