Factors associated with severe corneal endothelial damage following acute primary angle closure in Chinese subjects

PURPOSE

To investigate the corneal endothelial damage caused by acute primary angle closure (APAC) and related risk factors for severe corneal endothelial cell damage in Chinese subjects.

METHODS

In this multicentre retrospective study, 160 Chinese patients (171 eyes) diagnosed with APAC were recruited. Endothelial cell density (ECD) and morphological changes short after APAC were studied. Univariate regression and multivariate regression were used to identify risk factors associated with the extent of ECD reduction, including age, gender, education level, patients' location, systemic diseases, APAC duration (hours), highest recorded intraocular pressure (IOP), and presenting IOP. Factors associated with the probability of severe corneal damage (ECD lower than 1000/mm2) were analysed based on a linear function.

RESULTS

After one APAC episode, 12.28% eyes had ECD lower than 1000/mm2, 30.41% had ECD between 1000 and 2000/mm2, and 57.31% had ECD more than 2000/mm2. Attack duration was the only factor associated with severe endothelial damage (p < 0.0001). If the attack were to be subsided within 15.0 h, possibility of ECD lower than 1000/mm2 could be controlled under 1%.

CONCLUSION

Shortly after the abortion of APAC, 12.28% patients experienced severe endothelial cell damage with ECD less than 1000/mm2. The only factor associated with severe ECD decrease was attack duration. Immediate and effective treatment is pivotal for preserving corneal endothelial function in APAC patients.

Endothelial keratoplasty: The relationship between recipient anterior chamber depth and endothelial cell loss

PURPOSE

To determine the relationship between anterior chamber depth (ACD) and percent endothelial cell loss (ECL) after Descemet Stripping Automated Endothelial Keratoplasty (DSAEK).

METHOD

In 78 eyes receiving triple procedure (DSAEK combined with cataract extraction and posterior chamber intraocular lens (PCIOL) implantation), ACD was measured preoperatively with an intraocular lens (IOL) Master and ECL was calculated with specular microscopy at 6 months, 1, 2, 3, and 4 years postoperatively. ACD and ECL from all 78 eyes were compared using correlation analysis and students t test. Eyes were then separated into 2 groups based on ACD, group 1 with ACD < 3mm and group 2 with ACD ≥ 3mm. Students t test was then performed to compare group 1 and group 2 ECL at 6 months, 1, 2, 3, and 4 years postoperative.

RESULTS

Mean ACD for all 78 eyes was 2.93 ± 0.43 mm. Mean ECL was 32.7%, 27.6%, 29.6%, 32.5%, and 37.2% at 6 months, 1, 2, 3, and 4 years. No significant correlation between ACD and ECL was observed at any time point for the combined analysis of 78 eyes (P > .05). At 2 and 4 years postoperative, mean ECL was 32.6% ± 16.1% and 43.0% ± 23.2% in eyes with ACD < 3mm and 25.3% ± 13.0% and 29.6% ± 18.2% in eyes with ACD ≥ 3 mm (P = .041 at 2 years and .008 at 4 years).

CONCLUSION

ACD and ECL were not directly correlated; however, there may be a threshold ACD in which shallower anterior chambers preoperatively result in greater donor ECL over time.

New ex vivo model of corneal endothelial phacoemulsification injury and rescue therapy with mesenchymal stromal cell secretome

PURPOSE

To develop a reproducible ex vivo model of corneal endothelial cell injury using phacoemulsification in porcine eyes and to evaluate the effects of mesenchymal stromal cell secretome in this injury model.

SETTING

Department of Ophthalmology, University of Illinois at Chicago, Illinois, USA.

DESIGN

Experimental study.

METHODS

A corneal endothelial injury model was optimized using different powers and durations of ultrasound energy inside ex vivo porcine eyes. Conditioned media from corneal mesenchymal stem cells was collected under serum-free conditions from passages 4 to 6. Immediately after the phacoemulsification injury, the anterior chamber fluid was replaced with unconditioned media or conditioned media and incubated at 37°C for 4 hours. At the end, endothelial cell viability was evaluated using trypan blue staining and analyzed with ImageJ software.

