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

Introduction

By selectively replacing dysfunctional endothelium while retaining the patient’s overlying stroma, endothelial keratoplasty (EK) causes little to no change in corneal surface topography or refractive status.1-3 This allows rapid recovery of useful vision and provides significant benefits for patients compared with traditional penetrating keratoplasty (PKP).2,4-6

Although PKP has been performed for over 100 years, penetrating grafts still suffer from serious drawbacks, including the potential induction of large and unpredictable refractive changes.7-9 Furthermore, after PKP, the eye is permanently weakened and remains forever at increased risk of traumatic rupture, because the full-thickness incision never heals back to the strength of the “virgin” cornea.10,11 After PKP, there is also significant risk that ocular surface problems will interfere with recovery, because the fullthickness incision serves all corneal nerves, reducing the tendency to blink and produce tears, and loose or broken sutures can serve as a conduit for infection.12,13

With EK these concerns are minimized, or in many cases eliminated. EK can be performed through a small (3.0 – 5.0 mm) incision so that most of the structural integrity of the eye is maintained.5,14,15 Corneal innervation is retained,16 and with a properly constructed scleral tunnel incision, EK can be performed as a completely sutureless procedure, so postoperative ocular surface problems are minimal.14 Finally, EK is essentially refractive-neutral.5

Evolution of EK Techniques and

Manifest Cylinder Outcomes

A series of advances in EK techniques has allowed the use of progressively smaller incision sizes and essentially eliminated any concerns about induced astigmatism. Early methods of endothelial keratoplasty involved creation of an anterior flap and replacement of posterior stroma and endothelium, with use of sutures to secure the donor graft17-21 (See also Chapter 14, History of Lamellar and Penetrating Keratoplasty). However, these early methods suffered from many of the same drawbacks as PKP, including unpredictable corneal topography and induced irregular astigmatism, and hence, they were never widely adopted.

The current popularity of EK can be attributed to a series of key breakthroughs pioneered by Melles, along with contributions from many other surgeons (See also Chapter 14, History of Lamellar and Penetrating Keratoplasty). In 1997, Melles reported a posterior lamellar keratoplasty (PLK) technique whereby he replaced a 7.5 mm diameter area of

posterior stroma and endothelium through a 9 mm incision and used air rather than sutures to secure the donor graft to the recipient cornea.22,23 In 2000, Terry initiated a prospective clinical study of this fundamental technique, which he called deep lamellar endothelial keratoplasty (DLEK).24 In early PLK and DLEK series utilizing a 9.0 mm incision, mean postoperative manifest cylinder was 1.5 to 1.6 D.2,3 In the DLEK series, this represented a small, but statistically significant, increase of 0.4 D compared with the preoperative mean manifest cylinder (P=0.035, Table 22-1).2

In 2002, Melles demonstrated that a 9.0 mm posterior donor graft could be folded in half and inserted through a 5 mm incision in a completely sutureless PLK procedure.14 Terry showed that with small incision DLEK, postoperative mean manifest cylinder was statistically comparable to the preoperative value (Table 22-1).2,25

The next major EK advance occurred in 2003, when Melles reported that dysfunctional endothelium could be successfully removed from the recipient cornea by descemetorhexus, or stripping Descemet’s membrane, in lieu of the more difficult lamellar dissection and excision of posterior recipient stroma used in his original PLK technique.26 With some procedural refinements, this EK procedure became known as Descemet’s stripping with endothelial keratoplasty (DSEK).5 We found that DSEK produces no change in the mean manifest cylinder (Table 22-1).5 Gorovoy subsequently reported excellent clinical outcomes using a microkeratome to dissect the donor tissue, in an EK iteration known as Descemet’s stripping automated endothelial keratoplasty (DSAEK).27 We have found that DSAEK likewise does not induce any statistically significant change in mean refractive cylinder (Table 22-1).1

