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Comment by Tony Realini on:

46409 Aqueous humor dynamics during the day and night in volunteers with ocular hypertension, Fan S; Hejkal JJ; Gulati V et al., Archives of Ophthalmology, 2011; 129: 1162-1166

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The article by Fan et al. is noteworthy in two respects. Firstly it is likely one of the last papers published bearing the name of our beloved, departed colleague, Carl Camras. Second, it illustrates a major technical challenge in clinical aqueous humor dynamics studies, namely, the imprecise, assumption-laden methods available for measuring uveoscleral outflow.

A major technical challenge in clinical aqueous humor dynamics studies is the imprecise, assumption-laden methods available for measuring uveo-scleral outflow

The authors have pioneered the technique described in the article, and it is indeed the best that currently exists non-invasively in humans, but it is woefully inadequate and imprecise for making fine judgments. Nonetheless, by reaffirming what is already known about positional or diurnal effects on IOP, aqueous flow and CCT, their study lends at least some credence to a hypothesis that while total tonographic outflow facility, reflecting primarily facility of flow from the anterior chamber, through the trabecular meshwork and into Schlemm's canal, has little diurnal variation, uveoscleral out-flow indirectly calculated decreases significantly at night.

Our field cries for simple non-invasive technologies permitting precise, accurate and reproducible measures of all parameters of aqueous humor dynamics at any time of day or night

If true, his could explain nocturnal IOP spikes reported in recent studies from other laboratories. It would be interesting to know whether drugs that are known to increase uveoscleral outflow (e.g., pros-taglandin F2α analogues) are as effective at night as in the day-time, and if not, why not? There are so many questions, but so little data developed by solid techniques! The authors have gotten fairly far along this path of understanding, but our field cries for simple non-invasive technologies permitting precise, accurate and reproducible measures of all parameters of aqueous humor dynamics at any time of day or night.

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