Measuring Angle Kappa Using the Autorefractometer

Abstract Purpose: The aim of this study was to present a novel angle kappa (k) measurement method and angle k grading scale. Methods: Two hundred sixty eyes of 130 subjects were included in the study. All eyes were evaluated using autorefractometer front monitor image (Canon, RK-F1, and U.S.A). The distance from center of the pupil to the visual axis on the autorefractometer front monitor image (AR-FMI) was measured using Image J software (http://rsbweb.nih.gov/ij). Sixty eyes of 30 subjects were evaluated using the Lens-star 900 (Haag-Streit AG, Koeniz, Switzerland) and Lens-star 900 angle k values were compared with autorefractometer measurements to analyze reliability of the method. Factors that may influence the angle-k value were analyzed. Additionally, an AR-FMI angle-k grading scale was developed and presented in the study. Results: The mean AR-FMI angle-k was 0.41±22 mm and Lens-star 900 angle-k was 0.38±24 mm, respectively. Pearson correlation test was used to analyze the test reliability and there was statistically significant positive correlation among the two methods (r: 0.628, p<0.001). The mean AR-FMI angle-k was higher at old and adult subjects when compared with young subjects, and the difference was statistically significant (p:0.02 and p:0.04, respectively). According to the AR-FMI analyzes, old subjects had narrow and nasally decentralized pupils when compared with young subjects and differences were statistically significant (p<0.00 and p<0.03, respectively). According to the AR-FMI angle kappa grading scale; 36.1% of subjects was grade 1, 38.3 % was grade 2 in x coordinate, and 58.5% was grade 1 in y coordinate. Conclusion: A novel method to evaluate the angle-k and the factors influencing the angle-k were described in the current study. According to the results, angle-k can be measured using an easily evaluable, cost-effective device which is present in every ophthalmic clinic and a grading scale may be useful to analyze the angle-k and pupillary properties.