If you have glaucoma, avoid head-down yoga poses. Inverted positions increase fluid pressure in the eyes (intraocular pressure, or IOP)—and elevated IOP increases damage to the optic nerve in people with glaucoma.
In a study in PLOS ONE, researchers measured IOP in people with glaucoma before, during, and after they performed four inverted yoga poses for two minutes each. All poses—especially the downward facing dog (Adho Mukha Svanasana), followed by the standing forward bend (Uttanasana)—caused acute elevations in IOP (which dropped back to normal shortly after). Though similar responses were seen in people without glaucoma, who were also included in the study, healthy eyes are able to tolerate acute increases in IOP without damage. Previous research has reported significant IOP elevation with yoga headstands.
People with glaucoma, the leading cause of blindness in the U.S., should also avoid lifting heavy weights and exercises where the head is positioned below the heart.
Also see Which Type of Yoga Is for You?