The precision of unbiased estimates of numerical density of endothelial cells in donor cornea

Human Corneal Endothelial Cell Assessment From Tissues Preserved in Serum-Based and Synthetic Storage Media

PURPOSE

To assess the difference between endothelial cells from tissues preserved in media supplemented with fetal bovine serum (FBS) and recombinant human serum albumin (rHSA).

METHODS

In a donor-matched study, 48 tissues were preserved for 28 days at 31°C in Cornea Max and Cornea Syn supplemented with FBS and rHSA, respectively. Endothelial cells were visualized by 2 masked observers before and after preservation. Endothelial cell density (ECD) and the number of iatrogenic folds were counted manually. Alizarin red staining and tight junction protein (Zonula Occludens-1) were used to assess cell morphology (hexagonality and polymorphism). Intraobserver and interobserver cell counts were recorded and analyzed. Wilcoxon and one-way analysis of variance tests were used, where P < 0.05 was deemed statistically significantly different.

RESULTS

Significant amount of iatrogenic folds were observed in the tissues supplemented with FBS compared with rHSA postpreservation (P = 0.0007). Approximately 69% and 71% hexagonal cells (P = 0.0303) and 29% and 26% polymorphic cells (P = 0.0234) were observed in the FBS and rHSA groups, respectively. Postpreservation, operator 1 counted 1766 cells/mm in FBS and 1864 cells/mm in rHSA. Operator 2 counted 1702 cells/mm in FBS and 1858 cells/mm in rHSA. ECD counts from FBS (interoperator) were statistically significant (P = 0.0429). However, significance was not observed in the ECD counts (interoperator) from the rHSA-preserved tissues (P = 0.8738).

CONCLUSIONS

rHSA-supplemented media allow better visualization of the corneal endothelial cells. This reduces the rate of discard observed due to counting errors. Use of rHSA improves the current standard of care and reduces the use of animal-derived products.

The role of corneal endothelial morphology in graft assessment and prediction of endothelial cell loss during organ culture of human donor corneas

PURPOSE

Endothelial assessment is crucial in the release of corneas for grafting. We retrospectively analysed the role of endothelial morphology parameters in predicting endothelial cell loss during organ culture.

METHODS

Human donor corneas were cultured in minimal essential medium with 2% fetal calf serum and antibiotics. Initial endothelial morphology was assessed microscopically using score parameters polymegethism (POL), pleomorphism (PLE), granulation (GRA), vacuolization (VAC), segmentation of cell membranes (SEG), Descemet's folds (DF), trypan blue-positive cells (TBPC) and endothelial cell-free areas (ECFA). Some corneas were primarily rejected based on endothelial assessment. Endothelial cell density (ECD) was assessed at the beginning (I-ECD) and end of culture. Corneas were then placed in dehydration medium (as above + 5% dextran 500). In a subgroup, ECD was reassessed after dehydration. Endothelial cell loss during culture (ECL@Culture) and culture+dehydration (ECL-Culture&Dehydration) were calculated. Data were given as mean ± SD and analysed using multiple linear and logistic regression. Odds ratios (OR) and 95% confidence intervals (CI) were calculated.

RESULT

I-ECD was 2812 ± 360/mm² (n = 2356). The decision to reject a cornea due to endothelial assessment was associated negatively with I-ECD (OR = 0.77/100 cells, CI 0.7-0.82) and positively with ECFA (OR = 2.7, CI 1.69-4.35), SEG (OR =1.3, CI 1.01-1.68) and donor age (OR = 1.26/decade, CI 1.33-1.41). ECL@Culture was 153 ± 201/mm² (n = 1277), ECL@Culture&Dehydration was 169 ± 183/mm² (n = 918). ECL@Culture was associated positively with donor age, I-ECD, GRA and TBPC, and negatively with PLE, and DF. ECL@Culture&Dehydration was associated positively with age, sex, initial ECD, POL, PLE, VAC and TBPC.

CONCLUSION

Morphological parameters displayed associations with the exclusion of corneas from culture and with endothelial cell loss. Appropriate parameter selection for screening purposes may help improve graft quality.

