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

Moria ACC there is no control of the amount of corneal tissue that is exposed within the ring. Hence the diameter of tissue resection is determined by the diameter of the blade in the Hanna trephine. The Barron vacuum trephine does not seat optimally on the Moria ACC and hence proper trephination cannot be carried out with the Barron trephine in a Moria ACC.

For automated donor corneal lamellar disk, the Moria ALTK system is used that utilizes both the Evolution3 console and the microkeratome described above. The Moria ALTK system utilizes a different design for its ACC (Figure 12-1). This ACC has the capability of raising or lowering the mounted donor corneo-scleral button (Figure 12-1), thus altering the final diameter of the resected donor tissue. The diameter can be approximated by using the applanating lenses. The diameter by measurement on the donor cornea, does not necessarily match exactly with the final resected donor lamellar disk. Hence, it may be better to resect the donor tissue first before using the microkeratome on the recipient cornea.

Figure 12-1: The Moria ALTK system utilizes an ACC that has the capability of raising or lowering the mounted donor corneo-scleral button, thus altering the final diameter of the resected donor tissue.

Figure 12-2: The Moria ALTK system comprises of an artificial chamber that has a central post on which the donor corneoscleral button is placed with the endothelial side down after injecting Optisol solution from the donor corneal vial.

Figure 12-3: The Moria ACC encasing cylindrical unit with the central opening for the donor cornea.

The Moria ALTK system comprises of an artificial chamber that has a central post (Figure 12-2) on which the donor corneoscleral button is placed with the endothelial side down after injecting Optisol solution from the donor corneal vial. Next the encasing cylindrical unit with the central opening for the cornea (Figure 12-3) is moved into place such that the three posts (Figure 12-3) descend into the corresponding slots in the base of the ACC unit, taking care to maintain the central position of the donor cornea. Turning this encasing unit in a clockwise fashion locks it in place and the donor corneoscleral button is now firmly mounted on to this ACC, with uniform pressure being applied to 360° of the scleral rim. Titrate as needed, the intrachamber pressure by injecting additional fluid from

the attached syringe into the chamber, and locking the valve if the pressure is low, or alternatively aspirate fluid from the chamber if the intrachamber pressure is too high. The pressure can be checked using a Barraquer tonometer as needed. Next depending on whether a LSK or CB microkeratome is used with this unit, the appropriate ring is chosen (Figure 12-4) and screwed on to the unit. The amount of corneal tissue being exposed can now be adjusted by turning the rings and raising or lowering the central post (Figure 12-1). The applanation lenses provide an estimate of the diameter to be resected, ranging from 6 to 11 mm (Figures 12-5A and B). Figure 12-6 is a composite showing the set-up for the LSK microkeratome on the left and for a CB unit on the right. The LSK microkeratome

Figure 12-4: The ring to the left is used with the Moria LSK microkeratome and the ring to the right is used with the Moria CB microkeratome.

A

B

Figures 12-5A and B: (A) Moria ALTK system with applanating lenses ranging from 6.0 to 9.0 mm in diameter. (B) Moria ALTK system showing sequential assembly prior to use.

Figure 12-6: Moria ALTK system showing sequential assembly for the Moria LSK microkeratome (left) and the Moria CB microkeratome (right).

(Figures 12-7A and B) or a CB microkeratome (Figure 12-8) can be used to complete the lamellar excision of the donor corneal disk.

In summary, the 3 steps to the use of Moria ALTK system are as follows (Figure 12-9):

1.First, the donor cornea is sealed within the ACC, and the intrachamber pressure is adjusted to the required level.

2.Second, the surgeon selects the desired diameter of the cut.

3.Lastly, perform the donor corneal resection.

The ALTK’s adjustability and versatility reduce the incidence of induced corneal astigmatism. In this system the high-speed, high-power turbine (30,000 cuts/minute) creates a smooth keratectomy for a seamless-edge margin. The single piece construction of the microkeratome heads are pre-calibrated for various depths of cut (130-400 µm).