In summary, while the initial large-incision PLK/DLEK technique caused a small but statistically significant increase in mean manifest cylinder, subsequent smallincision EK iterations do not cause any significant change (Table 22-1).1,2 However, a transient increase in mean manifest cylinder may be noted during the first 1-3 months after surgery, if sutures are used to close the small incision (Figure 22-1).5 Also, even though the average manifest cylinder for the patient population does not change after small incision EK, individual patients may notice a mild shift in their refraction (Figure 22-2).5 Nevertheless, for most individuals, post-EK cylinder is likely to be within 1 D of the preoperative value, which is a major improvement over the prognosis with a PKP. After PKP, 4.0 – 5.0 D of mean refractive cylinder is common, and 10-15% of PK patients typically require hard contact lenses to help normalize the corneal surface so that they can obtain best visual acuity

Figure 22-1: Transient increase in mean refractive cylinder that may occur when an EK incision is closed with sutures.

Figure 22-2: Scatterplot comparing preoperative and postoperative refractive cylinder in 50 consecutive DSEK patients with 6-month followup.

(Table 22-1). In addition, a small but significant percentage of PKP patients require subsequent refractive procedures, such as limbal relaxing incisions or laser in situ keratomileusis, to help reduce their high astigmatic errors.29,31

In a preliminary report of outcomes from the first prospective, randomized study directly comparing EK with PK, the mean postoperative refractive cylinder was 5.0 ± 3.1 D in 6 PK eyes, compared with 1.0 ± 0.9 D in 4 large incision DLEK eyes.32 These results certainly confirm the findings from the larger, non-randomized series cited in

Table 22-1.

Spherical Equivalent Outcomes

EK also causes minimal change in mean spherical equivalent refraction, with some surgeons reporting no change and others reporting only a mild hyperopic shift.1,5,27 Spherical equivalent outcomes are probably

influenced by donor dissection technique. For example, during manual dissection of a donor corneal/scleral rim mounted on an artificial anterior chamber (See also Chapter 12, Artificial Anterior Chambers) there is a tendency for the dissection plane to be shallower in the periphery, resulting in a meniscus-shaped donor lenticule, which can cause a mild hyperopic shift. Many microkeratomes, including the Moria CB microkeratome (Moria S.A., Antony, France) used for DSAEK, tend to cut deeper in the periphery, which helps to compensate for the increased thickness in the peripheral cornea compared with the central cornea, and therefore a microkeratome can produce a posterior donor button that has a relatively planar contour across the visual axis (Figure 22-3). However, using a slower translational speed with the microkeratome tends to produce deeper cuts, and if the translational speed varies during the microkeratome pass, the posterior donor button may have a tapered contour. Extensive experience with cutting LASIK flaps

Figure 22-3: Visante optical coherence tomography cross sectional image of a DSAEK eye. The 9 mm diameter donor graft has a uniform thickness across the visual axis and becomes slightly thicker at each edge.

shows that microkeratome dissection depths can vary significantly from the nominal depth plate dimension and have a large standard deviation.33,34 Despite these variables, in our experience, microkeratome-dissection of the donor cornea results in no change in the mean spherical equivalent refraction after DSAEK.1 Some other physicians report a mild hyperopic shift with DSAEK.27

The relatively predictable refractive outcomes achieved with EK allow surgeons to perform cataract extraction and intraocular lens (IOL) implantation prior to corneal transplantation, and thus avoid endothelial cell loss from subsequent surgical trauma. By tracking their post-EK refractive outcomes, individual surgeons can develop a nomogram to use in their IOL calculations, to compensate for any shift in spherical equivalent refraction they are likely to get after subsequent EK surgery. It should be noted that performing cataract extraction prior to corneal transplantation represents a real paradigm shift. With PKP, it was usually preferable to postpone cataract extraction until after transplantation so that the selection of IOL power could be used to help address some of the unpredictable post-PKP refractive outcomes. With EK the cataract surgery can be performed first to help protect the donor endothelium.