Non-contact specular microscopy of human corneal endothelium

The non-contact specular microscope enables a large area of the corneal endothelium to be examined and photographed without any risk of traumatizing the anterior surface of cornea. This non-contact technique is described in detail. Standard deviation of the relative difference between two independent estimates of central endothelial density from 24 eyes was 3.7%. Standard deviation of the relative difference between counts from left and right eyes from 57 subjects was 4.7%. A significant negative correlation between age and endothelial cell density was found (r = -0.59, P less than 0.001, n = 76). The interindividual variation in cell densities was found to be larger in the old age group, indicating that cell loss during aging varies among different individuals.

Endothelial morphology related to disease activity in human corneas

Twenty normal and four groups of pathological corneas with the diagnoses aphakia, macula after herpetic keratitis. Fuchs' endothelial dystrophy and graft rejection were stained with trypane blue and alizarin red. The morphology of the endothelium was described in terms of cell density, coefficient of variation for cell area, percentage of hexagonal cells, percentage of joint meetings of more than three cells, nuclei per cell and nuclear shape. The groups of aphakia, keratitis, Fuchs' dystrophy and graft rejection were considered to represent increasing degrees of endothelial disease activity at the time of evaluation. The only parameter showing consistent variation with disease activity was the percentage of joint meetings of more than three cells.

Corneal Endothelial Viability After Femtosecond Laser Preparation of Posterior Lamellar Discs for Descemet-Stripping Endothelial Keratoplasty

PURPOSE

To evaluate the feasibility of the femtosecond (FS) laser in preparation of posterior lamellar discs (PLDs) and to study the effect on endothelial cell (EC) viability for Descemet-stripping endothelial keratoplasty.

METHODS

Fourteen human donor bulbi unsuitable for transplantation were used. A horizontal lamellar cut was prepared in the donor cornea with an FS laser by using a raster and/or a spiral spot pattern. The control group consisted of the paired cornea of the same donor. EC density was evaluated before and after preservation in organ culture. The PLD was stripped from the anterior part by using either a forceps or a blunt dissection technique. The damage to the endothelium was evaluated.

RESULTS

EC loss after organ storage was not statistically significant between the FS cornea group and the control group in the 15- (7.7% +/- 6.9% and 8.9% +/- 8.1%, respectively; P = 0.78) and 30-kHz (4.3% +/- 4.0% and 3.7% +/- 3.6%, respectively; P = 0.75) group. There was no significant effect of laser frequency (15 vs. 30 kHz) on EC loss (7.7% vs. 4.3%, P = 0.25). Dissection by using a forceps stripping technique resulted in higher EC loss than that with a blunt dissection technique (13.0% vs. 6.5%, P = 0.03).

CONCLUSIONS

EC loss after FS laser lamellar cutting is not dependent on the frequency (ie, energy level) of the laser. A blunt dissection technique of PLDs resulted in acceptable EC loss and supports the clinical use of the FS laser for the preparation of PLDs.

Specular microscopy ancillary study methods for donor endothelial cell density determination of Cornea Donor Study images

PURPOSE

To describe reliable methods for determining central corneal endothelial cell density (ECD) in a multicenter eye bank study.

METHODS

The Specular Microscopy Reading Center utilized a dual-grading procedure and adjudication process to classify image quality and determine ECD for a subset of donor endothelial images obtained in the Specular Microscopy Ancillary Study, which is part of the Cornea Donor Study. Two certified readers classified images as analyzable (excellent, good, fair) or unanalyzable and determined the ECD using a variable frame technique. An adjudicator also evaluated the images if quality classifications by the two readers differed by one grade, if any reader found the image unanalyzable, and/or if the ECD determination between the two readers was >or= 5%.

RESULTS

Image quality categorization by the two readers was identical for 441 (64%) of 688 donor images. The ECD differed by < 5% for 442 (69%) of the 645 analyzable images. The ECD determined by the adjudicator was < 5% different than the ECD determined by at least one reader for 193 (95%) of the 203 remaining images.

CONCLUSIONS

The dual-grading and adjudication procedures produce reliable, reproducible assessments of image quality and ECD. The importance of two independent readings is evident in that image quality ratings differed between the two readers by one grade in 36% of all images and ECD counts differed by >or=5% for 31% of analyzable images.

