Astigmatism reduction clinical trial: a multicenter prospective evaluation of the predictability of arcuate keratotomy. Evaluation of surgical nomogram predictability. ARC-T Study Group
F. W. Price, R. B. Grene, R. G. Marks and J. S. Gonzales
Corneal Consultants of Indiana, Indianapolis.
OBJECTIVE: To determine the accuracy of the Lindstrom surgical nomogram 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 included age of at least
18 years with 1 to 6 diopters (D) of naturally occurring corneal
astigmatism and less than 1 D of lenticular astigmatism. INTERVENTIONS: A
standardized astigmatic keratotomy surgical technique was performed on each
eye. Surgical measurements were determined using the Lindstrom surgical
nomogram for astigmatism. MAIN OUTCOME MEASURE: The Holladay, Cravy, Koch
vector analysis method was used to determine 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 analysis was used to develop a mathematical
model determining the factors predictive of the change in refractive
cylinder. The significant predictors for the amount of astigmatic
correction achieved were, in order of decreasing importance, the following:
number of incisions (R2 = 30%), incision length (R2 = 16%), age (R2 = 8%),
and gender (R2 = 2%). CONCLUSIONS: Astigmatism is a two-dimensional
measurement of both quantity and direction that is most appropriately
analyzed with vector analysis. The original Lindstrom surgical nomogram for
arcuate keratotomy 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
achieved greater correction than predicted by the original nomogram. The
most important factors predictive of greater astigmatic keratotomy surgical
effect are incision number, incision length, older age, and male gender.
