The present invention provides a method of lowering intraocular pressure which comprises administering a therapeutically effective amount of a pharmaceutical composition comprising 4-bromo-5-(2-imidazolin-2-ylamino)benzimidazole, or a salt thereof to the affected eye of a patient, as a single dose, wherein the affected eye has an intraocular pressure less than the baseline intraocular pressure for at least eight (8) hours.
