What astronauts can teach us about glaucoma
NASA’s Vision Impairment and Intracranial Pressure (VIIP) project was started after NASA realized many astronauts return from space with vision problems, and these problems may last for years after mission completion.
New Orleans-Researchers and clinicians may not know what glaucoma is, or what causes cupping and field loss, but it is well accepted that IOP plays a role, said John Berdahl, MD.
Speaking during the Innovators General Session at ASCRS 2016, Dr. Berdahl said glaucoma is much like the dark side of the moon.
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“We’ve only looked at one side of glaucoma (it being a one-pressure disease) much like we’ve only seen one side of the moon,” he said.
“It’s commonly believed that glaucoma is a pressure disease, and it’s likely true,” Dr. Berdahl said.
What remains unknown, however, is why IOP matters.
Why IOP matters
The “intra,” portion of the “IOP” term, however, is a misnomer, Dr. Berdahl said-noting clinicians should be referring to these pressure differences in relation to how they act-across two areas of the eye, not within them.
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Philosopher Herbert Spencer has been quoted as saying “how often misused words generate misleading thoughts,” and Dr. Berdahl said that is the case with IOP.
“Really, IOP is the transcorneal pressure difference,” he said. “This is important because it betrays how we think of IOP as the absolute pressure in the eye, but really it a measurement of how much higher the pressure is inside the eye compared to the pressure outside of the eye.”
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Atmospheric pressure in Denver is about 620 mm Hg, at sea level about 760 mm Hg, and 30 feet under water (average scuba dive) it is closer to 1,520 mm Hg, “and all those pressure differences affect the eye.”
But scuba divers don’t get glaucoma, he said.
Newton’s Third Law of Motion says equal and opposite forces cancel each other out, but “if one force is bigger than another (i.e., IOP is greater than cerebrospinal fluid, or CSF), then a net force is generated and movement (or cupping) could occur,” he said.
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