Endothelial cell density in porcine corneas after exposure to hypotonic solutions

PURPOSE

To evaluate exposure to sucrose solution (1.8%) and hypotonic balanced salt solution (BSS) for its effects on endothelial cell density of porcine corneas.

METHODS

Two groups of central discs from pig corneas were organ-cultured for 24 h. Twelve corneas per group were exposed to sucrose solution (1.8%) or hypotonic BSS for 4 min each. The paired corneal discs were not treated and served as controls. After further organ culture with and without dextran for 48 h, corneal endothelium was stained with alizarin red and examined by light microscopy. The endothelial cell densities were determined manually on three central images.

RESULTS

The endothelial cell density differed significantly between corneas exposed to sucrose and the control corneas (3982+/-382 cells/mm(2) and 4360+/-331 cells/mm(2) respectively, and 3876+/-364 cells/mm(2) versus 4374+/-168 cells/mm(2) respectively with 6% dextran). In contrast, the endothelial cell density did not differ significantly between corneas exposed to hypotonic BSS and the control corneas (4374+/-296 cells/mm(2) and 4317+/-193 cells/mm(2) respectively, and 4348+/-151 cells/mm(2) versus 4426+/-175 cells/mm(2), respectively with 6% dextran).

CONCLUSIONS

Exposure to 1.8% sucrose for 4 min induces a significant endothelial cell loss of 10% on average, whereas exposure to hypotonic BSS did not significantly influence the endothelial cell density.

Validity of Endothelial Cell Analysis Methods and Recommendations for Calibration in Topcon SP-2000P Specular Microscopy

PURPOSE

To report on the calibration of the Topcon SP-2000P specular microscope and the Endothelial Cell Analysis Module of the IMAGEnet 2000 software, and to establish the validity of the different endothelial cell density (ECD) assessment methods available in these instruments.

METHODS

Using an external microgrid, we calibrated the magnification of the SP-2000P and the IMAGEnet software. In both eyes of 36 volunteers, we validated 4 ECD assessment methods by comparing these methods to the gold standard manual ECD, manual counting of cells on a video print. These methods were: the estimated ECD, estimation of ECD with a reference grid on the camera screen; the SP-2000P ECD, pointing out whole contiguous cells on the camera screen; the uncorrected IMAGEnet ECD, using automatically drawn cell borders, and the corrected IMAGEnet ECD, with manual correction of incorrectly drawn cell borders in the automated analysis. Validity of each method was evaluated by calculating both the mean difference with the manual ECD and the limits of agreement as described by Bland and Altman.

RESULTS

Preset factory values of magnification were incorrect, resulting in errors in ECD of up to 9%. All assessments except 1 of the estimated ECDs differed significantly from manual ECDs, with most differences being similar (< or =6.5%), except for uncorrected IMAGEnet ECD (30.2%). Corrected IMAGEnet ECD showed the narrowest limits of agreement (-4.9 to +19.3%).

CONCLUSIONS

We advise checking the calibration of magnification in any specular microscope or endothelial analysis software as it may be erroneous. Corrected IMAGEnet ECD is the most valid of the investigated methods in the Topcon SP-2000P/IMAGEnet 2000 combination.

Age-related modifications of the corneal endothelium in adults

PURPOSE

To obtain the topographical distribution of the corneal endothelial cell density, in different age ranges.

METHODS

Three hundred eyes of 204 healthy subjects (110 males (M) and 94 females (F)) aged from 20 to 83 years were evaluated. Participants were divided into three groups according to age. First group (120 eyes) comprised patients aged from 20 to 44 years (mean 32.27 +/- 7.5), the second group (110 eyes) comprised patients aged from 45 to 70 years (mean 54.13 +/- 7.1) and the third group (70 eyes), comprised participants older than 70 years (mean 79.28 +/- 5.9). Specular microscopy was performed in the central zone and in four peripheral points.

RESULTS

Central and peripheral cell densities decrease with age (p < 0.05). In young adults the endothelial cell density did not show any significant variation in the central area with respect to the periphery (p > 0.05). In older adults the difference between central and peripheral endothelial cell densities showed the significance level of p = 0.05.

