Impact of oral vitamin D supplementation on the ocular surface in people with dry eye and/or low serum vitamin D

Purpose: To determine the possible association between serum vitamin D levels and dry eye symptoms, and the impact of an oral vitamin D supplement. Methods: Three linked studies were performed. (i) 29 older adult participants, (ii) 29 dry eyed participants, and (iii) 2-month vitamin D supplementation for 32 dry eyed/low serum vitamin D levelled participants. All participants were assessed by the Ocular Surface Diseases Index (OSDI) to determine dry eye symptoms, and the phenol red thread test (PRT) and/or Schirmer's tear test, tear meniscus height, non-invasive tear break up time, grading ocular surface redness and fluorescein staining of the cornea to detect the tear quality and ocular surface conditions. Blood samples were collected for serum vitamin D analysis and interleukin-6 (IL-6) levels. Results: Among older adult participants, vitamin D levels were negatively correlated with dry eye symptoms, the severity of dry eye, and associated with tired eye symptom. Vitamin D levels of people with dry eye diagnosis were not correlated with OSDI scores and IL-6 levels; while IL-6 levels showed correlation with tear production. In supplement study, vitamin D levels increased by 29 mol/l, while dry eye symptoms and grading of corneal staining appeared significant reductions. No significant changes in IL-6 levels. Conclusions: Low vitamin D levels (< 50 nmol/l) were associated with dry eye symptoms in older individuals but not those diagnosed with dry eye. Vitamin D supplement increased the vitamin D levels, and improved dry eye symptoms, the tear quality and ocular surface conditions.