Identification of persons with incident ocular diseases using health care claims databases.

PURPOSE

To assess the extent to which incidence rates calculated for common ocular diseases by using claims data may be overestimated according to the length of the disease-free look-back period used in the analysis.

DESIGN

Retrospective longitudinal cohort analysis.

METHODS

Billing records of 2457 persons continuously enrolled for 11 years in a managed-care network were searched for International Classification of Diseases (ICD-9-CM) diagnoses of cataract, open-angle glaucoma (OAG), nonexudative age-related macular degeneration (ARMD), and nonproliferative diabetic retinopathy (NPDR) at eye-care visits in the first half of 2001, the second half of 2010, and 2011. For each condition, incidence rates calculated by using "look-back" periods ranging from 0.5-9 years were compared with best estimates from a gold-standard period of 9.5 years.

RESULTS

With a 1-year disease-free look-back period, incidence was overestimated by 260% for cataract, 135% for OAG, 209% for ARMD, and 300% for NPDR. Expanding the disease-free look-back period to 3 years resulted in a reduction of incidence overestimation to 40% for cataract, 14% for OAG, 45% for ARMD, and 100% for NPDR. A 5-year look-back period yielded incidence rates that were overestimated by <30% for all 4 conditions.

CONCLUSIONS

In our claims-data analysis of 4 common ocular conditions, a disease-free interval ≤1 year insufficiently distinguished newly diagnosed from pre-existing disease, resulting in grossly overestimated incidence rates. Using look-back periods of 3-5 years, depending on the specific diagnosis, yielded considerably more accurate estimates of disease incidence.