CONCLUSIONS

Topographical distribution of the corneal endotheliul cell density is maintained lifelong. Age-related changes involve both center and periphery. The higher peripheral decrement observed in the ancient subjects could be considered as a major finding and in elderly a topographical disparity might occur.

An evaluation of image quality and accuracy of eye bank measurement of donor cornea endothelial cell density in the Specular Microscopy Ancillary Study

PURPOSE

The Specular Microscopy Ancillary Study was designed to examine donor corneal endothelial specular image quality, compare the central endothelial cell density determined by eye banks with the endothelial cell density determined by a central specular microscopy reading center, and evaluate donor factors that may have an impact on specular image quality and endothelial cell density accuracy.

DESIGN

Nonrandomized comparative trial.

PARTICIPANTS

Endothelial specular images of donor corneas assigned in the Cornea Donor Study.

METHODS

Certified readers assessed donor image quality (analyzable from fair to excellent vs. unanalyzable) and determined the central endothelial cell density. Independent adjudication was performed if there was a difference in the quality of grading or if the endothelial cell density varied by > or =5.0% between readers. Average reading center-determined endothelial cell density was compared with the endothelial cell density determined by each eye bank.

MAIN OUTCOME MEASURES

Evaluation of image quality and accuracy of endothelial cell density.

RESULTS

Of 688 donor endothelial images submitted by 23 eye banks, 663 (96%) were analyzable (excellent, 40 [6%]; good, 302 [44%]; fair, 321 [47%]), and 25 (4%) were unanalyzable by reading center standards. In situ retrieval and greater epithelial exposure correlated with a higher image quality grading. The eye bank-determined endothelial cell density of 434 of the 663 (65%) analyzable images were within 10% of the endothelial cell density determined by the reading center, whereas 185 (28%) were more than 10% higher and 44 (7%) were more than 10% lower. Greater variation in endothelial cell density between the eye banks and the reading center was observed with shorter time of death to preservation, presence of an epithelial defect, folds in Descemet's membrane, lower image quality, and the use of fixed-frame or center method endothelial cell density analysis.

CONCLUSIONS

Overall, donor endothelial specular image quality and accuracy of endothelial cell density determination were good. However, the data suggest that factors that may affect image quality and contribute to variation in interpretation of the endothelial cell density should be addressed, because the donor endothelial cell density is an important parameter for assessing long-term corneal graft survival.

Influence of Cataract Surgery on Corneal Endothelial Cell Density Estimation

PURPOSE

To assess the effect of cataract surgery on semiautomated human corneal endothelial cell density (ECD) estimation using noncontact specular microscopy.

METHODS

In this prospective clinical study, 62 consecutive patients undergoing cataract surgery were studied. To evaluate possible variations of accuracy and agreement under clinical circumstances, the corneal ECD was determined before and after cataract surgery. The parameter ECD (cells/mm) in the central and paracentral cornea was consecutively determined with 2 algorithms available in a noncontact specular microscope [fixed-frame method (FFM) and automatic center method (ACM)]. The postoperative evaluation was performed at 1 day, after 4 weeks, and after 6 months. The accuracy, the relative error, and the 95% limits of agreement (LoA) were determined for both counting methods.

RESULTS

The overall group-averaged accuracy was -19.4 cells/mm (0.86%) centrally and -17.3 cells/mm (0.76%) paracentrally. The LoA (95% CI) were within 234 cells/mm (10.4%) and 250 cells/mm (10.9%), respectively. After cataract surgery, a slight decrease in accuracy was noted in the central (2.09%) and paracentral areas (1.76%). The relative error increased from 3.66% to 6.02% centrally and from 4.96% to 6.55% paracentrally. The LoA (95% CI) increased from +/-194 cells/mm to +/-304 cells/mm centrally and from +/-275 cells/mm to +/-322 cells/mm paracentrally. In the later postoperative period, endothelial stabilization improved the accuracy and agreement in ECD estimation.