Bausch and Lomb ACC

Bausch and Lomb (B&L) ACC (Figure 12-10) can be used for manual dissection of the donor lamellar corneal disk. It is not designed for use with a microkeratome. The B&L ACC can be used for both DLEK and for anterior lamellar keratoplasty.

It consists of a solid metallic rectangular base (Figure 12-10, labeled A), with a central post (Figure 12-10, labeled B) on which the donor corneoscleral rim is placed with the endothelial side down after applying viscoelastic material and fluid from the donor corneal vial. The central post has two openings for egress of fluid used to alter the intrachamber pressure. The metallic base has a circular space

A

B

Figures 12-7A and B: Moria LSK microkeratome being used with the Moria ALTK system.

surrounding the central post (Figure 12-10, labeled C) for collecting the fluid that egresses out of the two openings in the central post. Two metallic channels (Figure 12-10, labeled D) are attached to the central post on one end and to metallic valves on the other end where a syringe filled with fluid can be attached. Once the donor corneoscleral rim is placed on the central post and the intrachamber space is primed with fluid, the circular fixation ring (Figure 12-10, labeled E) is placed over the donor corneoscleral rim and the C-arm (Figure 12-10, labeled F) is moved forwards such that it is above the flange of the fixation ring. Once the

Figure 12-8: Moria CB microkeratome being used with the Moria ALTK system.

C-arm is in its extended position the screw (Figure 12-10, labeled G) is tightened and this fixates the donor cornea within the B&L ACC. The intrachamber pressure is optimized by injecting fluid from the attached syringe and closing the valve to maintain the chamber pressure. The unit is now ready for lamellar dissection. Unlike the Moria ACC where the fixation pressure on the donor corneoscleral rim is applied 360° directly from the top (Figures 12-1 and 12-3), in the B&L ACC the C-arm applied pressure only on the proximal 180° of the flange of the fixation ring (Figure 12-10, labeled E) and the fixation ring in turn transmits the pressure to the scleral rim.

A Barron radial vacuum trephine (Katena, Inc.) of the desired diameter is placed on the moistened, epithelial surface of the donor cornea and suction is applied to fixate the trephine. Partial thickness trephination to the desired corneal depth is followed by lamellar dissection of the donor cornea to obtain a lamellar donor corneal disk [See also Section VIII, Deep Lamellar Endothelial Keratoplasty (DLEK)].

Disposable ACC

Barron Disposable ACC (Katena, Inc., Denville, NJ, USA)

The Barron ACC (Figures 12-11 and 12-12) is sterile, disposable, and it comprises of three pieces, namely, base with tissue pedestal, tissue retainer, and a locking ring. The base has two parts with silicone tubing, in-line pinch

Figure 12-11: Barron disposable ACC (Katena, Inc.).

clamps, and female luer-lock connectors. Either port may be used to inject or aspirate balanced salt solution, solution from the donor corneal vial, viscoelastic or air.

This ACC is a companion to the disposable Barron radial vacuum trephine. This ACC allows for trephination from the epithelial side. It is designed to hold a donor cornea (14-18 mm) on a bed of viscoelastic. The bright blue color of the unit provides a high contrast background to view the cornea.

Useful Surgical Suggestions and

Avoiding Complications

1.The corneoscleral rim that is obtained from the eye bank should have adequate scleral rim 360° (see below) for proper housing and fixation within the ACC of any kind. If the scleral rim is short on any one side, this will lead to tissue slippage, loss of intrachamber pressure, fluid leakage from the unit and inability to perform an adequate lamellar dissection of the donor cornea.

2.A second back-up cornea from the local eye bank will be especially in the early learning stage of DSAEK surgery. However, currently most US eye banks charge-a-fee for the second cornea and hence this may not be an option for US surgeons. This will help complete the surgery if the first cornea is damaged during surgical dissection.

