The ophthalmologist has available three distinct medical methods to reduce intraocular pressure: improvement of the facility of aqueous outflow; reduction of aqueous inflow, and reduction of ocular volume through the use of osmotic (hypertonic) agents. The first two methods are well known and are used extensively. The third is seldom used and then usually under urgent circumstances and with poor results. However, the osmotic method is theoretically so valuable that if an ideal agent for its application were available, it would be employed with greater frequency, under a greater variety of conditions, and with more success. An agent approaching this ideal is urea.
Though osmotic agents for reduction of intraocular pressure are infrequently used, they have a long history in ophthalmology and their mechanism of action is fairly well known. Hertel1 did extensive studies with a variety of osmotic agents and showed that intraocular pressure could be elevated with
GALIN MA, AIZAWA F, McLEAN JM. Urea as an Osmotic Ocular Hypotensive Agent in Glaucoma. AMA Arch Ophthalmol. 1959;62(3):347-352. doi:10.1001/archopht.1959.04220030003001