Purpose Dua’s layer (DL) has considerable relevance to DALK procedure and the hitherto clinically observed but unexplained formation of Types 1, 2 and mixed BB. In this study we explored the dynamics of the formation of different types of BB Methods 50 human sclerocorneal discs were injected with air under BSS and recorded. Videos were studied for leakage of air and formation of BB. Height and diameter of BB were measured. Specimens were subjected to electron microscopy and immunohistology for collagens & matricellular proteins. Age ranged from 3wk‐80yr Results Air injected in the cornea preferentially reached the limbus and moved circumferentially in a clockwise & anticlockwise direction as bands of 2‐3mm till they met, irrespective of direction of needle tip. The air then migrated centripetally to fill the stroma. Air leaked from the TM area at one or more points. Small bubbles formed in the centre and coalesced into a Type‐1BB. This rapidly expanded to attain a height of 5mm and a diameter of ≤9mm. The anterior stomal wall of Type‐1BB showed multiple 'holes' through which air leaked to lift DL. DL was impervious to air. Type‐2BB always started at the periphery. Distinct pores were seen in the peripheral stroma of DL. Most of these were located distal to attachment of DM and explained the leakage of air from TM. Some were located centrally to the attachment and explained formation of Type‐2BB. More than 80% of BB were Type‐1 Immunohistology did not offer an explanation for DL being impervious to air Conclusion DL is a distinct part of the surgical anatomy of the cornea. Identification of pores in DL periphery is novel and explains the formation of a Type‐2BB and the clinical observation of appearance of air in AC during DALK. Leakage is not through the TM

Purpose When transplanted as a graft AM is incorporated into the cornea. Our aim was to ascertain by immunohistology the fate of the incorporated membrane over time. Methods Corneal buttons from 8 eyes treated by AMT for bullous keratopahty and subsequently had penetrating keratoplasty were examined by electron microscopy and by immunohistology with markers for keratocytes (CD34), fibroblasts (vimentin) and myofibroblasts (SMactin). Time from AMT to PK was between 2 to 32 months Results Amnion tissue was covered with stratified corneal epithelium with well‐defined hemidesmosomes. At places a fluid cleft was seen between amnion and underlying Bowman’s zone. Transformed keratocytes/fibroblasts could be seen migrating from the anterior stroma, through breaks in the Bowman’s zone, into connective tissue of the amniotic membrane. Immunohistology showed that the cells populating amnion stroma were CD34 negative but positive for vimentin and smooth muscle actin. In 2 samples where corneal transplants were performed more than 1 year following AMT, some cells in the amniotic stroma showed CD34+ staining Conclusion The amniotic basement membrane facilitates epithelial cell migration and adhesion. Corneal stromal keratocytes can migrate through breaks in Bownans zone, into the amniotic tissue thus integrating it with the host. Despite the presence of large fluid clefts between amniotic membrane and Bowman’s zone, the overlying epithelium remained compact. Repopulation of the amniotic stroma by corneal keratocytes allows for rebuilding of corneal stroma with an indication that over time they may revert to the resting keratocyte immunophenotype.

No abstract

No abstract