RESULTS

Using specific parameters (50% power for 30 seconds), phacoemulsification inside fresh porcine eyes led to a consistent level of endothelial cell injury. Incubation with corneal mesenchymal stromal cell-conditioned media after the injury significantly reduced endothelial cells loss compared with unconditioned media (mean 1.29% ± 0.91% [SD] and 5.33% ± 3.24%, respectively, P < .05).

CONCLUSIONS

Phacoemulsification inside fresh porcine eyes provided a reproducible model to study endothelial cell injury. Treatment with corneal mesenchymal stromal cell secretome after injury appeared to significantly enhance the survival of corneal endothelial cells. This might provide a new strategy for preventing corneal endothelial cell loss after phacoemulsification or other endothelial injuries. Further in vivo studies are necessary to determine the therapeutic potential.

Corneal endothelial decompensation due to airbag injury

PURPOSE

We report a case of localized endothelial decompensation due to airbag deployment during a motor vehicle accident.

CASE REPORT

A middle-aged woman involved in a motor vehicle accident presented with diminution of vision in left eye. Initial ocular examination revealed corneal abrasion, localized central corneal edema and mild anterior chamber reaction. An anterior-segment ocular coherence tomography (AS-OCT) revealed focal paracentral corneal edema. Patient was managed with lubricating eye drops and antibiotic steroid combination. Significant endothelial cell loss compared to right eye was noted on specular examination. At one- month follow-up, visual acuity recovered to 6/6 but the pleomorphism and polymegathism persisted.

CONCLUSION

Airbag-related localized corneal endothelial decompensation is a less known occurrence. This case emphasizes on the fact that serial monitoring of endothelial counts and conservative management can prove beneficial in such scenarios.

Vasoactive Intestinal Peptide Promotes Corneal Allograft Survival

Corneal transplantation is the most prevalent form of tissue transplantation. The success of corneal transplantation mainly relies on the integrity of corneal endothelial cells (CEnCs), which maintain graft transparency. CEnC density decreases significantly after corneal transplantation even in the absence of graft rejection. To date, different strategies have been used to enhance CEnC survival. The neuropeptide vasoactive intestinal peptide (VIP) improves CEnC integrity during donor cornea tissue storage and protects CEnCs against oxidative stress-induced apoptosis. However, little is known about the effect of exogenous administration of VIP on corneal transplant outcomes. We found that VIP significantly accelerates endothelial wound closure and suppresses interferon-γ- and tumor necrosis factor-α-induced CEnC apoptosis in vitro in a dose-dependent manner. In addition, we found that intracameral administration of VIP to mice undergoing syngeneic corneal transplantation with endothelial injury increases CEnC density and decreases graft opacity scores. Finally, using a mouse model of allogeneic corneal transplantation, we found for the first time that treatment with VIP significantly suppresses posttransplantation CEnC loss and improves corneal allograft survival.

Trophic effect of PACAP on human corneal endothelium

Cornea's posterior surface includes endothelium maintaining stromal hydration and clarity. Due to their limited proliferative capability, the loss of endothelial cells can outcome in permanent opacity. In the last years, different studies have demonstrated the protective effect of pituitary adenylate cyclase-activating polypeptide (PACAP) in different ocular diseases. However, its role on human corneal endothelial cells (HCECs) has not been investigated, yet. Here, we have developed a culture protocol to differentiate HCECs from donor's cornea. PACAP treatment prevented damage induced by growth factors deprivation of cells grown on transwell supports as revealed by TERR measurements. Moreover, this peptide significantly increased tight junction proteins expression by conferring resistance to endothelial barrier. This effect is also related to promotion of cell viability as demonstrated by MTT assay. Furthermore, PACAP stimulated repairing of corneal endothelium lesion as shown by wound healing analysis. In conclusion, our data suggest that this peptide could represent an important trophic factor in maintaining functionality of human corneal endothelium.

