The overall goal of this procedure is to consistently produce lamellar corneal graft tissue that is suitable for transplant. This is accomplished by first establishing a sterile field in the laminar flow hood. Next, the cornea is secured in an artificial anterior chamber.
Then a microkeratome is used to make a smooth pass through and across the cornea. The final step is to carefully transfer the cornea from the artificial anterior chamber to storage medium. Ultimately, successful lamellar graft preparation is verified via slit lamp viewing of the cornea and specular microscopy of the endothelial cells.
The main advantage of this technique over existing methods like penetrating ker plasty, is with dsec only the posterior portion of the cornea is replaced, allowing a small incision surgery with fewer sutures, faster recovery, and improved refractive outcomes. Visual demonstration of this method is critical. The lamellar dissection steps for endothelial kersty are difficult to learn.
Precision and care are needed when cutting the tissue to preserve healthy corneal tissue. Begin by turning the nitrogen gas on in the laminar flow hood to 50 to 60 PSI. The turbine pressure on unit should read 3.3 to 3.4 bars.
Ensure the pressure on the Moria console is in the seven hundreds on pumps one and two. The pressure should be below 200 PSI. Using aseptic technique, prepare a sterile field with open sterilized kits and the donor corneal tissue, ensure that the pachymetry probe has been sterilized and cleaned isopropanol.
Then after removing the contents from the sterile tray, connect the infusion line to the stop cock and extend the spike end of the line out of the hood. Place the infusion line down and remove the sterile tray. Next, spike a bottle of balanced salt solution and hang it about four feet from the work area.
Now perform a six minute surgical scrub and dry with a sterile towel. Put on a sterile gown and two pair of sterile gloves in the hood. Open the instrument boxes and place their contents onto the sterile field.
Pour 10 to 20 cc of BSS into a metal basin or medicine cup and fill a sterile pipette. With that BSS connect the stop cock and infusion line to the infusion port of the anterior chamber and flush it with BSS. Stop flushing When BSS becomes visible on top of the piston.
Now position the artificial chamber onto sterile gauze and lower the piston by turning the graft tightening Ring counterclockwise approximately five millimeters using forceps. Center the cornea over the piston endothelial side down flush system with BSS until there are no air bubbles beneath the cornea. Gently move the cornea as needed.
Now fit the anterior chamber cover into the open spaces on the base locking ring and lock it in place with a small 15 degree clockwise turn. Then raise the piston and finish tightening the chamber to the base with a sterile gloved finger. Touch the top of cornea to check if there is enough pressure to perform the procedure.
Now place the pachymetry probe on surface of cornea and have an assistant record the reading. If the standard deviation is more than 10 microns, retake the measurement with a sterile gloved hand. Pass the turbine hose to the other hand and screw the turbine hose into the control unit.
After disposing of the contaminated gloves, place a few drops of BSS on top of the cornea unless the surgeon specifies. Otherwise, select a cutting blade based on the thickness of the cornea with thread facing toward you and number facing upward. Load the blade into right side of the microkeratome head pointed end first.
Always avoid contact with the blade holding the head at each side. Screw it onto the turbine, and screw the turbine onto the turbine hose. Test the blade oscillation by pressing the vacuum pedal once with the cutting head in BSS, pulse the turbine for five seconds.
Now make the piston finger tight. Next, mount the microkeratome onto the base at the post and position it to five o'clock. Then press and hold turbine pedal to oscillate blade.
Using your index finger and thumb, hold the microkeratome midway between the base and the top of the turbine. With the turn of the wrist, make a smooth even cut through and across the cornea. Make sure the microkeratome pass is smooth and even by using a constant speed, failure to do so can result in an uneven graft thickness.
Release the turbine pedal and lift microkeratome straight upward off the unit. Then turn off. Vacuum don a sterile glove and with the aid of an assistant, recheck the pachymetry reading, being mindful that the tissue is very thin and easily damaged.
Then place a few drops of sterile BSS onto residual stromal bed. Then place the anterior cap back onto the cornea in the chamber. Use a swab sphere to center the cap using available marking and to absorb any BSS underneath the anterior cap.
Now open the stop cock, turn the chamber sideways and lower the piston slowly enough to prevent cornea from deforming. Unlock the base and allow pressure from the BSS flow to press the artificial chamber cup to loosen the cornea from the cup. Use forceps to gently tug at its rim at the nine 12 and three o'clock positions.
Once loosened, grasp the rim at the 12 o'clock position and carefully transfer the cornea to the viewing chamber and endothelial side up. Then close the viewing chamber. Slowly allow the cap to separate from the anterior chamber.
This will ensure that the cornea does not collapse, which could cause damage to the endothelium. Finally, perform a slit lamp evaluation and a specular microscopy examination of the cornea. Then refrigerate the chambers and pack the cornea for transport to the surgeon.
Proper mechanical microkeratome dissection of the donor cornea results in smooth uniform lamellar corneal donor in six months of patric recordings, the mean pre-processing corneal thickness has been 558 microns and the post-processing thickness of the posterior corneal tissue has been 158 microns. The posterior corneal tissue must retain a high endothelial cell density to provide improved endothelial function to the transplant recipient. This was measured by specular microscopy in the past six months.
All of the corneal tissue deemed eligible for endothelial ker plasty had more than 2, 200 endothelial cells per square millimeter. The mean change in pre to post-processing ECD was negligible at 1.2%After watching this video, you should have a good understanding of how to prepare LA melo tissue for daic surgery. Once mastered, this technique can be done in 20 minutes if it is performed properly.
