Evaluation of a microkeratome-based limbal harvester device for limbal stem cell transplantation

A New Technique for Harvesting Limbal Stem Cell Tissue for Transplantation Using an Automated Microkeratome and a Novel Globe-Fixation System

PURPOSE

To introduce an unprecedented technique, instrumentation, and setup for the superficial limbus harvest from the human cadaver donor whole globe.

METHODS

We studied several superficial limbus harvest alternatives, developed a preferred approach with our available instruments, and optimized it on a handful of (seropositive) cadaver donors of whole globes.

RESULTS/TECHNIQUE

The globe was pressurized to about normal intraocular pressure by viscoelastic injection through the optic nerve stump. The globe was then mounted on a dynamic globe fixator that maintained a negative pressure in its stabilizing socket. Exertion of the negative pressure effectively elevated globe intraocular pressure (to over 40 mm Hg) and made the corneoscleral wall tight. The socket was then held tilted to the left side for about 35 to 40 degrees to put the limbal zone horizontally and mildly "chin-up." Next, the microkeratome was put on the uppermost and exposed limbus of the globe and activated, and the socket was rotated clockwise under the microkeratome head and its oscillating blade, allowing an effective 360-degree revolution of the microkeratome head around the limbal belt (for a right-handed operator and a counterclockwise cut).

CONCLUSIONS

We consistently succeeded in peeling intact 360-degree strips of the smooth superficial limbus by using blades with varying depths. Our method can be further equipped and optimized and be used by the eye banks and the surgeons for keratolimbal grafting as a more efficient limbal stem cell tissue harvest technique.

Total anterior corneal surface and epithelial stem cell harvesting: current microkeratomes and beyond

Currently, most corneal lamellar allografts are performed by manually dissecting donor corneoscleral material for transplantation. Manual dissection is technically challenging and time intensive, and excessive handling of tissue may decrease the likelihood of obtaining viable grafts. These mechanical factors, along with problems controlling immune rejection, have prevented limbal stem cell lamellar allografts in particular from becoming more widely used. Anterior lamellar keratoplasty is gaining in clinical importance and usage but is still only practiced by a limited number of surgeons. Recently, new mechanical and femtosecond laser microkeratomes have been adapted to harvest the anterior corneal surface, including the limbal stem cell region. Preliminary results have been encouraging and give hope that this technique may prove to be of benefit to patients in the future.

Eccentric lamellar keratolimbal grafts harvested with a manually guided microkeratome. Technical report

BACKGROUND

To perform lamellar keratolimbal allograft transplantation in a one-step procedure with a single graft, we investigated the feasibility of harvesting eccentric lamellar keratolimbal grafts from conventionally processed corneoscleral buttons using a manually guided microkeratome in conjunction with an artificial anterior chamber system.

METHODS

We used the Moria LSK-One microkeratome and the automated lamellar therapeutic keratoplasty (ALTK) system (Antony, France). Ten human donor eyes were used to obtain single-piece lamellar keratolimbal grafts. Specimens were processed for light and electron microscopy.

RESULTS

Eccentric keratolimbal grafts could be obtained from all human donor buttons. Grafts include a crescent-shaped limbal and a large corneal portion. No visible damage to the limbal region was discernible.

CONCLUSION

Our data show that the LSK-One microkeratome in conjunction with the ALTK system allows harvesting eccentric keratolimbal grafts from donor corneoscleral buttons.

Femtosecond Laser Keratome Creation of Partial Thickness Donor Corneal Buttons for Lamellar Keratoplasty

PURPOSE

To evaluate the thickness and diameter accuracy of the IntraLase femtosecond laser in harvesting corneal discs for lamellar keratoplasty. The stromal bed quality of resected corneas was evaluated by scanning electron microscopy.

METHODS

Two IntraLase units were used to create corneal discs at 225-, 300-, 400-, and 500-microm thickness settings and 7-, 8-, 8.5-, and 9-mm diameter settings (n = 28). Achieved thickness was measured using a digital caliper and achieved diameter was measured using imaging software. Samples were preserved and processed for scanning electron microscopy to observe stromal bed quality.

RESULTS

On both units, the mean deviation from attempted thickness was -9.5 +/- 8.6 microm (range: +6 to -28 microm). All of the obtained corneal discs were circular (horizontal versus vertical diameters, P > .05). The raster pattern produced a smoother stromal bed compared to the spiral pattern.

CONCLUSIONS

The IntraLase femtosecond laser keratome provides depth and diameter accuracy even at increased depth settings. Stromal bed was smooth with the raster pattern and can further be smoothed by excimer phototherapeutic keratectomy treatment. Femtosecond laser lamellar keratoplasty is a promising procedure and clinical data are needed to determine effectiveness.

