May 01, 2014
Glaucoma is a leading cause of irreversible blindness worldwide. It affects more than 2.7 million individuals age 40 or older in the United States — approximately 1.9 percent of this population. Glaucoma is the second-leading cause of blindness among blacks, after cataract, and the third-leading cause of blindness in whites, after age-related macular degeneration and cataract.
A retrospective study of residents of Olmsted County, Minn., however, shows that the probability of blindness due to open-angle glaucoma (OAG) in at least one eye decreased by nearly 50 percent over a 45-year period from 1965 to 2009. The population's incidence of blindness within 10 years of diagnosis of OAG also decreased in that time.
"Diagnostic criteria for glaucoma have undergone significant modifications over the last 40 years," says Arthur J. Sit, M.D., with the Department of Ophthalmology at Mayo Clinic in Rochester, Minn., who led the study team. "New diagnostic and progression analysis tools as well as new therapies for intraocular pressure (IOP) reduction continue to be developed and have undoubtedly benefited individual patients.
"Their effects on the rates of visual impairment in populations, however, is poorly understood. This longitudinal study will help us gain a better understanding of epidemiologic trends in glaucoma, optimize the distribution of health and medical resources, and provide feedback on the efficacy of novel management approaches on a population basis."
The team studied a cohort from the Rochester Epidemiology Project, which tracks the entire population of Olmsted County over multiple decades. Participants included all county residents age 40 or older who were newly diagnosed with OAG between Jan. 1, 1965, and Dec. 31, 2000. All medical records of every patient with OAG were reviewed to identify progression to blindness (visual acuity of 20/200 or less, or visual field constriction to 20 degrees or less).
The team used Kaplan-Meier analysis to estimate the cumulative probability of glaucoma-related blindness and U.S. Census Bureau data to calculate population incidence of blindness within 10 years of diagnosis. Rates for subjects diagnosed in the period 1965 to 1980 were compared with rates for subjects diagnosed in the period 1981 to 2000 using log-rank tests and Poisson regression models.
"Our research shows that the probability of blindness due to OAG in at least one eye and the annual population incidence of OAG-related blindness were both lower for patients diagnosed between 1981 and 2000 compared with patients diagnosed between 1965 and 1980 in the same geographic location," says Dr. Sit. According to an article published in the January 2014 issue of Ophthalmology:
- The probability of glaucoma-related blindness in at least one eye at 20 years decreased from 25.8 percent (95 percent confidence interval, 18.5-32.5) for subjects diagnosed between 1965 and 1980 to 13.5 percent (95 percent confidence interval, 8.8-17.9) for subjects diagnosed between 1981 and 2000 (P = 0.01).
- The population incidence of blindness within 10 years of the diagnosis decreased from 8.7 per 100,000 (95 percent confidence interval, 5.9-11.5) for subjects diagnosed between 1965 and 1980 to 5.5 per 100,000 (95 percent confidence interval, 3.9-7.2) for subjects diagnosed between 1981 and 2000 (P = 0.02).
- Higher age at diagnosis was associated with increased risk of progression to blindness (P < 0.001).
Possible reasons why the probability of OAG-related blindness in Olmsted County may be decreasing include changes in glaucoma management techniques from 1965 to the end of the follow-up period in 2009, including:
- Improvements in medical and surgical therapy
- Development of laser trabeculoplasty, automated perimetry, and optic disk and nerve fiber layer imaging
- A better understanding of glaucoma pathophysiology and the risk factors for progression
"It is also possible that changes in diagnostic criteria for glaucoma have resulted in earlier diagnosis of glaucoma, which could manifest as an increased duration until blindness, and a lower probability of blindness over 20 years," says Dr. Sit. "In addition, better public awareness may have resulted in a higher diagnosis rate of asymptomatic glaucoma, which would also reduce the risk of progressing to blindness in a fixed time period. The age of first diagnosis has not changed, suggesting that patients are not being diagnosed earlier, but are receiving more effective treatment after diagnosis.
"This reduction in the blindness rate is a testament to the work that has been done by everyone involved in glaucoma research and treatment. Nearly 14 percent of patients still go blind in at least one eye, however, so it is critical that we continue research to improve our knowledge and management of glaucoma and build awareness of the need for routine eye exams to detect this disease at an early stage," says Dr. Sit.
For more information
Malihi M, et al. Long-term trends in glaucoma-related blindness in Olmsted County, Minnesota. Ophthalmology. 2014;121:134.