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H. Wang, Z. Marlowe, S. Davio; Properties of OTC Dry Eye Products in the US Market. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4650.
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There are many over-the-counter (OTC) products that claim to be effective in providing relief, treatment, or prevention of dry eyes (DE). This study was conducted to investigate the physical properties of current US marketed products.
The pH, viscosity, osmolality and surface tension of various DE products were measured at room temperature. A total of 24 DE solution products were analyzed.
The pH range for the DE products was 5.7 (Hypo Tears®) - 8.3 (TheraTears®) with a mean of 7.2. The range of osmolarity results was 176 mOsm/kg (BlinkTears®) - 351 mOsm/kg (Optive®). The osmolarity results showed two distributions: one around 280-320 mOsmo/kg, approximately isotonic relative to human tears, and another around 225 mOsmo/Kg, hypotonic relative to tears. Viscosity levels for approximately one half of the products were close to those of natural tears (3 mPa·s) with the remaining products ranging up to 31.1 mPa•s. Surface tension (ST) values of OTC DE products covered a wide range. About forty percent of the tested products had ST close to that of pure water (74 mN/m). The remaining 60% had surface tensions distributed around that of natural tear (44 mN/m).
The physical properties of OTC dry eye products fall within discrete categories relative to natural tears. Near-physiological pH was observed with the majority of the current OTC products. Some products are isotonic and others are hypotonic, designed to counterbalance the hyperosmolarity of tears in DE patients. Viscosity values are mostly low and similar to tears, while others of higher viscosity seek to prolong residence time on the eye. Finally, ST of some products are close to that of tears, while others are close to that of water since surface-active agents necessary to lower ST can be irritating.
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