Differentiating between bullous and rhegmatogenous types of Descemet’s detachment after cataract surgery
Post-stromal hydration Bullous Descemet detachment: A: A bullous DD is seen (white arrows) originating from a paracentesis (black arrow). Air from a previous unsuccessful pneumodescemetopexy is seen. Trapped fluid and blood are present within the bullous DD. Blood gravitates down forming a fluid level (yellow arrow); B: A Relaxing Descemetotomy cut is made through the Descemet’s membrane (DM) to provide an egress route for the trapped fluid; C: Pneumodescemetopexy from the opposite quadrant is combined with steam rolling of the cornea; D: An attached DM and a clear cornea is seen on first postoperative day
Descemet’s detachment (DD) after cataract surgery is a relatively frequent complication. It may also be seen after other surgeries or trauma. The author has classified Descemet’s detachments into rhegmatogenous, tractional, bullous and complex detachments based on pathophysiology, clinical, ASOCT findings and treatment required.
The most common type of DD seen is the variety with a tear in the Descemet’s membrane (DM), generally seen as a free-floating undulating membrane in the anterior chamber (AC). The tear is generally, though not necessarily located at an incision and may be due to a blunt instrument, the phaco probe or the IOL injector pushing against the DM. This is the classical rhegmatogenous DD and treatment for this variety is simple – injection of air or long-acting gas from the opposite quadrant (pneumodescemetopexy) to drain supra-Descemetic fluid and appose the detached DM against overlying stroma followed by postoperative head positioning to keep the air/gas bubble over the area of detachment.
However, rarely a postoperative Descemet’s detachment does not resolve despite this commonly followed management and it is important to rule out a bullous variety of Descemet’s detachment in such cases. In addition, learning to identify a bullous DD at the time of primary surgery can save considerable heartburn later on. This article will discuss Bullous DD and its identification, management, prevention and treatment.
BULLOUS DESCEMET’S DETACHMENT
This is generally seen at the end of surgery while performing stromal hydration for the incision. If the cannula is held too posterior (close to the DM), the injected fluid may cause a hydroseparation of the DM from the overlying stroma. This is seen as a fluid wave moving forwards from the incision. The injected fluid creates a bullous detachment with fluid trapped under DM. Since there is no tear or cut in the DM, a plain pneumodescemetopexy does not work as there is no egress route for the trapped fluid to drain out through.
Bullous DD is seen intraoperatively as a fluid wave and may sometimes be overlooked. The classical free-floating detached DM is not seen. Postoperatively, it is seen as a well-defined area of detachment with no tear/flap and a planar or convex separation of the DM from overlying stroma. A fluid level may be seen if mixed with blood. ASOCT may be required for densely oedematous corneas and shows the classical configuration with absence of a tear. The undulating membrane with tear seen in rhegmatogenous DD is not seen here.
Relaxing Descemetotomy: Though small and peripheral bullous DD may resolve spontaneously, larger ones may require surgical management, especially if crossing the visual axis, if rapid visual rehabilitation is required or if the patient develops pain/bullae. Surgical principles are simple. A cut is created on the detached DM in order to make an exit route for the trapped fluid. This may be done by creating a keratome incision in to 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 can-opener cuts on the DM in the periphery under pressurised air infusion. Steam rolling of the overlying cornea together with pressurised air infusion through an air pump helps in draining the supra-Descemetic 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 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.
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 firstname.lastname@example.org