Efficiency of blood culture bottles for the fungal sterility testing of corneal organ culture media

BACKGROUND/AIM

The consequences of fungal contamination of an organ cultured cornea, though exceptional, are often disastrous for the recipient. Consequently, eye banks often quarantine corneas for 10 days or more before passing them for grafting. This period, though detrimental to the endothelial cell density of the delivered cornea, is necessary to detect contamination using conventional microbiological methods. The authors previously validated the use of a pair of aerobic and anaerobic blood bottles for sensitive and rapid detection of bacteria. To allow a short quarantine period, it remained only to optimise detection of fungi. The authors aimed to compare sensitivity and rapidity of fungal contamination detection by three methods: blood bottles, Sabouraud, and daily visual inspection of the organ culture medium.

METHODS

Four inocula (10(6), 10(4), 10(2), 10 colony forming unit (CFU) per ml) of 11 fungi (Candida albicans, C tropicalis, C glabrata, Saccharomyces cerevisiae, Rhodotorula rubra, Cryptococcus neoformans, Fusarium oxysporum, Aspergillus niger, A fumigatus, A flavus, Acremonium falciforme) were inoculated in a commercial organ culture medium containing a coloured pH indicator (CorneaMax, Eurobio, Les Ulis, France). The real live fungal inoculum was verified immediately after inoculation. After 48 hours at 31 degrees C, samples of the contaminated media were inoculated in three blood bottles: Bactec Aerobic/F, Bactec Mycosis IC/F, and Bactec Myco/F Lytic (Becton Dickinson, Le Pont de Claix, France), then placed in a Bactec 9240 rocking automat, and in four Sabouraud media (solid and liquid, 28 degrees C and 37 degrees C) with daily observation. Contaminated organ culture media were also checked daily for any change in turbidity and/or colour. Experiments were performed in triplicate.

RESULTS

Mycosis IC/F and Myco/F Lytic bottles were neither faster nor more sensitive than the aerobic bottle. The three methods were positive for all inocula, even the lowest (viable inoculum below 10 CFU/ml for each fungus). Contamination was detected within 24 hours by the aerobic bottles in 91% (40/44), by Sabouraud in 98% (43/44) (no significant difference) and by visual inspection in 66% of cases (29/44) (p<0.001 with the two others). Maximum times to detection were 46, 48 and 72 hours respectively.

CONCLUSION

This study further counters the preconception that fungal contamination is hard to detect in corneal organ culture media. This study is the last step in validating the use of a pair of blood bottles for the sterility testing of organ culture media, this time for fungi. Their use should make it possible to shorten microbiological quarantine and thus deliver corneas with higher endothelial cell density, without increasing the risk of recipient contamination.

Screening for diabetic retinopathy in France

Ocular complications of diabetes, particularly retinopathy, are the major cause of blindness in the working age population in industrialised nations. Laser photocoagulation has shown definite results in reducing visual morbidity with many more likely to benefit if diagnosed early enough. Institution of an efficient screening programme aimed at detecting patients at risk when they can still be effectively treated has been recognised as an urgent priority worldwide. In France, a signatory to the Saint Vincent's Declaration, an analysis of the national healthcare database reveals a gross inadequacy in the current extent of screening for diabetic retinopathy. The possible causative factors have been analysed and the necessary corrective measures, some of which are already under way, have been discussed. Ideally, screening by ophthalmologists at recommended intervals have been advised by national and professional health care associations. This has not been feasible owing to the lack of organised planning and serious manpower deficit caused by a progressive decline in the number of ophthalmologists. Recently, the need for an efficient, widely-available and user-friendly screening tool has led to the evaluation of multifield fundus photography in real time using digital nonmydriatic camera in comparison with more established methods of detecting diabetic retinopathy. Lastly, the future possibility of involving in France non-ophthalmologists like endocrinologists or general practitioner or non medical profession like orthoptists after proper training to meet the necessary manpower shortage has been addressed. Optimal use of telemedicine along with establishment of preferential reference channels for newly discovered cases of sight-threatening cases of retinopathy are public health priority necessary to give to the screening of diabetic retinopathy its full efficiency.

Is manual counting of corneal endothelial cell density in eye banks still acceptable? The French experience

AIM

To examine the differences in manual endothelial cell counting methods in French eye banks and to analyse whether these differences could explain some substantial discrepancies observed in endothelial cell density (ECD) for corneas made available for transplant.

