Purpose
To compare the quality of corneal tissue after 2 different procurement techniques, whole-globe enucleation and in situ excision.
Design
Cross-sectional study.
Methods
Data in the interval 2005 to 2008 were collected from the Lions Eye Bank of Oregon. A total of 3618 eyes underwent whole-globe enucleation (enucleation group) and 2048 eyes were subject to in situ excision (in situ group). Endothelial cell density (ECD) and death-to-preservation time (D-to-P) were analyzed. Grading scores ranging from 0 (excellent) to 4 (unacceptable for transplantation) were used to evaluate the epithelium, stroma, Descemet fold, and overall endothelium. The incidences of ECD less than 2000 cells/mm 2 (ECD <2000), primary graft failure (PGF), and postoperative infection were investigated.
Results
ECD was 2726 ± 419 cells/mm 2 in the enucleation and 2645 ± 395 cells/mm 2 in the in situ group ( P < .001). D-to-P was 9.81 ± 3.56 hours and 8.90 ± 3.65 hours, respectively ( P < .001). The mean grade of the stroma was 1.44 ± 0.51 in the enucleation group and 1.50 ± 0.56 in the in situ group ( P = .001). The mean grades of overall endothelium were 1.51 ± 0.72 and 1.58 ± 0.69, respectively ( P < .001). The incidence of ECD <2000 was 2.38% in the enucleation group and 2.39% in the in situ group ( P > .999), PGF rates were 0.72% and 0.68% ( P > .999), and postoperative infection levels were 0.14% and 0.39% ( P = .080).
Conclusion
Although there were minor differences in parameters related to the endothelium, in situ excision seemed equivalent to whole-globe enucleation when various parameters were evaluated.
Two procurement techniques are used to recover corneal tissue from donors. These are 1) whole-globe enucleation, with subsequent retrieval of the corneoscleral disc in the eye bank, and 2) in situ excision with direct storage of tissue in preservation medium. In the time since in situ excision was introduced by Vannas, it has been suggested that the associated risks of microbial contamination and endothelial cell loss are greater than when whole-globe enucleation is used. However, recent studies reported that in situ excision was a viable technique resulting in a higher initial corneal disc quality compared with that associated with whole-globe enucleation. In situ excision also offers some advantages compared with whole-globe enucleation, such as a simpler protocol and earlier placement of tissue in storage medium. Therefore, there has been a recent trend toward the preferential use of in situ excision, rather than whole-globe enucleation.
In situ excision using a large trephine was recently introduced. This may impose less trauma on the corneoscleral tissue and offer greater procedural simplicity. In previous studies, however, in situ excision was performed using curved corneal scissors, and comparisons of initial characteristics of tissue obtained with this technique and whole-globe enucleation used relatively broad criteria, with study sample sizes that were too small to allow detailed comparison of relevant parameters. Therefore, it remained unclear whether the 2 procedures were of equal quality in terms of detailed assessment of corneal donor tissue.
Here, we compared corneal donor disc quality after in situ excision using a large trephine and after whole-globe enucleation, using various assessment parameters and a detailed grading system.
Patients and Methods
Donor information and data on donor corneal assessment from 2005 to 2008 were retrieved from the Lions Eye Bank of Oregon (Portland, Oregon, USA). Donor information included donation year, donor age, right or left eye, and cause of death. Donor corneal assessment was measured using grading systems for each part of the donor corneoscleral button: the epithelium, stroma, Descemet fold, and the overall endothelium. The grading system used in this study assessed the overall quality of each part of the corneoscleral button using a scale of 0 to 4; 0 was excellent, 1 very good, 2 good, and 3 fair, and 4 indicated that the cornea was suitable only for scientific research, being unacceptable for transplantation ( Table 1 ). Endothelial cell density (ECD) was measured using a HAI EB-3000 XYZ Eye Bank specular microscope (HAI Laboratories, Lexington, Massachusetts, USA), and death-to-preservation time was recorded. Occurrence of infection and primary graft failure were also recorded.