[Analysis of the Effect of Non-phacoemulsification Cataract Operation on Corneal Endothelial Cell Nucleus Division]

PURPOSE

To investigate the effect of non-phacoemulsification cataract operation in two different patterns of nucleus delivery on the quantity and morphology of corneal endothelial cells and postoperative visual acuity.

METHODS

Forty patients diagnosed with cataract underwent cataract surgery and were assigned into the direct nuclear delivery and semi-nuclear delivery groups. Lens density was measured and divided into the hard and soft lenses according to Emery-little lens nucleus grading system. Non-phacoemulsification cataract operation was performed. At 3 d after surgery, the quantity and morphology of corneal endothelium were counted and observed under corneal endothelial microscope. During 3-month postoperative follow-up, the endothelial cell loss rate, morphological changes and visual acuity were compared among four groups.

RESULTS

Corneal endothelial cell loss rate in the direct delivery of hard nucleus group significantly differed from those in the other three groups before and 3 months after operation (P < 0.01), whereas no statistical significance was found among the direct delivery of soft nucleus, semi-delivery of hard nucleus and semi-delivery soft nucleus groups (all P > 0.05). Preoperative and postoperative 2-d visual acuity did not differ between the semi-delivery of hard nucleus and direct delivery of soft nucleus groups (P = 0.49), significantly differed from those in the semi-delivery of soft nucleus (P = 0.03) and direct delivery of hard nucleus groups (P = 0.14). Visual acuity at postoperative four months did not differ among four groups (P = 0.067).

CONCLUSION

During non-phacoemulsification cataract surgery, direct delivery of hard nucleus caused severe injury to corneal endothelium and semi-delivery of soft nucleus yielded mild corneal endothelial injury. Slight corneal endothelial injury exerted no apparent effect upon visual acuity and corneal endothelial morphology at three months after surgery.

Computation of the temperature rise at the corneal endothelium during cataract surgery by modeling of heat generation inside the anterior chamber

The corneal endothelium sustaining the transparency of the cornea is a vulnerable cell layer. Thermal exposure during phacoemulsification is considered to be a potential cause of post-operative cell loss. Knowledge of the temperature rise and particularly of its dependence on region and system settings could deliver useful information about a potential correlation with cell damage. However, there exists a lack of understanding of the process and location of heat generation. Analytical calculations and experiments enabled the quantification of different mechanisms acting as heat sources during phacoemulsification. Heat generation caused by viscous friction was estimated using both an analytical approach and a numerical simulation. In contrast to absorption of sound and self-heating of the probe, this effect was ascertained to be the main heat source. Calorimetric measurement of the power input verified this modeling. On the basis of these results, the local temperature distribution inside a porcine eye was computed time dependently using the finite-element method. Two different amplitude settings were compared with respect to the temperature increase at the corneal endothelium. Various conclusions on the mitigation of thermal exposure during treatment can be drawn from this finite-element simulation.

[Transplanted vascular endothelial cells to replace corneal endothelial cells by improved anterior chamber injection]

OBJECTIVE

To observe form and function changes of vascular endothelial cells (VEC) which were transplanted to the posterior surface of rhesus monkey cornea without Descemet's Membrane by anterior chamber injection, explore the feasibility of transplanting VEC to treat corneal endothelial injury, and find new method of corneal endothelial cell transplantation.

METHODS

Cultured VEC to proliferate in vitro.Rhesus monkeys were randomly divided into two groups: Experimental group (6) and control group (6) according to a random number table. The experimental group:transplant the culured VEC to the posterior surface of rhesus monkey cornea without Descemet's membrane by anterior chamber injection. The control group:Tear out the Descemet's membrane by capsulotomy needle without VEC transplantation. A ultrasound apparatus was adopted to measure the postoperative thicknes of the cornea and Goldman intraocular pressure meter measuring intraocular pressure in the postoperative 7 days, 14 days, 30 days, 60 days, 90 days, organize the data and entered into the computer , applicated the software of SPSS 11.5 for data independent samples t-test and analysis of variance. The eyes were removed respectively in postoperative 30, 60, 90 days to do pathological HE dyeing and scanning electron microscopy (SEM) observation of VEC in the posterior surface of cornea graft.

