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).

Methods: 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-R²=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.