Disclosures: Agarwal, Narang and John report no relevant financial disclosures.
April 15, 2020
5 min read
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Surgeons provide update on pre-Descemet’s endothelial keratoplasty

The ease of graft unrolling and the use of young donor tissue are distinct advantages with PDEK.

Disclosures: Agarwal, Narang and John report no relevant financial disclosures.
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Endothelial keratoplasty has revolutionized corneal transplantation. The menu that is available for the corneal surgeon now includes Descemet’s membrane endothelial keratoplasty, Descemet’s stripping endothelial keratoplasty and pre-Descemet’s endothelial keratoplasty.

Thomas "TJ" John
Thomas “TJ” John

While in DMEK there is no stromal tissue in the donor corneal disc with healthy donor endothelium, in DSEK and PDEK there is stromal tissue in the donor disc, greater in DSEK than in PDEK. The presence or absence of the stromal tissue plays a role in the degree of donor disc rigidity and its effect on tissue unrolling within the recipient anterior chamber before air-assisted attachment of these donor discs to the recipient inner corneal dome. The surgeon needs to be familiar with the surgical maneuvers associated with the unrolling of these different types of donor scrolls to facilitate the surgical procedure with the least amount of potential surgical trauma to the donor endothelium. Additionally, as one goes from DMEK to PDEK to DSEK, the donor-recipient interface moves upward from the Descemet’s membrane into the stroma. While DMEK and DSEK usually deal with relatively older donor corneal tissue, PDEK can expand the pool of the donor age group to include younger donor corneal tissue. These surgical advances in endothelial keratoplasty have provided the corneal surgeon with more choices when dealing with endothelial decompensation and visual impairment.

In this column, Drs. Narang and Agarwal provide a surgical update on PDEK and useful tips for this endothelial keratoplasty procedure.

Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor

Pre-Descemet’s endothelial keratoplasty emerged in 2013 in collaboration with Harminder Dua, MD, PhD, who put forward clinical evidence of the presence of Dua’s layer, or pre-Descemet’s layer (PDL), in human corneal tissue. After the documentation of surgical success with adult donor tissue, the feasibility of young and infant donor corneas was also reported with PDEK. The latter aspect sets PDEK surgery apart from other endothelial keratoplasty procedures as the use of young donor corneas has the inherent advantage of greater endothelial cell count and represents a new source of corneal donor tissue that was not considered to be feasible previously.

Donor graft

PDEK bubble.
Figure 1. PDEK bubble. A 30-gauge needle enters the sclera into the stroma of the cornea, injecting air to create a type 1 big bubble (a). Knife entry into the big bubble (b). Trypan blue injected inside the bubble (c). Scissors dissect the PDEK graft (d).

Source: Priya Narang, MS, and Amar Agarwal, MS, FRCS, FRCOphth

PDEK surgery in a one-eyed patient, part 1
Figure 2. PDEK surgery in a one-eyed patient, part 1. Pseudophakic bullous keratopathy with silicone oil in the eye (a). Silicone oil removal (b). Single-pass four-throw pupilloplasty (c). Descemetorhexis (d).

With the evolution of PDEK surgery, there emerged the concept of the type 1 bubble that involves the endothelium, Descemet’s layer and PDL (Figure 1). A 5 mL air-filled syringe attached to a 30-gauge needle in bevel-up position is introduced from the limbus up to the center of the corneal stroma, and air is injected. The type 1 bubble is a central dome-shaped bubble that typically spreads from center to mid-periphery and has distinct edges around the periphery. The splinting effect of the PDL provides extra stability to the graft and prevents it from being flimsy and difficult to unroll. The peripheral edge is punctured with a side-port blade, and the graft is stained with trypan blue. The graft is then cut all around the periphery with corneoscleral scissors (Figure 1) and is stored in the tissue culture media.

