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Excerpt:

Introduction Scuba diving has become a popular recreational sport, but it poses unique challenges for eye health. Divers are exposed to rapid ambient pressure changes underwater, which can influence intraocular pressure (IOP) and blood flow in the eyes. People with glaucoma – a condition where elevated IOP can damage the optic nerve – may worry about the effects of diving. Fortunately, experts report that diving per se hasn’t been shown to worsen glaucoma, likely because diving affects the difference between the pressure inside the eye and the surrounding water, not just the eye’s absolute pressure (). Nonetheless, divers with glaucoma must take precautions. This article reviews how water pressure, mask squeeze, and equalization affect IOP and ocular perfusion, weighs the health benefits of diving against its risks for glaucoma patients, and offers practical guidelines. Every recommendation is grounded in current research and best practices.How Underwater Pressure Affects the Eye Underwater, pressure increases by about one atmosphere every 10 meters (33 feet) of depth. In theory, higher external pressure could compress the eyeball and raise IOP. However, studies generally show the opposite effect: diving or simulated high-pressure environments tend to lower IOP slightly () (). For example, a recent systematic review found that experimental hyperbaric studies often reported reduced IOP under increased pressure (). One trial observed an ~8% drop in IOP measured 30 minutes after a 25-meter dive (); another noted that IOP remained below baseline even during the dive. The reasons are not fully understood, but may include changes in blood flow and oxygenation.Diving also alters ocular perfusion pressure (the difference between arterial blood pressure and IOP). Immersion and cold water trigger peripheral vasoconstriction, which can raise overall blood pressure. This tends to increase ocular perfusion pressure (). In concert, high blood oxygen levels (hyperoxia) cause constriction of retinal and choroidal blood vessels. In fact, one review notes that hyperbaric oxygen often causes ocular vasoconstriction and choroidal thinning, which can further reduce IOP (). In summary, the net effect of diving physiology seems to be a modest decrease in IOP and an increase in perfusion pressure – potentially beneficial for glaucoma if the optic nerve receives more blood flow. Still, the effects may vary and are incompletely understood.Mask Squeeze and Equalization A special concern for divers is the pressure difference between a diver’s mask and the surrounding water. Without equalization, the mask can “suck” on the face and eyes as the pressure increases, a phenomenon known as mask squeeze. To avoid this, divers are trained to equalize the mask by gently exhaling air through the nose into the mask during descent (). This keeps the internal mask pressure nearly equal to the ambient pressure. According to diving experts, skipping equalization can cause serious ocular barotrauma (): the vacuum can pull on the eye and eyelids, leading to bruising (periorbital ecchymosis), lid swelling, and subconjunctival hemorrhages (bleeding under the conjunctiva) (). In severe cases, it can even cause bleeding inside the eye (hyphema) or in the or

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