3.First dissect the donor cornea before operating on the recipient cornea.

4.If general anesthesia is used for surgery, the donor cornea can be prepared even before the patient is anesthetized. This will reduce the total time that the patient is under general anesthesia. Additionally, it will ascertain that a suitable lamellar corneal disk is ready for use even before the patient is anesthetized.

5.If there is tissue slippage and significant loss of intrachamber pressure, then it may be advisable to abandon the lamellar dissection and use the back-up cornea. Dissecting without proper stabilization of the donor cornea within the ACC, can result in multiplanar dissection, uneven interface, and more importantly, possible perforation of the lamellar disk.

6.If using the Moria ALTK system, check the blade and the microkeratome head before use and lubricate with BSS to limit any mechanical epithelial damage to the donor cornea.

7.If using the Moria ALTK system with the microkeratome, it is preferable that the surgeon has some prior experience with its use.

8.The Barron radial vacuum trephine usually does not fit on a Moria ACC, and hence use the appropriate matching units to facilitate and complete the procedure. A Hanna trephine will fit the Moria ACC and can be used routinely for this purpose.

9.The depth of cut on the Hanna trephine can be set in microns. With the Barron radial vacuum trephine, the depth is set by the number of quarter turns on its post.

10.Suitable lamellar dissection blades and knives should be available for the procedure.

11.In manual dissection, maintain a uniplanar lamellar dissection, by staying in the same plane of dissection

until the disk is fully excised. This will help in attaining a better donor-host interface.

12.The intrachamber pressure should always be checked before any trephination or lamellar dissection of the donor cornea. Adjust the intrachamber pressure as needed by injecting or aspirating fluid via the attached syringe.

13.Maintain the intrachamber pressure by closing the valve or applying the clamps provided with the unit.

14.The intrachamber pressure may be checked digitally or with the Barraquer tonometer. Inadequate intrachamber pressure will result in potential complications with the donor tissue.

Results and Conclusions

We compared three AACs to determine the optimal sizes of donor corneoscleral tissue (DCST).17 Twenty DCSTs were evaluated. The AACs tested were Bausch and Lomb, Moria ACC, and Moria ALTK. Twenty DCSTs were evaluated. The scleral skirt was measured from the limbus to the cut edge at 4 cardinal points (mean rim size, 3.14±0.61 mm; range, 2.07-4.19). DCSTs were mounted in the AACs, a target pressure of 65 mm Hg was set using Barraquer tonometer. Tissue slippage with seal rupture before reaching the target pressure was considered a failure. The mean scleral rim sizes that maintained a seal and failed to maintain a seal, respectively, were 3.4± 0.7 mm (range, 2.1-4.2) and 2.99 ± 0.51 mm (range, 2.13-3.5). Using Optimal Data Analysis (ODA) techniques, we found that the DCST should have a minimal scleral skirt of 3.6 mm for successful use in an AAC for lamellar or penetrating keratoplasty (epithelial approach).17

In summary, the introduction of these AAC into the field of corneal surgery has propelled further forward the field of lamellar corneal surgery and this momentum is expected to continue over time. Eye bank awareness and standardization of the required scleral rim size for lamellar corneal surgery are essential for successful outcome of the donor corneal tissue dissection and transplantation.

Acknowledgment

The author thanks Moria, Inc., and Katena, Inc., for providing figures for this chapter.

References

1. Ward DE, Nesburn AB. An artificial anterior chamber. Am J Ophthalmol 1976;82:796-8.

2. Wong DW, Chan WK, Tan DT. Harvesting a lamellar graft from a corneoscleral button: A new technique. Am J Ophthalmol 1997;123:688-9.

3. Ward DE, Nesburn AB. A modified artificial anterior chamber for use in refractive keratoplasty. Am J Ophthalmol 1980; 89: 742.

4. Beherens A, Dolorico AMT, Kara DT, et al. Precision and accuracy of an artificial anterior chamber system in obtaining corneal lenticules for lamellar keratoplasty. J Cataract Refract Surg 2002; 288:860-5.