METHODS

A questionnaire was sent to the 22 eye banks asking for details of the technical features of the light microscopes used, the microscope calibration, strategy for cell counting, the technical staff, and the method of presenting endothelial data.

RESULTS

All eye banks responded and 91% (20/22) used only manual counting methods, in real time, directly through a microscope, and 62 different technicians, with varying experience, were involved in such counting. Counting of cells within the borders of a grid that were in contact with two adjacent borders was the most common method (17/22, 77%). Of the eight banks (8/22, 36%) that did not calibrate their microscopes, six reported the highest ECD values. Of the 14 others (64%), six applied a "magnification correcting factor" to the initial cell counts. In five of these cases, the corrected ECD was lower than estimated on initial count. Most of the banks (12/22, 55%) counted 100 cells or less in one to six non-adjacent zones of the mosaic. 14 of the banks (14/22, 64%) also graded cell polymegethism while seven (7/22, 32%) also graded pleomorphism ("hexagonality").

CONCLUSIONS

Lack of microscope calibration appears to be the leading cause of variance in ECD estimates in French eye banks. Other factors such as differences in counting strategy, the evaluation of smaller numbers of cells, and the different extent of experience of the technicians may also contribute to intraobserver and interobserver variability. Further comparative studies, including cross checking and the outcome of repeated counts from manual methods, are clearly needed with cross calibration to a computer based image archiving and analysis system.

[Optimizing microbiological controls of corneal organ culture media]

BACKGROUND/AIMS

To compare the efficiency of an automated method using blood bottles with conventional microbiological tests for controlling sterility in cornea organ culture media.

METHODS

Two complementary studies were conducted. Experimental study: standard organ culture media were contaminated with four different inocula of 14 bacteria and 3 fungi. The bactericidal activity of organ culture media were evaluated after 48 hours of incubation at 31C. Observational study: 357 samples of organ culture media were collected over 1 year in our cornea bank. For both studies, media were inoculated in three blood bottles (aerobic, anaerobic, fungal) placed in an automat with automated detection every 10 minutes, and in three conventional microbiological media as a control. Changes in organ culture medium color and growth on conventional broth were checked daily by visual inspection. All samples were observed experimentally for 14 days. The sensitivity and rapidity of contamination detection were compared across the three methods: blood bottles, conventional method, and visual inspection of medium color.

RESULTS

Experimental study: organ culture medium eradicated five bacteria: S. pneumoniae, B. catarrhalis, E. coli, P. acnes and H. influenzae. For the others, (Methicillin-resistant S. aureus, Methicillin-sensitive S. aureus, S. epidermidis, S. haemolyticus, P. aeruginosa, A. baumannii, B. subtilis, K. pneumoniae, E. faecalis, C. albicans, C. kruzei, A. fumigatus) the blood bottle method, the conventional microbiological method, and the visual inspection detected microbiological growth respectively in 100%, 76.5%, and 70% of cases. Mean detection time using blood bottles was 15.1 hours (standard deviation, 13.8; range, 2-52). In cases of detection by the blood-bottle method and the conventional method, the former was always faster: 95.5% versus 65.2% detection within 24 hours (p=0.022). Observational study: the global contamination rate was 8% (29/357 analysis). The gain in sensitivity with blood bottles was 25% compared with the conventional method. Five bacteria (three coag. neg Staphylococcus, one E. faecalis, one P. paucimobilis) were detected only by the blood bottles. In addition, these were always detected more quickly with, respectively, 66.6% versus 26.6% detection with 24 hours (p=0.028).

CONCLUSIONS

Blood bottles detect contaminations of cornea organ culture media more efficiently and faster than conventional microbiological methods. They make it possible to reduce the quarantine period with an equally high security level. Consequently, they should be recommended in cornea preservation guidelines.

[Management of traumatic cataracts]

Traumatic cataract is the severe result of an accident often concerning young patients, sometimes children. Anatomical and clinical presentations vary depending on whether the lens is luxated, the wound involves perforation, or there is an intraocular foreign body. The associated wounds and the late complications, particularly retinovitreous ones, can impair the visual prognosis sometimes over the very long term. The correction of aphakia with an intraocular lens should be decided on a case by case basis.

