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

Figures 26-1A to D: Intralase applanation phases. (A) Centering,

(B) Initial contact, (C) Incomplete applanation, (D) Applanation completed. Note in B and C the formation of air/fluid meniscus between the applanation lens of the Intralase applanating cone and the side portion of the corneal surface not yet applanated. In D full applanation with almost complete disappearance of air/fluid meniscus.

and locked by turning it clockwise. High internal pressure was constantly obtained by marked elevation of the infusion bottle (not less than 1.5 m above the AAC). Corneal thickness was measured using an ultrasound pachymeter (model 850, Bausch and Lomb) in the center of the cornea and in 4 quadrants on the vertical and horizontal meridians.

As the Intralase applanation lens makes a full contact with the corneoscleral button a green LED is illuminated and is visible in the operating microscope and on the display panel (Figure 26-2). As the beam delivery device is lowered further after initial contact, the applanation force increases. At a preset position of the objective lens deflection corresponding to the maximum allowed eye pressure, a sensor is actuated and a red LED, which is visible in the operating microscope as well as on the video display, is illuminated. Further downward movement of the beam delivery device is disabled, but upward movement is still enabled. We considered a good applanation a slight further downward movement of the beam delivery device after the green light is illuminated, at this level a homogeneous applanation is obtained and concentric folds visible in the posterior stroma are minimal. We think that edematous stroma in donor tissue causes circular folds as the cornea is flattened by the intralase applanation lens and they tend to increase as the applanation force increases. Proper setting of the femtolaser was then carried out. Laser parameters were: stromal depth 400 μm, bed energy 1.1 μJ (lamellar cut) and no side cut, line/spot separation 9/9 μm in a raster pattern, firing rate 60 kHz, and 9.0 mm diameter. Intralase software enabled 400 μm as maximum stromal depth. The

Figures 26-2A to D: Intralase applanation phases as observed through the operating microscope or the video display. (A) Initial contact: large air-fluid meniscus is present between the applanating surface of intralase cone and the area of the non-applanated cornea. (B) Further lowering of the cone, minimum decentering and almost complete disappearance of the air meniscus. (C) Full contact with cornea surface. Absence of air-fluid meniscus. Counter-pressure has not reached the right level to ensure good quality laser dissection. Note circular folds appearance in the deeper layer of the stroma (D) Green LED illumination indicates the pressure has reached a safe level to allow for a good laser dissection. Note that the circular folds in the midperipheral cornea have increased in number.

pre-laser corneal pachymetry was used to calculate the expected posterior lamellar thickness subtracting 400 μm from the central corneal pachymetry. Energy setting was input as a compromise between the high level required to obtain a good stromal dissection with smooth surface and minimal residual stromal bridges and the low energy to prevent possible endothelial damage. Forceps separation of the posterior lamella required more tissue stress with bed energy setting below 1.1 μJ. Line/spot separation 9/9 μm is the shortest distance allowed between single spots and lines of spots. Larger distances can be used, but in such a case bridges of uncut stroma are more easily seen. The raster pattern was chosen instead of the double raster to reduce the amount of bed energy released. The 9.0 mm diameter was chosen to ensure inclusion of all the dissected plane in the 8.00 mm diameter of the corneal punch allowing for inclusion of all the dissected plane even with a 1 mm decentered punch trephination (Figure 26-3).

At the end of the procedure the treated corneoscleral button is again placed in the storage medium and sent to the surgical theatre. Few minutes after laser treatment, both visible air bubbles and dissection plane cannot be visualized under the operating microscope. The corneoscleral button is punched from the endothelial side using an 8.0 mm Hanna trephine (Moria, S.A., Doylestown, PA).

Figure 26-3: Gas bubble formation are the byproducts of the femtolaser stromal photodisruption. Laser parameters: stromal depth 400 μm, bed energy 1.1 μJ (lamellar cut) no side cut, line/spot separation 9/9 μm in a raster pattern, firing rate 60 kHz, and 9.0 mm diameter.

Proper centration of the donor tissue is essential (Figure 26-4). Both anterior and posterior cut corneal lamellae remain resting on the donor punching block adherent to each other and covered by the organ culture storage media until use. Two Uttrata forceps are then used to gently separate anterior from posterior lenticule. The cleavage plane is usually found in the posterior fourth of the stromal tissue and the two lamellae are separated taking care to avoid excessive stress and folding of the posterior lamella (Figure 26-5). Once separation has occurred, three small marks are placed gently touching the stromal side cut by a

Figure 26-4: Donor corneal trephination is carried out from the endothelial side using the Hanna trephine.

marker pen: a single one on the distal part and pair of two close marks 90 degree apart clockwise after the single mark

[Editorial Note: Alternative staining technique (See also Chapter 32, Use of Dyes in DSAEK and DLEK) may be considered, since recent studies (Terry et al personal communication) seem to

indicate endothelial cell loss associated with the use of marking pen on the stromal surface of the donor corneal disk]. Once placed in the recipient anterior chamber, to ensure that the stromal side of the lenticule comes in contact with the stromal side of the recipient cornea, the pairs of marks have to be positioned clockwise proximal to the single mark (Figure 26-6).

