The link between the cornea and vitamin D₃ levels has been explored in several studies, including a 1938 report that found that dogs fed a low calcium and vitamin-D deficient diet subsequently developed corneal epithelial thinning, edema of the substantia propria with irregularity of its lamellar structure and reduplication of the endothelium with hydropic degeneration.^1-5 Another study noted that the cornea contains a significant native concentration of vitamin D and that 25(OH)D₃ and its active metabolite 1,25(OH)₂D₃ enhance the corneal epithelial barrier function.⁶

Adding to this body of work, a Turkish research group recently evaluated serum 25-hydroxy vitamin D, vitamin B12 and folic acid levels in progressive and nonprogressive keratoconus patients.¹ Their study included 55 patients with keratoconus (28 progressive and 27 nonprogressive) and an age- and sex-matched control group of 30 healthy individuals.

The researchers evaluated the effect of sex, age, calcium and vitamin parameters on keratoconus progression across the control, progressive and nonprogressive groups. Serum vitamin D levels were significantly lower in both progressive and nonprogressive keratoconus groups compared with the control group, but no significant differences were noted among the three groups for serum vitamin B12, folic acid or calcium levels.

The researchers found that decreased vitamin D significantly increased nonprogressive keratoconus probability by 1.23 and progressive keratoconus probability by 1.29 more than the control group. They concluded that evaluating serum vitamin D levels in patients with keratoconus at onset and follow-up examinations may help to predict disease course.