Comparison of apparent and three-dimensional pupillary diameter measurements in cataract patients and their impact on multifocal intraocular lens selection

The pupillary diameter (PD) clinically observed and measured by conventional devices represents a apparent PD of the anatomical pupil projected onto the corneal plane, yet the relationship between this apparent PD and three-dimensional PD (3D PD) in cataract patients remains unclear. This prospective cross-sectional observational study aimed to investigate the relationship between apparent PD and 3D PD in cataract patients and its clinical impact on multifocal intraocular lens (MIOL) selection. This study included 114 eyes from 72 cataract patients. Apparent PD and 3D PD were measured using Pentacam AXL. Statistical analyses included comparative, correlation, nonlinear relationship, and agreement methods. The clinical impact was assessed through predicted MIOL selections. Apparent PD significantly exceeded 3D PD (3.68 ± 0.76 vs. 2.50 ± 0.44 mm, P < 0.001), with a mean magnification ratio of 47.2 ± 16.5%. The magnification effect increased with pupil size: in eyes with apparent PD < 3.0 mm, 3.0-4.5 mm, and > 4.5 mm, the magnification ratios were 36.18%, 46.93%, and 63.57%, respectively. Strong positive correlation was found between 3D PD and apparent PD (r = 0.84, P < 0.001). For MIOL selection (PD > 2.8 mm threshold), apparent PD identified 90 eyes as suitable while 3D PD identified only 19 eyes, resulting in altered MIOL selection in 71 eyes (62.28%). Apparent PD overestimates 3D PD by 47.2% in cataract patients, increasing the likelihood of MIOL selection due to PD overestimation. Clinicians should consider this magnification effect during preoperative MIOL evaluation to avoid overestimation of functional PD.