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Comment by Jost Jonas on:

20979 Cerebrospinal fluid pressure is decreased in primary open-angle glaucoma, Berdahl JP; Allingham RR; Johnson DH, Ophthalmology, 2008; 115: 763-768

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Berdahl and associates demonstrate the possible association between cerebrospinal fluid (CSF) pressure and primary open-angle glaucoma (POAG) by retrospectively reviewing a large database of individuals undergoing lumbar puncture at one institution over 12 years. While the methodology is generally sound, there are a few questions that must be addressed. The authors, in the methods section, point out that the diagnosis of glaucoma had to be made or confirmed by a glaucoma specialist. Given that general ophthalmologists also commonly make such a diagnosis, those patients diagnosed as having glaucoma by general ophthalmologists without confirmation from glaucoma specialists were presumably excluded. In the discussion, however, the authors state that nearly all POAG cases were examined by a glaucoma specialist leading one to assume that some were not. This inconsistency is puzzling and should be explained.

In the sample size calculation, the authors point out that 49 patients would have been required for the study to have adequate power to detect a difference between cases and controls and it is then noted that exactly 49 patients met the criteria for the control group. It is not clear whether or not this was coincidental or that the investigators stop looking for controls once an adequate number had been identified. Given that cases were selected form the entire data set, the controls should, of course, be representative of all patients meeting the criteria for controls in the study population.

It is possible that rather than low CSF pressure being associated with glaucoma, higher than average CSF pressure may be protective against glaucoma

The authors note that normal CSF pressure is generally between 5 and 15 mmHg, and given that the mean CSF pressure in the POAG and control groups was 9.2 and 13.0 mmHg respectively, it is possible that rather than low CSF pressure being associated with glaucoma, higher than average CSF pressure may be protective against glaucoma. Despite the obvious methodological limitations of the study, the relationship between CSF pressure and POAG is intriguing and should certainly be investigated prospectively in future studies.

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