Wearing Eyeglasses
When observing, you can usually leave your glasses off if you are farsighted (can't focus on nearby objects) or nearsighted (can't focus on distant objects). Most telescope focusers can compensate for these problems. With astigmatism, you can leave your glasses off at high powers (unless your astigmatism is severe), since astigmatism shows up primarily at the periphery of your cornea, and most high power observing involves examining small objects in the center of the field. At low powers, leave your glasses on if you have astigmatism.