Microkeratome Preparation of Lamellar Corneal Grafts

Advances in eye banking and corneal tissue processing

PURPOSE OF REVIEW

Eye bank processing of donor corneal tissue has helped to revolutionize and popularize newer corneal transplantation surgeries. In particular, Descemet stripping automated endothelial keratoplasty (DSAEK) and Descemet membrane endothelial keratoplasty (DMEK) have benefited from eye banks preparing donor corneal tissue in advance of the surgery. As a result of these eye banking advances, surgeons have been able to rapidly adopt these new techniques.

RECENT FINDINGS

This article reviews the techniques that are now being utilized to prepare donor tissue for endothelial keratoplasty (EK) with a focus on Ultrathin-DSAEK, prestamped, prestained, preloaded DMEK tissue, and advancements to improve the safety of donor corneal tissue.

SUMMARY

Collaborative efforts between surgeons and eye banks have been at the core of advances that have been made in EK over the past decade. Corneal surgery starts in the eye bank, and it is important for corneal surgeons to understand the process and appreciate the efforts that have been made to provide them with suitable and safe donor corneal tissue.

Global cell-by-cell evaluation of endothelial viability after two methods of graft preparation in Descemet membrane endothelial keratoplasty

Purpose

To describe a novel method of global cell viability assessment for Descemet membrane endothelial keratoplasty (DMEK) and the comparison of two contemporary methods of donor tissue preparation.

Methods

DMEK transplants were prepared using two different methods: liquid bubble separation and manual peeling (n=8 each group). Samples were incubated with Hoechst, calcein-AM and ethidium homodimer prior to mounting on a curved imaging chamber. Z-stacked fluorescence microscopy images were combined to produce an in-focus global image capable of resolving all cell nuclei. Image processing software was used to define a calcein-positive live cell area, count all cell nuclei within this area and subtract ethidium-positive dead cells to derive the total viable endothelial cell count. Corrected global cell density was calculated by dividing the number of viable cells by the graft area, which had been corrected for imaging a curved surface.

Results

Corrected global cell density was lower than the central endothelial cell density in both groups: 85.5% of the pre-preparation central endothelial cell density in the peel group and 75.8% in the bubble group. Corrected global cell density was significantly lower in the liquid bubble separation group than in the peel group (p=0.04).

Conclusions

Eye bank estimations of central endothelial cell density overestimate true cell density after graft preparation in DMEK. A peel method is less damaging and more consistent than a liquid bubble method. Cell loss correlated strongly with the degree of stromal hydration prior to bubble separation in the liquid bubble group.

Risk factors for donor endothelial loss in eye bank-prepared posterior lamellar corneal tissue for descemet stripping automated endothelial keratoplasty

PURPOSE

The aim of this study was to investigate donor, tissue, and precut procedure risk factors for endothelial cell density (ECD) loss in posterior lamellar corneal tissue preparation by an eye bank for Descemet stripping automated endothelial keratoplasty.

METHODS

A total of 259 corneoscleral rims precut by the Singapore Eye Bank from October 2011 to August 2013 were evaluated. Donor characteristics, tissue characteristics, and precut procedure parameters were analyzed.

RESULTS

The mean donor age was 57.18 ± 11.35 years, and the mean cutting transition time was 4.16 ± 0.75 seconds. The mean ECD was 2826 ± 225 and 2787 ± 224 cells per square millimeter before and after precutting, respectively, with an average ECD change of -1.38% ± 3.28%. The precutting procedure failure rate was 1.2%. Mutivariate regression analysis showed that an older donor age, a higher ECD before cutting, and a slower cutting transition speed were significant factors. Corneas with an ECD >2800 cells per square millimeter before precutting, cutting transition time >5.5 seconds, and corneas with donor age >65 years were significantly more likely to have greater than 5% ECD loss after precutting (odds ratio, 6.42, 1.66, and 1.62; 95% confidence interval, 1.44-29.43, 1.45-2.72, and 1.66-5.82, respectively). Donor source, death-to-preservation time (range, 0.67-10.88 hours), death-to-precutting time (range, 0-7 days), and graft thickness (range, 43-232 μm) were not statistically significant factors.

CONCLUSIONS

The ECD loss in the precut tissue prepared by the eye bank was very low. The risk factors identified provide better understanding of how to improve the quality and safety profiles when preparing graft tissue for Descemet stripping automated endothelial keratoplasty.

A comprehensive analysis of eye bank-prepared posterior lamellar corneal tissue for use in endothelial keratoplasty

PURPOSE

The purpose of this study was to assess eye bank-prepared corneal tissue with regards to the accuracy of postcut tissue thickness, endothelial cell loss, and rate of successful processing.

METHODS

Details of all 913 corneal tissues processed with an automated microkeratome for use in posterior lamellar transplantation, over a 1-year period, were obtained from a large eye bank. The number and success rate of all attempted cutting procedures were analyzed. The thickness of the corneal button obtained after cutting was compared with the graft thickness requested by the operating surgeon. Changes in endothelial cell density (ECD) during tissue processing were evaluated.

RESULTS

The rate of successful tissue preparation increased over the time period examined, from 95% in the first quarter to 99.5% in the fourth quarter. Graft material was frequently slightly thicker than requested by the operating surgeon with 28.3% of tissues cut thicker than requested. Postcut ECD over the entire period increased by an average of 4.7% and was closely related to the starting ECD.

