Dynamics of big bubble formation in deep anterior lamellar keratoplasty by the big bubble technique: in vitro studies.

PURPOSE: To examine the movement of air injected in the cornea in simulated deep anterior lamellar keratoplasty (DALK), from the needle tip to the formation of different types of big bubbles (BB) and to ascertain how air travels through the stroma and pre-Descemet's layer [Dua's layer (PDL)] to create a type-1 (air between PDL and deep stroma) and type-2BB (air between PDL and Descemet's membrane).

METHODS: Air was injected in 57 sclerocorneal discs and the passage recorded. Leaking points and sites of commencement of type-1 and type-2BB were examined by scanning electron microscopy. Stromal distribution of air pockets was studied by light microscopy. Uninjected corneas served as controls.

RESULTS: Injected air followed a consistent pattern, initially as radial tracks to the limbus, then as circumferential bands along the limbus and finally centripetally to create predominantly a type-1BB. Type-2BB started at the periphery, by air emerging through clusters of tiny fenestrations discovered in the periphery of PDL. Fifteen to 20 such clusters were also seen in control samples on either side of the Descemet's attachment. Type-1BB was formed by air emerging through wide spaces between lamellae of deep stroma. Histologically, the circumferential band revealed an aggregation of air pockets in the mid-stroma.

CONCLUSION: The consistent pattern of passage of air is indicative of the architecture and microanatomy of the corneal stroma where collagen lamellae are orthogonally arranged centrally and as a circular annulus at the periphery. The novel peripheral fenestrations explain the peripheral commencement of a type-2BB and the escape of air into the anterior chamber during DALK.