RESULTS

Corneal transpareney:In the experimental observation period (3 months), the experimental group had better transparency than the control group with normal anterior chamber depth and without bullous keratopathy. And the corneal neovascularization was exist in the cornea graft in experimental group in the third month. After 3 months, the corneal thickness of experimental group (500 ± 14) µm was significantly lower than the control group (618 ± 11) µm, Corneal thickness values between experimental and control groups were statistically significant differences in changes (all P < 0.05, t-values were -3.256, -4.419, -12.896 postoperative 1, 2, 3 months). Changes of intraocular pressure difference between the experimental group and the control was not statistically significant (all P > 0.05, t-values were -1.179, -2.166, -2.536 postoperative 1, 2, 3 months). The pathological:the cell layer was visible in the posterior surface of cornea graft. The control group:can't find the cell sample structure.SEM:Experimental group showed that VEC with irregular shape uniformly distributed on the inner surface of cornea and growing well, a small amount of white blood cells can be seen between VEC, and part of cellular debris exist in the trabecular meshwork. Control group showed a fiber material without VEC.

CONCLUSIONS

Ultrasonic emulsification can established a repeatability and simple model of corneal endothelial injury in Rhesus monkeys.VEC can be transplanted to the corneal surface by Anterior chamber injection and the cells can grow on the surface and play a barrier role in maintaining the state of dehydration and transparency of the cornea to a certain extent. After transplantation, organizational structure and morphology of the anterior chamber angle does not produce pathological effects in the short term. Prompt that transplant the culured VEC to the posterior surface of rhesus monkey cornea without Descemet's Membrane by anterior chamber injection to substitute the function of the corneal endothelial cells may be a new idea for treatment of corneal endothelial damage.

[Construction of corneal endothelium deficiency model by cryo-injury and its application]

OBJECTIVE

To set up an animal model of corneal endothelium deficiency and test the bio-safety and pump function of B4G12 cells with this model.

METHODS

Thirty SD rats were divided into cryo-injury group and cryo-injury with B4G12 cell transplantation group. Models of corneal endothelium deficiency were created by cryo-injury with liquid nitrogen, and then B4G12 cells were transplanted into the eyes by anterior chamber injection. Corneas were checked under slit lamp and confocal microscope observations at some specific time points, pathological staining was also performed.

RESULTS

The corneal endothelial cells were removed completely from the Descemet's membrane after cryo-injury. Cells transplanted firmly stuck to the Descemet's membrane. The corneas in the cryo-injury group were swelling with haze, while in the transplantation groups, the corneas restored transparence and normal thickness 2 weeks after the surgery. Confocal microscope and HE staining confirmed that in the cryo-injury group, the Descemet's membrane was denuded and the cornea stroma layer was in edema, on the contrary, in the other group, the transplanted cells completely covered the Descemet's membrane.

CONCLUSION

Cryo-injury can be used for building the rat model of corneal endothelium deficiency, no neoplasm and inflammation reaction were found during the observation after B4G12 cells transplanted and B4G12 cells had the pump function in vivo.

Organ culture, but not hypothermic storage, facilitates the repair of the corneal endothelium following mechanical damage

PURPOSE

To evaluate the reparative capacity of the mechanically injured endothelium of corneas stored under organ culture (OC) or hypothermic conditions.

METHODS

The central endothelium of 12 pairs of human corneas with similar endothelial parameters was damaged to create a 1 mm(2) lesion. One cornea from each pair was stored under OC and one under hypothermic conditions. The endothelial cell density (ECD), coefficient of variation, hexagonality and percentage of dead cells were assessed before and after damage and on days 7, 14, 21 and 28 of storage.

