DONT do it. This is what your situation is, in short, as listed above.
If you don't do an Ophtho rotation, then most (if not all) programs are going to question your commitment to the field...with your dad being your ONLY Ophtho letter writer, that would honestly do nothing for you. You need to get at least 1 Ophtho rotation under your belt and get a LOR from that one.
Maybe you should consider applying in a year and doing research, Ophtho rotations, etc to augment your application.
Being an FMG you are already at a disadvantage...so unless you scored 270+ on Step 1 or something insane like that, you really need to do more than have your own father write your only Ophtho letter...really
good luck