Anterior segment biometric changes following SMILE surgery and their implications for effective intraocular lens position calculation.

objectiveThis study quantified short-term postoperative changes in corneal refractive power, axial length, and anterior chamber depth following SMILE surgery using two complementary instruments, and assessed the correlation between anterior chamber depth change and corneal ablation depth. The suitability of selected IOL power calculation formulae for post-SMILE eyes was evaluated through theoretically derived effective lens position (ELP) estimates.

methodsThis prospective study enrolled a consecutive cohort of patients undergoing SMILE surgery during the second half of 2020 at a tertiary referral center affiliated with Hebei Medical University. Uncorrected visual acuity, manifest refraction, intraocular pressure, and slit-lamp biomicroscopy were assessed preoperatively and at one and three months postoperatively. Corneal dioptric power, central corneal thickness, and anterior chamber depth were measured with the Pentacam; corneal power, aqueous depth, and axial length were obtained with the IOL Master. Corneal thickness and ablation depth were additionally recorded. Continuous data are expressed as mean ± standard deviation. All analyses were performed in SPSS (IBM Corp., Armonk, NY, USA), with P < 0.05 considered statistically significant. A linear mixed model (LMM) was applied to account for inter-eye correlation. Pairwise comparisons of internal anterior chamber depth (ICACD), total corneal refractive power (TCRP), simulated keratometry (SimK), mean keratometry (Km), and ELP across time points, instruments, eye laterality, and formulae incorporated Bonferroni correction. Pearson correlation analysis examined associations between continuous variables.

resultsAxial length (AL) was significantly reduced at one and three months postoperatively relative to the preoperative baseline (p < 0.05). ICACD measurements from the Pentacam and IOL Master were strongly and positively correlated. Km, SimK, and TCRP each changed significantly from baseline at both postoperative time points (p < 0.05), with Km exceeding SimK and SimK exceeding TCRP consistently across all assessments. ELP estimates from the Holladay 1 and Haigis formulae were closely correlated (p < 0.01).

conclusionsFollowing SMILE, the reduction in total axial length observed at one and three months, spanning from the anterior corneal surface to the macula, reflected corneal tissue removal, while the endothelium-to-macula distance remained unaffected. Of the corneal refractive power metrics assessed, TCRP proved the most accurate, with SimK and Km following in descending order. Short-term ACD measurements from the Pentacam and IOL Master were in close agreement, and ICACD showed no significant correlation with corneal ablation depth. Although SMILE-induced anterior chamber shallowing may compromise ELP estimation, the Holladay 1 and Haigis formulae yielded highly consistent ELP predictions over the short-term follow-up period.