I had been teaching Salamba Sirsasana (supported head pose, or headstand) to one of my students. She had struggled hard to learn the pose, first conquering fear, then strength, then equipoise. Then another barrier came her way. Her ophthalmologist diagnosed her with low tension glaucoma. One of the first things we learn in Iyengar yoga when teaching Salamaba Sirasana is when not to teach it: in cases of high blood pressure, menstruation, and eye problems.
My wife who works as an opthalmic assistant directed me to an article (now deleted) where the author of this study painstakingly measured eye pressure in each of the inverted asanas in the Iyengar method. As expected, Salamba Sirsana is off the charts in terms of high ocular pressure. A major finding is that pressure increases the most during the first minute of the Salamba Sirsasana, then it stabilizes up to 13 minutes mark, then it increases again. This means for those who have eye problems and are wanting to try headstand “just for a little while,” that first minute can be the most damaging to the optic nerve. Here is an article with similar information to the deleted one.
So should people completely omit inversions in their yoga practice if they have eye problems? The answer is “no” as some inversions decrease eye pressure. Conversely, in Viparita Karani (inverted lake posture), the study showed eye pressure actually dropped to levels equal below that of the resting measurement.