To evaluate the biological effects and cytotoxicity of gel-type artificial tears on human corneal keratocytes and conjunctival cells in vitro .

Human corneal keratocytes and conjunctival epithelial cells were exposed to Soothe® and Systane® at variable concentrations. Evaluations were conducted through an MTT-based calorimetric assay to measure the metabolic activity and through a lactate dehydrogenase (LDH) assay to assess cellular damage. Apoptotic response was examined using fluorescent microscopy and flow cytometric analysis, and cellular morphologic results were evaluated with a transmission electron microscope.

The inhibitory effects of corneal keratocyte and conjunctival cell proliferations increased at higher concentrations and longer exposure times to Soothe® and Systane®. The LDH titers increased after Soothe® exposure, but showed no significant difference after Systane® exposure. Soothe® and Systane® treatments both produced fluorescence, representing apoptotic cells. In flow cytometry, the maximal apoptotic response was observed for both types of artificial tears, although Systane® showed less edema, as well as reduced cytoplasmic and nuclear cell degeneration compared to those of Soothe®.

The apoptotic responses of Soothe® and Systane® are associated with inhibitory effects of human corneal keratocyte and conjunctival epithelial cell proliferations. To inhibit the cellular proliferation of human corneal keratocytes and conjunctival epithelial cells, Systane® may be less severe than Soothe® at higher concentrations and longer exposure times.