Do optometrists treat cataracts?

Nonsignificant ones. Presence of a cataract does not mean it needs to be removed (natural aging change of the eye). Optometrists can change a glasses prescription as a cataract grows/affects refractive error (i.e. Myopic shift). Only when it's visually significant (affecting daily life) and otherwise good potential then the cataract is removed by an ophthalmologist via cataract surgery.
No. Although the optometry lobbies around the country are pushing for more surgical rights, they are not medical doctors, they are not surgeons, they have never been trained as surgeons and do not have experience performing surgery.
Surgeons only! Only a surgeon can truly treat cataracts, by performing removal of the cloud lens of the eye and replacing it with a lens implant. Optometrists do not attend medical school, and do not learn to perform this surgery. The can, in many states, be involved in the preoperative and postoperative care.
No. They can diagnose a cataract, but do not perform surgical removal of the cataract. Only eye physicians (ophthalmologists) can perform cataract surgery.
No, optom. is not MD. A person who might need glasses or contact lenses for nearsightedness (myopia), farsightedness, astigmatism, or presbyopia (needs reading glasses), but otherwise has no eye symptoms, can see an optometrist (a non-medical doctor). Ophthalmologists are medical eye doctors who do cataract surgery, other eye surgeries, treat eye diseases, prescribe medications, etc...