Thyroid Dysfunction and Ten-Year Incidence of Age-Related Macular Degeneration

PURPOSE. Epidemiologic evidence of a relationship between thyroid dysfunction and age-related macular degeneration (AMD) is inconsistent and unclear. We aimed to assess the prospective associations between serum thyroid-stimulating hormone (TSH) and free thyroxine (FT4) measurements, as well as thyroid dysfunction (hyperthyroidism and hypothyroidism) and incidence of AMD. METHODS. Categories of thyroid dysfunction were defined according to a serum TSH screen followed by serum FT4 assessment, and were available in 906 participants (aged 55+ years) at risk of AMD incidence (from 1997-1999 to 2007-2009). Continuous serum FT4 measures were available regardless of TSH screening results in 583 participants at risk of AMD incidence. Age-related macular degeneration was assessed from retinal photographs. RESULTS. Participants with overt hyperthyroidism compared to those with normal thyroid function at baseline had increased risk of developing any incident AMD, after adjusting for age, sex, smoking, fish consumption, and variants in AMD susceptibility genes (CFH and ARMS2): odds ratio (OR) 3.51 (95% confidence interval [CI] 1.16-10.65). Participants who reported current use of thyroxine (n = 67; 7.3%) versus those who were not current users (n = 839) had a 68% increased risk of incident AMD, multivariable-adjusted OR 1.68 (95% CI 1.01-2.82). Similarly, participants who had ever been on thyroxine medication (n = 77; 8.4%) compared to those who had never been on thyroxine (n = 829) also had a higher risk of any AMD, multivariable-adjusted OR 1.91 (95% CI 1.18-3.09). CONCLUSIONS. Overt hyperthyroidism was independently associated with an increased risk of incident AMD. Thyroxine usage in older adults was also positively associated with incidence of AMD.