Tomographic and topographic predictive factors of big bubble formation during deep anterior lamellar keratoplasty in keratoconus

Purpose To identify preoperative predictors of big bubble (BB) formation during deep anterior lamellar keratoplasty (DALK) in patients with keratoconus (KC). Design Retrospective cohort study in an Italian tertiary centre. Study population Consecutive patients with KC undergoing DALK from January 2021 to July 2023. Observation procedure Tomographic and topographic data including K-max, K-mean, keratometric astigmatism, thinnest point, mean peripheral corneal thickness, difference between the mean peripheral corneal thickness and the thinnest point (peripheral-minimal corneal thickness), position (central/paracentral) and cone area (%), Amsler-Krumeich classification and anterior segment optical coherence tomography (AS-OCT) analysis to assess the severity stage. Main outcome measures Rate of BB formation and type; multivariate logistic regression analysis was used to analyse all preoperative parameters in patients with BB formation versus failure. Results Pneumatic dissection succeeded in 98 of 140 eyes (70.0%), with 94 type 1 bubbles (67.1%) and four type 2 bubbles (2.9%). BB formation succeeded more frequently in patients with lower K-max (p=0.032), lower K-mean (p=0.010), higher thinnest point (p=0.017), lower peripheral-minimal corneal thickness (p=0.009) and lower Amsler-Krumeich stages (p=0.021). According to the AS-OCT analysis, BB formation was more frequent in the lower stages (p<0.001). After the logistic regression (pseudo-R-2=0.176, constant=3.21, 95% CI 1.14 to 5.29, p=0.002), AS-OCT classification was found to be the only factor that predicted BB formation (coefficient=-0.81, 95% CI -1.18 to -0.43, p<0.001). Conclusions AS-OCT classification is a reliable predictor for BB formation. Tomographic and topographic analyses indicated that a steeper and more ectatic cornea is more prone to BB failure.