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There is relationship between progressive field loss and increased intraocular pressureThis important study by Kiuchi et al. (1169) reports a relationship between progressive field loss and increased intraocular pressure (IOP) in the supine position in normal tension glaucoma (NTG). All study patients underwent a diurnal tension curve to prove the diagnosis of NTG and MD slope was used as the criterion for field progression. IOP was measured 30 minutes after lying down using a Perkins tonometer and the magnitude of change in IOP was determined by comparing the difference between IOP in the sitting and lying position. The authors report a mean increase in IOP of 3.8 mmHg 30 minutes after lying down and they report a statistically significant correlation between increased supine IOP (and magnitude of change) and the MD slope. The study has certain strengths and weaknesses. The strengths of the study include the fact that this is one of only a small number of studies to have investigated the relationship between lying down and progressive glaucoma using a prospective design. There are, however, a number of weaknesses. Firstly we are not told how many eyes dropped out for not meeting inclusion criteria, IOP measurements were not masked, using MD slope as a measure to define progression doesn't exclude cataract, lack of a control group, etc. I would have liked to have seen magnitude of change in IOP correlated to disc progression or disc hemorrhage and/or a measure of field progression that excluded media opacification. The authors also describe a surprising correlation between higher supine systeased change in IOP.
Despite the described weaknesses, this study reports an intriguing relationship between change in IOP from sitting to lying and progressive field loss in NTG. If this work is confirmed by others using more robust research methodologies we may find ourselves recommending the same therapy for progressive NTG as prescribed for esophageal reflux -namely elevation of the head of the bed!