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Introduction
Allergic conjunctivitis is a common ocular allergic disease, with a high incidence of ~20% of the total population in China (1). It predominantly occurs as a result of type I and IV hypersensitivity, of which the main symptoms include ocular itching, frequently with conjunctival hyperemia and edema (2). Allergic conjunctivitis is divided into the following clinical subtypes: i) Seasonal allergic conjunctivitis; ii) perennial allergic conjunctivitis; iii) vernal keratoconjunctivitis; iv) atopic keratoconjunctivitis; and v) giant papillary conjunctivitis (3). Diagnosis and classification of allergic conjunctivitis is predominantly based on clinical features, laboratory or pathological tests (4).
The early reactions in the pathogenesis of allergic conjunctivitis are mediated by mast cells and T cells. Following contact with the allergen, the antigen is combined with specific immunoglobulin E (IgE), resulting in mast cell degranulation and the release of inflammatory mediators (5). Mast cell degranulation activates endothelial cells, promoting the expression of chemokines and adhesion molecules (6). This attracts inflammatory cells to the conjunctival membrane, and activates conjunctival fibroblasts and epithelial cells to participate in the generation of conjunctivitis, with this process occurring within a few seconds following contact with the antigen, and the effects lasting from tens of minutes to several hours (7). In addition, interleukins (ILs) are released by fibroblasts, and mast cells are activated and release secondary messengers, promoting the allergic reaction to enter the late phase (8). The released cytokines, including IL-4, IL-5, IL-6, IL- 8, IL-13, tumor necrosis factor-α (TNF-α) and vascular cell adhesion molecule-1, act on the conjunctiva and recruit inflammatory cells, including eosinophils, basophils, neutrophils and helper T lymphocytes, producing the second peak of immune inflammatory reaction (9).
Naphazoline hydrochloride is an adrenergic drug, stimulating adrenergic α-receptors resulting in vasoconstriction (10). Clinically, it is predominantly used for allergic and inflammatory nasal congestion, acute and chronic rhinitis and eye congestion. Additionally, it is also used for bacterial and allergic conjunctivitis and reduces blepharospasm (11). Olopatadine is a drug with dual effects, as a selective antagonist of histamine 1 receptors and a stabilizer of mast cells, and works faster than non-steroidal anti-inflammatory agents and mast cell stabilizers (12). However, the effects and mechanisms of olopatadine and naphazoline hydrochloride on allergic conjunctivitis remain to be fully elucidated. The current study hypothesized that olopatadine and naphazoline...