The Role of Vitamin D in Corneal Epithelial Barrier Function, Ocular Microbiome, Ocular Inflammation, and Visual Acuity of Children With Allergic Conjunctivitis

The prevalence of allergic conjunctivitis (AC) has rapidly increased in recent decades, resulting in a significant global public health concern. The ocular surface is a unique mucosal immune compartment in which immunological features act in concert to foster a tolerant microenvironment (immune privilege). The corneal epithelial barrier is the first line of defense that forms a protective barrier against pathogens, pollutants, and allergens. The ocular microbiota has a role in maintaining the homeostasis of the ocular surface and preservation of barrier function. Vitamin D functions as enforcing intercellular junctions and maintaining intestinal epithelial barrier integrity; metabolites from the gut microbiota may also regulate expression of vitamin D receptor (VDR). Low serum vitamin D levels have been shown to predispose to a variety of allergic disorders. A recent study shows that corneas contain vitamin D and VDR; vitamin D enhances corneal epithelial barrier function. However, research data of the role of vitamin D in ocular microenvironment of AC are insufficient and controversial. In recent research, the investigators found allergic inflammation of ocular surface weakened corneal epithelial barrier, modulated the signal pathway of retinal pigment epithelial cells, and enhanced scleral tissue remodeling, resulting in myopia in progression. However, there are few studies available to investigate the role of vitamin D in ocular surface microenvironment, ocular inflammation, and visual acuity in AC. Moreover, understanding the interaction of vitamin D, ocular microbiota, and ocular inflammation may provide a new target for the development of therapeutic interventions of ocular allergy and restore visual function.