Visual Outcomes

Current EK techniques provide rapid visual recovery and an easy postoperative course compared with PKP. Full recovery of best vision could be a year with the original PLK/DLEK technique.35 The apposition of 2 handdissected surfaces in PLK/DLEK probably resulted in interface irregularities that may have caused some visual degradation in the early postoperative period. Over a period of time, stromal remodeling by the keratocytes probably helped normalize the interface and improve best-corrected vision.

Figure 22-4: Visual acuity vs. time for consecutive series of patients with endothelial dysfunction treated with DSEK and DSAEK. All eyes are included regardless of whether pre-existing retinal problems limit visual potential.

Visual recovery seems to be faster with DSEK and particularly with DSAEK compared with the earlier EK techniques ((Figure 22-4). Removal of Descemet’s membrane leaves an extremely smooth recipient interface, and microkeratome dissection of the donor tissue typically produces a smoother donor interface compared with hand dissection. This combination can produce faster visual recovery. However, an important caveat when comparing the outcomes with different EK techniques is that the patients in the various reported series were not randomized, so there may have been demographic differences or differences in mean visual potential in different treatment groups.

Fuchs’ corneal dystrophy is the most prevalent indication and bullous keratopathy the second most common indication for EK. We have also found that excellent visual outcomes can be obtained when EK is used to treat iridocorneal endothelial (ICE) syndrome. So far we have treated 3 ICE syndrome patients and all have achieved visual acuities of 20/20 to 20/30 after DSAEK.36

Achieving 20/40 vision is a key goal for many patients because that is often the benchmark required to obtain a driver’s license.5 The percentage of patients who achieve 20/40 visual acuity after EK compares quite favorably with the percentage after PKP.5 Since PK substantially alters corneal topography, it is not uncommon for 10-15% of the treated eyes may require a hard contact lens to normalize the anterior surface of the cornea in order to achieve best visual acuity.29,30 In contrast, EK does not significantly alter corneal topography, so hard lenses are not required for best vision. This is an important advantage with EK because some patients cannot tolerate hard lenses and older patients in particular may find them difficult to manage.

Factors Affecting Visual Outcomes

What preoperative or surgical factors correlate with visual acuity after EK? Multivariate analysis indicates that preexisting retinal disease or amblyopia in the treated eye is the most statistically significant factor (P<0.0001) limiting visual acuity after EK.1 Interestingly, post-EK visual outcomes are also significantly correlated with recipient age even after eyes with known pre-existing retinal disease are excluded (Figure 22-5),1 indicating that younger patients have a better visual prognosis.

Figure 22-5: Scatterplot showing correlation between patient age and best spectacle-corrected visual acuity (BSCVA) after DSEK or DSAEK. Eyes with pre-existing retinal problems or amblyopia were excluded.

Whereas DLEK and flap-associated DLEK (FDLEK) do not significantly increase total corneal thickness, DSEK and DSAEK do, because they add donor stroma without removing any recipient stroma (See also Chapter 13, Definition, Terminology and Classification of Lamellar Corneal Surgery). Initially there was concern that the increased corneal thickness might degrade visual acuity. However, our analysis of several hundred eyes has shown that postEK central corneal thickness is not significantly correlated with Snellen acuity (Figure 22-6, P= 0.25). Retinal problems could be a confounding variable in this type of analysis, so the analysis was restricted to those eyes with no known retinal problems.1

Anterior stromal scarring also can cause significant light scattering and degrade visual acuity after EK (Figure 22-7). Therefore, patients are likely to recover better vision if the EK is performed before long-standing edema causes anterior stromal scarring, because EK does not replace anterior stromal tissue, and it is not yet known, whether stromal remodeling can ultimately reverse long-standing changes.

The most frequent post-EK complication is detachment of the donor tissue in the first week after surgery.16,37 The donor tissue can usually be re-attached by simply reinjecting an air bubble to again press the donor graft up

Figure 22-6: Scatterplot showing no significant correlation between central corneal thickness measured by ultrasonic pachymetry and best spectacle-corrected visual acuity after DSEK/DSAEK.

