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Editors Selection IGR 16-4

Intraocular Pressure: Circadian IOP patterns and visual field damage in NTG

Comment by John Liu on:

48938 Circadian (24-hour) pattern of intraocular pressure and visual field damage in eyes with normal-tension glaucoma, Lee YR; Kook MS; Joe SG et al., Investigative Ophthalmology and Visual Science, 2012; 53: 881-887

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In this well-designed prospective study, Lee and colleagues employed the best possible conditions in collecting 24-hour data of IOP under habitual body positions from newly diagnosed and untreated glaucoma patients whose office sitting IOP readings were in the normal range. The 24-hour variations of IOP in approximately one third of study patients were rather small and regarded to have no 24-hour IOP peak. For the remaining study patients, the 24-hour IOP peaks appeared more during the nocturnal period, about three times, than during the diurnal period. The authors also showed that the nocturnal IOP elevations were related to the change of habitual body position for sleep. If one considers only the sitting IOP for 24 hours, the nocturnal IOP elevation cannot be demonstrated. Although there are moderate correlations between the diurnal IOP peak and the 24-hour IOP peak as well as the nocturnal IOP peak, individual IOP elevations during the nocturnal period can be substantial in some patients and make their office IOP readings misleading for glaucoma diagnosis and treatment. All these results agree in general with other recent reports on 24-hour IOP in different groups of glaucoma patients having various ranges of office IOP. Taken together, there is little doubt that real life IOP peaks in most glaucoma patients including so-called normal-tension glaucoma would occur outside regular office hours. The next step forward is to figure out which 24-hour IOP parameter is associated with glaucoma development and progression. For this matter, the authors also presented their findings. Despite a large number of 177 well-characterized glaucoma patients enrolled, no correlation was found between various 24-hour IOP parameters, including the daytime IOP, and visual field defects used as the glaucomatous damage. This suggests that a cross-sectional, onetime 24-hour IOP measurement with more than a hundred study subjects does not have a statistical power to judge the correlation between any 24-hour IOP parameter and glaucoma development. The authors should be complimented for their efforts in reaffirming that a huge challenging task is ahead when we try to obtain critical information of how 24-hour IOP plays its role in glaucoma pathogenesis.

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