Rise in intraocular pressure following an oral water load has previously been thought to be a consequence of osmotic changes, water moving from the diluted blood into the less dilute aqueous. The present study of 234 water drinking tests demonstrates that osmotic considerations alone are not an entirely adequate explanation. Increase in intraocular pressure precedes decrease in serum osmolality in 20% of the cases.
Intraocular pressure rises so rapidly following ingestion of water that a testing technique must be used in which pressure is measured at least every 15 minutes after drinking the water. In the present series, if a single measurement had been made one hour after drinking, the peak intraocular pressure would have been missed in 97% of the cases.