Determination of vitamin D in tears of healthy individuals by the electrochemiluminescence method

BACKGROUND: Vitamin D is a fat‐soluble steroid hormone which can be converted into various forms and is of extreme physiological importance to our body. However, its functions and local metabolic pathways in some organs, such as the eye, have not yet been well studied. We aimed to verify the correlation between vitamin D levels in blood and tear fluid and the possibility of using tear fluid as a biological material for monitoring eye disorders in the future. METHODS: The electrochemiluminescence method was used to examine blood and tear samples collected with Schirmer test strips from 21 individuals without ocular disease. RESULTS: At the 95% confidence interval, mean tear fluid vitamin D = 37.8 ± 3.6 ng/mL, which is higher than the serum level, with a mean of 30.3 ± 7.7 ng/mL; Lin's concordance correlation coefficient = −0.018 (−0.174; 0.139), Pearson's coefficient = −0.070, and the Bland‐Altman coefficient = −11.12 (−30.40; 8.16). Results were obtained using the program Stata version 11.0. CONCLUSION: It is possible to determine vitamin D levels in tear fluid using the electrochemiluminescence method, and as the results do not correlate with blood, there is possibility of using tear fluid as a biological matrix for detection of vitamin D, which may increase the possibilities of new studies in eye disorders.