| Grade | Definition | |
|---|---|---|
| Epithelium | 0 | Defects: none; intact epithelium. Haze: none or just a trace of haze. |
| 1 | Mild haze; exposure without sloughing; intact epithelium. | |
| 2 | Mild-to-moderate haze; exposure with some sloughing or epithelial defects. | |
| 3 | Moderate-to-heavy haze; exposure with sloughing and/or epithelial defects. | |
| 4 | Heavy haze; exposure with sloughing; opacities; many defects (may be suitable for endothelial keratoplasty if endothelium/posterior stroma evaluation is acceptable). | |
| Stroma | 0 | None or just a trace of edema; no arcus; no opacities; and an 8-mm clear zone. |
| 1 | Slight edema; clear or light arcus no more than 1.5 mm from the limbus. | |
| 2 | Mild-to-moderate edema; clear-to-moderate arcus no more than 3 mm from the limbus. | |
| 3 | Moderate-to-heavy edema; moderate-to-heavy arcus or cloudiness 2-4 mm from the limbus. | |
| 4 | Heavy edema and/or heavy arcus; cloudiness; and opacities. | |
| Descemet fold | 0 | No folds or striae. |
| 1 | Few shallow folds or striae. | |
| 2 | Mild-to-moderate folds or striae. | |
| 3 | Moderate-to-heavy folds or striae. | |
| 4 | Heavy folds or striae. | |
| Endothelium | 0 | Adequate density of endothelial cells that are uniform in size and shape. |
| 1 | Adequate density of endothelial cells that are uniform in size and shape; no guttatae. | |
| 2 | Adequate density of endothelial cells, which are not all uniform in size and shape; few guttata cells without uniformity in size or shape; many guttatae. | |
| 3 | Moderate density of endothelial cells with no uniformity in size or shape; moderate guttatae. | |
| 4 | Few endothelial cells. |
Whole-Globe Enucleation
The operation field (lid, nose, and forehead) was prepared with 10% (volume-volume percentage, % v/v) povidone-iodine and covered with a sterile drape. A lid speculum was placed. Using tenotomy scissors, the conjunctiva was opened by cutting a circle around the cornea. Scissors were used to perform a blunt dissection back to the region of the muscles, and the 4 recti muscles were isolated and severed. The globe was elevated and the optic nerve was severed using enucleation scissors. The eye was removed and irrigated with balanced salt solution (BSS; Alcon Laboratories Inc, Fort Worth, Texas, USA). Next, the eye was transferred into a moist chamber. A plastic ball coated with lanolin cream was inserted into the orbital cavity and the eyelids were closed. A moist cotton ball was placed over each eye and a dry gauze sponge was applied over the cotton ball and secured with paper tape. A similar procedure was applied to the other eye. The entire globe was soaked in 1% povidone-iodine for 3 minutes and immersed in saline for 1 minute at the central eye bank facility. Then the globe was rinsed with BSS to avoid possible corneal endothelial toxicity of povidone-iodine, immediately prior to introduction of the tissue to the sterile field, and the corneoscleral button was retrieved in Optisol GS (Bausch & Lomb, Irvine, California, USA).
In Situ Excision
Five percent povidone-iodine (Alcon Laboratories) was instilled for 2 minutes, after which it was rinsed completely free from the eye using BSS (Alcon Laboratories). The operation field (lid, nose, and forehead) was prepared with 10% v/v povidone-iodine and covered with a sterile drape. A lid speculum was placed. Using tissue forceps and tenotomy scissors, the conjunctiva was cut at the limbus in a circle around the cornea. The corneoscleral button was incised using a cutting trephine (diameter 18 mm; Stephens Instruments, Lexington, Kentucky, USA), leaving a 2- to 4-mm scleral rim. In some circumstances, the trephine might not cut a complete circle through the sclera. Using Castroviejo scissors, cutting the scleral rim could be completed. Corneoscleral rim removal was completed by grasping the rim with a pair of forceps and pulling the ciliary body downward and away from the cornea. After careful removal to avoid application of unnecessary tension to the corneal button, the button was transferred to a preservation chamber. To reconstruct the donor’s external appearance, cotton was placed in the scleral shell, as needed. An eye cap (Dodge Co, Cambridge, Massachusetts, USA) was placed over the cotton and the lids were gently closed over the eye caps. A similar procedure was performed on the other eye.
Statistical Analysis
Data were analyzed using SPSS version 14.0 software (SPSS Inc, Chicago, Illinois, USA). Categorical variables were described as numbers of subjects and compared using Fisher exact test and linear-by-linear association between the 2 groups. Continuous variables were described as means and standard deviations and were compared using the Mann-Whitney U test. A P value < .05 was considered to be statistically significant.