CONCLUSIONS

The estimation of ECD after cataract surgery employing current algorithms was achieved with a clinically acceptable level of accuracy and agreement. However, the analysis of images in the early postoperative period as well as paracentral corneal areas revealed larger variabilities. This revealed that the FFM and ACM counting methods cannot be used interchangeably under all circumstances. The ACM seemed preferable when only low-quality images were available and permitted determination of additional qualitative endothelial cell parameters.

Urgent Need for Normalization of Corneal Graft Quality Controls in French Eye Banks

BACKGROUND

Assessment of corneal tissue quality before graft is mainly based upon the determination of endothelial cell density (ECD) by eye banks. These cells are responsible for corneal transparency, and ECD correlates with graft survival. In France and often elsewhere in Europe, ECD is measured using a "naked-eye" procedure under a light microscope. To measure objectively the reliability of ECD determination in France, we developed four test corneas with a known ECD.

METHODS

The test corneas consisted of 1 mm2 of human corneal endothelium with stained cell borders. The 64 technicians of the 21 French eye banks counted according to the protocol applied in their respective centers.

RESULTS

More than half of the 256 counts (152, 59%) deviated by more than 10% from actual ECD. Of the counts, 85 (33%) were over-estimated, and 67 (26%) were under-estimated. Deviation ranged between 42% under-estimation and 82% over-estimation. Eight banks (38%) constantly over-estimated, and nine (43%) under-estimated ECD. Half of the inter-technician gaps within an eye bank were more than 10%, with a maximum of 51%.

CONCLUSIONS

This audit highlights the unacceptable lack of reliability of manual ECD assessment in French eye banks. This surely indicates the delivery of poor quality corneas for graft in certain centers and wastage in others. We urgently advocate normalization of French counting methods. This may require upgrading to a computer-aided method.

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.

Assessment of the reliability of human corneal endothelial cell-density estimates using a noncontact specular microscope

PURPOSE

We sought to determine the variance in endothelial cell density (ECD) estimates for human corneal endothelia.

METHODS

Noncontact specular micrographs were obtained from white subjects without any history of contact lens wear, or major eye disease or surgery; subjects were within four age groups (children, young adults, older adults, senior citizens). The endothelial image was scanned, and the areas from > or =75 cells measured from an overlay by planimetry. The cell-area values were used to calculate the ECD repeatedly so that the intra- and intersubject variation in an average ECD estimate could be made by using different numbers of cells (5, 10, 15, etc.).

RESULTS

An average ECD of 3,519 cells/mm2 (range, 2,598-5,312 cells/mm2) was obtained of counts of 75 cells/ endothelium from individuals aged 6-83 years. Average ECD estimates in each age group were 4,124, 3,457, 3,360, and 3,113 cells/mm2, respectively. Analysis of intersubject variance revealed that ECD estimates would be expected to be no better than +/-10% if only 25 cells were measured per endothelium, but approach +/-2% if 75 cells are measured.

CONCLUSION

In assessing the corneal endothelium by noncontact specular microscopy, cell count should be given, and this should be > or =75/ endothelium for an expected variance to be at a level close to that recommended for monitoring age-, stress-, or surgery-related changes.

Long-term results with organ cultured, cryopreserved human corneal grafts. Re-examination of 17 patients

Seventeen organ cultured cryopreserved corneas were grafted in 1978-79. When published in 1982, 12 of the grafts (71%) were clear with an average thickness of 0.51 mm and an endothelial density of 1028 cells/mm2. A re-examination of these patients after 13 years is presented. Seven grafts (58%) were clear. Average CCT was 0.51 mm and endothelial cell density was 988 cells/mm2. Visual acuity was 0.4 or better. The morphology resembled that seen after 1 year with large, multinucleated cells. It is concluded that cryopreserved grafts show a fair long-term survival. Cryopreservation may still present a possibility in the establishment of a corneal bank with the perspective of supplying histocompatible donor material.