5. Behrens A, Ellis K, Li L, Sweet PM, Chuck RS. Endothelial lamellar keratoplasty using an artificial anterior chamber and a microkeratome. Arch Ophthalmol 2003; 121:503-8.

6. Springs CL, Joseph MA, Odom JV, Wiley LA. Predictability of donor lamellar graft diameter and thickness in an artificial anterior chamber system. Cornea 2002; 21:696-9.

7. Behrens A, Dolorico AM, Kara DT, Novick LH, McDonnell PJ, Chao LC, Wellik SR, Chuck RS. Precision and accuracy of an artificial anterior chamber system in obtaining corneal lenticules for lamellar keratoplasty. J Cataract Refract Surg 2001; 27: 1679-87.

8. Ignacio TS, Nguyen TT, Sarayba MA, Sweet PM, Piovanetti O, Chuck RS, Behrens A. A technique to harvest Descemet’s membrane with viable endothelial cells for selective transplantation. Am J Ophthalmol 2005;139:325-30.

9. Wiley LA, Joseph MA, Springs CL. Tectonic lamellar keratoplasty utilizing a microkeratome and an artificial anterior chamber system. Cornea 2002; 21:661-3.

10. Azar DT, Jain S, Sambursky R, Staruss L. Microkeratome-

assisted posterior keratoplasty. J Cataract Refract Surg 2001; 27:353-6.

11.Buratto L. Globe holder and artificial anterior chamber. Refract Corneal Surg 1990; 6:205-6.

12.Maguen E, Azen SP, Pinhas S, Villasenor RA, Nesburn AB. Evaluation of sources of variation on the accuracy and reproducibility of microkeratome sections with the modified artificial anterior chamber. Ophthalmic Surg 1982; 13:217-20.

13.Maguen E, Villasenor RA, Ward DE, Nesburn AB. A modified artificial anterior chamber for use in refractive keratoplasty. Am J Ophthalmol 1980; 89:742-4.

14.Springs CL, Joseph MA, Odom JV, Wiley LA. Predictability of donor lamellar graft diameter and thickness in an artificial anterior chamber system. Cornea 2002; 21:696-9.

15.Wolter JR, Kunkel SL. Artificial anterior chamber made of rigid PMMA contact lenses. CLAO J 1985; 11:107-12.

16.Li L, Behrens A, Osann KE, Sweet P, Chuck RS. Corneal lenticule harvest using a microkeratome and an artificial anterior system at high intrachamber pressure. Journal of Cataract and Refractive Surgery 2002; 28:860-5.

17.John T, Selvadurai D, Ruszkowski E, Pivoney CJ, McCoy K: Evaluation of three artificial anterior chambers using donor human corneoscleral explants. Presented at the Annual Meeting of The Cornea Society and Eye Bank Association of America, Federated Scientific Session Meeting, New Orleans, LA, October 23, 2004.

Introduction

A new terminology that I (TJ) introduced is called selective tissue corneal transplantation (STCT)1-4 that describes a new concept and, perhaps, the future direction of the field of corneal replacement surgery. STCT is defined as the selective removal of the diseased portion of the patient’s cornea and its replacement with anatomically similar healthy donor corneal tissue.2 Hence, in cases where the corneal opacities are confined to within the corneal stroma, with healthy corneal endothelium, then, only that portion of the cornea with the opacity is removed, leaving behind the remainder of the patient’s cornea. Such lamellar corneal surgery preserves the patient’s corneal endothelium and thus eliminates the possibility of corneal endothelial graft rejection. This is of great benefit to the patient of all ages. However, in cases of endothelial decompensation with corneal edema without associated corneal opacities or with only mild corneal opacity that does not involve the visual axis, then descemetorhexis (DX) with endokeratoplasty (EK) (DXEK) which is synonymous with Descemet’s Stripping Automated Endothelial Keratoplasty (DSAEK)1-4 may be the preferred surgical choice, thus maintaining the patient’s corneal integrity without any corneal wound or corneal sutures. Lastly, if there is a full-thickness corneal scar that involves the endothelium, then the standard penetrating keratoplasty (PKP) will be required for patient’s visual rehabilitation.

