Correlation between tear fluid and serum vitamin D levels

Background:Vitamin D deficiency is associated with a range of systemic diseases including ocular disorders.The objective of this study is to measure tear vitamin D levels and investigate the correlation between serum and tear vitamin D levels.Methods:A total of 48 healthy volunteers without any systemic and ocular disease were recruited for this observational cohort study.Serum was collected using clot activator coated Vacutainer®Plus tubes.Tear fluid was collected using Schirmer’s strips.Serum and tear total 25-hydroxyvitamin D levels were measured by competitive chemiluminescent ELISA and the correlation between the levels were studied.Results:The measured serum 25-hydroxyvitamin D level ranged between 3.3 and 27.5 ng/ml(Mean±SEM,9.4±0.7 ng/ml;Median 8.4 ng/ml).Significantly(p<0.0001)higher level of 25-hydroxyvitamin D was detected in the tears(Mean±SEM,17.0±1.6 ng/ml;Range 3.2–45.8 ng/ml;Median,16.3 ng/ml)compared to serum.An average of~2 fold(Mean±SEM,1.9±0.2;Range 0.4–5.8;Median,1.7)higher 25-hydroxyvitamin D was observed in tears compared to serum in the subjects.In addition,a positive correlation was observed between serum and tear 25-hydroxyvitamin D levels(r=0.5595;p<0.0001).Conclusions:A higher level of 25-hydroxyvitamin D was observed in the tear fluid compared to that of the serum.It would be beneficial to consider tear vitamin D levels to study its role with reference to ocular surface diseases.