Results
A total of 6923 eye donations were received in the interval 2005 to 2008 by the Lions Eye Bank of Oregon. Donated corneas without sufficient accompanying donor information or with incomplete corneal evaluation were excluded. A total of 5666 donations were eligible for inclusion in this study. Whole-globe enucleation was performed on 3618 eyes and in situ excision on 2048 eyes. There were no significant differences in donor age, right or left eye, and cause of death between the 2 groups. However, there was a significant increase in in situ excision over time ( Table 2 ).
| Whole-Globe Enucleation (n=3618) | In Situ Excision (n=2048) | |
|---|---|---|
| Eye, n (%) | ||
| OD | 1806 (49.92) | 1025 (50.05) |
| OS | 1812 (50.08) | 1023 (49.95) |
| Age (years) | 57.49 ± 14.15 | 57.80 ± 12.83 |
| Cause of death, n (%) | ||
| Cancer | 738 (20.40) | 394 (19.24) |
| CVA | 558 (15.42) | 266 (12.99) |
| Heart disease | 1116 (30.85) | 708 (34.57) |
| Respiratory disease | 442 (12.22) | 232 (11.33) |
| Trauma | 313 (8.65) | 160 (7.81) |
| Other disease | 451 (12.47) | 288 (14.06) |
| Year a | ||
| 2005 | 1001 (77.72) | 287 (22.28) |
| 2006 | 1060 (78.40) | 292 (21.60) |
| 2007 | 916 (66.42) | 463 (33.58) |
| 2008 | 641 (38.92) | 1006 (61.08) |
The averages of the grading scores for the epithelium and Descemet fold did not differ significantly between the 2 groups ( Table 3 ). However, significant differences in grading scores were noted in some years. Epithelium scores showed significant between-group differences in all years except 2008. When the averages of the grading scores for the stroma and overall endothelium were compared, there were statistically significant differences between the 2 groups. In 2006 in particular, the average scores of the stroma, Descemet fold, and the endothelium were significantly better in the whole-globe enucleation group (stroma, 1.423 ± 0.490 vs 1.495 ± 0.557; Descemet fold, 1.436 ± 0.454 vs 1.491 ± 0.422; overall endothelium, 1.492 ± 0.715 vs 1.647 ± 0.835). The ECD average was 2758.01 ± 419.46 cells/mm 2 in the enucleation group and 2674.29 ± 388.50 cells/mm 2 in the in situ excision group ( P < .001, Table 4 ). From a chronological perspective, ECD in the whole-globe enucleation group was better in 2007 and 2008 compared with the in situ excision group. Death-to-preservation time showed statistically significant differences between the 2 groups in all years: 9.81 ± 3.56 hours in the enucleation group vs 8.90 ± 3.65 hours in the in situ excision group ( P < .001). The incidence of ECD less than 2000 cells/mm 2 was 2.38% in the enucleation group and 2.39% in the in situ excision group; the incidence of primary graft failure was 0.72% and 0.68%, respectively; and the incidence of infection was 0.14% and 0.39%, respectively ( Table 5 ). There were no statistically significant differences between the 2 groups in any of these parameters ( P > .999, P > .999, and P = .080, respectively).
| Year | Whole-Globe Enucleation | In Situ Excision | P Value | |
|---|---|---|---|---|
| Epithelium | 2005 a | 2.036 ± 0.610 | 2.144 ± 0.533 | .020 |
| 2006 a | 1.919 ± 0.572 | 1.988 ± 0.474 | .017 | |
| 2007 a | 1.935 ± .0.474 | 1.992 ± 0.478 | .013 | |
| 2008 | 1.923 ± 0.455 | 1.931 ± 0.460 | .553 | |
| Total | 1.956 ± 0.542 | 1.983 ± 0.481 | .065 | |
| Stroma | 2005 | 1.364 ± 0.498 | 1.387 ± 0.584 | .792 |
| 2006 a | 1.423 ± 0.490 | 1.495 ± 0.557 | .017 | |
| 2007 | 1.510 ± 0.527 | 1.489 ± 0.467 | .875 | |
| 2008 | 1.506 ± 0.537 | 1.539 ± 0.583 | .464 | |
| Total a | 1.443 ± 0.514 | 1.500 ± 0.557 | .001 | |
| Descemet fold | 2005 | 1.388 ± 0.483 | 1.357 ± 0.477 | .399 |
| 2006 a | 1.436 ± 0.454 | 1.491 ± 0.422 | .021 | |
| 2007 | 1.496 ± 0.457 | 1.482 ± 0.420 | .675 | |
| 2008 | 1.473 ± 0.431 | 1.446 ± 0.431 | .097 | |
| Total | 1.445 ± 0.461 | 1.448 ± 0.435 | .663 | |
| Overall endothelium | 2005 | 1.391 ± 0.786 | 1.371 ± 0.678 | .565 |
| 2006 a | 1.492 ± 0.715 | 1.647 ± 0.835 | .025 | |
| 2007 | 1.617 ± 0.698 | 1.628 ± 0.630 | .229 | |
| 2008 | 1.547 ± 0.645 | 1.592 ± 0.666 | .293 | |
| Total a | 1.506 ± 0.724 | 1.577 ± 0.692 | <.001 |
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