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J. Nemeth, K. Hagyo, B. Erdelyi; Fluctuation in the Refraction During the Interblink Period Measured By Wavefront Analysis . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2004.
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Purpose: The corneal topography is not stable during the time between blinks due to the tear film build–up and break–up processes. The present investigation examines the overall refractive stability of the eyeball in the interblink period. Methods: A specially developed high–speed wavefront analysis (7 measurements/second) was used to follow the total refractive alterations between successive blinks. Ten eyes of 10 normal subjects (7 females, 3 males; mean age 26.8 ± 6.0 years) were examined using the Wasca Wavefront Analyzer during the first 21 seconds after complete blinks. In order to avoid instrument–induced myopia and spontaneous accommodation, a distant fixation target was employed. Results: In the first 3 seconds after blinking, the refraction was shifted towards hyperopia by 0.5 diopters in seven of the 10 subjects. At later times typical trends were not found, only apparently random fluctuations, on average 0.12 diopters for spherical and spherical equivalent values, and 0.09 diopters for cylindrical values. The variability of the measurements was significantly reduced at a time approximately 6 seconds after a blink, compared to that found immediately after blinking. Instillation of artificial tears had no influence either on the refraction (p>0.3), or on the variability of the measurements (p>0.2). Conclusions: Both the total refraction of the eye, and the reliability of the wavefront measurements, vary significantly during the inter–blink period. The measurement error is lowest at a post–blink time of 6 seconds. Thus, from this aspect, it is recommended to perform wavefront measurements around this time–point. However prospective investigations are needed to determine which measurement time–point is most appropriate for planning different refractive surgeries.
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