Because the vast majority of the United States population aged 65 years or older has Medicare, a national health service insurance plan that covers hospitalizations and physician services, it is possible to pursue population-based research on the elderly using Medicare data. Specifically, a database on service utilization in a 5% population sample is available to researchers. In 1995, there were more than 1.9 million patients in the 5% utilization files; this number increased to more than 2 million in 1998. Approximately 85% of patients are non-Hispanic whites, 9% are black, 2% are Hispanics, and 1% are Asian. In 1995, 6.5% of the population was diagnosed with open angle glaucoma, while in 1998 7.8% of the population had this diagnosis. From 1995 to 1998, the number of argon laser trabeculoplasties and trabeculectomies decreased from 6,651 argon laser trabeculoplasties and 2,853 trabeculectomies in 1995 to 4,198 argon laser trabeculoplasties and 2,211 trabeculectomies in 1998. The number of implantations of drainage devices increased slightly over the same time period from 123 in 1995 to 162 in 1998. Attempts to explain this decline in trabeculoplasties and trabeculectomies from 1995 to 1998 require consideration of external factors. Potential reasons are the introduction of new anti-glaucoma medications in the United States, such as latanoprost and brinzolamide; possible systematic changes in the perceptions of the role of glaucoma surgery in the management of glaucoma patients; or the decrease in reimbursement for these procedures during this period.