Comparing healthcare resource use and costs for patients with Normal Tension Glaucoma across levels of severity: a nationally representative sample of commercially insured US adults age 40 and older
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Introduction: Normal tension glaucoma (NTG) is a subset of open-angle glaucoma (OAG), which is the most prevalent form of glaucoma globally. Projections into 2040 predict a 74% increase to 111.8 million people affected worldwide. Though global burden of disease is increasing, little has been done to understand the burden of disease for patients with NTG regarding their annual healthcare resource utilization (HCRU) or costs and how disease severity may impact this burden. Objective: Our objective was to estimate the HCRU and costs for patients with NTG as well as their payers. We sought to understand if costs and HCRU depends on one’s severity of disease and whether or not laterality of disease modifies the effect of this relationship. Methods: Our study was a retrospective cohort study of 6,330 US patients, 40 years of age and older, within the IBMÂ® MarketScanÂ® Commercial and Medicare Supplemental databases. Patients were enrolled if they were 40 years or older and had two or more qualifying NTG diagnoses, with the first of the two qualifying diagnoses being the patients’ index date. Baseline demographic and clinical characteristics were assessed for a 12-month pre-index period. The follow up period was 12-months post-index. Our analysis was carried out for two cohorts – those with unilateral disease and those with bilateral disease. The relationship between severity and HCRU was analyzed by fitting a generalized linear model with a Poisson distribution and log link for office visits. We relaxed the Poisson assumption and modeled prescription counts with a negative binomial model and log link to account for overdispersion. Costs were modeled with a generalized linear model with a gamma distribution and a log link. Cost data were adjusted to 2019 dollars. Results: Patients with severe, bilateral disease, filled over two additional prescriptions annually (2.5, 95% CI [2.0, 3.1]) when compared to their mild counterparts and accounted for 111 (95% CI [83.5, 139.1]) extra days of supply of glaucoma medications. These patients face $121 (95% CI [87, 155]) more out-of-pocket (OOP), and payers an additional $348 (95% CI [$207, $488]), than their counterparts with a mild diagnosis on an annual basis. Conclusion: Our results suggest that patient burden is higher for those with severe disease compared to those with mild NTG. The excess burden is not only attributed to additional HCRU, but also by a higher financial burden, which accompanies their higher resource use. Patients were not alone in harboring burden as payers experienced a much larger financial burden from patients with severe disease compared to those with mild NTG. Most of the cost differences can be attributed to additional prescription use.