A

B

Figure 22-7: Confocal microscopy images of the anterior stroma in 2 DSAEK patients. The eye shown in (A) has 20/25 visual acuity and normal stromal appearance. This image was taken just beneath the epithelium as evidenced by the columnar basal epithelial cells near the bottom of the image and the sub-epithelial nerve crossing the center of the image. The stroma appears dark except for bright bean-shaped keratocyte nuclei. This indicates that most of the incident light is passing through to the retina and not being reflected back into the microscope. The eye shown in (B) has 20/60 visual acuity; the scarring in the anterior stroma is causing significant light scattering and is probably responsible for the sub-optimal best corrected vision.

against the recipient cornea. We have not detected a statistically significant difference in visual acuity between eyes that had a second air injection and those that did not.1 Sometimes full-thickness folds can occur in an EK donor graft and degrade visual acuity.38 In some cases, folds may occur if an oversized PLK/DLEK donor button is squeezed into an undersized excised area of the recipient cornea. With DSEK or DSAEK, the donor is simply laid on the flat recipient stromal surface, but folds can still develop and be difficult to remove especially with very thin donor grafts.

Implications

The excellent visual and refractive outcomes achieved with EK are producing a paradigm shift in determining the best time for a patient to have a corneal transplant. The risks and long recovery period after a traditional PKP caused many patients to postpone transplantation for as long as possible. In fact, patients often tried to postpone having a PKP until after retirement so that the prolonged recovery period would not jeopardize their job. In contrast, postoperative recovery after EK is quite rapid. In fact, some patients recover 20/25 vision within a week of their EK procedure. Thus, EK significantly improves the risk/benefit ratio of having a corneal transplant.

Often patients with Fuchs’ corneal dystrophy have already begun to experience significant impairment of their daily activities, like driving on sunny days or reading in an office with overhead fluorescent lighting, although their Snellen acuity measured in a darkened room still measures 20/30 or 20/40. It has been our experience that when patients with Fuchs’ corneal dystrophy with Snellen acuity of 20/30 in both eyes has an EK performed in one eye, they usually report at their one-month exam that the treated eye has much better quality of vision, even if the Snellen acuity is 20/30 in both the treated and untreated eyes. They frequently mention that colors appear more brilliant with the treated eye. This suggests that Fuchs’ guttata cause significant light scattering and visual disturbances that are not detected with Snellen acuity testing in a darkened room. By removing the guttata, EK can significantly reduce visual disturbances and improve the quality of life for many patients with endothelial dysfunction.5

Another nice feature of the EK technique is that visual outcomes are relatively predictable. Fewer eyes may achieve 20/20 visual acuity after EK compared with PKP. On the other hand, anisometropia after PKP can limit some eyes to a final visual acuity no better than 20/200, whereas after EK visual acuity of 20/70 or worse is extremely rare in eyes that do not have pre-existing retinal problems.1

What’s Next?

Melles and Tappin are currently perfecting methods of reliably implanting only Descemet’s membrane and healthy endothelium from donor corneas, without including any donor stromal tissue39-41 [See also Chapter 36, True Endothelial Cell (Tencell) Transplantation, and Chapter 37, Descemet Membrane Endothelial Keratoplasty (DMEK)]. Their techniques, respectively called Descemet’s membrane endothelial keratoplasty (DMEK) and true endothelial cell transplantation (Tencell), do not increase the total corneal thickness nor introduce dissected surfaces. Early results suggest these techniques may yield more 20/20 outcomes. A current challenge is that without attached stroma for support, bare Descemet’s membrane is quite fragile, so a significant percentage of donor corneas are rendered unusable during the harvesting and implantation procedures.39-42

The excellent outcomes achieved with EK are increasing the demand for cornea transplants, and the demand is outstripping the worldwide supply of donor corneas. A number of groups are working to culture endothelial cell sheets for use with EK (See also Chapter 38, Corneal Endothelial Reconstruction with a Bioengineered Cell Sheet, and Chapter 39, Future of Posterior Lamellar Keratoplasty). Success in such an endeavor may ultimately help alleviate the current worldwide shortage of suitable donor corneas.43-46

References

1. Price MO, Price FW, Jr. Descemet’s stripping with endothelial keratoplasty comparative outcomes with microkeratomedissected and manually dissected donor tissue. Ophthalmology 2006;113:1936-42.

