A patient returns to your office reporting that her eyes feel strange when she reads 6 mm below the optical centers of her new glasses. The prescription in her right eye is -4.00 DS and -7.00 DS in her left eye. How much vertical prism is induced when she reads?
A. 1.8 prism diopters base down
B. 4.2 prism diopters base down
C. 6.6 prism diopters base down
D. 2.4 prism diopters base down