RESULTS

The mean ECD of corneas subsequently stored under OC or hypothermic conditions was 2764/mm(2). Immediately after damage, a denuded Descemet's membrane with a few remaining dead cells was observed at the injured area. After 7 days of storage under OC conditions, almost no dead cells were observed at the place of injury. A non-significant worsening of the qualitative parameters (polymegatism and pleomorphism) was found. After 14 days, ECD was 1933/mm(2) and 2478/mm(2) centrally and pericentrally, respectively. Similar values were found after 21 and 28 days of storage. The lesions with remnant dead cells persisted throughout hypothermic preservation. From day 14 the corneas became cloudy and in poor condition, while the pericentral ECD was 2523/mm(2).

CONCLUSION

The reparative capacity of the cornea is maintained under OC but not under hypothermic conditions. For corneas containing dead endothelial cells, OC is therefore the method of choice because it may improve the quality of the stored tissue.

[Endothelial damage after planned extracapsular cataract extraction and phacoemulsification of hard cataracts]

PURPOSE

To evaluate and compare the endothelial damage after planned extracapsular cataract extraction (ECCE) and phacoemulsification of very hard cataracts.

METHODS

In this prospective, randomized study, 41 patients with age-related and very hard cataract were divided into two groups: in group 1 (21 patients) an extracapsular cataract extraction was performed and in group 2 (20 patients), phacoemulsification. In both groups, intraocular lenses were implanted in the capsular bag. Preoperatively and 1, 3 and 6 months postoperatively, a complete ophthalmological examination, endothelial specular microscopy, and ultrasonic pachymetry were done. Endothelial cell loss, pleomorphism, polymegathism and corneal thickness were studied.

RESULTS

Both groups presented an endothelial cell loss in the postoperative time, as compared with the preoperative values, but there were no significant differences among the postoperative values (1, 3 and 6 months). Six months after surgery, mean cell loss was 28.50% in group 1 and 34.77% in group 2. There were no differences among the indexes of pachymetry, polymegathism and pleomorphism between the two groups.

CONCLUSIONS

Endothelial response was not statistically different between the two studied groups.

Long-Term Follow-Up of the Corneal Endothelium After Artisan Lens Implantation for Unilateral Traumatic and Unilateral Congenital Cataract in Children

PURPOSE

To retrospectively estimate the long-term corneal endothelial cell loss in children after perforating corneal trauma and implantation of an iris-fixated anterior-chamber intraocular lens (IOL), either the Artisan aphakia lens or the Artificial Iris Implant, and to compare this corneal endothelial cell loss to that in children who received an Artisan aphakia lens to correct aphakia after cataract extraction for unilateral congenital cataract.

METHODS

A retrospective study was performed, evaluating the charts and endothelial photographs of 6 patients with unilateral traumatic cataract, with a mean age at IOL implantation of 9.5 years (range: 5.8-12.8 years) and a mean follow-up after IOL implantation of 10.5 years (range: 8.0-14.7 years), and of 3 children who were operated on for unilateral congenital cataract at a mean age of 2.7 years and who received an Artisan aphakia IOL, with a mean follow-up after IOL implantation of 9.5 years (range: 4.7-14.5 years). Parameters that were studied were central endothelial cell density (CECD) in both the operated and the normal eye at the last follow-up visit, percentage of cell loss in the operated eye compared with the normal eye, and length and location of the corneal scar in the injured eye.

RESULTS

: In the traumatic cataract group, CECD was, on average, 41% (range: 22%-58%) lower in the operated eye (1.647 +/- 322 [SD] cells/mm) than the normal eye (2.799 +/- 133 cells/mm). A significant negative linear correlation was found between the length of the corneal perforation scar and CECD. In the congenital cataract group, no statistical difference in CECD was found between the operated (3.323 +/- 410 cells/mm) and the unoperated (3.165 +/- 205 cells/mm) eye.

CONCLUSION

Endothelial cell loss 10.5 years after iris-fixated IOL implantation for traumatic cataract was substantial and related to the length of the corneal scar of the original trauma. In children operated on for congenital cataract, no difference was found in CECD in the operated and unoperated eyes 9.5 years after Artisan aphakia IOL implantation.

