ASTIGMATISM REDUCTION CLINICAL-TRIAL - A MULTICENTER PROSPECTIVE EVALUATION OF THE PREDICTABILITY OF ARCUATE KERATOTOMY - EVALUATION OF SURGICAL NOMOGRAM PREDICTABILITY

Objective: To determine the accuracy of the Lindstrom surgical nomogra m for astigmatism. Design: A prospective multicenter study. Patients: One hundred sixty eyes of 95 patients underwent astigmatic keratotomy in eight centers by nine surgeons. Inclusion criteria for the study in cluded age of at least 18 years with 1 to 6 diopters (D) of naturally occurring corneal astigmatism and less than 1 D of lenticular astigmat ism. Interventions: A standardized astigmatic keratotomy surgical tech nique was performed on each eye. Surgical measurements were determined using the Lindstrom surgical nomogram for astigmatism. Main Outcome M easure: The Holladay, Gravy, Koch vector analysis method was used to d etermine the change in refractive cylinder results. Refractive changes also are presented without vector analysis merely using the absolute change in refractive cylinder and axis. Results: Multiple regression a nalysis was used to develop a mathematical model determining the facto rs predictive of the change in refractive cylinder. The significant pr edictors for the amount of astigmatic correction achieved were, in ord er of decreasing importance, the following: number of incisions (R(2) = 30%), incision length (R(2) = 16%), age (R(2) = 8%), and gender (R(2 ) = 2%). Conclusions: Astigmatism is a two-dimensional measurement of both quantity and direction chat is most appropriately analyzed with v ector analysis. The original Lindstrom surgical nomogram for arcuate k eratotomy used in this study is still quite useful although it tended to underpredict results for many patients, especially those having two incisional surgeries. Some older subjects having minimal surgery achi eved greater correction than predicted by the original nomogram. The m ost important factors predictive of greater astigmatic keratotomy surg ical effect are incision number, incision length, older age, and male gender.