The Vulnerable Balance Between Glaucoma and CSFP

Pressure imbalance on lamina cribrosa lies at the heart of glaucomatous optic neuropathy. Roibeárd Ó hÉineacháin reports from the 9th World Glaucoma E-Congress

The difference in pressure exerted on the lamina cribrosa by IOP and cerebrospinal fluid pressure (CSFP) could be a potential additional key to the vulnerability of the optic nerve in glaucomatous optic neuropathy may be, according to Prof Jost Jonas MD, FARVO.

The optic neuropathy that characterises glaucoma is unlikely to be primarily vascular because glaucomatous optic neuropathies share many features absent in vascular optic neuropathies. Such features include neuroretinal rim loss and optic cup deepening. Both high and normal pressure glaucoma show parapapillary beta zone atrophy. A loss of equilibrium between the IOP, the CSFP, and blood pressure may more likely be at fault.

“The CSFP is the counterpressure against IOP. The theory could be that glaucoma patients with normal IOP have a low orbital CSFP leading to an increased translaminar cribrosa pressure difference,” Dr Jonas said.

There are several peer-reviewed studies in the published literature showing lower CSFP and a higher translaminar-cribrosa pressure (TLCP) difference (the difference between IOP and CSFP) in glaucoma patients compared with controls. For example, in a retrospective study, mean CSFP was significantly lower in 28 open-angle glaucoma patients than in a control group of 49 non-glaucomatous patients (Berdahl et al, Ophthalmology 2008;115:763¬–768).

In addition, linear regression analysis showed that the cup-todisc ratio correlated independently with the intraocular pressure, CSFP, and TLCP difference.

In another study, lumbar CSFP was significantly lower in normal-pressure glaucoma patients than in the high-pressure glaucoma group or the control group. The TLCP difference was also significantly higher in the normal-IOP glaucoma group and the high-IOP glaucoma group than in the control group (Ren et al, Ophthalmology 2010;117:259–66).

Glaucomatous optic nerve damage correlated with IOP, CSFP, and TLCP difference. However, in a multivariate analysis, visual field loss only had a significant association with the TLCP difference and had no significant association with IOP or CSFP. In the control group, CSFP significantly correlated with both systolic blood pressure and IOP. The TLCP difference was not significantly associated with blood pressure. Higher CSFP also correlated with younger age and body mass index.

Using the data from the controls, Dr Jonas created a formula for deriving CSFP from BMI and diastolic blood pressure and then subtracting the result from IOP as the TLCP difference. When they applied the formula to the populations of the Beijing Eye Study and the Central India and Medical Study, they found open-angle glaucoma, but not angle-closure glaucoma, was significantly associated with a higher TLCP difference but not with IOP in both studies.

Jost B Jonas MD is a comprehensive ophthalmologist, clinical scientist, and Chairman of the Department of Ophthalmology of the Medical Faculty Mannheim of Heidelberg University. Jost.Jonas@medma.uni-heidelberg.de

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