The term DX was first introduced by Sinha et al in 2003 to describe the excision of retained Descemet’s membrane (DM) following a PKP.5 They rationalized that both the lens capsule and DM are basement membranes, and since the term capsulorhexis is commonly used in cataract surgery, the term DX is appropriate for the DM and called it DX. Subsequently, others6,7 have used a similar technique to excise DM from a recipient cornea. The term EK was first used by Busin et al8 in flap-associated posterior lamellar keratoplasty (PLK) (See also Chapter 14, History of Lamellar and Penetrating Keratoplasty). EK refers to transplantation of a thin donor corneal disk comprising of donor stroma, DM, and a functional, healthy endothelium to the recipient’s cornea [See Section 9, Descemet’s Stripping Automated Endothelial Keratoplasty (DSAEK)].1 Based on the above descriptions, the term DXEK appears to be well suited for this type of corneal surgery. Other terms that describe the same surgical procedure include, Descemet’s stripping with endothelial keratoplasty (DSEK) and Descemet’s stripping automated endothelial keratoplasty (DSAEK).1 Since, the term DSAEK is well established, to avoid confusion, in this chapter the term DSAEK will be used.

Currently, full-thickness penetrating keratoplasty (PKP) is the gold standard worldwide for corneal replacement surgery. However, lamellar keratoplasty (LKP) is rapidly gaining popularity among corneal surgeons all over the world. Improved instrumentation (See also Chapter 11, New/ Useful Surgical Instruments in DSAEK), refinements in microsurgical techniques [See also Section 9, Descemet’s Stripping Automated Endothelial Keratoplasty (DSAEK)], availability of new artificial anterior chambers (See also Chapter 12, Artificial Anterior Chambers), and microkeratomes seem to have forward propelled this renewed interest in LKP to greater heights. Additionally, anterior LKP (ALK) for the most part is an extraocular, non-open-sky, less invasive procedure than a PKP and it avoids intraocular complications such as endophthalmitis, glaucoma, iatrogenic cataract formation, anterior synechiae, and iris prolapse.9-14 In contrast posterior lamellar keratoplasty (PLK) is an intraocular procedure.

With the renewed interest in LKP there have been various terminologies that have been introduced into the medical literature that is often confusing to the ophthalmic surgeons. Some of these terminologies and abbreviations include, lamellar keratoplasty (LK),15 deep lamellar anterior keratoplasty (DLAK),15 deep lamellar endothelial keratoplasty (DLEK),15 deep stromal anterior lamellar keratoplasty (DSALK),16 deep lamellar keratoplasty (DLKP),17 deep lamellar keratoplasty (DLK),18 deep anterior lamellar keratoplasty (DALK),19 and posterior lamellar keratoplasty (PLK).2° All of these varied terminologies refer to the recipient cornea.

Donor Cornea

Another equally important area to be focused upon when dealing with LKP, is the thickness of the donor cornea. Most lamellar corneal surgeons are well aware that the donor corneal disk thickness can vary. The corneal thickness in: (a) anterior superficial lamellar resection is usually less than 160 µm (ALR), (b) mid-stromal lamellar resection (MSR) is 160 – 400 µm, and (c) almost fullthickness donor graft (FTDG), usually devoid of endothelium following Hallerman’s original idea,21-23 and later on adopted by many others.1,24-33

This chapter addresses these issues regarding LKP terminology and presents a unified, easy to use comprehensive classification for both anterior and posterior lamellar keratoplasty, for standardization purposes. These classifications for optical LKP, are named as “John-Malbran ALK Classification” (Figure 13-1) and “John PLK Classification”(Figure 13-2).