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S. M. Kymes, M. A. Kass, J. P. Miller, M. O. Gordon, the Ocular Hypertension Treatment Study group; The 20-Year Incidence of Primary Open Angle Glaucoma Among People With Ocular Hypertension---A Decision Analytic Approach. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5055.
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Glaucoma is the second most common cause of blindness in the U.S. and is estimated to affect more than 2.2 million Americans over the age of 40. Ocular hypertension is an important risk factor for primary open angle glaucoma (POAG). Most longitudinal studies attempting to estimate the risk of POAG among ocular hypertensives have a duration of five years or less, thus underestimating the effect of mortality on long-term incidence. We model the 20-year incidence of POAG in a simulated cohort of people with ocular hypertension and examine the influence of treatment on incidence.
A Markov Model was constructed using data from the Ocular Hypertension Treatment Study (OHTS). Parameters included the age-specific risk of POAG estimated from the OHTS participants, treated and untreated. Expected mortality was based upon U.S. census data. A microsimulation approach was used to model the expected incidence of POAG in a cohort of 25,000 ocular hypertensive individuals (i.e. individual trials).
The results are provided in the Table below. In the absence of treatment, the expected 20-year incidence of POAG was 29.3%. The incidence of POAG was highest among those 50-70 years old at the time of diagnosis and lowest among the subgroup over age 70. In this subgroup, almost 90% of cohort members died during the 20-year period resulting in a 20-year incidence of POAG that is 16% less than people 50-70. Treatment of ocular hypertensives with a 2% annual risk of developing glaucoma reduced the 20-year incidence of POAG in the cohort by 35%. Limiting treatment to those with a 5% annual risk of developing POAG reduced the incidence of POAG in the cohort by 15%.
Using a decision analytic approach we found that in the absence of treatment almost 1/3 of ocular hypertensives in this cohort developed POAG over their lifetime. However, among those over the age of 70 the 20-year incidence of glaucoma was lower due to the higher probability of death before the development of glaucoma.
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