SPECIAL FOCUS: CATARACT & REFRACTIVE the AC through the paracentesis, thus creating a cut on the DM through which trapped fluid escapes. This cut on the DM has been described by the author as a Relaxing Descemetotomy cut. For a centrally located bullous DD, the relaxing Descemetotomy may be performed ab-interno by passing a bent 26-gauge needle into the AC and carefully making small relaxing canopener cuts on the DM in the periphery under pressurised air infusion. Soosan Jacob MD Steam rolling of the overlying cornea together with pressurised air infusion through an air pump helps in draining the supraDescemetic fluid completely and hastening DM reattachment. For bullous DD extending to the inferior limbus, a keratome entry is made at the inferior limbus to cut through the detached DM to allow gravitational drainage of fluid. All techniques also require pneumodescemetopexy and postoperative head positioning. The Nd:YAG laser may also be used to drain a centrally located BDD internally. Venting incisions that are sometimes used as an adjunct with pneumodescemtopexy for rhegmatogenous DD may not work effectively for bullous DD. This is because in the absence of a tear, venting incisions in isolation may not be able to evacuate the fluid sufficiently. For a large bullous DD, two limbal-relaxing Descmetotomy incisions can be made perpendicular to each other (thereby negating any astigmatism as well). In contrast, venting incisions are small, are
The most common type of DD seen is the variety with a tear in the Descemet’s membrane (DM)
made in the mid-peripheral cornea as opposed to the limbal location of the relaxing Descemetotomy and therefore have limited effect on drainage of fluid. Large venting incisions carry the risk of scarring, irregular astigmatism, epithelial ingrowth, infective keratitis etc.
PREVENTION Care should always be taken to insert the needle or the cannula completely through the incision before injecting. During stromal hydration at the end of surgery, the cannula should not be placed too posterior against the stroma. It is important to recognise the absence of a tear and treat the bullous DD appropriately during primary surgery itself.
OTHER CAUSES FOR BULLOUS DD Fluid, blood, viscoelastic or air may cause a bullous DD. A bullous detachment can also occur while injecting Trypan blue for staining the capsule if the needle has not been fully inserted through the wound. This blue staining of the cornea does eventually resolve but may take time. Accidental injection of viscoelastic into the cornea during cataract surgery causing a bullous DD, if not identified, has been reported to have been mistaken for the lens capsule and Descemetorhexis performed on the detached DM instead of capsulorhexis. Viscoelastic may also find its way into the cornea and detach the DM during viscocanalostomy. Air injected purposely during Anwar’s big bubble deep anterior lamellar keratoplasty (DALK) creates a central bullous detachment that also includes the pre-Descemet’s layer when a Type 1 bubble forms. Sometimes, a Type 2 bubble forms while attempting the big bubble in DALK and this is a true bullous DD. Dr Soosan Jacob is Director and Chief of Dr Agarwal’s Refractive and Cornea Foundation at Dr Agarwal’s Eye Hospital, Chennai, India and can be reached at dr_soosanj@hotmail.com
EU-CC-NP-0014
EUROTIMES | MAY 2019
11