I am highly handed. I fly airplanes and ride bikes left-handed. I write and brush my teeth with my right hand. I am catastrophic trying to do any of those with the opposite hand.

manintheboat says the official optometrist test is to look at something far away, put your hands up in a small circle, so you encircle the image, then very slowly bring it to your face. She says that's a pretty reliable test insofar as people very rarely end up coming up with varied answers.