I have read that a detailed video computerized scan is employed pre-procedure in order to determine, besides detailed corneal topographical information, "refractive stability." Can someone explain to me exactly how that stability is determined, and the implications thereof. The reason I ask is that my son (aged 21) had his preop exam completed, and the doctor determined his refraction to be "unstable". I don't know if this statement was based upon the change in his MR and cycloplegic refration from the time he was 17, or the video info. His prescription (CL and glasses) have remained consistent during the interim. The only inconsistency in the "story" is the length of time his CLs were removed prior to each exam...3 days for the 2002 exam (-9.25), and 2 1/2 weeks for the current one(-8.5). Any insight would be greatly appreciated. Any bibliographical info would be appreciated as well.