2. Terry MA, Ousley PJ. Deep lamellar endothelial keratoplasty visual acuity, astigmatism, and endothelial survival in a large prospective series. Ophthalmology 2005;112:1541-8.

3. Melles GR, Lander F, van Dooren BT, Pels E, et al. Preliminary clinical results of posterior lamellar keratoplasty through a sclerocorneal pocket incision. Ophthalmology 2000;107:1850- 6; discussion 1857.

4. Price FW, Jr. Corneal transplantation as a refractive surgical procedure. Journal of Refractive Surgery 2005;21:216-7.

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

6. Melles GR. Posterior lamellar keratoplasty: DLEK to DSEK to DMEK. Cornea 2006;25:879-81.

7. Riddle HK, Jr., Parker DA, Price FW, Jr. Management of postkeratoplasty astigmatism. Curr Opin Ophthalmol 1998; 9:15-28.

8. Binder PS, Waring GO. Refractive Keratotomy for Myopia and Astigmatism (Ed. Waring GO) 1157-1186 (Mosby Year Book, St. Louis, MO), 1992.

9. Touzeau O, Borderie VM, Allouch C, Scheer S, et al. Effects of penetrating keratoplasty suture removal on corneal topography and refraction. Cornea 1999;18:638-44.

10.Elder MJ, Stack RR. Globe rupture following penetrating keratoplasty: how often, why, and what can we do to prevent it? Cornea 2004;23:776-80.

11.Renucci AM, Marangon FB, Culbertson WW. Wound dehiscence after penetrating keratoplasty: Clinical characteristics of 51 cases treated at Bascom Palmer Eye Institute. Cornea 2006;25:524-9.

12.Thompson RW, Jr., Price MO, Bowers PJ, Price FW, Jr. Longterm graft survival after penetrating keratoplasty. Ophthalmology 2003;110:1396-402.

13.Price FW, Jr., Whitson WE, Johns S, Gonzales JS. Risk factors for corneal graft failure. J Refract Surg 1996;12:134-43; discussion 143-7.

14.Melles GR, Lander F, Nieuwendaal C. Sutureless, posterior lamellar keratoplasty: A case report of a modified technique. Cornea 2002;21:325-7.

15.Terry MA, Ousley PJ. Small-incision deep lamellar endothelial keratoplasty (DLEK): Six-month results in the first prospective clinical study. Cornea 2005;24:59-65.

16.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;32:411- 8.

17.Barraquer J. In The Comea World Congress (Eds. King H Jr MJ) 586-604 (Rutterworths, Washington, DC), 1965.

18.Busin M, Arffa RC, Sebastiani A. Endokeratoplasty as an alternative to penetrating keratoplasty for the surgical treatment of diseased endothelium: Initial results. Ophthalmology 2000;107:2077-82.

19.Ehlers N, Ehlers H, Hjortdal J, Moller-Pedersen T. Grafting of the posterior cornea. Description of a new technique with 12month clinical results. Acta Ophthalmol Scand 2000;78:543-6.

20.Guell JL, Velasco F, Guerrero E, Gris O, et al. Preliminary results with posterior lamellar keratoplasty for endothelial failure. Br J Ophthalmol 2003;87:241-3.

21.Azar DT, Jain S. Microkeratome-assisted posterior keratoplasty. J Cataract Refract Surg 2002;28:732-3.

22.Melles GR, Eggink FA, Lander F, Pels E, et al. A surgical technique for posterior lamellar keratoplasty. Cornea 1998;17:618-26.

23.Melles GR, Lander F, Beekhuis WH, Remeijer L, et al. Posterior lamellar keratoplasty for a case of pseudophakic bullous keratopathy. Am J Ophthalmol. 1999;127:340-1.

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

25.Fogla R, Padmanabhan P. Initial results of small incision deep lamellar endothelial keratoplasty (DLEK). Am J Ophthalmol 2006;141:346-51.

