Exploring the interplay of chord α and chord μ with pyramidal wavefront aberrometry and ocular biometric indices among pre-operative refractive surgery candidates

Background To investigate the relationships between chord α and chord µ with age, ocular biometric indices, and wavefront aberrations in pre-operative refractive surgery candidates. Methods This cross-sectional study included 111 right eyes of 111 patients. Ocular biometrics and chord values were measured using the ZEISS IOLMaster 700. Corneal and ocular aberrations were assessed with the PERAMIS pyramidal aberrometer. Data were analyzed using Pearson’s correlation, ANOVA, and simple linear regression to evaluate the interplay between variables. Results A moderate positive correlation was found between chord α and chord µ (r = 0.60, p < 0.001). Chord α demonstrated moderate positive correlations with subjective spherical refraction (r = 0.45) and spherical equivalent (r = 0.41), and moderate negative correlations with anterior chamber depth (r = -0.53) and axial length (r = -0.40) (all p < 0.001). In contrast, correlations involving chord µ were exclusively weak, though it showed significant associations with several higher-order aberrations, including corneal trefoil (r = 0.35) and ocular coma (r = 0.31). Refractive status significantly affected both chord values (p ≤ 0.02), with severely myopic eyes showing the lowest values. Regression analysis identified anterior chamber depth as the strongest anatomical predictor for chord α (R² = 0.28). Conclusion Chord α serves as a more robust indicator of the eye's anatomical characteristics than the more variable chord µ. Our findings underscore the clinical importance of optical decentration in surgical planning, as larger chord values may indicate a greater risk of pre-existing aberrations and potential impacts on visual quality.