In Descemet-stripping (automated) endothelial keratoplasty (DSEK/DSAEK), the diseased endothelium is replaced with a graft consisting of a thin layer of posterior stroma, Descemet membrane, and endothelium.1 When DSEK/DSAEK was first introduced, graft insertion was performed using a McPherson forceps to position a bifolded, “taco-shaped” donor posterior corneal disk over a plastic glide into the recipient anterior chamber.2–6 Busin7,8 described a technique in which the donor tissue is pulled into the anterior chamber with an instrument introduced through an incision at the opposite limbus. Recently, others9–12 have described the use of a pulling suture and a cartridge system to deliver the graft into the anterior chamber.
Push-in techniques may subject the graft to uncontrolled vertical tissue compression and pull-through techniques, to uncontrolled horizontal tissue compression. Both may result in donor tissue damage, particularly endothelial cell loss.7–15 The pull-through techniques that have been described may induce additional trauma to the recipient tissues; for example, by requiring a secondary incision. We describe a 30-gauge needle insertion technique in which the advantages of a single incision push-in technique are combined with those of a pull-through technique, thereby minimizing donor tissue damage.
A self-sealing 5.0 mm scleral tunnel incision is made at 12 o'clock using a crescent knife. Two side-port incisions are made at 10:30 and 13:30 with a surgical knife. Through a side port, the anterior chamber (AC) is filled with air using an air cannula. Under air, a descemetorhexis is performed using a reversed Sinskey hook (D.O.R.C. International). With a slit knife, the superior incision is then completed into the AC and a plastic glide, 3.0 mm in width and with an anterior concave curve, is positioned through the incision extending into the AC.
A corneoscleral rim with a manually pre-cut dissection plane at approximately 90% stromal depth is then placed on a punch block and an 8.5 or 9.0 mm diameter donor posterior lamella is trephined. A drop of an ophthalmic viscosurgical device is applied to the endothelial surface and with a fine forceps, the lamella is folded over 50/50, similar to a taco. A drop of trypan blue (VisionBlue 0.06% ophthalmic solution, D.O.R.C. International) is applied to the stromal (outside) surface to improve visualization of the graft during implantation. The folded graft is then placed on the plastic glide with the hinge located nasally.
With a needle holder, a 30-gauge needle is bent slightly at the distal third to create a curve (Figure 1). The upper wound lip is lifted with a Colibri forceps and with the needle, the folded graft is positioned just in front of the incision. The needle tip is then placed at the inferior end of the hinge; ie, at the edge of the graft facing the incision (Figure 2, A). With the curve of the needle facing anteriorly, the graft is inserted into the AC by moving the needle toward the 6 o'clock position (Figure 2, B). Moving the needle along an inferotemporal arc and then removing the glide along a superonasal arc brings the graft from a 50/50 into a 60/40 or 70/30 position to facilitate unfolding the graft (Figure 2, C).
The anterior and posterior lips of the graft are thoroughly rinsed with balanced salt solution, with the cannula approaching the graft from the hinge. With gentle irrigation of the AC, the graft lips are separated and an air bubble is positioned inside the taco. With the 30-gauge needle, the graft is then unfolded by moving the needle temporally at the superior stromal interface (between the graft and the host).
The needle graft insertion technique was performed in 15 consecutive eyes of 15 patients. Six months after surgery, the mean manually corrected endothelial cell density (ECD) (Topcon SP3000p noncontact autofocus specular microscope) was 1940 cells/mm2 ± 560 (SD) (n = 14). The mean preoperative ECD (Axiovert 40 inverted light microscope, Zeiss) measured in the eyebank was 2675 ± 270 cells/mm2 (n = 14) (Table 1).
Initially, graft insertion in DSEK/DSAEK was performed with a McPherson forceps.1–3 Although this instrument offers the advantage of firm control over the graft during its insertion into the AC, the use of forceps may have 3 disadvantages. First, vertical compression of the donor tissue may induce endothelial cell damage, especially because surgeons are accustomed to providing counterpressure with a forceps while inserting foldable intraocular lenses.11,13 Second, a forceps acts contraintuitively at retraction from the AC since the legs of the instruments have to be opened vertically to “release” the donor tissue, while the horizontal incision tends to “close” the legs at the same time. As a result, the forceps may catch the tissue so the graft is pulled back again toward or into the incision. Third, during implantation, the donor tissue obscures the posterior leg of the implantation forceps, creating a risk for damaging underlying intraocular structures, in particular the crystalline lens in phakic eyes.
To overcome these problems, several authors have described a method to pull the DSEK/DSAEK graft into the anterior chamber; for example, pulling the graft across the AC with a forceps entering the AC at the opposite limbus or with a suture similar to McCannell sutures for iris reconstruction.7–14 However, pull-through techniques may also have disadvantages. Grasping the graft with a forceps extending across the AC requires a secondary incision and may damage the iris and/or crystalline or synthetic intraocular lens. Suture placement through the edge of a graft is time consuming and may introduce additional risk for uncontrolled damage to the donor endothelium.
Although no correlation between graft thickness and final best corrected visual acuity has been reported in DSEK cases,16 the visual outcome in DMEK strongly suggests that thinner grafts provide better clinical results.17 For this reason, posterior grafts may be manually dissected at 40 to 70 μm to obtain the best possible outcome in DSEK. These thin DSEK grafts are too floppy to be handled by forceps and would make suture placement challenging. We therefore started using a 30-gauge needle to hook the thin DSEK graft on the stromal side to gently insert it over a glide into the recipient AC. Because the needle enters the donor stroma in a 12 to 6 o'clock direction, retraction of the needle in a 6 to 12 o'clock direction is smooth as the needle does not get stuck in the tissue.
Because the 30-gauge needle can be used to grasp the folded graft at its inferior edge, the actual insertion of the tissue into the AC mimics the maneuver of a pull-through technique. At the same time, needle graft insertion does not require additional manipulation of the donor and/or host tissues. Therefore, the insertion of a posterior graft with a 30-gauge needle may combine the advantages of a push-in technique with those of a pull-through technique. It is simple and safe because the position of the needle at the stromal interface can be monitored during the entire insertion and also inexpensive and readily available because no special instruments are required.
Although we documented donor ECD before and after surgery, a direct comparison may require caution. In Europe, donor corneas are often evaluated in vitro with light microscopy (unlike systems in the United States that use specular microscopy), whereas the postoperative in vivo measurements are performed with specular microscopy. Because the preoperative and postoperative measurements are not performed using the same method, a direct comparison of cell density measurements may not be valid.
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