Interface fluid syndrome in laser in situ keratomileusis after complicated trabeculectomy

A 69-year-old man developed stromal edema and a pocket of fluid in the laser in situ keratomileusis (LASIK) interface wound in the left eye after acute endothelial cell loss from complicated trabeculectomy. He eventually required penetrating keratoplasty along with cataract surgery. Histologic examination of the corneal button showed an edematous 720 microm central residual stromal bed, a 54 microm empty space at the level of the central interface wound, and a 154 microm LASIK flap. The endothelial cell count was 0 to 2 cells per high-power field, corresponding to a cell density of 450 to 500 cells/mm(2). Four years after LASIK, the central interface wound was susceptible to forming a pocket of serous fluid after the corneal endothelial function was compromised.

Phacoemulsification associated corneal damage evaluated by corneal volume

PURPOSE

To determine the usefulness of the Pentacam corneal volume assay in the assessment of corneal endothelial damage caused by phacoemulsification and aspiration (PEA).

DESIGN

Prospective, comparative, observational case series.

METHODS

PEA was performed in 85 eyes by three surgeons under different conditions. Central cell density (CD) was determined using a specular microscope before and one month after surgery. Pentacam was used before and one day, one week, and one month after surgery to determine 3- and 10-mm corneal volumes.

RESULTS

For all surgeons, no significant differences in the 3-mm corneal volumes were noted between the before and one-month after surgery values. However, 10-mm corneal volumes at one month were significantly higher than preoperative levels. No correlation was noted between the increasing rate of the 10-mm corneal volume and decreasing rate of CD.

CONCLUSIONS

Pentacam-determined corneal volumes may be useful in assessing PEA-caused corneal damage.

Assessment of the corneal endothelium in acute ultraviolet keratitis

BACKGROUND

The purpose of this prospective case-control study was to investigate whether exposure to ultraviolet (UV) light produces detectable damage to the corneal endothelium in patients presenting with acute UV keratitis.

MATERIAL/METHODS

Non-contact specular microscopy was performed on 20 consecutive patients who presented to our clinic from July 2000 to July 2002 with acute UV keratitis and similarly on 20 age-matched healthy controls. Both the coefficient of variation in mean cell size (CV) and the mean cell density (CD) were compared in these two groups using the Student t-test.

RESULTS

Mean age was 28.6 years in the study group and 28.4 years in the control group. The mean CD in the patient group was 2609.6 (SD = 103.47) and in the control group 2632.87 (SD = 117.05). No statistically significant difference was found between the mean CDs in these two groups (p = 0.93). The mean CV in the patient group was 46.7 (SD = 4.40) and in the control group 45.4 (SD = 5.60). Similarly, there was no statistically significant difference between the mean CVs in these two groups (p = 0.85).

CONCLUSIONS

UV light exposure does not seem to have a direct immediate effect on the corneal endothelium in humans with acute UV keratitis. Whether UV light produces cumulative and/or longer-term damage requires further studies with a larger number of patients and a longer follow-up time.

Replication competence and senescence in central and peripheral human corneal endothelium

PURPOSE

To compare replication competence and senescence in human corneal endothelial cells (HCECs) between the central and peripheral areas and between younger and older donors.

METHODS

Human corneas were obtained from the eye bank and separated into two groups: young (younger than 30 years) and old (older than 50 years). Corneas were cut in quarters and a 2-mm scrape wound was created in the endothelium from the periphery to the center. Unwounded endothelium acted as a negative control. Corneal pieces were incubated for 24, 36, 48, 60, 72, 84, and 96 hours in medium containing 8% fetal bovine serum (FBS) plus additional growth factors. Tissue was fixed, immunostained for minichromosome maintenance (MCM)-2, a marker of replication competence, and mounted in medium containing propidium iodide (PI) to visualize all nuclei. Fluorescence microscope images were used to count PI-stained and MCM2-positive HCECs in three 100-microm2 areas within the central and peripheral wound area. Results are expressed as mean number of cells/100 microm2. Senescent HCECs in ex vivo corneas were identified by staining for senescence-associated beta-galactosidase activity (SA-beta-Gal). Whole corneas were cut in quarters and incubated in staining solution containing SA-beta-Gal at pH 6.0. The number of cells stained for SA-beta-Gal and the grade of SA-beta-Gal intensity in three 100-microm2 areas were averaged for the central and peripheral areas from each donor. For all studies, results were compared between central and peripheral cornea and between younger and older donors.