After preparation of the corneal lenticule, attention is directed to the host cornea and a limbal temporal incision is made with a 3.2 mm keratome blade. In patients undergoing a triple procedure (keratoplasty, cataract extraction, and intraocular lens [IOL] implantation), surgery is performed through the same incision using phacoemulsification and a phaco-chop technique. The host corneal epithelium is marked with an 8.0 mm Weck trephine (Solan Medtronics, Jacksonville, FL) stained with gentian violet dye. A paracentesis is made 2 hours clockwise from the limbal incision to allow manipulation of a second instrument. The AC is maintained with an irrigating cannula, and a reverse-bent 30 gauge needle is used to incise the host endothelium and Descemet’s membrane corresponding to the 8.0 mm epithelial trephine mark. A John DSAEK Descemet’s Stripper (ASICO, Westmont, IL, AE-2874, Patent Pending) is then used to carefully remove the diseased host endothelium and Descemet’s membrane within the circumference of the Descemet’s incision (Figures 26-7A to D) (See also, Chapter 11, New/Useful Surgical Instruments in DSAEK). The limbal incision then is widened to approximately 5.2 mm using the keratome.

The endothelial surface of the donor lenticule is coated with a small amount of viscoelastic (Healon), and the donor disk is gently folded into a “taco-shape” using the Uttrata forceps. The folded donor corneal lenticule is then inserted

into the anterior chamber choosing between two different techniques. To minimize risk of crush injury to the donor endothelium an IOL holder with curved platforms that do not oppose centrally, is used to grasp and insert gently the folded lenticule (Figure 26-8). In a second technique, a 5.2 mm keratome is used as a glide. The folded lenticule resting on the keratome is gently pushed with a spatula in the AC through the limbal incision that can be widened to 6.2 mm to allow a smoother insertion (Figure 26-9). A double 10-0 nylon suture is used to close the limbal wound before filling the AC with balanced salt solution (BSS) (Alcon, Fort Worth, TX). To properly unfold the donor corneal lenticule having the endothelial side facing the AC and stromal surface in contact with the recipient stroma, the balanced salt solution is inserted directing the fluid in the virtual space between the touching endothelial surfaces. Proper contact is checked noting that the double marks are located clockwise before the single one (Figure 26-10). The AC is then filled with air and 8 minutes is allowed for the air to help in the donor-recipient corneal adherence. After 8 minutes, part of the air bubble is removed and replaced with BSS (Figure 26-11). Patient receives 1 drop each of ciprofloxacin (Alcon, Fort Worth, TX) [Editorial Note: Newer antibiotics such as levofloxacin 1.5% (Iquix 1.5%, Vistakon Pharmaceuticals, Jacksonville, FL) may be used one drop QID], cyclopentolate 1% (Bausch and Lomb, Tampa FL), and prednisolone acetate 1% (Pred Forte 1%, Allergan, Inc., Irvine, CA) at the end of the procedure. The operated eye is patched and a shield is applied over the patch and they are taped in place. Postoperatively, patients receive topical antibiotics and cycloplegia for 1 week and topical prednisolone acetate 1% ophthalmic suspension (Pred Forte 1%, Allergan, Inc., Irvine, CA) 3 times per day for 1

month. After 1 month, the topical prednisolone is tapered gradually over a 3-month period.

Results

The group of patients included 4 consecutive cases with corneal edema from (1) Fuchs’ endothelial dystrophy, (3) pseudophakic bullous keratopathy, without significant corneal stromal scarring who underwent Femto-DSEK.

Preoperative and postoperative pachymetry of the donor cornea and the calculated and actual thickness of the endothelial lenticule are reported in Table 26-1. In vivo measurements of the endothelial lenticule were carried out with the Heidelberg Cornea Tomograph (Heidelberg Engineering, Inc., Heidelberg, Germany). Cell count density in each donor cornea and in the endothelial lenticule 6 months after surgery, as well as postoperative visual acuity are reported in Table 26-2.

Figure 26-11: The anterior chamber is filled with air and allowed to remain in the anterior chamber for 8 minutes. Following the 8 minute waiting period, the air bubble size is decreased and replaced with sterile balanced salt solution.

Figure 26-12: In vivo measurements of the endothelial lenticule thickness obtained with the Heidelberg Cornea Tomograph (Heidelberg Engineering, Inc.).

