Why the abbreviation for the Doctor of Optometry is O. D.?

Solution 1:

OED has

D. n. = Doctor (in academical degrees, as a Latin word following, and as English preceding, other initials), as D.D. (Divinitatis Doctor), Doctor of Divinity, LL.D. (Legum Doctor), Doctor of Laws, M.D. Doctor of Medicine, Ph.D., Doctor of Philosophy, D.C.L., Doctor of Civil Law, D.Lit., Lit.D., Doctor of Literature, D.Phil., Doctor of Philosophy, D.Sc., Doctor of Science.

Note that PhD can also be DPhil; LitD (or LittD) can be DLit; DSc can also be ScD. They are not interchangeable: different universities have different methods. My brother is not MD but DM.

The answer is that OD names the degree in Latin whereas DO is from an English name. Actually, the University of Aston's degree which Wikipedia mentions is not DO at all but DOptom.

It would certainly be useful to know what the Latin phrase is which results in OD, but I can't find any reference online, even from universities which offer that degree.