CONCLUSIONS

There was a very high rate of successful tissue preparation (98.5%), and early failed attempts at tissue cutting were likely the result of the initial learning curve of the involved technicians. Practical considerations resulted in tissue being cut marginally thicker than requested; this is an issue about which the operating surgeon should be aware, because it may possibly influence tissue handling. The quality of the obtained material, as measured by ECD, was excellent, although the calculated ECD may be prone to measurement artifact.

Lamellar keratoplasty with a novel anterior chamber system and organ cultured donor corneas

PURPOSE

To present a novel artificial anterior chamber system for anterior and posterior lamellar keratoplasty.

METHODS

The artificial anterior chamber system MOZARTTM in conjunction with the AMADEUSTM II microkeratome was evaluated for its applicability in anterior and posterior lamellar keratoplasty using organ cultured donor corneas.

RESULTS

Twelve patients underwent microkeratome-assisted lamellar keratoplasty for corneal opacifications due to either anterior stromal scaring or endothelial decompensation. Eight patients underwent Descemet stripping automated endothelial keratoplasty (DSAEK) and 4 patients underwent anterior lamellar keratoplasty (ALK). A 400-microm and 250-microm cutting head was used for DSAEK and ALK, respectively. In all patients, an 8.5-mm suction ring was applied. For the 250-microm cutting head, a mean anterior lamella thickness of 244+/-12 microm was found. For the 400-microm cutting head, a mean anterior lamella thickness of 390+/-18 microm was found. The graft diameter was 8.85+/-0.5 mm for the 8.5-mm suction ring with both cutting heads. Deswelling of the anterior donor lamella was 11.5% compared to 30% of the posterior lamella transplant after 6 months of follow-up.

CONCLUSION

The AMADEUSTM II microkeratome in conjunction with the MOZARTTM artificial anterior chamber system proved to be a suitable device for modern lamellar keratoplasty. Swelling and deswelling characteristics of organ cultured corneas need to be further investigated to optimize the deswelling time prior to donor cornea sectioning in lamellar keratoplasty.

Precut tissue for Descemet's stripping automated endothelial keratoplasty: vision, astigmatism, and endothelial survival

PURPOSE

To report 6 and 12 month results using precut tissue for Descemet's stripping automated endothelial keratoplasty (DSAEK) and correlate donor characteristics with clinical outcomes.

DESIGN

Prospective, noncomparative, interventional case series.

PARTICIPANTS

We reviewed 100 donor corneas precut for 100 eyes of 90 DSAEK patients.

METHODS

Our first 100 consecutive cases of DSAEK with precut tissue were entered into a prospective protocol. Donor characteristics and the visual, refractive, topographic, and specular microscopy results at 6 and 12 months were analyzed. Correlation analysis comparing donor characteristics with clinical outcomes was performed.

MAIN OUTCOME MEASURES

Six- and 12-month postoperative best spectacle-corrected visual acuity (BSCVA), refractive astigmatism, topographic keratometry (K), and specular endothelial cell densities (ECD) were measured prospectively and then compared with preoperative values. Donor characteristics analyzed included death to preservation time, death to surgery time, precutting resection to surgery time, and graft thickness.

RESULTS

Six months after DSAEK surgery, BSCVA improved from 20/83 to 20/38. (P<0.01). In eyes with no known comorbidity (n = 60), 92% had a vision of >/=20/40 at 6 months and 20% obtained > or =20/20. Astigmatism changed an average of 0.09 diopters (D) and K changed by +0.09 D, both of which were not significant and were stable to 12 months. The postoperative mean ECD (n = 65) was 1918 cells/mm(2) at 6 months, and represented a 31% cell loss from preoperatively (P<0.001). The mean ECD (n = 61) was 1990 cells/mm(2) at 12 months, and represented a 29% cell loss from preoperatively (P<0.001) with no significant change from 6 to 12 months (P = 0.172). Improvement of visual acuity from preoperative to postoperative in eyes without comorbidity was not correlated with any donor characteristic. Greater endothelial cell loss correlated with higher preoperative ECD levels (P<0.001) and with a trend toward longer precut resection to surgery times at both 6 months (P = 0.049) and 12 months (P = 0.051).

CONCLUSIONS

Precut tissue by Eye Banks for use in DSAEK surgery provides an improvement in vision with no significant change in astigmatism. Donor endothelial cell loss from 6 to 12 months is stable and is comparable with reports involving tissue that is cut intraoperatively.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosures may be found after the references.

Descemet's stripping endothelial keratoplasty

PURPOSE OF REVIEW

Descemet's stripping endothelial keratoplasty (DSEK) is rapidly becoming the preferred treatment for corneal endothelial dysfunction. Familiarity with recent advances in techniques and instrumentation can help reduce the initially steep learning curve and incidence of complications.

RECENT FINDINGS

DSEK produces excellent visual outcomes with minimal change in corneal surface topography or refraction. It can successfully treat corneal dysfunction associated with Fuchs' endothelial dystrophy, bullous keratopathy, iridocorneal endothelial syndrome or a failed penetrating graft. Donor dissection has become automated, and new techniques have been devised to facilitate graft insertion and unfolding. Some surgeons now routinely perform DSEK with topical anesthesia. Graft detachment is the most frequent early postoperative complication, but new methods can help promote donor adherence. The incidence of graft-rejection episodes is lower after DSEK compared with standard penetrating keratoplasty, possibly because wound healing is a lesser concern, and many DSEK patients are maintained on low-dose topical steroids indefinitely. Early efforts to transplant just the endothelial cell layer show promise.

SUMMARY

DSEK provides quicker visual rehabilitation and an improved safety profile compared with standard penetrating keratoplasty. Continued evolution of this relatively new technique is helping to reduce complications and further improve outcomes.