What if glaucoma is actually a “two-pressure” disease caused by a differential between intraocular pressure (IOP) and cerebrospinal fluid pressure (CSFp)?
Atlanta-What if glaucoma is actually a “two-pressure” disease caused by a differential between intraocular pressure (IOP) and cerebrospinal fluid pressure (CSFp)?
Doctors have known for years that IOP is not the only factor in development or progression of glaucoma and have seen that intracranial pressure (ICP) can affect the optic nerve. If axonal transport is affected by an imbalance between IOP and CSFp, the result could be glaucomatous damage if IOP is high or the CSFp is low, while ocular hypertension may develop if IOP is low and the CSFp is higher, says John Berdahl, MD.
Both retrospective and prospective studies have supported this theory, according to Dr. Berdahl, who is in private practice in Sioux Falls, SD. But, why does it matter? In short, it could be revolutionary.
“If we can decouple IOP from ICP and get control over either one of them relative to the other,” he says, “we’ve got a whole new way to treat glaucoma, and it’s a redefinition of the disease.”
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He explained that if the average IOP, which he prefers to call transcorneal pressure difference, is 16 mm Hg and the average ICP is 12 mm Hg, then the normal translaminal pressure difference is about 4 mm Hg. But if IOP is elevated to 22 mm Hg and the ICP goes down to 9, the translaminal pressure difference would be 13 mm Hg.
“What if we could change the pressure in front of the eye and decrease the pressure by 10? That should translate into the eye, according to Pascal’s law, and take that 22 down to 12. The pressure gradient is only 3, and we’re protecting that eye from glaucoma,” he says.
His proposal for accomplishing this is to devise goggles that would put a slight vacuum in front of the eye to reduce some of the atmospheric pressure. Glaucoma could then be treated in a nonsurgical, nonpharmacologic, and titratable manner, Dr. Berdahl says.
“We’re pretty sure the physics is on our side,” he says. “Biology isn’t predictable, but physics is.”
Dr. Berdahl proposed two reasons why doctors should care about this theory.
“We’re all eye doctors, and glaucoma is still a leading cause of blindness,” he says. “But if that’s not enough, it matters in case we ever have to get off of this rock.”
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Dr. Berdahl says that NASA is studying vision changes and anatomical alterations to the eyes during extended space flights, a pattern of changes officially termed vision impairment and intracranial pressure (VIIP).
The changes associated with VIIP include globe flattening, hyperopic shift, choroidal folds, and optic disc edema. VIIP could be an even more significant concern on potential flights to Mars than it already is on the International Space Station, where an astronaut is in space on average for about six months. Astronauts headed to Mars would spend about six months in flight each way and stay on the planet 18 to 22 months.
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The day that a person sets foot on Mars, targeted for 2030, would be a “unifying moment” for the world, Dr. Berdahl says.
“And if eye doctors can play a small part in this by helping astronauts, I’m in,” he says.
He is part of a group of experts working with NASA on solving the problems associated with VIIP, which is considered both a health and safety concern, and has also speculated about whether his theoretical goggles would be useful for treating eye problems in zero gravity as well as on earth.
To that end, Berdahl has started a company to research and test the goggles. While they appear to have a number of advantages, the concerns yet to be resolved include wearability and the need for convincing scientific evidence.