Assessment of Chord Mu and Chord Alpha in Relation to Post-ICL Implantation Visual Quality

Purpose: To evaluate the clinical influence patterns of pre-operative chord mu and chord alpha on optical quality after Implantable Collamer Lens (ICL) (Visian; STAAR Surgical) implantation, thereby providing evidence-based guidance for surgical planning. Methods: This study included 92 patients (181 eyes) who underwent ICL implantation. The OPD-Scan III system (Nidek) was employed for the preoperative assessment of both chord mu and chord alpha. Changes in higher order aberrations were analyzed 3 months postoperatively. Postoperative optical aberration patterns were assessed for their dependence on preoperative chord mu and chord alpha measurements. Results: The mean value of chord mu was 0.25 ± 0.13 mm, and the median chord alpha was 0.22 mm (interquartile range: 0.19 mm). Chord mu exhibited a relatively dispersed distribution, whereas chord alpha was primarily distributed along the horizontal axis. Notably, 1/chord alpha exhibited a significant linear positive correlation with axial length ( R 2 = 0.1739, P < .001), reflecting the non-linear decay of chord alpha with axial elongation. The relationship was characterized by a generalized estimating equation using Gamma distribution and inverse link function. At 3 months postoperatively, analysis revealed statistically significant elevation in vertical coma and oblique trefoil ( P < .05), whereas other optical parameters including total higher order aberrations, primary coma, trefoil, spherical aberration, and horizontal coma remained stable ( P > .05). Correlation analysis revealed no significant association between changes in higher order aberrations and preoperative chord mu or chord alpha ( P > .05). Conclusions: Neither preoperative chord mu nor chord alpha significantly affects higher order aberrations after ICL implantation, suggesting that the procedure has a relatively high tolerance regarding chord mu and chord alpha selection.