Eyeworld

FEB 2012

EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.

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February 2012 EW NEWS & OPINION 19 use of the microkeratome, which still remains the only instrument that can guarantee optimal smooth- ness of the stromal surface of DSAEK grafts. Over the past 2 years, I have standardized the method to the ex- tent that I presently perform only UT-DSAEK with practically no waste of donor tissue. Procedure for UT-DSAEK Step 1: Debulking The tissue is mounted on a dispos- able artificial anterior chamber. To keep pressure in the artificial cham- ber constant at an ideal level of 80- 90 mm Hg, bottle height should be 120 cm above the tissue and the tub- ing is clamped at 50 cm from the en- trance into the chamber. Next, the tissue thickness is measured by means of ultrasound pachymetry. Pachymetry should be performed before and after the first debulking step to determine the actual tissue thickness and choose the appropri- ate microkeratome head(s). Then remove approximately 2/3 of the anterior stroma, using a disposable 300- or 350-micrometer cutting head, which should be passed for at least 4 seconds. The removed lamella may be retained for a subse- quent anterior LK case. Finally, the thickness of the residual stromal bed is measured. Step 2: Refining The tissue remains mounted on the artificial anterior chamber and the dovetail of the chamber is rotated 180 degrees in order to perform the second cut from a direction opposite to the one used for the debulking cut. The second cut (the refinement cut) is made with a 90- to 200-mi- crometer microkeratome head, de- pending on the tissue thickness, with the goal of ultimately creating a graft that is approximately 100 mi- crometers or less (see guidelines in table below). Each microkeratome pass is performed very slowly and Pachymetry ranges <150 micrometers Between 150 and 180 micrometers Between 180 and 210 micrometers Between 210 and 230 micrometers Between 230 and 250 micrometers Figure 3. Pull-through delivery of UT-DSAEK graft. The tip of the modified Busin glide is inserted into a 3 mm nasal clear cornea incision and a 23-G forceps is entered from the temporal side and used to grasp the tissue and pull it into the anterior chamber steadily (for at least 6 seconds). By starting the two cuts from opposite directions, the second cut is deeper exactly where the first cut was shal- lower. As a result, the risk of perfora- tion is minimized and the final shape of the graft is planar (Figure 1). These values have been ob- tained after several tests with tissue preserved at 37 degrees C in organ culture. The same criteria of choice for the second cut may not apply to tissue preserved differently (i.e., preservation at 4 degrees C). Step 3: Mark stromal side Using trypan blue, mark the periph- ery with a 9.0 round marker to visu- alize extension of the dissection. Then, mark asymmetrically (i.e., "F") the central stroma for proper posi- tioning. Step 4: Extend dissection Extend the dissection by hand into the periphery (this does not affect vision), if necessary. Step 5: Remove tissue Bend the tubing and open the plunger (to prevent collapse and en- dothelial damage) and remove the tissue from the front. Figure 4. Post-op appearance (overview and narrow-beam slit lamp pictures) of a UT-DSAEK graft 3 months after surgery. Best spectacle-corrected visual acuity is 20/20. The graft is barely visible with a central thickness of 65 micrometers, as measured by anterior OCT Step 6: Punch tissue to proper size Measure the vertical diameter of the recipient cornea and punch donor tissue to a size that would leave 0.5 mm of free recipient bed peripher- ally to the donor tissue (usually graft diameter varies between 8.25 and 9 mm). To prevent an incomplete punch, pull the rim upward, prior to removing the trephine. UT grafts obtained this way are very similar to grafts used for DMEK, which consist only of Descemet's and endothelium. Indeed, despite the presence of a layer of deep stroma, donor tissue cut extremely thin tends to curl, and its manipula- tion with forceps becomes extremely difficult. Therefore I developed a new glide, which added to the old design a loading platform necessary to scoop the UT graft from the punching block, thus eliminating the use of forceps for this maneuver (Figure 2). In addition, as the thin donor tissue takes up the form of a thin roll like a DMEK graft, the fun- nel of the glide was made shorter and narrower, allowing insertion into a wound of 3 mm. The pull- Choice of microkeratome head for second cut No second cut Use 50 micrometers Use 90 micrometers Use 110 micrometers Use 130 micrometers Source: Massimo Busin, M.D. through delivery is performed with a dedicated 23-gauge forceps, which is inserted from the temporal side and led across the anterior chamber to catch the tissue inserted into the nasal wound (Figure 3). When I compare UT-DSAEK to DSAEK and DMEK, my conclusion is that all three offer an acceptable rate of cell loss. With the ultra-thin pro- cedure, the speed of visual recovery is faster than conventional DSAEK and equivalent to DMEKā€”and the proportion of patients who achieve final acuity of 20/20 is higher than conventional DSAEK and perhaps also DMEK. In short, this procedure offers the potential to achieve the visual results of DMEK with the ease of handling and tissue preparation of DSAEK. EW Editors' note: Dr. Busin has financial interests with Moria (Antony, France). References 1. Price FW Jr., Whitson WE, Marks RG. Pro- gression of visual acuity after penetrating keratoplasty. Ophthalmol 1991;98(8):1177-85. 2. Zaidman GW, Goldman S. A prospective study on the implantation of anterior chamber intraocular lenses during keratoplasty for pseudophakic and aphakic bullous keratopa- thy. Ophthalmol 1990;97(6):757-62. 3. Neff KD, Biber JM, Holland EJ. Comparison of central corneal graft thickness to visual acuity outcomes in endothelial keratoplasty. Cornea 2011;30(4):388-91. Contact information Busin: mbusin@yahoo.com

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