Pre-Descemet Endothelial Keratoplasty

9 Pre-Descemet Endothelial Keratoplasty

Priya Narang and Amar Agarwal

9.1 Introduction

Endothelial keratoplasty (EK) consists of Descemet membrane endothelial keratoplasty (DMEK) and Descemet stripping endothelial keratoplasty (DSEK) as the major variants, whereas many surgeons worldwide have also employed their automated version of Descemet membrane automated endothelial keratoplasty (DMAEK) and Descemet stripping automated endothelial keratoplasty (DSAEK). In terms of visual output, DMEK as an EK procedure has always been successful in spite of it being technically challenging as compared to other subtypes. Melles et al described DMEK that represents the perfect anatomical replacement of the diseased Descemet membrane (DM)–endothelium complex with a healthy donor DM–endothelium complex.1,2

Pre-Descemet endothelial keratoplasty (PDEK),3 being a new variant in the field of EK, further extends the lexicon of EK, which mainly consists of the separation of the pre-Descemet layer (PDL) along with the DM–endothelium complex from the residual donor stroma by the formation of a type 1 bubble (bb).4 The feasibility of the PDEK procedure with both adult and infant donor tissue3,5 makes it highly acceptable in the era of donor tissue shortage.

9.2 Importance of Air Dissection and Types of Bubbles

Air dissection is a well-established entity that relegates the use of microforceps or a microkeratome for dissection of the corneal stroma. An air-filled syringe is used to inject air into the stroma with the endothelial side up and is advanced under direct observation at a required depth beneath the endothelium. The advantage with air dissection is that it is cost-effective because it is done manually by the surgeon. The major drawback is that it requires a certain amount of surgical skill on behalf of the surgeon because the needle that is employed to inject air must be introduced at the correct depth below the DM–endothelium complex.

9.2.1 Type 1 Bubble

This is the kind of bb that is essential to obtain for performing a PDEK procedure. This bb typically spreads from the center to the periphery and is dome shaped. The diameter of the bb usually varies from 7.5 to 8.5 mm; this bb never extends to the extreme periphery due to adhesions between the PDL and the residual stroma. Injection of air leads to separation of the PDL–DM–endothelium complex in toto from the residual stromal bed ( Fig. 9.1). This type 1 bb is created using a 30-gauge needle connected to a 5 mL syringe with the bevel up ( Fig. 9.2).

9.2.2 Type 2 Bubble

This type of bb is typically formed when the air enters the plane between the PDL and the DM–endothelium complex. A type 2 bb typically spreads from the periphery to the center and is around 10 to 11 mm in diameter. It extends up to the extreme periphery because there are no adhesions between the PDL and the DM ( Fig. 9.3). With the formation of this bb, it becomes essential to perform a DMEK instead of a PDEK procedure. Immense care should be taken when a type 2 bb is formed because it has a thin wall, and if it is subjected to excessive air push the bb can rupture leading to perforation of the graft and eventually transcending into donor tissue wastage.

9.2.3 Type 3—Mixed Bubble

When both type 1 and type 2 bbs are formed and they coexist, a mixed bubble is said to have been achieved. This is a type 3 big bb ( Fig. 9.4). These types of bbs pose a surgical challenge to the surgeon because they require delicate handling and manipulation to avoid bb rupture.

9.3 Surgical Technique

9.3.1 Donor Graft Preparation

Bubble Creation

The donor button with the corneoscleral rim is dissected from the whole cornea and is placed with the endothelial side up. For the process of bb creation, a 30-gauge needle is used that is attached to an air-filled 5 mL syringe. The needle is introduced with a bevel-up position from the periphery up to the midperipheral area at a considerable depth from the DM so as to create a plane of separation between the PDL and the residual stroma ( Fig. 9.5a). If one does not get a bb after repeated attempts (more than 10 at least) with air one can try with fluid using the McCarey Kaufman (MK) medium or Optisol (Chiron Ophthalmics) or balanced salt solution (BSS). If a bb still does not form then the surgeon can use visocoelastic. Air is injected and a dome-shaped type 1 bb is formed that is approximately 8 mm in diameter.

Graft Staining

The graft is stained with trypan blue that allows a considerable clear visualization of the graft. The bb is penetrated with a side-port blade at the extreme periphery ( Fig. 9.5b), and trypan blue is injected inside ( Fig. 9.5c). The bb is then cut all across the periphery with corneoscleral scissors ( Fig. 9.5d) and is placed in the storage media. The donor graft is loaded onto the injector when ready for insertion ( Fig. 9.6).

9.3.2 Recipient Bed Preparation

The procedure is performed under local anesthesia with supplemental anesthesia administered as necessary.

In cases of bullous keratopathy, the initial step consists of scrapping and debridement of the epithelium. This facilitates an enhanced intraoperative view during the surgical procedure. An anterior chamber maintainer (ACM) or a trocar anterior chamber maintainer (TACM)6 is introduced in to the eye that is connected to the air pump. This helps to maintain adequate anterior chamber depth at all times, and it also ensures the appropriate shift between air and fluid infusion as and when required ( Fig. 9.7). A 2.8 mm corneal tunnel is made and two side port incisions are framed. With the anterior chamber completely inflated with air, the DM is scored and stripped using a reverse Sinskey hook. Inferior iridectomy is performed with a vitrectomy probe introduced from the corneal incision. This maneuver ensures prevention of pupillary block at a later stage.

9.3.3 Donor Graft Insertion

The graft is held gently with a nontoothed forceps and is placed into the cartridge of a foldable intraocular lens that is filled with BSS ( Fig. 9.7).7 Air infusion is stopped and the graft is gently injected into the anterior chamber through a clear corneal incision, avoiding wound-assisted implantation. Graft orientation is verified and the graft is gently unfolded using air and fluidics. Corneal indentation and massaging are also performed to facilitate the graft unrolling. Once the graft has partly unrolled, a small air bb is injected beneath the graft, which helps it to adhere to the corneal surface. The peripheral edges of the graft can be unrolled by gently manipulating it with a reverse Sinskey hook. Once the graft has fully unrolled, air infusion is started, which facilitates total adherence of the graft to the recipient bed. Corneal sutures are taken and there is complete closure of all wounds to achieve a well-formed anterior chamber in the postoperative period ( Fig. 9.8 and Fig. 9.9).

9.3.4 Postoperative Care

In the immediate postoperative period, the patient is advised to lie in a supine position for approximately 3 hours and to continue doing so for most of the day. Slit lamp examination confirms the graft centration and location. On the second postoperative day, intraocular pressure is checked and the patency of the inferior iridectomy is confirmed. Topical antibiotics and steroids are prescribed, which are slowly tapered over a period of 4 months.

May 28, 2018 | Posted by in OPHTHALMOLOGY | Comments Off on Pre-Descemet Endothelial Keratoplasty
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