Microkeratome versus femtosecond laser predissection of corneal grafts for anterior and posterior lamellar keratoplasty

PURPOSE

To compare 2 different techniques for predissection of human anterior and posterior lamellar corneal grafts for eye bank storage.

METHODS

A mechanical microkeratome (group 1, N = 5) and a femtosecond laser (group 2, N = 5) were used to dissect intended 350-microm-deep lamellar planes in deepithelialized donor corneas mounted on an artificial anterior chamber. These corneas were replaced in Optisol GS at 4 degrees C postoperatively and examined 2 days later to simulate a clinical scenario. Ultrasonic pachymetry of corneal lamellar sections was measured before and after separation of the lamellar grafts. Group 1 sections were separated by the mechanical microkeratome, whereas group 2 sections were manually separated 2 days after laser dissection. Endothelial cell viability was evaluated in posterior grafts.

RESULTS

Total corneal thicknesses immediately before dissection were 559 +/- 61 (group 1) and 578 +/- 79 microm (group 2; P = 0.46). Immediate postdissection anterior and posterior graft thicknesses were 361 +/- 68 and 203 +/- 74 microm (group 1), respectively. Achieved anterior and posterior graft thicknesses 2 days later were 282 +/- 44 and 413 +/- 35 microm (group 1) and 324 +/- 112 and 397 +/- 51 microm (group 2), respectively. Percentage of devitalized endothelial cells were 3.4% +/- 1.6% (group 1) and 1.6% +/- 1.2% (group 2; P = 0.35).

CONCLUSIONS

Centralized predissection by both techniques, cold storage, and shipping by airmail results in viable grafts without significant endothelial cell loss 2 days later.

A technique to harvest Descemet's membrane with viable endothelial cells for selective transplantation

PURPOSE

To describe a surgical technique using an artificial anterior chamber to facilitate harvest of Descemet's membrane (DM) and endothelium for corneal endothelial cell transplantation.

DESIGN

Laboratory investigation.

METHODS

Corneoscleral buttons of seven human donor eyes were mounted endothelial side up on an artificial anterior chamber. Keeping the endothelial side with its usual concavity, a manual trephination was made on the posterior surface with a 9.0-mm trephine, inside the Schwalbe line and just past the DM in depth. The chamber was filled with air, causing the endothelial side of the donor cornea to assume a convex configuration. The DM along with its endothelium was separated from the posterior stroma using a blunt cyclodialysis spatula. Drops of trypan blue 0.3% and alizarin red S 0.2% (n = 6) were applied. The stained DMs were examined under a light microscope and photographed to calculate the percentage of endothelial cell damage. Histology was done on the unstained cornea.

RESULTS

The DM carrying endothelium was successfully removed from the posterior stroma in all seven eyes. Although the DM appears to be very friable, all samples were removed in toto without rupture. Vital staining showed a mean endothelial cell loss of 8.46% (standard deviation (SD) 6.9). Direct light microscopy demonstrated the preservation of endothelial cell morphology.

CONCLUSIONS

This technique appears to be a safe and straightforward method to harvest DM for endothelial cell transplantation. Further studies are underway to determine the optimal method of insertion of the obtained healthy DM with endothelial cells through small corneal incisions.

A Portable Microkeratome for Harvesting the Human Anterior Corneal Surface

A portable, gas-driven turbine microkeratome device capable of harvesting the entire anterior corneal surface for lamellar transplantation on human donor globes was evaluated. The device consisted of a modified LASIK microkeratome with an enlarged suction ring, head, and blade. Vacuum was achieved by a simple hand pump. Lamellar keratectomy was performed on 5 fresh human donor globes. Lenticule dimensions were measured on days 0, 3, 6, and 9 after storage in preservation media at 4 degrees C. On day 0, the obtained lenticules were 13.9 +/- 0.9 mm and 13.5 +/- 0.4 mm, vertical and horizontal diameters, respectively. The average central lenticule thickness was 152.2 +/- 52 microm. Each lenticule was uniform in thickness over 5 measurement points (P = 0.74). Repeat measurements of corneal thickness over the 9 days showed no statistically significant difference (P = 0.51). On day 9 lenticules were 14.6 +/- 0.3 mm and 14.6 +/- 0.4 mm, vertical and horizontal diameters, respectively. When day 0 was compared to day 9, vertical diameter also showed no statistically significant difference (P = 0.16), whereas horizontal diameter was significantly different (P < 0.001). This device proves to be an economical alternative to electric-powered systems for the harvest of transplantable corneal sections.