Impact of Densitometry-Detected Subtle Residual Lenticule on Post-SMILE Corneal Higher-Order Aberrations: A Contralateral Eye Study

Background To investigate the impact of subtle residual lenticule (SRL) on corneal higher-order aberrations (HOAs) after small incision lenticule extraction (SMILE). Methods This prospective, contralateral eye study included 33 myopic patients with unilateral SRL identified 3 months postoperatively. SRL was defined as retained fragments spanning fewer than two quadrants, identified via a novel protocol using corneal densitometry and anterior elevation maps, and confirmed with anterior segment optical coherence tomography (AS-OCT). Postoperative changes (Δ) in corneal HOAs (6.0/8.0 mm zones) were compared between SRL and control eyes. Multiple linear regression explored factors associated with Δ8.0mm spherical aberration (SA) and horizontal coma (HC). Results Compared to controls, SRL eyes showed significantly greater changes in 6.0 mm/8.0 mm total HOA root mean square (ΔRMS: P = 0.006 / P < 0.001) and ΔSA (P = 0.026 / P = 0.001), and a negative shift in HC (8.0 mm zone; P = 0.001). Regression analysis identified only SRL presence associated with negative Δ8.0mm HC (P = 0.004). Conversely, increased Δ8.0mm SA was associated with higher preoperative myopia and a smaller postoperative effective optical zone (all P < 0.001), not directly with SRL (P = 0.990). Conclusions The presence of SRL after SMILE is associated with statistically significant increases in postoperative HOAs, notably a negative shift in horizontal coma. Furthermore, the densitometry-guided protocol offers a practical tool for screening these subtle fragments. Complete lenticule removal remains the ideal goal for optimizing postoperative optical quality.