CSF PRESSURE IS CRITICAL

The cerebrospinal fluid (CSF) pressure is a potentially critical parameter in the pathology of primary open-angle glaucoma, a finding with possible implications for research, reports Jost B Jonas MD, University Eye Clinic, Mannheim, Germany. 
“Physiological relations in the dynamics of the change in intraocular pressure (IOP) and orbital cerebrospinal fluid pressure may play a role in the onset and progression of glaucomatous optic neuropathy,” he told the 11th Congress of the European Glaucoma Society in Nice.
Previous population-based, clinical and laboratory studies point to a positive correlation between CSF pressure, blood pressure and IOP.
However, the research also shows that, although arterial hypertension is significantly associated with elevated IOP, it is not associated with glaucoma. Like IOP, CSF pressure is also elevated in people with hypertension, but both blood pressure and CSF pressure tend to be low in patients with normal tension glaucoma. What the findings suggest is that glaucoma may result from some sort of malfunction in the body’s normal mechanisms for maintaining the equilibrium  between the fluid pressures of the intraocular space, the systemic circulation and the brain, Dr Jonas said.

prevent damage
He noted that in patients without glaucoma, the CSF pressure rises to match that of the IOP and so is able to counter the IOP and prevent damage to the optic nerve.  In an eye with primary open-angle glaucoma, on the other hand, the IOP exceeds the CSF by such a degree that it creates an abnormal pressure gradient on the lamina cribrosa that in turn influences the physiology of optic nerve fibres and their axoplasmic flow.
Evidence supporting that theory comes from the Beijing Eye study and the Central India Eye and Medical Study which showed that, in patients with angle glaucoma,  a smaller rim and thinner retinal nerve fibre layer was associated with a higher trans-lamina cribrosa pressure difference but not with a higher IOP.
Dr Jonas added that on that basis there could be several scenarios where glaucomatous damage to the optic nerve is likely to occur. They include patients with high IOP but normal CSF, those with normal IOP but low CSF and those with arterial hypotension in whom cyclical reductions in CSF pressure exceed those of IOP.
Another implication of the research is that many situations where IOP is elevated pose no threat to the optic nerve head in healthy individuals. For example, a trumpet player may have high IOP while in performance, but will not be vulnerable to optic nerve head damage because the brain pressure is also increased. The same may be true when a person stands on their head or is in a supine position, Dr Jonas added.

Jost B Jonas: Jost.Jonas@augen.ma.uni-heidelberg.de