I'll be presenting a course on "Ophthalmic Application of Prism" at the OAA conference in June, and I want to make sure I have my "ducks in a row" before I answer a question that came up last time I talked about prism in a course...

Specifically, "Does a change in vertex distance affect the amount of prescribed prism?" My answer was "No, because changes in vertex distance can only effect the elements of a prescription that involve focal lengths. Since prism only refracts and does not converge or diverge light, it is unaffected by focal length."

Was this a correct assumption, or do I need to find the emails of all the attendees of that course (yeah, right)?

Thanks as always,
Pete