Some metabolic changes during human corneal organ culture

In order to evaluate the changes in medium composition during closed system corneal organ culture at 30 degrees C, pH, pO2, glucose and lactate was measured 1 to 7, 14 and 28 days after incubation of a total of 49 human corneas. During organ culture pO2 decreased from 17.3 kPa to 8.8 kPa at day 28. The average oxygen consumption was initially 0.16 mumole/h/cm2, but decreased rapidly to an average of 0.04 mumole/h/cm2 during the first weeks of incubation. The glucose concentration fell from 5.1 mM to 0.25 mM after 28 days, and the lactate concentration rose from 2.5 mM to 11 mM. The concentration changes were for both substances highest during the first 14 days of organ culture. The pH fell from 7.36 to 6.64 after 28 days. These findings indicate that the cultured human cornea predominantly metabolizes glucose anaerobically, and that the metabolic activity decreases during incubation. The limiting metabolic factors for prolonging the culture period seem to be development of severe acidosis and glucose depletion in the medium.

Evaluation of the endothelium of human donor corneas by induced dilation of intercellular spaces and trypan blue

The endothelium of 30 pairs of human cadaver corneas was stained by trypan blue and the intercellular spaces were visualized by induced dilation prior to corneal culture. Trypan blue staining and induced dilation of intercellular spaces by 0.9% and 0.45% NaCl were found to be atraumatic. Only a fraction of damaged cells were stained by trypan blue. Endothelial cell losses in culture did not correlate with the number of trypan-blue stained cells, the post-mortem time, or donor age.

Changes of the corneal endothelium following intracapsular cataract extraction with implantation of semiflexible anterior chamber lenses. I. Results of the early post-operative period

A consecutive group of 103 patients with senile cataract underwent intracapsular cataract extraction and implantation of a semiflexible anterior chamber lens. After 6 month of follow-up, there was an average decrease of 20% +/- 15% in central corneal endothelial cell density and an average vertical disparity of 32% +/- 20% between central and superior endothelial areas. The endothelial cell loss was not correlated with pre-operative cell density. There was a positive correlation between age and cell loss and between age and vertical disparity. Findings in eyes with cornea guttata did not differ significantly from those without guttata. Anterior vitrectomy did not increase endothelial cell loss significantly. Maintenance of a deep anterior chamber by pre-operative oculopression or by instillation of Na-hyaluranate had no significantly different effect on the corneal endothelial cell loss.

Organ-culture preservation of human corneas

Human corneas were preserved up to 40 days in a modified tissue culture medium at 31 degrees C. The corneal endothelium was examined by light microscopy before and after culture. After staining with trypan-blue the number of dead cells was counted and by swelling of the intercellular borders in a 1.8 per cent sucrose solution the cellular mosaic was observed. A loss of endothelial cells was found varying from 0-30 per cent. During culture the stroma increased considerably in thickness. Prior to transplantation the cornea was thinned during 24 h in culture medium containing 5 per cent Dextran T500. The combination of the organ culture procedure and the evaluation of the endothelium enables preservation of human corneas for at least 30 days. In addition the quality of the endothelium is guaranteed and the transport of corneas can be carried out at room temperature.

Influence of endothelial cell count of donor's cornea on endothelial cell loss

In an experimental study porcine corneas were trephined using different trephining procedures. For every series of trephinations, the initial cell count of the donor cornea was found to play a role in the resulting damage induced by the cutting procedure. Pretreatment of corneas and modifications of trephining conditions did not change the negative correlations between cell count and damage due to trephining.

The effect of the prostaglandin-inhibitor naproxen on the endothelial cell-loss after cataract extraction

The influence of the anti-inflammatory, prostaglandin-inhibitor naproxen on the endothelial cell-loss after cataract-surgery was studied. Twenty-six patients received the drug, and 27 comprised a control group. The cell-loss, estimated one year after surgery, was found to be significantly lower in the naproxen-treated group than in the control group.

Fresh and cultured corneal grafts compared by post-operative thickness and endothelial cell density

Thirty-nine corneas were removed within 6 h post mortem and stored in a moist chamber at 4 degrees C before grafting. The mean donor age was 33 years and the average time between death and grafting was 11 h. Thirty cadaver corneas were selected after trypane blue staining and cultured at 31 degrees C for 24 h before grafting. The mean donor age was 61 years and the mean time between death and culture was 18 h. During the first 10 postoperative days fresh grafts were thinner than cultured grafts. One year after the transplantation the two groups did not differ significantly in regard to the clinical result, corneal thickness, or endothelial cell loss. This indicates that corneas from old donors with extended post mortem time can be used for transplantation after individual evaluation and corneal culture.

