—We do not perform A-scan ultrasound measurements of the axial length of the globe as part of the preoperative diagnostic studies in the PERK study for many reasons.Axial length measurements are not necessary to rule out progressive pathologic myopia, since the stability of refraction must be proved in every patient and indirect ophthalmoscopy performed preoperatively to search for the signs of pathologic changes in the posterior pole.1Although A-scan ultrasound performed with a water bath stand-off could be used to show changes in axial length produced by changes in corneal shape after radial keratotomy, these measurements can be made more
Waring GO. Radial Keratotomy-Reply. Arch Ophthalmol. 1984;102(3):356. doi:10.1001/archopht.1984.01040030276012
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