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S.K. Fish, S.C. Pflugfelder, C.S. de Paiva; The Effect of Tear Film Composition on Refraction . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3887.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine whether changes in the tear film composition can effect overall refractive status. Methods: The baseline refractive status was measured in each of the six subjects using the Hartmann–Shack wavefront sensor (Visx) and then the tear film manipulation was performed by adding 0.05 cc of carboxymethylcellulose sodium 0.5% (Refresh Tears, Allergan) to the right eye and 0.1 cc of sodium hyaluronate 1% (Healon, Pharmacia) to the left eye. The refractive status of each eye was then measured at 3 designated time intervals after instillation (1, 5, and 10 minutes). This procedure was performed once in one subject, twice in four subjects and three times in one subject for a total of 12 experiments. The average refraction and changes from baseline were calculated and analyzed for each time point. The reliability and reproducibility of refractive status measurement by the wavefront sensor was also analyzed. Results: The mean baseline refractive errors (displayed in spherical equivalent form) were –0.49 diopters and –1.00 diopters (D), respectively for carboxymethycellulose (CMC) and sodium hyaluronate (SH). For CMC, the average change from baseline at 1, 5, and 10 minutes was –0.11 D, –0.07 D, and +0.05 D. For SH, the average change from baseline at 1, 5, and 10 minutes was –0.37 D (P = 0.0482), –0.12 D, and +0.04 D. A change in the negative direction represents a myopic shift, whereas, a change in the positive direction represents a hyperopic shift. Since not all of the subjects had the greatest change from baseline at the same time point, the average maximal change from 1 to 10 minutes was calculated. The average maximum change from baseline was –0.02 D and –0.35 D (P = 0.0132) for CMC and SH, respectively. The repeated measurements of the refractive errors by the wavefront sensor for each subject were similar and the differences were not found to be significant. Conclusions: Addition of sodium hyaluronate 1% to the tear film appears to induce a small, but significant myopic shift. This may have clinical implications for measuring refractive error.
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