Characteristics of Angle Kappa in Cataract Patients and Changes under Photopic and Mesopic Conditions

Objective: To observe the characteristics and rule of change of the angle Kappa in cataract patients under photopic and mesopic conditions. Methods: In this case series study, a total of 788 eyes in 394 cataract patients receiving cataract surgery in the Affiliated Eye Center of Xiamen University were selected from May 2016 to October 2017. All patients were examined by OPD-Scan Ⅲ. The collected data included the clinical data of patients (such as age, gender, ocular history and surgical history), as well as preoperative biometric data, including mean corneal keratometry (mean K), and corneal spherical aberration (CSA), white-to-white distance (WTW), photopic pupil diameter (Photopic), mesopic pupil diameter (Mesopic), distance and angle of photopic angle Kappa (PDist@Angle), distance and angle of mesopic angle Kappa (MDist@Angle), and distance and angle from the mesopic pupil center to the photopic pupil center (MPDist@Angle) and so on. Specific tests included Rank sum test, Chi-square test, and multiple regression statistical analysis. Results: There were no significant differences in the biometric data, such as mean K, MPDist, PDist, WTW, and CSA between the two eyes (P>0.05), but the differences in photopic pupil diameter, mesopic pupil diameter, and MDist between the two eyes were statistically significant (Z=2.276, 3.284, 2.388, all P<0.05). The angle Kappa for most patients in the two eyes under photopic or mesopic conditions was positive, and the pupil center usually shifted inferotemporally when the illumination was changed from photopic to mesopic. The clinical and biometric data for both eyes were analyzed by multiple regression analysis with MPDist. The regression equation of the right eye was MPDist=0.033+0.505×MDist+0.041×CSA-0.319×PDist (F=45.0, P<0.001), while that of the left eye was MPDist=-0.002+0.547×MDist+0.013×Mesopic-0.350×PDist (F=61.6, P<0.001). Conclusions: In cataract patients, most eyes have a positive angle Kappa, and the variation in pupil size under different illuminations affect the size of the angle Kappa. Large differences can be detected in photopic pupil size, mesopic pupil size and the direction and shift of the pupil center during photopic and mesopic alternation. There was a linear regression relationship between MPDist changes and PDist, MDist, Mesopic, CSA. Among them, MPDist of both eyes were negatively correlated with PDist, and MDist of both eyes had relatively larger influence on MPDist changes. Key words: angle Kappa; cataract; photopic and mesopic pupil