Two prism diopters correspond to which degree of visual field?

• A. 0.5 degree
• B. 1 degree
• C. 2 degrees
• D. 3 degrees

Answer: (B)

Prism diopters measure how much a prism bends light, which corresponds to an angular shift of the eye’s line of sight. For small angles, 1 prism diopter deflects by about 0.57 degrees. Therefore, 2 prism diopters produce roughly 1.14 degrees of shift, which rounds to about 1 degree. In other words, two prism diopters correspond to approximately one degree of visual field.