26.Melles GR, Wijdh RH, Nieuwendaal CP. A technique to excise the descemet membrane from a recipient cornea (descemetorhexis). Cornea 2004;23:286-8.

27.Gorovoy MS. Descemet-stripping automated endothelial keratoplasty. Cornea 2006;25:886-9.

28.Davis EA, Azar DT, Jakobs FM, Stark WJ. Refractive and keratometric results after the triple procedure: Experience with early and late suture removal. Ophthalmology 1998;105:62430.

29.Pineros O, Cohen EJ, Rapuano CJ, Laibson PR. Long-term results after penetrating keratoplasty for Fuchs’ endothelial dystrophy. Arch Ophthalmol 1996;114:15-8.

30.Price FW, Jr., Whitson WE, Marks RG. Progression of visual acuity after penetrating keratoplasty. Ophthalmology 1991;98:1177-85.

31.Claesson M, Armitage WJ, Fagerholm P, Stenevi U. Visual outcome in corneal grafts: A preliminary analysis of the Swedish Corneal Transplant Register. Br J Ophthalmol 2002;86:174-80.

32.Baratz KH NC, Hodge DO, Bourne WM. A prospective, randomized study of deep lamellar endothelial keratoplasty versus penetrating keratoplasty: Early results. Invest Ophthalmol Vis Sci 2005;46:E-Abstract 2703.

33.Thompson RW, Jr., Choi DM, Price MO, Potrezbowski L, et al. Noncontact optical coherence tomography for measurement of corneal flap and residual stromal bed thickness after laser in situ keratomileusis. J Refract Surg 2003;19:507-15.

34.Reinstein DZ, Srivannaboon S, Archer TJ, Silverman RH, et al. Probability model of the inaccuracy of residual stromal thickness prediction to reduce the risk of ectasia after LASIK part II: quantifying population risk. J Refract Surg 2006;22:861-70.

35.Terry MA, Ousley PJ. Rapid visual rehabilitation after endothelial transplants with deep lamellar endothelial keratoplasty (DLEK). Cornea 2004;23:143-53.

36.Price MO, Price FW, Jr. Descemet’s stripping endothelial keratoplasty for treatment of iridocorneal endothelial syndrome. Cornea 2006;in press.

37.Terry MA, Hoar KL, Wall J, Ousley P. Histology of Dislocations in Endothelial Keratoplasty (DSEK and DLEK): A LaboratoryBased, Surgical Solution to Dislocation in 100 Consecutive DSEK Cases. Cornea 2006;25:926-32.

38.Faia LJ, Baratz KH, Bourne WM. Corneal graft folds: A complication of deep lamellar endothelial keratoplasty. Arch Ophthalmol 2006;124:593-5.

39.MellesGR,OngTS,VerversB,vanderWeesJ.Descemetmembrane endothelial keratoplasty (DMEK). Cornea 2006;25:987-90.

40.Melles GR, Lander F, Rietveld FJ. Transplantation of Descemet’s membrane carrying viable endothelium through a small scleral incision. Cornea 2002;21:415-8.

41.Tappin M. A method for true endothelial cell (Tencell) transplantation using a custom made cannula for the treatment of endothelial cell failure. Eye 2007;21:775-9.

42.Zhu Z, Rife L, Yiu S, Trousdale MD, et al. Technique for preparation of the corneal endothelium-Descemet membrane complex for transplantation. Cornea 2006;25:705-8.

43.Sumide T, Nishida K, Yamato M, Ide T, et al. Functional human corneal endothelial cell sheets harvested from temperatureresponsive culture surfaces. FASEB J 2006;20:392-4.

44.Shimmura S, Miyashita H, Konomi K, Shinozaki N, et al. Transplantation of corneal endothelium with Descemet’s membrane using a hyroxyethyl methacrylate polymer as a carrier. Br J Ophthalmol 2005;89:134-7.

