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Editors Selection IGR 9-4

Intraocular pressure: IOP variation and progression

Comment by Kuldev Singh on:

19975 Association between intraocular pressure variation and glaucoma progression: data from a United States chart review, Lee PP; Walt JW; Rosenblatt LC et al., American Journal of Ophthalmology, 2007; 144: 901-907

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Lee et al. (1540) address a controversial topic: the relative importance of IOP variation between patient visits as a risk factor for glaucoma progression. The authors study two overlapping cohorts of subjects, in one of which IOP information that is recorded after initiation of treatment or documented visual field progression is appropriately excluded in the analysis. Progression can lead to treatment which can lead to IOP variation, making it difficult to establish causality in such studies. Another variable that must be adjusted for is the influence of IOP level on IOP variation, the higher the IOP, the greater the expected IOP variation, all other factors being equal. The authors point out the multiple limitations of their methodology including the retrospective, post hoc nature of the study design and the small sample size with the latter being compounded by a paucity of IOP information from some subjects. Nevertheless, the authors conclude that 'IOP variability is an important predictor of glaucoma progression' and that 'SD (standard deviation) is a convenient mea-sure of variability to assess glaucoma progression risk.' The surprise finding that the IOP range, the difference between the highest and lowest IOP, is inversely correlated with progression is marginalized by the authors as possibly relating to chronological factors that could not be appropriately adjusted for. The authors do not address the possibility that, all other things being equal, wide IOP fluctuations are somehow protective? In contrast, the possible impact of similar chronological factors on SD apparently do not lead the authors to doubt the validity of their conclusions.

Progression can lead to treatment which can lead to IOP variation, making it diffi cult to establish causality in such studies

This paper does not resolve the ongoing debate regarding whether or not IOP variation is an important risk factor for glaucoma pro-gression. The most elegant work on this topic remains the analysis by Bengtsson and Heijl which shows that IOP variation between visits is not a significant risk factor for glaucoma progression in the Early Manifest Glaucoma Trial. One good analysis trumps several with lesser standards.

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