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M.A. Bullimore, M.J. Dobos, Jr., M.D. Twa; Repeatability and Validity of Refractive Error Using the Bausch and Lomb Zywave . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4081.
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Purpose: The Bausch and Lomb Zywave is a Hartmann-Shack wavefront sensor that measures ocular aberrations and gives an estimate of refractive error, representing the second order aberrations of the eye. We examined the repeatability and validity of refractive errors estimated by the Zywave and the effect of manipulating pupil size. Methods: Fifteen participants (mean age = 29.5 ± 7.7 years) attended on two occasions separated by at least one week. Contact lens wearers and patients with ocular disease or diabetes were excluded. On each occasion, refractive error was measured using the Zywave and a Nidek ARK-700A Auto Refractor. Three measurements were taken of each participant’s right eye with both instruments under both manifest and cycloplegic (1% Tropicamide) conditions. At one visit, each participant received a manifest and cycloplegic subjective refraction. Repeatability and validity were assessed by determining the 95% limits of agreement for each comparison (between-session or between-technique). The Zywave allows refractive error to be calculated for a specified pupil size, so we compared estimates for 3, 5, and 7 mm diameters with those for the Zywave default diameter of 3.51 mm. Results: For manifest spherical equivalent, the repeatability of the Zywave (95% LoA = –0.37 to +0.47 D for default pupil diameter) was better than that of the Nidek (95% LoA = –0.60 to +0.65 D). For cycloplegic conditions, the repeatability of both instruments improved (Zywave = –0.23 to +0.27 D and Nidek = –0.54 to +0.50 D). Specifying the pupil diameter on the Zywave had little effect on the repeatability of the Zywave under cycloplegic conditions (95% LoA = –0.24 to +0.24 D, –0.26 to +0.31 D, and –0.34 to +0.30 D for 3, 5, and 7 mm, respectively). Similar trends were observed for astigmatic data. Manipulating the pupil size on the Zywave from 3 to 7 mm changed the mean cycloplegic spherical equivalent from –2.60 ± 3.02 D to –3.36 ± 2.91 D. The results for the 3 mm pupil agreed best with the subjective refractive error (mean = +0.26 D; 95% LoA = –0.48 to +0.97 D). Conclusions: The Zywave provides valid and repeatable estimates of refractive error. We attribute the myopic shift for larger pupils to the eye’s spherical aberration. Future work will assess the repeatability of the Zywave for higher order aberrations and their influence on refractive error.
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