Corneal lenticule harvest using a microkeratome and an artificial anterior chamber system at high intrachamber pressure

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.

Femtosecond laser lenticule transplantation in rabbit cornea: experimental study

PURPOSE

To evaluate the feasibility of femtosecond laser-induced lenticule transplantation in the rabbit cornea and to observe the relative histologic characteristics of corneal tissue and nerve repair after transplantation.

METHODS

Eight healthy, purebred, New Zealand white rabbits underwent femtosecond laser small-incision lenticule extraction (SMILE) surgery in the right eye. Lenticules were inserted into a femtosecond laser-created corneal stromal pocket in the left eye, which was defined as femtosecond laser corneal lenticule transplantation. Postoperative observation and examination were completed to evaluate the surgery.

RESULTS

In the early postoperative period, inflammation of the cornea was noted, tissue around the lenticule was edematous, and cells were activated. Tissue edema remained at postoperative day 10. By 1 month, edema had resolved, activated cells gradually became quiescent, and nerve fiber regeneration was observed. By 3 months, the lenticule integrated into the recipient cornea, extracellular matrix gradually cleared, and thicker nerve fibers were noted. By 6 months postoperative, morphology and distribution of the corneal stromal fibers were close to normal, and the number of nerve fibers was reduced.

CONCLUSIONS

Femtosecond laser corneal lenticule transplantation in rabbits is feasible, as the lenticule was shown to thrive and integrate with the recipient stroma. Nerve regeneration begins after 1 month.

Histologic evaluation of human posterior lamellar discs for femtosecond laser Descemet's stripping endothelial keratoplasty

PURPOSE

To evaluate the histologic changes in corneal structure after femtosecond laser preparation of posterior lamellar discs, more specifically, the smoothness of the stromal bed and the accuracy of the predicted depth of the horizontal lamellar cut.

MATERIALS AND METHODS

Nineteen human donor eyes unsuitable for transplantation were used. Femtosecond laser was used to prepare a horizontal lamellar cut in donor corneas at a depth of 400 microm. Transmission electron microscopy images were used to evaluate the changes in the corneal structure and to measure the damage zone. Scanning electron microscopy images were used to determine the relative depth of the horizontal lamellar cut, and the stromal bed was examined to determine the smoothness of the surface.

RESULTS

Transmission electron microscopy images showed a mean damage zone of 6.8 +/- 3.1 microm, which consisted of irregularly oriented collagen fibrils and electron-dense granular material. The collagen lamellae, both anteriorly and posteriorly of the damaged zone, showed a regular parallel configuration. The relative depth of the horizontal lamellar cut as percentage of the total corneal thickness in the center and periphery was 70.4% +/- 4.5% and 55.6% +/- 5.9%. Scanning electron microscopy images of the stromal bed showed a relatively smooth surface.

CONCLUSION

The femtosecond laser is effective to prepare a deep horizontal lamellar cut in a standardized method. The stromal bed is smooth and without extensive adjacent tissue damage. The is thinner in the center and thicker at the edges, which may produce a mild hyperopic shift after femtosecond laser-assisted Descemet's stripping endothelial keratoplasty.

Automated lamellar therapeutic keratoplasty (ALTK) in the treatment of anterior to mid-stromal corneal pathologies

PURPOSE

To evaluate the efficacy of automated lamellar therapeutic keratoplasty (ALTK) in the treatment of anterior to mid-stromal corneal pathologies.

METHODS

A prospective clinical study was undertaken in 15 eyes of 15 patients who underwent ALTK using the ALTK System (Moria/Microtek Inc., Doylestown, Pennsylvania, USA). The parameters evaluated were uncorrected and best corrected visual acuity (BCVA), keratometry, pachymetry, contrast sensitivity, glare acuity, intraoperative surgical time and complications, postoperative time to epithelialization, graft clarity and postoperative complications.

RESULTS

The mean surgical time was 46 +/- 9 mins. The BCVA, contrast sensitivity and glare acuity significantly improved at 6 months postoperatively. The mean decimal BCVA was 0.08 +/- 0.03 preoperatively, which improved to 0.33 +/- 0.30 at 6 months, when 11 eyes had BCVA > or = 6/18. The median epithelialization time was 3 days (range 1-10 days).

CONCLUSIONS

Automated lamellar therapeutic keratoplasty appears to be safe and effective for diseases affecting the anterior to mid-stroma of the cornea.

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.

Microkeratome Preparation of Lamellar Corneal Grafts

PURPOSE

To evaluate the thickness and viability of microkeratome-prepared lamellar corneal grafts in cold storage.

METHODS

Ten human corneas were sectioned with a mechanical microkeratome with a 350-microm depth head and stored in Optisol GS at 4 degrees C for 2 days to simulate an eye bank scenario. Central corneal thickness before and after mechanical microkeratome sectioning was measured by ultrasonic pachymetry. Endothelial cell viability was evaluated by trypan blue and alizarin red staining.

RESULTS

Total corneal thickness immediately before microkeratome dissection was 562 +/- 51 microm. Anterior and posterior graft thicknesses were 296 +/- 111 microm and 270 +/- 74 microm, respectively, immediately after dissection, and 282 +/- 38 microm and 429 +/- 31 microm, respectively, 2 days after storage. There was significant swelling in the posterior (P=0.005) but not the anterior grafts (P=0.386). The percentage of devitalized endothelial cells was 3.0% +/- 1.2%.

CONCLUSIONS

Corneal lamellar grafts may possibly be precut in a centralized facility and stored cold before further distribution.