TABLE 26-2: Endothelial cell density and visual acuities following femtosecond laser (Intralase®) - Descemet’s stripping endothelial keratoplasty (Femto-DSEK)

Conclusions

Despite excellent postoperative results, visual acuity (VA) after deep lamellar endothelial keratoplasty (DLEK) rarely exceeded 20/30 due to presumed optical aberrations at the graft-host interface.11 Unlike DLEK, Descemet’s stripping automated endothelial keratoplasty (DSAEK), employs mechanical stripping of the diseased host endothelium along with the patient’s Descemet’s membrane and replacement with a healthy homograft of endothelium,

Descemet’s membrane, and a thin layer of donor stromal tissue harvested with an automated microkeratome.12 These technical refinements have resulted in improvements in smoothness of both recipient and donor stromal surfaces thus minimizing interface aberrations. We used femtosecond laser to create posterior lenticules of variable thickness from donor corneas. Previous studies have demonstrated by scanning electron microscopy that in the posterior lamellar cuts, there is a slightly more irregular texture of the interface than in the standard anterior femtosecond laser assisted in-situ keratomileusis (LASIK) cuts. Increased scatter and attenuation of the laser energy that accompanies deep treatment in edematous corneas8 and the less compactly organized lamellar layers of the posterior stroma as compared with the superficial stroma13 are the likely causes for the increased roughness noted in the posterior cut surface. Nevertheless, one major advantage of the femtolaser cut over the mechanical microkeratome cut is the ability to set deeper cuts, thus obtaining thinner lenticules with less donor stroma included in the donor corneal disk. Replacement of the diseased endothelial cells along with the Descemet’s membrane with only the donor Descemet’s membrane along with healthy donor endothelial cells represents the ideal treatment for patients with diseased corneal endothelium. Femtosecond laser theoretically may achieve these results provided that deeper than 400 µm cuts can be obtained and no damage to the endothelial cells is induced by the laser energy. Further studies are needed mainly to evaluate the endothelial cell damage by laser energy. Our small series disclosed that marked cell loss occurred after 6 months and two patients required lenticule replacement. Femtosecond laser (Intralase, Advanced Medical Optics, Santa Ana, CA) damage to endothelial cells during posterior laser dissection to cut a 7 mm diameter, 100 µm lamellar disk from the endothelial side was recently investigated.14 The average endothelial cell loss in human eye bank donor buttons ranged between 6% and 14% according to different types of viscoelastics used as a “cushion” to protect the endothelium during applanation and laser delivery. Applanation alone without laser dissection resulted in cell loss of 9% therefore, the laser application although not marked, laser dissection causes endothelial damage in addition to the applanation process.

Many other factors affect endothelial cell counts in DLEK surgery. Recently, it has been reported that folding of the donor corneal disk and added manipulations of the donor disk in small-incision DLEK surgery, results in deleterious effect on the endothelial cell survival. Techniques that involve even more donor disk manipulations, such as triple folding and rolling of the donor tissue, combined with

squeezing of the tissue through an even smaller 3 mm incision15 may have an even greater endothelial cell damage and death of these cells as compared to other surgical techniques described above.

In conclusion, the femto-DSEK offers potential advantages over the automated microkeratome with regard to a better sizing of the posterior donor lenticule with reduced lenticule thickness. Additionally, the femtosecond laser has the unique capability of obtaining a smooth surface and precise stromal cuts for laser-assisted donor corneal preparation. Further work needs to be done to explore the possibilty of removing only the host Descemet’s membrane and endothelium and replacing it with a similar donor disk. Such an approach, if possible, would result in the postoperative thickness of the recipient cornea to be almost comparable to that of the normal corneal thickness. At the present time DSEK remains as an additive procedure with an increased overall corneal thickness.

References

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

2. Terry AM, Ousley PJ. Endothelial replacement without surface corneal incisions or sutures: Topography of the deep lamellar endothelial keratoplasty procedure. Cornea 2001;20:14–18.

3. Melles GR, Lander F, Nieuwendaal C. Sutureless, posterior lamellar keratoplasty: A case report of a modified technique. Cornea 2002;31:325–7.

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

5. Kurtz RM, Liu X, Elner VM, et al. Photodisruption in the human cornea as a function of laser pulse width. J Refract Surg 1997; 13:653–8.

6. Nordan LT, Slade SG, Baker RN, et al. Femtosecond laser flap creation for laser in situ keratomileusis: Six-month follow-up of initial U.S. clinical series. J Refract Surg 2003;19:8–14.

7. Sugar A. Ultrafast (femtosecond) laser refractive surgery. Curr Opin Ophthalmol 2002;13:246–9.

8. Soong K, Mian S, Abbasi O, Juhasz T. Femtosecond Laser– Assisted Posterior Lamellar Keratoplasty Initial Studies of Surgical Technique in Eye Bank Eyes. Ophthalmology 2005; 112:44–49.

