Question 1 of 14

(demo test)

This is a very common question on any board exam, and tests your knowledge of Prentice's rule:

     PD = h * F

     (where PD is the induced prism; "h" is the distance from the optical center in cm; and "F" is the power of the 
     lens in diopters)

In this question, PD = 3 prism diopters and "F" is 15.  We are solving for "h":

     h = PD / F

     h = 3 / 15

     h = 0.2 cm

     h = 2 mm

Now we have to determine if we are looking above or below the optical center.  A minus lens is basically two prisms placed apex-to-apex with a base up prism superiorly and a base down prism inferiorly.  Also remember that the eye wants to move toward the base with induced prism.

Since we want the patient to compensate for a right hypertropia, we want to induce a base-down prism effect by having his right eye look 2 mm BELOW the optical center of the lens.  An equivalent way of saying this is we want to move the optical center 2 mm UP in the right lens.  

However, this is not an answer choice!  Another way of achieving this is to move the optical center up by 1 mm for the right lens and down by 1 mm for the left lens (i.e. choice "D").