Contact and noncontact specular microscopy

A contact specular microscope was compared with a noncontact endothelial camera on 20 eyes of 10 consecutive patients presenting for cataract surgery. No difference was found in the percentage of photographs acceptable for cell counting or the time for photography by one or other camera. A close correlation was found in cell density estimations by the 2 methods. Most patients prefer the noncontact mode of examination.

Variation in central and vertical corneal endothelial cell density in normal subjects

Twenty normal subjects, aged 20 to 50, who had never worn contact lenses underwent determinations of central, inferior and superior corneal endothelial cell density using the Heyer-Schulte specular microscope. Analysis of variance revealed that superior cell density was significantly larger than central cell density, and that central cell density was significantly larger than inferior cell density (P less than 0.00001). In addition, 4 of these subjects had measurements taken on 4 separate sessions. Analysis of variance revealed that central and vertical cell density determinations were reproducible across measurement sessions. The finding of a vertical gradient in cell density was in contrast to 2 published reports which found no vertical differences in the normal cornea. Consequently, those data were re-analyzed using correct statistical procedures and similar vertical differences were obtained for one series of patients. The finding of a vertical gradient in endothelial cell density challenges the appropriateness of relying upon measurement of the central corneal field as an indicator of the pre-operative endothelial cell density.

Cryopreservation of human cadaver corneas regenerated at 31 degrees C in a modified tissue culture medium

Human corneas were obtained 2-82 h post mortem, cultured for 20-28 h, in a modified tissue culture medium, frozen at a controlled rate, and thawed rapidly. The thawed corneas were subjected to 20-28 h of additional culture. Immediately after thawing, a mean endothelial cell damage of 11% was indicated by trypane blue staining. The mean endothelial cell loss during the subsequent culture was 34%. This cell loss was not related to post mortem time, to donor age, to cell loss during the primary culture, or to endothelial cell density.

Shrinkage in preparatory steps for SEM. A study on rabbit corneal endothelium

Since specular microscopy of the cornea offers the opportunity to observe and measure cells in vivo without any outside interference this method forms an unrivalled basis for estimation of tissue shrinkage during various preparatory methods. Therefore a study was performed with the purpose of evaluating the degree of artifacts in each preparatory step from the living tissue "in vivo" to the final SEM specimen. The study was performed on rabbit corneas, the endothelium serving as measuring target. The in vivo state was recorded by specular microscopy. Unfixed corneas were studied by light microscopy unstained and stained by alizarin red S or silver nitrate. Fixation was performed intracamerally with 1.5% glutaraldehyde (Gla) by a pH, osmolarity, viscosity and intraocular pressure identical with the physiological values of rabbit eyes. Fixation was completed by immersion in 2.5% Gla for 1/2 h. Gla-fixed corneas were evaluated as above before osmification. Dehydration was performed either by graded acetone, by acetone in a gradient-free system, both followed by critical point drying (CPD). At all steps cells were counted using the same reference frame. The number of cells/mm2 was estimated and statistical analysis showed a shrinkage of 22 per cent (area) in unfixed tissue, 26 per cent (area) in normally dehydrated tissue and 37 per cent (area) in gradient free dehydrated tissue processed for SEM.

Per operative trypan blue vital staining of corneal endothelium. Eight years' follow up

An 0.1% aqueous trypan blue solution was injected into the anterior chamber during cataract extraction for the purpose of disclosing endothelial cell damage if present. Follow-up examination of 24 patients after eight years revealed no side-effects of trypan blue, as judged by corneal opacities, compared with non-vital-stained aphakic and non-operated control eyes.

A study in the measurement of corneal endothelial cell density using the specular microscope

Six subjects who never wore contact lenses underwent six determinations of corneal cell density using each of two measurement modes: Mode A: the eye was applanted once and pairs of photographs were taken; Mode B: the eye was applanated and a single photograph was taken. For each measurement mode data were collected on two separate sessions (Test, Retest). Chi-square analysis revealed a significantly larger proportion of uncountable photographs from the first measurement session, and analysis of variance revealed that Mode A was less reliable than Mode B upon retesting. It was concluded that Mode B was the preferred measurement mode, and that many more than six determinations be made on the initial session in order to obtain six readable photographs. Finally, estimates of inter and intra-session variation, intra-pair variation, and inter and intra-observer variation are given.

