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D. Szczesna, H. Kasprzak, U. Stenevi; Interferometric Assessment of the Efficacy of Artificial Tears in Dry Eyes. Invest. Ophthalmol. Vis. Sci. 2008;49(13):106.
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The aim of this study was to quantitatively evaluate tear film stability in dry eyes as well as the efficacy of a range of artificial tears on tear film kinetics and its variability in time.
A non-invasive, interferometric method was used for evaluating tear film stability and its kinetics. Interferometry allows sensitive, highly accurate, dynamic measurements of the tear film surface in real time. Instability of tear film, caused by evaporation and diffusion to cornea, results in appearance of breakups and subsequent decrease in interference fringe pattern regularity. Sequences of interferograms were recorded in real time during the inter-blink intervals at 25Hz and stored on a computer. Spectral analysis of interferograms was carried out on selected frames from the measured sequence to quantitatively evaluate tear film surface irregularity. The parameter M2, described in our recent paper (Acta Ophthal. Scand. 2007, 85:202-208), was used as a measure of tear film deterioration. The lower the values of the parameter M2 the more stable tear film is. Tear film stability in a group of 14 patients diagnosed with dry eye syndrome was measured before, 5 minutes after and 2 hours after instillation of artificial tears. Tear film was measured also on different days and with a range of artificial tears.
Almost in all cases, the values of the parameter M2 were above those recorded earlier for normal eyes with stable tear film. Also, patients with dry eyes indicated faster increase of the parameter M2 after the blink. The figure shows exemplary values of the parameter M2 measured in the drying cornea of a subject (black line), 5 minutes (grey line), and 2 hours (dark grey line) after instillation of eye drops. Nevertheless, the improvement of tear film stability after instillation of eye drops varied across the subjects and in some cases was not as visible as shown in the figure.
The proposed interferometric method allows non-invasive, highly accurate and quantitative measurement of the efficacy of eye drops on the kinetics and stability of tear film in dry eyes.
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