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ABSTRACT
Several reports have documented a contralateral intraocular pressure (IOP) lowering effect after unilateral instillation of timolol. Data derived from the Glaucoma Laser Trial (GLT), a randomized trial of the efficacy and safety of argon laser trabeculoplasty (ALT) as compared with the efficacy and safety of topical medications as initial therapy for primary open-angle glaucoma (POAG), demonstrated an estimated mean pressure reduction of 0.5 mm Hg in the contralateral eye that had received ALT. This contralateral effect is smaller than that observed in other studies of POAG patients. Lower initial IOP, longer duration of treatment with timolol, and/or improved outflow facility modulation in the ALT-treated eyes may be responsible for the smaller contralateral effect of timolol observed in the GLT patients.
Since its introduction by Katz and coworkers1 in 1976, timolol maléate, a nonselective beta adrenergic agent, has been shown to be effective in lowering intraocular pressure (IOP). The IOP-lowering effects for eyes receiving timolol have been established after single-dose administration as well as after longterm treatment.2"4 In addition, several studies have demonstrated clinical,39 histologic,10 and fluorophotometric11 effects on the untreated contralateral eye after unilateral installation of timolol. Reports of the magnitude and clinical significance of these effects have differed. Interpreting these reports and understanding the mechanism by which IOP is lowered in the contralateral eye under these circumstances is especially difficult since the way that timolol reduces aqueous production in treated eyes is not fully understood.
The Glaucoma Laser Trial (GLT) was a randomized, controlled clinical trial designed to assess the efficacy and safety of argon laser trabeculoplasty (ALT) as compared with the efficacy and safety of treatment with topical medication as the initial therapy for patients with newly diagnosed primary open-angle glaucoma (POAG). One eye of each patient received ALT while the other eye was started on a "stepped* medication regimen starting with timolol as described below. Observation of the change in IOP in the ALT-treated eye as timolol was added to or removed from the other eye under the stepped medical regimen provided the information concerning the contralateral effect of timolol we report here.
Most previous studies of the contralateral effect of timolol involved single-dose or short-term instillation of the drug and examined the effect on contralateral eyes that had...