[Modification in amplitude of nycthemeral changes in intraocular pressure under timolol]

Diurnal variations of intraocular pressure are probably related to indolamines, prostaglandins, and the sensory nervous system. Because timolol maleate is able to block beta-1, beta-2, and dopaminergic receptors, as well as to act like an antagonist of serotonin, we evaluated its effect on diurnal variations of intraocular pressure. Eighty-eight intraocular pressure curves were established in 22 normal young volunteers. Intraocular pressures were measured in both eyes before and one week after the beginning of monolateral treatment with timolol 0.5% twice daily. The results showed a decrease in amplitude of diurnal variations of 24% (P = 0.07 in paired t-test) in timolol-treated eyes and no significant change in the contralateral eyes. The difference between both eyes was statistically significant in paired t-test (P = 0.01). Knowing the type of receptors on which timolol is susceptible to act, and furthermore, the type of neuro-transmitter which may be involved in the regulatory mechanisms of diurnal variations of intraocular pressure, we suggest that timolol could reduce the amplitude of these variations by means of interactions with indolamines.