Measurement of Angle Kappa With Synoptophore and Orbscan II in a Normal Population

ABSTRACT PURPOSE: To obtain normative values of angle kappa in a normal population by synoptophore and Orbscan II and to compare the reliability of these devices. METHODS: Three hundred consecutive healthy individuals were enrolled in the study. A complete orthoptic and ophthalmologic examination was performed. Synoptophore and Orbscan II corneal topography were used to measure angle kappa. To evaluate the association of the angle kappa and refraction measures, individuals were further classified according to the degree of myopia and hyperopia. The spherical equivalent error measures were grouped into six categories: ≥-3.00 diopters (D); -2.75 to -1.50 D; -1.25 to -0.50 D; +0.50 to +1.25 D; +1.50 to +2.75 D; and ≥+3.00 D. Paired t test and Pearson's correlation test were used for statistical analysis. RESULTS: The mean age of the individuals was 28.74±1.63 years (range: 20 to 40 years). The angle kappa values obtained by synoptophore and Orbscan II were normally distributed. In the myopic group, angle kappa values decreased significantly towards negative refractive errors. In contrast, a correlation existed between large positive angles and positive refractive errors in the hyperopic group. Angle kappa values obtained by Orbscan II were significantly higher in all groups when compared to synoptophore (P<.0001). A significant correlation was noted between synoptophore and Orbscan II measurements (r=0.932, P<.0001). CONCLUSIONS: A significant correlation exists between positive refractive errors and large positive angle kappa values. Refractive surgeons must take into account angle kappa, especially in hyperopic patients, to avoid complications related to decentration of the ablation zone. [J Refract Surg. 2007;23:456-460.]