9. Seitz B, Langenbucher A, Hofmann-Rummelt C, SchlotzerSchrehardt U, Naumann GOH. Nonmechanical Posterior Lamellar Keratoplasty Using the Femtosecond Laser (femtoPLAK) for Corneal Endothelial Decompensation. Am J Ophthalmol 2003;136:769–72.

10.Tamburrelli C, Mosca L, Fasciani R, Balestrazzi E. Femtosecond Laser Descemet’s Stripping Endothelial Keratoplasty: Initial Studies of Surgical Technique in Human Eyes ASCRS Session: 2-C San Diego 2007 April 28-May 01.

11.Terry MA, Ousley PJ. Replacing the endothelium without corneal surface incisions or sutures. The first United States clinical series using the deep lamellar endothelial keratoplasty procedure. Ophthalmology 2003;110:755–64.

12.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.

13.Fine BS, Yanoff M. Ocular Histology: A Text and Atlas (2nd edn). Hagerstown, MD: Harper and Row; 1979:163–92.

14.Sikder S, Snyder RW. Femtosecond laser preparation of donor tissue from the endothelial side. Cornea 2006;25(4):416-22.

15.Terry MA, Wall JM, Hoar KL, Ousley PJ. A Prospective Study of Endothelial Cell Loss during the 2 Years after Deep Lamellar Endothelial Keratoplasty. Ophthalmology 2007;114: 631–39.

Introduction

Descemet stripping automated endothelial keratoplasty [(DSAEK), synonymous with Descemetorhexis with endokeratoplasty (DXEK)]1-14 is an “against-gravity-line” surgery (AGLS) (Author’s terminology) (See also Chapter 13, Definition, Terminology, and Classification of Lamellar Corneal Surgery). Excluding DSAEK surgery, all other ophthalmic surgical procedures such as surgeries on the cornea, iris, lens, vitreous and retina, are all “in-gravity- line” surgery (IGLS) (Author’s terminology). Since, DSAEK is an AGLS, if the donor disk is not well attached to the inner surface of the patient’s cornea and remain attached, then the disk will detach and rest in the inferior part of the anterior chamber (AC) and rest on the iris surface.1 This is a potentially unwanted postoperative result and every measure should be taken by the surgeon to decrease his donor disk detachment rate.

Surgical Techniques to Increase Donor Disk Adherence to Recipient Cornea

Currently, there are at least 3 different techniques to increase and augment donor disk attachment to the recipient cornea (Figure 27-1) as listed below:

1.Corneal slits (Price FW)

2.Roughening the peripheral circular area of recipient corneal stroma (Terry MA)10

3.Use of large air bubble (John T).

Corneal Slits

Price FW described the use of corneal slits to increase donor disk attachment. Conceptually, this is a good procedure to enhance donor disk adherence. In Dr. Price’s experience, this surgical technique has significantly decreased the donor disk detachment rate. Four corneal slits are made, one in each quadrant within the circle of Descemetorhexis (DX) (Figures 27-2A to D). Each of these recipient corneal slits are about 2.0 mm in length and they vary in depth to enter the donor-recipient interface. These corneal slits are of no use if the interface is not reached. Once the slit incision reaches the donor-recipient interface, it will often result in draining any aqueous humor that may be trapped in the interface (Figure 27-3). Drainage of such trapped fluid will collapse the fluid layer in the interface, and help in the adherence of the donor corneal disk to the recipient cornea. The same type of incision is then repeated in the remaining 3 quadrants. One or more of these slit-incisions may drain

Figure 27-1: Schematic representation of 3 different surgical techniques to increase donor corneal disk attachment to the recipient cornea. One or two inferior peripheral iridotomies are performed pre-operatively when the large air bubble technique is used.

any trapped fluid from the interface. It may be difficult to ascertain that the depth of these incisions is adequate. One such indication is the mild movement of the donor disk, when the incising blade has actually reached the donorrecipient interface. These slit-incisions should only be performed with an air bubble inside the anterior chamber (AC) that pushes the donor disk against the inner corneal surface of the recipient cornea (Figure 27-4).

There is significant resistance from the recipient cornea when making these slits with a steel blade (Figures 27-2 and 27-3). Such an incision should only be made gently, by a “to-and-fro” motion without any significant corneal deformation. The amount of fluid that may be drained from the slit-incision is usually small (Figure 27-3). If a diamond blade is used for these slit incisions, there is very little or no resistance from the recipient cornea and it makes the procedure much easier as compared to using a steel blade. There is little or no recipient corneal deformation when using a diamond blade.

Postoperatively, these four quadrant slits are visible at the slit-lamp and remain visible over time. These corneal slits do not disappear. Also, one has to keep in mind that these slits although small, are made on the host corneal surface. The author does not routinely perform slit-incisions