Densitometry-detected subtle residual lenticule and post-SMILE corneal higher-order aberrations: a contralateral-eye study

To investigate the association between subtle residual lenticule (SRL) and corneal higher-order aberrations (HOAs) after small incision lenticule extraction (SMILE). This prospective, contralateral eye study included 33 myopic patients with unilateral SRL at 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). Changes (Δ) in corneal HOAs (6.0 mm/8.0 mm zones) were compared between SRL and control eyes. Multiple linear regression explored factors associated with Δ8.0 mm spherical aberration (SA) and horizontal coma (HC). 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 revealed an exploratory relationship between SRL and negative Δ8.0 mm HC ( P = 0.004). Conversely, increased Δ8.0 mm 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). The presence of SRL after SMILE is associated with statistically significant increases in postoperative HOAs, notably a negative shift in HC. Furthermore, the densitometry-guided protocol may serve as an adjunctive screening aid for these subtle fragments. Complete lenticule removal remains the ideal goal for optimizing postoperative optical quality.