Strabismus Increases Glaucoma Risk in California Medicare Beneficiaries

To examine the associations between strabismus subtypes and glaucoma subtypes in California (CA) Medicare beneficiaries.

Cross-sectional study.

All 2019 CA Medicare beneficiaries who were ≥65 years old, had both Parts A & B coverage, and had ≥1 Part B claim.

The primary exposures were any strabismus and its subtypes including paralytic and vertical strabismus, esotropia, and exotropia, as defined by International Classification of Diseases, 10th revision (ICD-10) codes. Primary outcomes were any glaucoma, primary open-angle glaucoma (POAG), and normal tension glaucoma (NTG), defined by ICD-10 codes. The associations between strabismus and glaucoma were estimated using multivariable logistic regression models adjusting for age, sex, race and ethnicity, hyperopia, myopia, hyperthyroidism, and systemic disease burden defined by Charlson Comorbidity Index (CCI) score. The effect estimate was expressed as an adjusted odds ratio (aOR) with a 95% confidence interval (CI).

Odds ratios between exposures and outcomes.

The study population included 2,716,629 beneficiaries. Of those, 220,664 (8%) had glaucoma and 19,899 (1%) had strabismus. In the adjusted logistic regression models, beneficiaries with paralytic strabismus had a 78% increased odds of POAG (OR: 1.78; 95%; CI: 1.60-1.98; p < .0001) and 175% increased odds of NTG (aOR: 2.75; 95% CI: 2.10-3.62; p < .0001). Beneficiaries with vertical strabismus had an 80% increased odds of POAG (aOR: 1.80; 95% CI: 1.60-2.02; p < .0001) and 203% increased odds of NTG (aOR: 3.03; 95% CI: 2.28-4.02; p < .0001). Beneficiaries with esotropia had an 84% increased odds of POAG (aOR: 1.84; 95% CI: 1.66-2.03; p < .0001) and 175% increased odds of NTG (aOR: 2.75; 95% CI: 2.12-3.60; p < .0001). Beneficiaries with exotropia had a 170% increased odds of POAG (aOR: 2.70; 95% CI: 2.45-2.96; p < .0001) and 198% increased odds of NTG (aOR: 2.98; 95% CI: 2.24-3.97; p < .0001).

In the 2019 CA Medicare population, beneficiaries with strabismus and its subtypes were all associated with greater odds of POAG and NTG. Further investigations are needed to characterize the mechanisms between these associations, and future studies are needed to examine optimal glaucoma screening and management strategies in patients with strabismus.