Brimonidine is more selective for the α-2 adrenoreceptor. It is thought that Brimonidine Tartrate lowers IOP by enhancing uveoscleral outflow and reducing aqueous humour formation.
Timolol is a beta1 and β-2 non-selective adrenergic receptor blocking agent. Timolol lowers IOP by reducing aqueous humour formation. The precise mechanism of action is not clearly established, predominant action may be related to reduced aqueous formation. However, in some studies a slight increase in outflow facility was also observed.