True or False: When checking for vertical prism in lensometry, the prism values for each eye occur at the same time since we moved the position of the glasses?

• A. True
• B. Sometimes
• C. Not enough information
• D. False

Answer: (D)

Vertical prism in lensometry comes from vertical decentration of each lens relative to that eye’s pupil. Because each eye has its own optical path and the frame sits differently in front of each pupil, moving the glasses changes the alignment for each eye independently. So the prism amount you read for one eye isn’t automatically the same as for the other, and you don’t get both prism values as a single, simultaneous result just from moving the glasses. In practice you assess the prism for each eye separately, even though the instrument may display both readings, the values aren’t guaranteed to occur identically or at the same moment simply by repositioning the glasses.