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F. Arnalich-Montiel, B. Allan; Effective Blur Used as a Strategy to Guide Pre-Treatment Physician Adjustments to the Spherical Power Delivered in AMO Customvue Wavefront Guided Lasik. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2924.
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The Effective Blur (EB) term in Wavescan Schack-Hartmann aberrometry (www.amo-inc.com) information summaries represents the dioptric spherical equivalent of higher and lower order aberrations combined. Several factors including accommodation, chromatic aberration, and higher order aberrations contribute to differences between the manifest refractive spherical equivalent (MRSE) and the spherical equivalent calculated from pure sphere and cylinder for a 4mm pupil in Wavescan Shack Hartmann aberrometry (Wavescan 4mm SE). We aimed to determine whether the difference between EB and pre-operative MRSE values could be used to guide pre-treatment physician adjustments to the spherical power delivered in AMO CustomVue wavefront guided LASIK.
We performed a retrospective review of pre-treatment Wavescan data and 3 month postoperative refractive results in 283 myopic eyes treated with the CustomVue system. For comparison with the actual postoperative MRSE (5% nomogram boost, non-systematic physician adjustment), the effect of systematic pre-treatment adjustment based on the difference between EB and the pre-operative MRSE was modelled by back calculation. SPPS-12 statistical analysis was used to describe data and make the comparisons. The main outcome measure was variance in postoperative MRSE values.
When using the EB term to guide pre-treatment physician adjustment, we found a 5% trend toward overcorrection, whereas using non-systematic physician adjustment tend to slightly overcorrect by 1.6% if a 5% boost was applied. The spread of the results, SD of 0.55 and variance of 0.32, was higher if using EB to adjust the wavefront mean equivalent sphere, if compared to no adjustment, or intuitive adjustement which showed a SD of 0.45 and 0.47 respectively.
Although higher order aberration may account for the difference noted between MRSE and the spherical equivalent calculated from Wavescan 4mm, using the effective blur term to adjust spherical power delivered in wafefront guided LASIK do not seem to improve the dispersion of the results. Other factors may account for this difference and shoulg be taking into consideration to improve the overall results and predictibility.
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