Drs Wegner, Harris, and Ugi are correct in reminding us that therapy for glaucoma should protect the patient 24 hours per day and that comparisons of drug efficacy at one time of day do not tell the whole story. They are also accurate in their prediction that the superior efficacy of timolol compared with dorzolamide during the day is the opposite at night during sleep.
There are now data to confirm their prediction. Vanlandingham et al1 measured the effect of dorzolamide at night in sleeping subjects and found that aqueous flow was reduced from 1.28 µL/min to 1.17 µL/min, a 9% reduction (P=.03). Since timolol does not affect nocturnal flow in sleeping humans,2 it seems reasonable to suppose that dorzolamide is the more efficacious of the 2 as an ocular hypotensive agent at night during sleep.
Brubaker R. Dorzolamide and Timolol as Suppressors of Aqueous Humor Flow—Reply. Arch Ophthalmol. 1998;116(8):1133. doi: