Ординатура / Офтальмология / Английские материалы / Corneal Endothelial Transplant (DSAEK, DMEK & DLEK)_John_2010

Jacksonville, FL) QID may be used. In the USA, chloramphenicol drops are not used]. Patient is instructed to posture prone for 30 minutes. The patient should be examined the next day to ensure that DM is attached to the donor stroma.

Advantages

i.Tissue specific grafting and therefore potentially better visual outcome due to better interface quality. Less potential problems secondary to mismatch of corneal curvature. DM without a stromal carrier will conform easier to any corneal shape and adhere well to the host’s posterior stromal surface.

ii.As in DSEK, TEnCell transplantation preserves the recipient corneal architecture as it does not involve dissection of the host’s posterior stroma.

iii.TEnCell transplantation preserves tectonic form and results in a more robust eye compared to a PK. With present instrumentation, the wound construction is approximately 8.0 mm long and a limbal or scleral section can be used.

iv.As TEnCell requires fewer sutures compared to a PK, there is less induced astigmatism. Sutures can be safely removed after 3 months.

v.The thin, flexible donor button produced by this technique may enhance the rate of successful attachment onto the recipient cornea.

vi.Like PLK, DLEK and DSEK, TEnCell transplantation offers rapid visual recovery with excellent visual results.

vii.The procedure can be repeated in cases of primary endothelial cell failure.

viii.The procedure can be performed under local anesthesia.

Figure 36-23: Anterior segment photograph demonstrating the difference in corneal clarity and thickness between grafted and diseased endothelium.

ix. Inexpensive equipment is required. There is potential for its use in developing countries.

Disadvantages

i.Very new technique.

ii.Steep learning curve.

iii.Requires good quality donor tissue for successful harvesting.

iv.At present, the wound is larger (8 mm) compared to other methods of PLK requiring sutures.

Complications

•During harvesting

o Tearing of harvested tissue at the edges of Schwalbe’s line.

o Drying of DM during harvesting. This can be avoided if the tissue is kept moist with balanced salt solution.

•During implantation

o Loss of tissue during insertion in the AC o Tissue wrinkling

o Tissue decentration.

•During withdrawal of the cannula

o Detachment or loss of tissue during withdrawal from the AC.

•During suturing

o Detachment of tissue and incarceration into the suture tract.

o Loss of air-bubble.

Early Postoperative Complications

The most common complication is detachment of the harvested tissue. If the detachment is partial, the tissue can be reattached by reinflation of the AC with air.

If the tissue is completely detached, the endothelium tends to form a scroll which can be difficult to reapply. In this situation, we have found it necessary to repeat the procedure. While waiting for repeat surgery, the patient develops marked corneal edema. The application of a bandage contact lens is advisable until further surgery is performed.

Pupil block glaucoma can be an early postoperative complication as a result of over-inflation of the AC with air.

Late Complications

There have been no cases of endothelial cell rejection so far, although this clearly remains a possibility.

Case Example

A 68-year-old male patient with Fuchs’ endothelial dystrophy underwent routine small incision cataract extraction with foldable intraocular lens implantation. Visual rehabilitation was complicated by corneal decompensation. Patient underwent a TEnCell transplantation.

His preoperative best corrected visual acuity was 6/18. The central corneal thickness was 750 μm. No endothelial cell count could be obtained due to significant corneal edema.

The first TEnCell transplant attempt was aborted because the endothelial harvest was unsuccessful. The second attempt two weeks later was uneventful and the transplantation was successful.

Postoperative best corrected visual acuity was 6/6, 19 months later. Central corneal thickness was 574 μm. Endothelial cell count was 649 cells/mm2. Figure 36-22 demonstrates the postoperative result and Figure 36-23

demonstrates the difference in corneal clarity between grafted and diseased endothelium.

The Future

TEnCell transplantation is a challenging new technique. Specific endothelial cell transplantation has been the aim of many corneal surgeons13-18 and this is the first in vivo description of such a technique. Subsequent transplantation has shown endothelial cell counts of up to 2000 cells/ mm2.

Recent work has shown that cultivation and transplantation of human cultured endothelial cells in an animal model is feasible.19 TEnCell tranplantaion may find an application in the transplantation of layers of cultured endothelial cells into human eyes.

The experience is still limited due to the small number of patients treated, but as the numbers increase and as new instrumentation becomes available, our belief is that TEnCell transplantation may become more widely adopted, offering potentially excellent visual outcomes for the patient.

References

1. Melles GR, Eggink FA, Lander F, Pels E, Rietveld FJ, Beekhuis WH, Binder PS. A surgical technique for posterior lamellar keratoplasty. Cornea 1998;17(6):618-26.

2. Terry MA, Ousley PJ. Deep lamellar endothelial keratoplasty in the first United States patients: Early clinical results. Cornea 2001;20(3):239-43.

3. Price FW Jr, Price MO. Descemet’s stripping with endothelial keratoplasty in 50 eyes: A refractive neutral corneal transplant. J Refract Surg 2005;21(4):339-45.

4. Price FW Jr, Price MO. Descemet’s stripping with endothelial keratoplasty in 200 eyes: Early challenges and techniques to enhance donor adherence. J Cataract Refract Surg 2006;32(3):411-8.

5. Price MO, Price FW Jr. Descemet’s stripping with endothelial keratoplasty. Comparative outcomes with microkeratomedissected and manually dissected donor tissue. Ophthalmology 2006; [Epub ahead of print].

6. Melles GR, Remeijer L, Geerards AJ, Beekhuis WH. The future of lamellar keratoplasty. Curr Opin Ophthalmology 1999; 10(4):253-9.

7. Yeh PC, Azar DT, Colby K. Selective endothelial transplantation: Novel surgical techniques for the treatment of endothelial dysfunction. Int Ophthalmol Clin 2004;44(1):51-66.

8. Tappin M. A method for true endothelial cell (Tencell) transplantation using a custom-made cannula for the treatment of endothelial cell failure. Eye 2006; [Epub ahead of print].

9. Spence DJ, Peyman GA. A new technique for the vital staining of the corneal endothelium. Invest Ophthalmol 1976;15(12): 1000-2.

10. Taylor MJ, Hunt CJ. Dual staining of corneal endothelium with trypan blue and alizarin red S: Importance of pH for the dyelake reaction. Br J Ophthalmol 1981;65(12):815-9.

11. Singh G, Bohnke M, von-Domarus D, Draeger J, Lindstrom RL, Doughman DJ. Vital staining of corneal endothelium. Cornea 1985-1986;4(2):80-91.

12. Melles GR J, Wijdh RHJ, Nieuwendaal MD. A technique to excise the Descemet’s membrane from a recipient cornea (Descemetorhexis). Cornea 2004;23(3):286-8.

13. Jumblatt M, Maurice M, McCulley J. Transplantation of tissuecultured corneal endothelium. Invest Ophthalmol Vis Sci 1978;17:1135–41.

14. Gospodarowicz D, Greenburg G, Alvarado J. Transplantation of cultured bovine corneal endothelial cells to rabbit cornea: Clinical implications for human studies. Proc Natl Acad Sci USA 1979;76:464–8.

15. Maurice D, McCulley J, Perlman M. Development in use of cultured endothelium in corneal transplantation. Doc Ophthalmol Proc Ser 1979;20:151–3.

16. Behrens K, Ellis L, Li PM, Sweet RS Chuck. Endothelial lamellar keratoplasty using an artificial anterior chamber and a microkeratome. Arch Ophthalmol 2003;21:503-8.

17. Mohay J, Lange TM, Soltau JB, Wood TO, McLaughlin BJ. Transplantation of corneal endothelial cells using a carrier device. Cornea 1994;13:173–82.

18. McCulley JP, Maurice DM, Schwartz BD. Corneal endothelial transplantation. Ophthalmology 1980;87:194–201.

19. Mimura T, Yamagami S, Yokoo S, Usui T, Tanaka K, Hattori S, Irie S, Miyata K, Araie M, Amano S. Cultured human corneal endothelial cell transplantation with a collagen sheet in a rabbit model. Invest Ophthalmol Vis Sci 2004;45(9): 2992-7.

Introduction

Corneal transplantation surgery has achieved new heights in terms of advanced surgical techniques used by corneal surgeons where only the diseased portion of the cornea is replaced by a similar healthy donor corneal tissue. This is in contrast to penetrating keratoplasty where the fullthickness of the cornea is replaced regardless of the corneal layer that is involved in the disease process. A new terminology is called selective tissue corneal transplantation (STCT) that is defined as the selective removal of the diseased portion of the patient’s cornea and its replacement with anatomically similar healthy donor tissue.1 The newer surgical technique of corneal transplantation namely, Descemet stripping automated endothelial keratoplasty (DSAEK)2-4 has gained worldwide acceptance and is rapidly becoming the preferred surgical choice for dealing with corneal endothelial decompensation resulting in corneal edema, bullous keratopathy and loss of best corrected visual acuity. This type of surgical procedure is an example of STCT. This procedure, namely DSAEK, is an additive procedure where the postoperative corneal thickness far exceeds the range of normal corneal thickness and the donor-recipient interface is a stroma-to-stroma interface. The newer technique of STCT described by Melles et al5 is called Descemet membrane endothelial keratoplasty (DMEK) where only the Descemet’s membrane and endothelium of the patient’s cornea is replaced by a similar healthy donor corneal tissue. This is a more “natural” form of STCT where the postoperative corneal thickness should be within the range of normal corneal thickness and donorrecipient interface is Descemet’s membrane to stroma, a more “natural” final anatomic result. However, DMEK has its challenges in terms of the surgical techniques involved in this new procedure.

This chapter describes a surgical technique of performing DMEK with emphasis in simplifying the surgical technique, that may help in gradually moving DMEK over time, to the forefront of STCT for endothelial decompensation. The technique is based on the concept of the “big bubble”, which was used by Anwar and Teichman2,3 to dissect the corneal stroma from the underlying Descemet’s membrane and endothelium when performing anterior lamellar keratoplasty for keratoconus. Busin’s technique described in this chapter is substantially different in many ways, but like the “big bubble” technique for keratoconus, air is used to achieve a complete dissection between the donor Descemet’s membrane and corneal stroma. This surgical technique described below, includes both harvesting the donor tissue and delivering it into place and attaching it to the patient’s cornea.

Surgical Technique

The preferred anesthesia is with a peribulbar block. However, other forms of anesthesia including general anesthesia may be considered by the surgeon.

Step-by-Step Surgery

The initial surgical step involves the removal of Descemet’s membrane and endothelium from the central part (8.0 to 9.0 mm in diameter) of the posterior surface of the recipient cornea (Figure 37-1). Then, the donor cornea is mounted in an artificial anterior chamber and about 2/3rd of the anterior corneal stroma is removed using a microkeratome, the same way it is done when performing DSAEK surgery (Figure 37-2). This step is not essential, but allows the

Figure 37-1: Intraoperative photograph showing the removal of patient’s Descemet membrane and endothelium from the central part (8 to 9 mm in diameter) of the posterior surface of the cornea.

Figure 37-2: The donor cornea is mounted within an artificial anterior chamber and about 2/3rd of the anterior corneal stroma is removed using a microkeratome the same way it is done when performing DSAEK surgery.

Figure 37-3: A 25 gauge needle connected to a 5.0 cc sterile syringe is inserted, bevel up, into the peripheral donor cornea, 1.0 mm from the limbus, and advanced in a tangential direction immediately beneath the endothelium for about 2.0 mm.

Figure 37-6: Part of the air is removed from the bubble by using an empty syringe with a 30 gauge needle and achieves a partial collapse of the big-bubble.

Figures 37-4 and 37-5: Air is then injected until detachment of Descemet membrane is achieved and a large bubble is obtained.

surgeon to convert to DSAEK, in case he does not succeed in preparing the endothelial graft. Then the donor cornea is removed from the artificial anterior chamber and placed with the endothelium facing up. Next, a 25 gauge needle connected to a 5.0 cc sterile syringe is inserted, bevel up, into the peripheral donor cornea at about 1.0 mm from the limbus and advanced in a tangential direction immediately beneath the endothelium for about 2.0 mm (Figure 37-3). Air is then injected until detachment of Descemet membrane is achieved and a large bubble is obtained (Figures 37-4 and 37-5).

Next, the surgeon removes part of the air from the bubble by using an empty syringe with a 30 gauge needle and achieves a partial collapse of the big-bubble (Figure 37-6). The same needle is used to inject few drops of trypan blue (Vision Blue) into the air-bubble (Figure 37-7). Finally aspirate all the air still present in the space created by the big-bubble (Figure 37-8). As a result of the total bubble collapse, the trypan blue stain outlines the portion of Descemet membrane that is detached from the donor corneal stroma and allows for subsequent, precise punching (trephination) inside the outer limit of dissection. An 8.0 to 9.0 mm trephine is used to punch the donor corneal tissue. Pressure is maintained, while moving the sclerocorneal rim with forceps, thus achieving total detachment of the central donor tissue from the peripheral part of the donor cornea (Figure 37-9). The donor disk obtained using this technique, consists of deep, often thicker, because air-blown corneal stroma and overlying detached Descemet’s membrane and healthy donor corneal endothelium. The stromal disk is held with forceps, which serves as a carrier for the donor endothelium, and the tissue

Figure 37-7: A few drops of trypan blue (Vision Blue) is injected into the air-bubble created within the donor cornea.

Figure 37-8: All the air is aspirated within the space created by the big-bubble.

as a whole is transported onto the plate of the Busin glide. It is then advanced through the distal part of the glide and the thin donor disk is pulled gently until it protrudes out of the funnel of the Busin glide (Figure 37-10). Finally, a coaxial microincision retinal forceps is used to drag the donor graft into the anterior chamber through a nasal clear-cornea incision with a bimanual “pull-through” maneuver similar to that used for DSAEK surgery (Figure 37-11). This entire surgical step is performed under continuous irrigation through an anterior chamber maintainer placed at the 12 o’clock position.

As the endothelium is lying flat on the stroma all the time, the risk of inserting it upside down is minimized with this maneuver. An additional advantage of this technique is that the bubble formation counteracts the natural

Figure 37-9: Pressure is maintained, while moving the sclerocorneal rim with forceps, thus achieving total detachment of the central donor tissue from the peripheral part of the donor cornea.

Figure 37-10: The thin donor disk is pulled gently until it protrudes out of the funnel of the Busin glide.

Figure 37-11: A coaxial micro-incision retinal forceps is used to drag the donor graft into the anterior chamber through a nasal clear-cornea incision with a bimanual “pull-through” maneuver.

Figure 37-12: The donor tissue floats as a flat membrane inside the anterior chamber and does not require complex manipulation to unroll it.

Figure 37-13: The recipient anterior chamber is air filled after closing all the corneal incisions with interrupted 10-0 nylon suture.

tendency of the endothelial layer to roll onto itself. As a result, the donor tissue floats as a flat membrane inside the anterior chamber and does not require complex manipulation to unroll it (Figure 37-12). The final step is the air fill, which is completed after closing all the corneal incisions with interrupted 10-0 nylon suture ((Figure 3713). The air in the air-filled anterior chamber is allowed to reabsorb spontaneously over time (usually 2-3 days). To prevent a pupillary block, a peripheral iridectomy is performed inferiorly before delivering the donor tissue into the recipient anterior chamber.

Surgical Pearls and Tips

1.DMEK graft tends to curl with the endothelium inward. It is important to recognize the correct tissue orientation prior to attaching the donor tissue to the recipient cornea.

2.Trypan blue staining helps in the proper orientation of the donor tissue and in the centration of the donor disc to the patient’s cornea.

Postoperative Follow-up/Drug

Regimen

Postoperative medications are the same as for penetrating keratoplasty or DXEK/DSAEK as per surgeon’s choice, namely, topical steroid and antibiotic drops qid.

References

1. John T (Editorial). Selective tissue corneal transplantation: A great step forward in global visual restoration. Expert Rev Ophthalmol 2006;1:5-7.

2. John T. Surgical Techniques in Anterior and Posterior Lamellar Corneal Surgery. New Delhi, India: Jaypee Brothers Medical Publishers; 2006.

3. John T. Step by Step in Anterior and Posterior Lamellar Keratoplasty. New Delhi, India: Jaypee Brothers Medical Publishers; 2006.

4. Ide T, Yoo SH, Kymionis GD, Goldman JM, Pereez VL, O’Brien TP. Descemet-stripping automated endothelial keratoplasty: Effect of anterior lamellar corneal tissue-on/-off storage condition on Descemet-stripping automated endothelial keratoplasty donor tissue. Cornea 2008;27:754-7.

5. Melles GR, Ong TS, Ververs B, van der Wees J. Descemet membrane endothelial keratoplasty (DMEK). Cornea 2006; 25:987-90.