PDEK surgery in a one-eyed patient, part 2
Figure 3. PDEK surgery in a one-eyed patient, part 2. PDEK graft injected inside the anterior chamber (a). Graft unrolled and checked if it is right side up (b). Air injected inside the eye to fix the center of the graft, and then the air pump is switched on (c). PDEK graft unrolled fully using reverse Sinskey hook for the peripheral edges (d).
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Surgical maneuver

PDEK surgery in a one-eyed patient, part 3
Figure 4. PDEK surgery in a one-eyed patient, part 3. Preoperatively, pseudophakic bullous keratopathy with silicone oil in the eye (a). Vision at 9 months postop is 6/18. Surgery done: Silicone oil removal with single-pass four-throw pupilloplasty and PDEK (b). Fellow eye: No light perception (c).
PDEK surgery with glued IOL, part 1
Figure 5. PDEK surgery with glued IOL and single-pass four-throw pupilloplasty, part 1. Pseudophakic bullous keratopathy with anterior chamber IOL (a). Scleral flaps prepared for glued IOL (b). Anterior chamber IOL explantation after vitrectomy (c). Glued IOL (d).

In complicated cases with decentered IOLs and corneal decompensation, a combined procedure is performed wherein the IOL is explanted and a three-piece IOL is placed with the glued IOL technique. In eyes with pupillary defect, a pupilloplasty procedure is advocated as it helps to prevent the slippage of air in the posterior chamber, thereby facilitating donor graft adherence (Figures 5 to 7).

The recipient bed is prepared, and descemetorhexis is performed. The PDEK graft is loaded onto the cartridge of a foldable IOL, and the graft is injected inside the anterior chamber. The donor lenticule is unrolled using air and fluidics (Figures 2 to 4).

PDEK surgery with glued IOL, part 2
Figure 6. PDEK surgery with glued IOL and single-pass four-throw pupilloplasty, part 2. Single-pass four-throw pupilloplasty (a). Double-infusion cannula fixed (b). Descemetorhexis (c). PDEK graft unrolled fully using a reverse Sinskey for the peripheral edges (d).

Donor graft visualization

The haze of the recipient cornea often bars visualization of the donor graft, which is a critical step because the graft needs to be oriented and unfolded correctly. In order to overcome this, the visualization of the donor graft can be enhanced by staining it with dye and also by usage of an endoilluminator or oblique light being projected onto the surface of the cornea.

PDEK surgery with glued IOL, part 3
Figure 7. PDEK surgery with glued IOL and single-pass four-throw pupilloplasty, part 3. Preoperatively, pseudophakic bullous keratopathy with anterior chamber IOL (a). Vision at 3 months postop is 6/9. Surgery done: Anterior chamber IOL explantation with glued IOL, single-pass four-throw pupilloplasty and PDEK (b).

Pressurized infusion in anterior chamber

Donor graft adherence is another important aspect of the surgery. The surgeons often use pressurized infusion of air inside the anterior chamber once the graft has correctly unfolded. The air infusion pressure is monitored and maintained around 30 mm Hg to 40 mm Hg.

PDEK preop and postop
Figure 8. PDEK preop and postop. Preop, pseudophakic bullous keratopathy with corneal scarring (a). Postop at 45 days. Surgery done: Glued IOL with single-pass four-throw pupilloplasty and PDEK (b).

Double-infusion cannula technique

This technique involves placement of two infusion cannulas, one in the anterior chamber and the other in the posterior chamber, in cases that need to undergo a secondary IOL placement with PDEK. The anterior chamber cannula is used for air infusion whereas the posterior chamber cannula allows adequate fluid infusion inside the eye. This helps to maintain the tonicity of the eye and prevents deepening of the posterior chamber, which is not unusual in vitrectomized eyes.

Discussion

Studies have reported good visual outcomes with the PDEK procedure (Figure 8), with a percentage of endothelial cell loss that is comparable to other endothelial keratoplasty techniques. The average graft diameter achieved in PDEK is around 7 mm to 8 mm, and the average graft thickness varies from 25 µm to 35 µm.

The ease of graft unrolling and the use of young donor tissue are distinct advantages with PDEK. In addition, precut PDEK tissue is available, which can help surgeons overcome the issue of tissue loss.

Disclosures: Agarwal, Narang and John report no relevant financial disclosures.