Mechanisms of staurosporine induced apoptosis in a human corneal endothelial cell line

BACKGROUND

Apoptosis very probably plays a key part in endothelial cell loss during corneal storage in organ culture as well as hypothermic storage. However, the mechanisms underlying endothelial apoptosis are poorly understood. The response of a human corneal endothelial cell (HCEC) line to staurosporine, a known inducer of apoptosis, was investigated to gain insights into the intracellular modulators that participate in endothelial cell death.

METHODS

Immortalised HCECs were studied after 3, 6, 12, and 24 hours of incubation with 0.2 micro M staurosporine. Cell shedding was monitored. Hoechst 33342 fluorescent DNA staining combined with propidium iodide was used for apoptosis/necrosis quantification and morphological examination. The caspase-3 active form was assessed using western blot, proteolytic activity detection, and immunocytochemistry. The cleaved form of poly(ADP-ribose) polymerase (PARP) was assessed using immunocytochemistry and western blot. The ultrastructural features of cells were screened after 12 hours with staurosporine or vehicle.

RESULTS

The specific apoptotic nature of staurosporine induced HCEC death was confirmed. The ultrastructural features of staurosporine treated cells were typical of apoptosis. HCEC shedding and DNA condensation increased with time. Caspase-3 activity was detected as early as 3 hours after exposure with staurosporine, peaking at 12 hours of incubation. The presence of cleaved PARP after 3 hours confirmed caspase-3 activation.

CONCLUSIONS

These data suggest strongly that HCEC cell death induced by staurosporine is apoptosis. The main consequence of HCEC apoptosis is shedding. Staurosporine induced apoptosis of endothelial cells involves activation of caspase-3, and could be a useful model to study strategies of cell death inhibition.

[Facial anesthetic blocks in the treatment of acute pain during ophthalmic zoster]

BACKGROUND

Ophthalmic zoster is frequently accompanied by severe pain in the frontal and nasal divisions of the ophthalmic nerve. Treating this pain is often difficult, particularly in elderly patients, owing to iatrogenic effects and to interactions with the pre-existing diseases and treatments frequently present in this age group. The aim of our study was to consider the efficacy and toxicity of the frontal and nasal nerve blocks in the treatment of severe pain during acute ophthalmic zoster in the elderly.

MATERIAL AND METHODS

A prospective study was conducted on 20 patients (mean age, 76 +/-7 years; range, 63-88) presenting with acute ophthalmic zoster with severe pain (less than 1 month since onset), which had resisted analgesic medication. All patients had a visual analogue score for pain (VAS) of 4 or more and received one or more anesthetic blocks of a compound of bupivacaine with adrenaline associated with clonidine at the frontal branch and sometimes the nasal branch levels of the ophthalmic nerve. Pain was measured daily by VAS for 5 days, and the blocks were repeated if the VAS was still 4 or higher. Patients were checked for local or systemic side effects.

RESULTS

The number of anesthetic blocks per patient ranged from one to four (mean: 2.3 +/-0.7). All patients experienced less pain after the first injection. The mean preinjection VAS was 7.4 +/-1 and fell to 4.8 +/-1.0, 4.1 +/-1.1, 3.5 +/-1.0, 3.2 +/-0.6 and 2.8 +/-0.9 at day 1, day 2, day 3, day 4 and day 5, respectively (p<0.001). It was possible to reduce analgesic medication permanently in all patients. No local or systemic side effect was observed.

CONCLUSION

Anesthetic blocks of the frontal and nasal branches, repeated if necessary, give fast and effective relief from the severe pain of acute ophthalmic zoster. They are fully tolerated and simple to administer, making them an excellent indication in the complementary treatment of the pain of hyperalgic acute zoster in the elderly.

Sensitivity and rapidity of blood culture bottles in the detection of cornea organ culture media contamination by bacteria and fungi

AIMS

To test the bactericidal activity of standard organ culture medium, and to compare the sensitivity and rapidity of blood culture bottles with conventional microbiological methods for detection of bacteria and fungi inoculated in a standard cornea organ culture medium.

METHODS

The bactericidal activity of contaminated standard organ culture medium containing 100 IU/ml penicillin, 0.1 mg/ml streptomycin, and 0.25 micro g/ml amphotericin B was evaluated after 48 hours of incubation at 31 degrees C with five inocula of 14 bacteria. Two yeasts (Candida spp) and one Aspergillus were also tested. Contaminated media were then inoculated in three blood bottles (aerobic, anaerobic, fungal) placed in a Bactec 9240 automat; three conventional microbiological broths were the control. Changes in colour of organ culture medium and growth on conventional broth were screened daily by visual inspection. The sensitivity and rapidity of detection of contamination were compared between the three methods: blood bottle, conventional, and visual.

