Intraocular pressure (IOP) is a major risk factor for the development of glaucoma. In addition, it is the only modifiable factor in the prevention and subsequent treatment of glaucomatous optic neuropathy. Most clinicians only have access to a single IOP measurement during a patient visit that may only occur once every four months. These snapshots in time are probably not adequate for the optimal management of glaucoma. Diurnal IOP curves can provide a better estimate of each patient's individual IOP variation throughout the day. However diurnal curves do not typically cover another crucial time, the nocturnal period. Glaucomatous eyes have been shown to have different IOP curves during the nocturnal period compared to healthy controls. In addition, different classes of glaucoma drugs have variable IOP lowering effects during the nocturnal hours compared to the diurnal/wake period. For example, the betablocker timolol was shown to lower IOP during daytime hours but failed to lower IOP during the nocturnal period in the habitual position. Similarly, the alpha-agonist brimonidine failed to lower IOP overnight after significantly lowering IOP during the diurnal period. On the other hand, the prostaglandin analogues, including latanoprost and travoprost, lowered IOP throughout the diurnal and nocturnal periods although nocturnal lowering appears less than the daytime hours. Therefore it is crucial to determine an accurate IOP curve for each form of medication during both wake and sleep hours.
