Aims To investigate and define the nature of big bubbles (BB) formed by injection of viscoelastic in deep anterior lamellar keratoplasty.

Methods Intrastromal injections of 0.1 and 0.3 mL of sodium hyaluronate 1.2% and 0.6% were made into sclera-corneal discs (n = 32) at superficial (anterior-third), midstromal (middle-third) and deep (posterior-third) levels to simulate deep anterior lamellar keratoplasty. Postinjection optical coherence tomograms (OCT) were obtained with the needle in situ. The samples were sectioned and examined histologically. Twelve control samples were injected with air.

Results With superficial injections (n=8) only intrastromal accumulation of viscoelastic was noted. With midstromal injections (n=10) intrastromal accumulation of viscoelastic (n=6) and intrastromal big bubbles (IBB) (n=4) with substantial and variable stromal tissue in the walls were noted. No type 1, type 2 or mixed BB were noted. With deep injections (n=14), type 1 BB (n=4), IBB (n=4) and mixed BB (n=6) were obtained.

There was no difference in the results with the two different concentrations of viscoelastic used. With air injection (n=12), 10 type 1 and 1 type 2 BB and 1 mixed BB were obtained. No IBB was noted.

Conclusions BB obtained by injection of viscoelastic and air can be different. The former tends to occur at the site of injection, especially with midstromal injections, takes the form of tissue separation by stretch and tearing and does not cleave in a consistent plane like air. Surgeons should be aware of IBB created by viscodissection and not confuse it for a type1 BB. Intraoperative OCT should help identify IBB.