20 Spectral Domain Optical Coherence Tomography Evaluation of Pre-Descemet Endothelial Keratoplasty Graft

Pre-Descemet endothelial keratoplasty (PDEK), a recent modification of endothelial keratoplasty, involves the transplantation of the pre-Descemet layer (Dua layer) along with the Descemet membrane (DM) with endothelium. In this selective tissue transplantation, the pre-Descemet layer provides additional thickness to the thin DM. Dua et al1 describe the pre-Descemet layer as a tough, fibrous layer about 10.15 ± 3.6 µm. The technique allows easy intraoperative tissue handling and less injury to the donor harvested graft. The initial results showed good postoperative outcomes and fewer surgical complications.² The technique inherited the basic advantages of early visual rehabilitation and lowered graft rejection similar to DM endothelial keratoplasty (DMEK).^3,4 The postoperative graft position, seen clinically by slit lamp, but high-resolution spectral domain optical coherence tomography (SD-OCT) provides additional information in the configuration of endothelial grafts. This chapter describes the postoperative graft configuration using SD-OCT.

20.1.1 Pre-Descemet Endothelial Keratoplasty

A corneoscleral disc with an approximately 2 mm scleral rim is dissected from the whole globe or obtained from an eye bank. A 30-gauge needle attached to a syringe is inserted from the limbus into the midperipheral stroma (► Fig. 20.1a). Air is slowly injected into the donor stroma until a type 1 big bubble is formed (► Fig. 20.1a, b). Trephination is done along the margin of the big bubble. The bubble wall is penetrated at the extreme periphery and trypan blue is injected to stain the graft, which is then cut with a pair of corneoscleral scissors and is covered with the tissue culture medium (► Fig. 20.1c).

Under peribulbar anesthesia, a trephine mark is made on the recipient cornea respective to the diameter of the DM to be scored on the endothelial side. A 2.8 mm tunnel incision is made at 10 o’clock near the limbus. The anterior chamber (AC) is formed and maintained with saline injection or infusion. The margin of recipient DM to be removed is scored with a reverse Sinskey hook and then peeled (► Fig. 20.1d, e). The donor lenticule (endothelium–DM–pre-Descemet layer) roll is inserted in the custom-made injector (► Fig. 20.1e, f) and is injected in a controlled fashion into the AC (► Fig. 20.1g). The donor graft is oriented endothelial side down and positioned onto the recipient posterior stroma by careful, indirect manipulation of the tissue with air and fluid (► Fig. 20.1h). Once the lenticule is unrolled, an air bubble is injected underneath the lenticule to lift it toward the recipient posterior stroma (► Fig. 20.1i). The AC is completely filled with air for the next 30 minutes, followed by an air–liquid exchange to pressurize the eye. The eye speculum is finally removed and the AC is examined for air position. The patient is advised to lie in a strictly supine position for the next 3 hours.

20.1.2 Spectral Domain Optical Coherence Tomography

Postoperative SD-OCT scans were performed by an experienced examiner, and the scans were evaluated by expert ophthalmologists. An anterior segment five-line raster pattern in an axis of 0 to 180 degrees and 90 to 270 degrees was used. The raster scan had five lines (length 3 mm) and 250 µm distance between the lines. The scan was centered at the corneal vertex for a central 3 mm scan. Additional inferior, temporal, nasal, and superior positional scans were also taken. Graft thickness (GT) was measured in micrometers with the tool caliper in the SD-OCT. Graft detachment was graded as group I for completely attached grafts or minimal edge detachment; group II for graft detachments less than one-third of the graft surface area, not affecting the visual axis; group III for graft detachments more than one-third of the graft surface area; and group IV for completely detached grafts. Epithelial thickness and recurrence of bulla were noted. The graft–host junction was visualized for interface opacification. A graft split was defined as the separation of the pre-Descemet layer and the DM. Postoperative central corneal thickness (CCT) was also measured in all follow-ups. Twelve eyes of 12 patients with mean age 65 ± 3.8 years were evaluated. There were nine women and three men. The donor age ranged from 1 to 56 years. The graft size ranged from 7.5 mm to 8 mm. All the eyes had preoperative pseudophakic bullous keratopathy as the indication for endothelial transplantation.

20.1.3 Pre-Descemet Endothelial Keratoplasty Graft in Optical Coherence Tomography

The mean GT in PDEK was 37.3 ± 3.5 µm (range 32–44 µm). The graft undergoes minimal dehydration in the postoperative period. The mean GT on day 7, day 30, and day 90 was 35.5 ± 3.4 µm (32–40 µm), 33 ± 1.8 µm (32–36 µm), and 30.3 ± 2.6 µm (28–36 µm), respectively. There was a significant difference in the GT over the time period (Friedman test, p = 0.000) (► Fig. 20.2). There was no significant difference (p = 1.000) between the central (3 mm) and peripheral (4–6 mm) GT. The graft was well adhered (► Fig. 20.3) in 9 of 12 eyes on day 1. Two eyes had group II detachment (► Fig. 20.4), and 1 eye had group III graft detachment (► Fig. 20.5). One eye with grade III detachment underwent air injection. The graft was well apposed on post–air injection day 1; however, there was redetachment on day 12, and bubbling was redone subsequently. In group I eyes with a well-adhered graft, a small, shallow, peripheral detachment was seen in the inferior (2 eyes) and nasal quadrant (1 eye). The mean detachment depth was 24.6 ± 8.3 µm. Descemet folds were noted in 2 eyes on day 1 (► Fig. 20.6), which resolved on day 7 with medical management and supine position. A smooth, concave configuration of the posterior cornea was obtained in all eyes by 1 month. None of the eyes had complete graft detachment or lenticular drop.

Fig. 20.1 Pre-Descemet endothelial keratoplasty. (a) Type 1 bubble is formed in the donor cornea by injecting air via 30-gauge needle. (b) Trypan blue is injected into the bubble. (c) Trephination is done and the graft is cut with a pair of corneal scissors. (d,e) The margin of recipient Descemet membrane to be removed is scored with a reverse Sinskey hook and then peeled. (f) Donor lenticule roll is inserted in the custom-made injector and (g) is injected in a controlled fashion into the anterior chamber. (h) The donor lenticule is positioned onto the recipient posterior stroma and unrolled with air and fluid. (i) Finally an air bubble is injected underneath the lenticule to lift it toward the recipient posterior stroma and followed by air–fluid exchange.

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