Short tunnel length – A novel cause of vertical gas breakthrough in femtosecond laser-assisted in situ keratomileusis (Femto-LASIK)

Femtosecond laser facilitates greater precision in flap creation for laser-assisted in situ keratomileusis (LASIK). However, rare intraoperative flap-related complications have been reported, including vertical gas breakthrough (VGB). Femtosecond laser applies short pulses of energy in the stroma, generating microplasma. This leads to the interface of microscopic air bubbles.[1] VGB is the escape of bubbles from the stroma to the corneal surface when the laser is fired. Few case reports in the literature have attributed VGB to focal defects in the Bowman membrane,[2] corneal abrasion,[3] corneal scarring and thinned stroma,[4] and epithelial basement membrane dystrophy.[5] There is a paucity of reasonable inferences in the literature about the possible causes of VGB [Table 1]. We report a unique cause of VGB - short tunnel length in the Wavelight Fs200 femtosecond laser platform. In this simple myopic LASIK, the flap diameter was 8.5 mm, and it was 90 µm thick. The thinnest pachymetry was 514 µm and the residual stromal bed of 333 µm (after excimer ablation), canal width 1.7 mm. The pulse energy was 0.85 µJ. There was no loss of suction and no scarring in the cornea. However, the tunnel did not reach the sclera. The tunnel crossing beyond the limbus is important for the gas to escape. In the case of a short tunnel, the gas may egress uncontrollably via an alternative route to some other area, leading to the formation of an opaque bubble layer and consequently incomplete dissection of tissue plane areas, which may compromise the surgery such as difficulty with flap separation causing irregularities if manual dissection is attempted. As the uncut area was in the periphery in our case, we decided to proceed with the surgery, and the excimer was fired after exposing the central optical zone [Video 1]. The case could be managed as the uncut area was small and in the periphery, and an additional femtosecond laser cut was not required unlike Wei et al.[6] The patient had a vision of 20/20 till the last follow-up at 3 months. To the best of our knowledge, a short tunnel length leading to VGB is a novel addition of intraoperative flap-related complications, which may be avoided by crossing the tunnel length beyond the limbus. {"href":"Single Video Player","role":"media-player-id","content-type":"play-in-place","position":"float","orientation":"portrait","label":"Video 1","caption":"","object-id":[{"pub-id-type":"doi","id":""},{"pub-id-type":"other","content-type":"media-stream-id","id":"1_c4xmei52"},{"pub-id-type":"other","content-type":"media-source","id":"Kaltura"}]} Table 1: Literature review of vertical gas breakthrough