Predictors of Bubble Formation and Type Obtained with Pneumatic Dissection During Deep Anterior Lamellar Keratoplasty in Keratoconus

Abstract Purpose To identify predictors of bubble formation and type during big-bubble deep anterior lamellar keratoplasty (BB-DALK) performed in keratoconus at different stages of severity. Design Retrospective Cohort Study. Methods Setting : University Magna Graecia (Catanzaro, Italy); Study Population: Consecutive keratoconus patients undergoing BB-DALK from September 2014 to February 2019; Observation Procedure: Keratometric astigmatism, mean keratometry value (K-mean), highest keratometry value (K-max), thinnest point, anterior segment Optical Coherence Tomography (AS-OCT)-based stage of ectasia. Main Outcome Measures : Rate of bubble formation and type; number and fate of micro/macro-perforation; conversion to mushroom keratoplasty (MK); comparison of parameters in patients with bubble formation vs failure and in type 1 vs type 2 bubble; areas under the curves (AUC) of preoperative parameters for distinguishing between bubble types. Results Pneumatic dissection succeeded in 113/155 eyes (72.9%), with 100 type 1 bubbles (88.4%), 11 type 2 (9.8%) and 2 mixed-type (1.8%). Micro-perforations were managed conservatively in type-1 bubbles; macro-perforations occurring in both types of bubbles required conversion to MK. Preoperative K-mean and K-max values were significantly higher in eyes in which bubble formation succeeded (respectively, P=0.006 and P Conclusions Older age and advanced stages of keratoconus were predictors of type 2 bubble formation during BB-DALK that was associated with an increased risk of complications.