Endothelial cell density in donor corneas

In 68 pairs of donor corneas the endothelial cells were visualized by provoked swelling of the cell borders in isotonic saline. In cornea from donors below 50 years of age numerical cell density was correlated to age. This was not the case in corneas from older donors. The cell densities in paired corneas were correlated. The cell density in the second cornea of a pair was found to be within x +/- 10.97% (+/-1.98SD) of the first cornea. The precision of this estimate could only be improved insignificantly by correction for age, sex, mean cell density or variation of the mean.

Optical principles for estimation of endothelial cell density with the non-contact specular microscope

In non-contact specular microscopy of corneal endothelium, endothelial cell density is overestimated due to the angle of observation and the curvature of cornea. On the basis of theoretical considerations, it is concluded that if the angle of observation is kept at a small value the curvature of cornea contributes only insignificantly to this overestimation, the major determinant being the angle of observation. When an angle of 46 degrees is chosen between slit illumination and optical axis of the microscope it is calculated that estimates of endothelial cells should be multiplied with a factor of 0.959 to correct for the angle effect. Six eye were photographed with both a contact and non-contact specular microscope and endothelial cell density estimated. Mean observed difference in cell counts was +5.5% without correction and +1.2% with correction for angle effect. 95% confidence limits for the difference with correction were -3.7 and +6.0% respectively showing that estimates of endothelial cell density obtained with the non-contact specular microscope agree closely with those obtained by contact specular microscopy when corrected for angle of observation.

Toxicity of dimethylsulfoxide (DMSO) to human corneal endothelium in vitro

Human cadaver corneas were obtained 10--12 h after clinical death, incubated in organ culture for 20--28 h and exposed 2, 4, 6, 8, 6, 4, and 2% DMSO successively for 10 min at each concentration. Endothelial cell damage was recognized by morphological alterations during reformation of a coherent cell sheat after expulsion of damaged cells. DMSO was found to cause latent cell damage at 31 degrees C. No cell damage was found at 4 degrees C when DMSO was dissolved in minimum essential medium (Eagle) plus Dextran or when DMSO was dissolved in human albumin plus sucrose. DMSO was found to be toxic at 4 degrees C in pure serum and in Dulbecco's medium.

Clinical specular microscopy

Clinical specular microscopy (CSM) has recently been introduced as a means of qualitative and quantitative examination of the human corneal endothelium at high magnification. With the aid of CSM, a decline in endothelial cell density with age has been documented and several endothelial abnormalities from disease or trauma can be detected. Donor material for corneal grafting can be examined by CSM and keratoplasty procedures can be designed to decrease endothelial damage. Cataract surgical procedures can cause endothelial cell loss. According to most studies, intracapsular extraction causes less cell loss than does phacoemulsification, and cataract extraction with intraocular lens (IOL) insertion causes the greatest loss. Cell loss from IOL can be minimized by decreasing lens-corneal contact. Elevated intraocular pressure may lead to endothelial cell loss, as may therapy with epinephrine. Endothelial toxicity of other drugs and solutions can be studied by CSM. While long term studies are necessary to correlate the morphologic changes detected by CSM with future endothelial function, shortterm studies can be helpful in developing medical and surgical techniques that minimize corneal endothelial trauma.

Human corneal endothelium in organ culture. The influence of temperature and medium of incubation

Forty-four human corneas from patients between 21 and 86 years were incubated in Eagle's minimum essential medium with Earle's salts 10--46 h post mortem. The influence of incubation temperature and composition of the medium on endothelial survival was evaluated. Whole corneas were stained by alizarine red. Recent cell loss was indicated by morphological alterations in the endothelial pattern. After 20--28 h of incubation minimum cell loss was found at 31 degrees C when 8% Dextrane-250 and 20% serum or 8% Dextrane-500 and 10% serum was added to the medium.