RESULTS

Organ culture medium eradicated five bacteria irrespective of the starting inoculums: Streptococcus pneumoniae, Branhamella catarrhalis, Escherichia coli, Propionibacterium acnes, and Haemophilus influenzae. For micro-organisms where the medium was ineffective or bactericidal only (methicillin resistant Staphylococcus aureus, methicillin sensitive Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus haemolyticus, Pseudomonas aeruginosa, Acinetobacter baumannii, Bacillus subtilis, Klebsiella pneumoniae, Enterococcus faecalis, Candida albicans, Candida kruzei, Aspergillus fumigatus), the blood bottle, conventional, and visual methods detected microbial growth in 100%, 76.5%, and 70% of cases respectively. Mean detection time using blood bottles was 15.1 hours (SD 13.8, range 2-52). In cases of detection by the blood bottle method and the conventional method, the former was always faster: 95.5% against 65.2% detection within 24 hours (p=0.022) respectively.

CONCLUSIONS

Blood bottles detect more efficiently and more rapidly a wider range of bacteria and fungi than the conventional microbiological method and the visual inspection of organ culture media.

Automated tri-image analysis of stored corneal endothelium

BACKGROUND

Endothelial examination of organ culture stored corneas is usually done manually and on several mosaic zones. Some banks use an image analyser that takes account of only one zone. This method is restricted by image quality, and may be inaccurate if endothelial cell density (ECD) within the mosaic is not homogeneous. The authors have developed an analyser that has tools for automatic error detection and correction, and can measure ECD and perform morphometry on multiple zones of three images of the endothelial mosaic.

METHODS

60 human corneas were divided into two equal groups: group 1 with homogeneous mosaics, group 2 with heterogeneous ones. Three standard microscopy video images of the endothelium, graded by quality, were analysed either in isolation (so called mono-image analysis) or simultaneously (so called tri-image analysis), with 50 or 300 endothelial cells (ECs) counted. The automated analysis was compared with the manual analysis, which concerned 10 non-adjacent zones and about 300 cells. For each analysis method, failures and durations were studied according to image quality.

RESULTS

All corneas were able to undergo analysis, in about 2 or 7.5 minutes for 50 and 300 ECs respectively. The tri-image analysis did not increase analysis time and never failed, even with mediocre images. The tri-image analysis of 300 ECs was always most highly correlated with the manual count, particularly in the heterogeneous cornea group (r=0.94, p<0.001) and prevented serious count errors.

CONCLUSIONS

This analyser allows reliable and rapid analysis of ECD, even for heterogeneous endothelia mosaics and mediocre images.

[Cornea donation consent by telephone]

BACKGROUND

The cornea donation process often runs into problems of obtaining family consent. A face-to-face interview is often not possible for logistical reasons. We carried out a prospective study on the effectiveness of telephone contact in obtaining donation consent.

MATERIAL AND METHODS

Consent was obtained by a single, non medical, hospital coordinator. He contacted families selected on good staff-family relations during the patient's stay. If a face-to-face interview was not possible, a telephone interview was conducted using a standardized procedure.

RESULTS

Over 21 months, 334 families were contacted, either in a face-to-face interview (142, 42.5%) or by telephone (192, 57.5%). Donation consent was obtained in 66.5% of cases, 106 times by telephone (47.7%) and 116 times in the face-to-face interview (52.3%). The acceptance rate was 55.2% by telephone and 81.6% face to face (p<0.001).

CONCLUSIONS

The telephone interview was an effective method for obtaining consent for cornea donation. Although the acceptance rate using this method is lower than the face-to-face interview, using the telephone should not be overlooked as this enabled procurement of nearly half the corneas in our hospital.

[Automated analyser of organ cultured corneal endothelial mosaic]

PURPOSE

Until now, organ-cultured corneal endothelial mosaic has been assessed in France by cell counting using a calibrated graticule, or by drawing cells on a computerized image. The former method is unsatisfactory because it is characterized by a lack of objective evaluation of the cell surface and hexagonality and it requires an experienced technician. The latter method is time-consuming and requires careful attention. We aimed to make an efficient, fast and easy to use, automated digital analyzer of video images of the corneal endothelium.

