Compared to the negative control (C−; 0.51 ± 0.08 ng/L), the serum DHVD3 (the active metabolite of vitamin D3) was found to be significantly downregulated in the untreated TSP-1 KO mice that developed dry eye (C+) (0.31 ± 0.08 ng/L, p < 0.01 vs. C−). This evidence concerns the gene THBS1 and dry eye syndrome.