Clinical importance of accurate refractor vertex distance measurements prior to refractive surgery.

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To determine directly measured vertex distances in a consecutive series of patients refracted at a refractor and to examine the clinical importance of such a measurements for improving refractive surgical results. Vertex distance measurements were obtained in 189 consecutive patients by using a new device capable of taking direct and accurate measurements behind a refractor. Eyelid thickness was measured with an industrial caliper in five patients. The average true vertex distance was 20.4 mm with a range of 10 to 34 mm. Eyelid thickness was 3 mm in all five patients. Precise measurement of true refractor vertex distance is important for accuracy of refractive surgical procedures. The practice of assuming an average vertex distance of 12 to 14 mm for all refractive patients underestimates the vertex distance in many patients refracted at the refractor, resulting in overcorrecting minus and undercorrecting plus refractions.