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M. Y. Avila, C. Peña, M. Rojas; Evaluation of Artificial Tears Retention in Human Eyes. Invest. Ophthalmol. Vis. Sci. 2007;48(13):6023.
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To develop a method for measuring precorneal retention time of artificial tears.
Artificial tears were marked with fluorescein at 0.02%. After topical instillation of 20 ul of artificial tears or saline with fluorescein, the rate of decay of fluorescence from the corneal surface was measured in 60 normal humans, with a biomicroscope equipped with a CCD camera. Light was filtered with cobalt blue filter and images were converted into its red ,green and blue components and green emitted light component was quantified in a defined area over the cornea. Autofluoresence was subtracted and the fluorescence values were normalized. Elimination rate and time for 50% of the signal to be eliminated was calculated from the fluorescence values. (ET 50) from parameters derivated from least-squares exponential fits.
The rate of decay of the fluorescence was measured by 20 minutes. Decay was increased in solution saline group with a linear rate. Low-viscosity solutions showed a faster exponential decay of the fluorescence in the follow order SSN (ET 50 2.08 min) hidroxypropylmetylcellulose 0.3% (ET 50 1.70 min) , and Polyethylene glycol/Propylen glycol/HP-guar (ET 50 1.36 min). Gel solutions also showed a exponential decay in the follow order Carbomer 974 0.254%,(ET 50 0.90 min) Carboximetilcellullose 0.01%/purite (ET 50 0.92 min) and carbomer 0.03%/mannitol (ET 50 0.84 min) Also low viscosity agents showed a higher fluorescence in the middle time in comparison with high viscosity agents
Monitoring decay of fluorescence from artificial tears provides a estimation of permanency of artificial tears in the corneal surface. With this methodology is founded that Saline has the lowest retention time in comparison with artificial tears with the higher permanency of polyethileneglycol/Propylenglycol/HP guar tears and that gels showed a higher permanency with the higher permanency of the carbomer 0.03%/mannitol
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