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S.R. Montezuma, L. Pasquale; Modeling the Number Needed to Screen for Primary Open–Angle Glaucoma . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3424.
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© ARVO (1962-2015); The Authors (2016-present)
Glaucoma screening programs could be useful to prevent glaucoma blindness. The US Preventive Task Force found insufficient evidence to recommend for or against glaucoma screening. We generated models of the impact of glaucoma screening programs under virtual conditions so as to stimulate research into areas that would justify the implementation of glaucoma screening programs.
We surveyed the literature to acquire data on the prevalence of glaucoma, estimates of glaucoma blindness in untreated populations, visual field progression in treated glaucoma and the sensitivity/specificity of glaucoma screening strategies. We used this data to generate various models to calculate the number needed to screen (NNS) or the number of patients screened to avert one case of unilateral glaucoma blindness in 10 years accounting for treatment failure.
In model 1 (Caribbean model composed of African derived population with primary open–angle glaucoma (POAG) prevalence of 6%), we assume an untreated blindness rate of 20% and a treated blindness rate of 1% in 10 years; the NNS varies between 126 and 301 for screening sensitivities/specificities of 70% / 70% to 90% / 90%. In model 2 (European model composed of a homogeneous Caucasian population with POAG prevalence of 2%), the NNS varies ranges from 139 to 328 for screening sensitivities / specificities of 70% / 70% to 90% / 90%. In model 3 (inner urban US model composed of 50% Caucasian and 50% African American population with POAG prevalence of 2% and 6% respectively), we assume 25% of cases will have normal tension open–angle glaucoma (NTOAG) with untreated/treated blindness rate of 8% and 1% respectively in 10 years and the balance of POAG patients with an untreated/treated blindness rate of 20% and 1% in 10 years; the NNS was 258 for screening sensitivity and specificity of 85%. In this scenario, assuming screening exam charges are $50/exam and the median charge associated with treating POAG is $784 per patient per year (see Wentzloff et al. ARVO 2006), then costs with averting one case of glaucoma blindness is $20,740.
Screening strategies with low sensitivity and specificity could still have an impact on reducing glaucoma blindness particularly in high risk populations. More research is needed to develop effective strategies to screen for glaucoma.
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