Abstract
Purpose: :
DALK surgery is an increasingly popular modality of restoration of corneal clarity and function in eyes with a healthy endothelium. The big bubble technique, as originally described by Dr. Mohammed Anwar, is one method of achieving a successful DALK with excellent clinical results. The comparatively fast visual recovery is attributed to the deep dissection achieved with this technique that presumably creates a clean plane of separation between the corneal stroma and Descemet’s membrane (DM). We describe OCT and histologic assessment of eyebank corneas on which DALK was performed, utilizing both big bubble and manual dissection techniques, to assess precisely the depth of the dissection plane.
Methods: :
Human corneoscleral rims were mounted on an artificial chamber and the big bubble technique attempted. After surgical preparation, the specimens remained mounted on artificial anterior chambers for photographic and VisanteTM anterior segment OCT evaluation. The specimens were fixed in formalin and histologic assessment was performed.
Results: :
In three corneas, the big bubble was successfully achieved with clinically apparent baring of DM. In one of those three tissues, the big bubble ruptured through DM during the manual dissection of the overlying stromal tissue. Intra-operative and OCT examination revealed that the rupture occurred at the site of the prior cataract surgery wound. In a fourth tissue the big bubble could not be obtained and a manual cut-down to near DM was completed. Photographic and OCT evaluation revealed a smooth interface with apparent dissection to DM in the 3 big bubble technique tissues. The specimen that underwent manual dissection displayed a satisfactorily thin posterior lamella. Histological evaluation, however, revealed a single collagenous lamella of corneal stromal tissue adherent to DM in the big bubble cases.
Conclusions: :
The big bubble technique achieves a very deep and uniform lamellar corneal dissection for DALK. Our study provides histopathologic evidence that the dissection plane occurs in the deep stroma and leaves a single layer of stroma adherent to the DM. Unlike the DM stripping step of DSAEK surgery, the DALK dissection does not occur between the stroma and DM as is commonly postulated. In cases where the big bubble cannot be achieved, adequate depth of dissection approaching that of the big bubble can be accomplished with manual dissection. Prior cataract surgery incisions may be a risk factor for failure of the big bubble technique.
Keywords: cornea: clinical science • transplantation • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)