Risk factors for opaque bubble layer in femtosecond-laser-assisted laser in situ keratomileusis (an Egyptian study)

Abstract

Aim To determine the risk factors responsible for opaque bubble layer (OBL) formation in femtosecond-laser-assisted in situ keratomileusis (FSL-LASIK). Patients and methods A retrospective, comparative study was carried out from January 2015 to January 2017 in El-Watany Eye Hospital. Two hundred eyes who were eligible for FSL-laser-assisted in situ keratomileusis (FSL was done using FS200, wavelight, Germany SR/1025-1-380) were classified into two groups. Group I: the study group with OBL formation during surgery (100 eye) and group (II): the control group without OBL formation during surgery (100 eye). Preoperative best-corrected visual acuity, spherical equivalent, and dilated fundus examination were done and corneal tomography including keratometric readings: flat keratometric readings (K1), steep keratometric readings (K2), and central corneal thickness (CCT) measurements. Programmed flap parameters were collected. Statistical analysis Statistical analysis was done using IBM SPSS, version 24. Results Among the studied 101 patients, OBL occurs bilaterally in 58 eyes among 29 patients and OBL occurs unilaterally among 42 patients. There was a statistically significant difference between OBL and non-OBL regarding preoperative steep keratometry (K2) (P<0.01) and CCT (P=0.03), where the corneal pachymetry was more than 545 µm in 57 (57%) eyes of OBL group versus 42 (42.0%) eyes in non-OBL eyes. There was no statistically significant difference between both groups regarding canal length offset (P=0.123), corneal flap thickness (P=0.489), corneal flap diameter (P=0.064), and flap hinge angle (P=0.074). Conclusion Increased corneal thickness, corneal canal length offset, and steep keratometry were significant risk factors of OBL formation. Regarding regression analysis, CCT and corneal astigmatism were statistically significant independent predictors of OBL formation.