Abnormal, harmful, or undesirable effect on an organism that causes anatomical or functional damage, irreversible physical changes, or increases the susceptibility to other biological, chemical, or environmental stresses.
Optometrists can prescribe glasses, contact lenses, eye exercises, vision aids and therapy, and (in some states) oral and topical medications to treat certain eye diseases. Ophthalmologists are doctors of the eye. They have graduated from medical school and are licensed to practice medicine, so their credentials are either doctor of medicine (MD) or doctor of osteopathy (DO).
Yes, you can wear safety goggles over your prescription glasses. Keep in mind that not all goggles are designed to fit over prescription glasses, so make sure they're deep enough to provide enough room for your glasses. I'd also recommend an indirect-vented goggle with anti-fog lens.