METHODS

The hardware included a PC Pentium III ((R)) 800 MHz-Ram 256, a Data Translation 3155 acquisition card, a Sony SC 75 CE CCD camera, and a 22-inch screen. Special functions for automated cell boundary determination consisted of Plug-in programs included in the ImageTool software. Calibration was performed using a calibrated micrometer. Cell densities of 40 organ-cultured corneas measured by both manual and automated counting were compared using parametric tests (Student's t test for paired variables and the Pearson correlation coefficient).

RESULTS

All steps were considered more ergonomic i.e., endothelial image capture, image selection, thresholding of multiple areas of interest, automated cell count, automated detection of errors in cell boundary drawing, presentation of the results in an HTML file including the number of counted cells, cell density, coefficient of variation of cell area, cell surface histogram and cell hexagonality. The device was efficient because the global process lasted on average 7 minutes and did not require an experienced technician. The correlation between cell densities obtained with both methods was high (r=+0.84, p<0.001). The results showed an under-estimation using manual counting (2191+/-322 vs. 2273+/-457 cell/mm(2), p=0.046), compared with the automated method.

CONCLUSIONS

Our automated endothelial cell analyzer is efficient and gives reliable results quickly and easily. A multicentric validation would allow us to standardize cell counts among cornea banks in our country.

Cornea procurement from very old donors: post organ culture cornea outcome and recipient graft outcome

AIM

To study the suitability of corneas from very old donors for graft after banking and their clinical and endothelial outcomes in recipients.

METHODS

419 corneas stored in organ culture were divided into group 1, donors under 85 years (330 corneas) and group 2, "very old" donors aged 85 years and over (89 corneas). Endothelial cell density (ECD) before and after organ culture, discard rate before and after storage, and clinical and endothelial outcomes of the 196 penetrating keratoplasties (PKP) (158 in group 1 and 38 in group 2) were compared in a prospective longitudinal study.

RESULTS

Initial ECD was lower in group 2 than in group 1 and elimination for low ECD was more frequent in group 2 (respectively 38% v 20.2%, p=0.001). At the end of storage, because very old corneas lost fewer ECs than younger ones (respectively 4.2% v 9.5%, p=0.022), ECD was comparable between the two groups. The corneas of very old donors had a poorer macroscopic appearance at procurement and during surgery. Despite this, in grafted patients, overall graft survival in groups 1 and 2 (respectively 87.4% v 80.6%, p=0.197), visual acuity, and ECD did not differ at completion of the study (mean follow up 25 months).

CONCLUSION

This study suggests that endothelial cell count during banking ensures that functional and cellular results of PKPs are not dramatically influenced by very old donor age. Considering Europe's ageing population, the very elderly should not be deemed off limits for corneal procurement.

[Use of a pair of blood culture bottles for sterility testing of corneal organ culture media]

PURPOSE

To test the effectiveness and rapidity of a pair of blood culture bottles in the diagnosis of bacterial and fungal contamination of corneal organ culture media.

MATERIAL

and methods: Seven hundred and sixty one microbiological analysis of storage media (Inosol(R) and Exosol(R), Opsia, Toulouse, France), sampled in all phases of the organ culture at 31 degrees C of 410 consecutive corneas, were analyzed. Each medium was inoculated in a pair of Bactec Plus Aerobic/F(R) and Bactec Lytic/10 Anaerobic/F(R) blood bottles (Becton Dickinson, Cockeysville, MD) and placed in a Bactec 9240 incubator for 14 days at 37 degrees C and in a Sabouraud broth at 20 degrees C. Changes in color or turbidity of storage media were evaluated daily at the corneal bank. Recipients were screened after graft for signs of infection.

RESULTS

The overall contamination rate was 2.4% (18/761). Contamination was detected in less than 1 day in 78% (14/18) and in less than 2 days in 94% (17/18). Positivity of the microbiological controls of starting media preceded medium color changes in 10 out of 14 cases. Bactec blood bottles allowed detection of bacteria as well as Candida sp. yeasts.

DISCUSSION

The use of a pair of aerobic and anaerobic blood culture bottles is a simple, effective and rapid method for the diagnosis of a wide range of microbiological contaminations of organ-cultured corneas during banking.

CONCLUSION

The validation of this protocol will require a prospective study to compare it with the conventional microbiological method.

[Corneal harvesting from donors over 85 years of age: cornea outcome after banking and grafting]

PURPOSE

To study the suitability of corneas from very old donors for graft after organ culture and their clinical and endothelial outcomes in recipients after perforating keratoplasty.