45.Mimura T, Yamagami S, Yokoo S, Usui T, et al. Cultured human corneal endothelial cell transplantation with a collagen sheet in a rabbit model. Invest Ophthalmol Vis Sci 2004;45:2992-7.

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Introduction

Descemet membrane stripping automated endothelial keratoplasty (DSAEK) is currently the most popular surgical technique among corneal surgeons all over the world for selective tissue corneal transplantation (STCT),1 namely, where there is patient corneal endothelial decompensation and it needs to be replaced with healthy donor corneal endothelium in order to clear the corneal edema and visually rehabilitate the patient and return him back to his normal activities, in a relatively short time as compared to full-thickness penetrating keratoplasty (PKP).

In this chapter, every effort is taken to introduce the reader to a step-wise fashion of DSAEK procedure and thus increase the comfort level of the surgeons in doing this procedure2,3 (See also Chapter 20, Endothelial Keratoplasty: A Step by Step Guide to DSEK and DSAEK Surgery).

Surgical Technique

DSAEK may be considered as a 3-step procedure (Figure

23-1):

1.Choosing the trephine diameter

2.Donor disk

3.Host cornea.

the most suitable eye in which to use a 9.0 mm diameter donor corneal disk. In this eye a smaller diameter disk, e.g. 7.5 mm or occasionally even a 7.0 mm diameter donor disk may be the most desirable diameter. On the other hand, in a large diameter cornea, with a deep anterior chamber, a 9.0 mm diameter donor disk may be the best choice. The basic premise is to introduce as much healthy donor endothelium as possible, without subjecting the patient to any additional postoperative complications. A large diameter donor corneal disk in a small diameter, crowded anterior segment, will be prone to potential peripheral anterior synechiae (PAS), angle closure glaucoma, peripheral donor disk deformation due to progressive PAS, chronic anterior uveitis due to peripheral iris rubbing on the donor disk, inflammation-related macular edema, and even graft failure.

A simple approach to choosing the donor disk diameter is to open a surgical caliper that is set at 9.0 mm and if there is at least 1.0 mm clearance, 360 degrees, then the donor disk diameter of choice is 9.0 mm. If this caliper (9.0 mm setting) reaches the limbus or beyond the limbus, then decrease the setting to 8.0 mm, or 7.5 mm, or occasionally 7.0 mm, until there is a 1.0 mm or more peripheral room (Figure 23-2) for introduction of various surgical instruments as needed during the DSAEK surgery and postoperatively to prevent PAS.

Figure 23-1: DSAEK may be considered as a 3-step procedure.

Step 1: Choosing the Trephine Diameter

This is one of the most important steps in doing DSAEK surgery. Not all eyes are “made” the same. Hence, in my opinion it may not be a good idea to go with a fixed-diameter donor corneal disk, e.g. 9.0 mm diameter for all eyes undergoing DSAEK surgery. A small diameter cornea in a hyperopic eye with a crowded anterior segment may not be

Step 2: Donor Disk

The second step is the preparation of the donor corneal disk. I prefer to cut my own tissue in the operating room rather than to use pre-cut tissue that is prepared in an eye bank by an eye bank technician (See also Chapter 19, Eye Banking and Donor Corneal Tissue Preparation in DSAEK, and Chapter 30, Use of Eye Bank Pre-cut Donor Tissue in DSAEK).

This entails the use of a Moria automated lamellar therapeutic keratectomy (ALTK) system and a Moria CB microkeratome to perform DSAEK procedure (Moria, Antony, France).

There are many ways to set-up the Moria ALTK system, and Figure 23-3 shows a relatively simple way to set-up the artificial anterior chamber (AAC) for DSAEK procedure. Make sure all tubing connections are tight to prevent leakage of fluid. The donor cornea is mounted on to the central post within the AAC that is primed with the Optisol GS fluid such that during the mounting process there is no contact between the healthy donor corneal endothelium and the metal surface. While mounting the donor cornea if the surgeon simultaneously injects Optisol GS fluid, it will prevent capture of any air bubble within the AAC. The mounting rings are tightened to encase the donor cornea