To investigate the biological effects of preservative-free artificial tear drops on cultured human corneal epithelial cells in vitro .

The effects of the preservative-free artificial tear drops (Kynex® 0.1%, Kynex II® 0.18% [Alcon, Seoul, Korea] and Hyaluni eye drops® 0.15%, 0.3% [Taejun, Seoul, Korea]) on the human corneal epithelial cells were evaluated. An methyl thiazolyl tetrazolium (MTT)-based colorimetric assay was performed to assess the cellular metabolic activity and a lactate dehydrogenase (LDH) leakage assay was used to determine cellular toxicity. The eye drop ingredients were analyzed for electrolyte composition, pH, and osmolarity. We performed a scratch assay and cellular morphology test using electronic microscopy.

The metabolic activity of corneal epithelial cells was higher than controls at 24 hours after exposure and then decreased at 48 and 72 hours after exposure ( p < 0.05). The LDH titers of the 4 eye drops were higher compared with controls ( p < 0.05). Sodium hyaluronate 0.18% contained lower concentrations of Na⁺ or Cl^- and showed lower osmolarity values compared with the other eye drops. The cellular migration based on the scratch assay was more delayed and cellular damage such as loss of microvilli, rough endothelial reticulum (RER), and mitochondria dilatation was greater than controls based on electron microscopy.

Long-term exposure to preservative-free sodium hyaluronate eye drops may induce decreased metabolic activity and cellular damage. Thus, preservative-free artificial tears should be used carefully to prevent cellular toxicity.