METHODS

We stored 419 corneas at 31 degrees C for 13.1 +/- 4 days (mean +/- SD) and then divided them according to donor age: group 1, donors under 85 years of age (n=3 3 0, 79%, 16-84 years old), and group 2, donors over the age of 85 (n=8 9, 21%, 85-100 years old). Endothelial density at the time of harvest and before and after organ culture, rates of suitability for grafting, and clinical and endothelial outcomes of the 196 keratoplasty procedures were compared in a prospective longitudinal study of the 2 groups, with a mean follow-up of 25 months. The corneas were grafted with no pre-established policy on matching with the age of the receiver. Statistical analysis was carried out on SPSS 10.0: Chi(2), Student t test, and Kaplan Meier survival curves.

RESULTS

The average age of the donors was 72.1 +/- 16.7 years. The macroscopic aspect of the corneas was judged to be of slightly lower quality in group 2. No statistically significant difference was found in overall suitability for transplantation (group 1, 45% vs group 2, 54%, p=0.17) but elimination for low endothelial density was more frequent in group 2 (67% vs 39%, p=0.001). Cell density at the beginning of organ culture was lower in very old corneas than in younger corneas (respectively, 2116 +/- 368 vs 2 311 +/- 360 cell/mm(2), p=0.002) but no difference was apparent at the end of organ culture (respectively, 2 011 +/- 285 vs 2 090 +/- 296, p=0.12) because very old corneas lost fewer cells than younger ones (respectively, 5.6% vs 10.0%, p=0.001). There was no correlation between donor/receiver age (r=0. 337) but group 1 corneas were slightly more frequently allotted to receivers with normal endothelium (p=0.019). During surgery, the two groups did not differ in terms of the macroscopic aspect of the grafts. In the 196 grafted patients, and without age-matching, overall graft survival (86% vs 79%, p=0.275), visual acuity, and endothelial density (1 194 +/- 469 vs 1098 +/- 545 cells/mm(2), p=0.387) did not differ at the completion of the study.

DISCUSSION

The corneas from very old donors were macroscopically of poorer quality and had a lower cellular endothelial density at harvesting, but these differences disappeared after organ culture because of greater cell loss in corneas from younger donors. Selection by organ culture ensures that functional, anatomical, and cellular results are not influenced by very old donor age.

CONCLUSION

Considering the aging population in countries with a high standard of living, the techniques available for selecting corneas based on endothelial quality, and the increasing need for corneal grafts, the very old age should not be deemed off-limits for corneal harvesting.

Value of two mortality assessment techniques for organ cultured corneal endothelium: trypan blue versus TUNEL technique

BACKGROUND/AIM

It is known that trypan blue staining is not a good predictor of loss of corneal endothelial cells (ECs) during organ culture. As it is primarily an indicator of membrane integrity, it would also not be expected to identify ECs undergoing apoptosis. The aim of this study was to determine the ability of the in situ TdT dUTP mediated nick end labelling (TUNEL) technique to detect cell death in the corneal endothelium caused by apoptosis during organ culture, compared with conventional vital staining with trypan blue.

METHODS

31 human corneas were organ cultured at 31C for 3-35 days. Staurosporine was used to induce apoptosis in five control corneas. The endothelium was assessed by trypan blue and by the in situ TUNEL technique. The percentages of trypan and TUNEL positive ECs were compared. Their links with sex, donor age, time from donor death and organ culture, initial and final EC density and cell loss were studied.

RESULTS

TUNEL stained ECs were observed in all corneas. TUNEL positive ECs were mostly located either in corneal folds or at the periphery of corneal folds showing central shedding. The mean percentage of cell death at the end of storage, assessed by the trypan blue technique, was 1.47% (SD 2.63, range 0.03-12); assessed by the TUNEL technique it was 12.7% (SD 16.4 range 0.6-65.5). There was a significant correlation between the two techniques (r = 0.7, p<0.001). The percentage of TUNEL stained ECs was correlated negatively with EC density at the end of storage (r = -0.47, p <0.005) and positively with percentage EC loss during storage (r = 0.46, p < 0.05).

CONCLUSION

This study demonstrates that organ cultured corneas systematically carry non-viable ECs that are implicated in cell death by apoptosis and go undetected when trypan blue staining is used. Because the in situ TUNEL assay detects earlier events in the cell death process than does trypan blue, it should be used to quantify endothelial viability, especially for experiments with new storage media.