RESULTS

In both age groups (n = 4/group), cells repopulated the wound area in a time-dependent manner. In corneas from older donors, significantly fewer HCECs migrated into the wound bed in the central cornea than in the periphery. At each time point, the density of cells in the central wound area was lower in corneas from older donors than from younger donors. In both age groups, the mean percentage of MCM2-positive cells increased with time until wound healing. In both age groups, more MCM2-positive cells were present in the wounded area of the peripheral than of the central cornea. At 36, 48, 60, and 72 hours after wounding, the percentage of MCM2-positive cells in the central or peripheral area of older corneas was significantly less than in the corresponding region in younger corneas. No MCM2-positive staining was observed in unwounded areas at any time point. HCECs in corneas from younger donors (n = 4) showed little to no SA-beta-Gal activity in either the central or peripheral area. SA-beta-Gal activity was easily detectable in corneas from older donors (n = 4) and a significantly higher percentage of central HCECs showed strong SA-beta-Gal activity compared with HCECs in the periphery.

CONCLUSIONS

In ex vivo corneas, HCECs from the peripheral area retain higher replication competence, regardless of donor age. HCECs in the central area of corneas from older donors retain replicative competence, but the relative percentage of cells that are competent to replicate is significantly lower than in the periphery or in the central area of corneas from younger donors. This reduction in replicative competence negatively correlates with the observed increase in the population of central HCECs exhibiting senescence-like characteristics.

Cold-Induced Injury to Porcine Corneal Endothelial Cells and Its Mediation by Chelatable Iron

PURPOSE

During hypothermic storage of the cornea, corneal endothelial damage restricts storage times. We previously reported a new, iron-dependent mechanism of cold-induced injury to cultured liver cells. In this study, we sought to evaluate whether corneal endothelial cells incur a similar kind of injury.

METHODS

Cultured porcine corneal endothelial cells were exposed to 4 degrees C in either cell culture medium, Krebs-Henseleit buffer, Optisol-GS solution, or McCarey-Kaufman medium for 5 hours to 14 days and then rewarmed under cell culture conditions (3 hours). The cultures were assessed for lethal cell injury (LDH release); cellular, nuclear, and mitochondrial morphologic alterations; lipid peroxidation; and mitochondrial membrane potential.

RESULTS

Corneal endothelial cells sustained substantial injury following cold storage and rewarming in cell culture medium (47% +/- 8% and 64% +/- 20% cell death after 2 and 5 days cold storage, respectively). The injury displayed some apoptotic features, and cells lost mitochondrial membrane potential before cell death occurred. The iron chelators deferoxamine, 1,10-phenanthroline, and 2,2'-dipyridyl and the antioxidant butylated hydroxytoluene completely inhibited this cell injury. Marked iron-dependent cell injury and lipid peroxidation also occurred during and after cold incubation in Krebs-Henseleit buffer and, most importantly, iron-dependent cell injury was also observed after cold incubation in Optisol solution and in McCarey-Kaufman medium.

CONCLUSIONS

Cultured porcine corneal endothelial cells incur a strong iron-dependent injury elicited by hypothermia. This cold-induced injury might provide an explanation for the known corneal endothelial susceptibility to hypothermic preservation injury, which thus might be amenable to therapeutic interventions (ie, by iron chelators).

Traumatic Dislocation and Successful Re-enclavation of an Artisan Phakic IOL With Analysis of the Endothelium

PURPOSE

To present a case of traumatic dislocation of an Ophtec Artisan phakic intraocular lens (PIOL) and an analysis of the endothelial cell count.

METHODS

The patient presented with blurred vision in his left eye after sustaining a brow laceration. History included uncomplicated bilateral implantation of an Artisan PIOL to correct myopia.

RESULTS

The brow laceration was sutured and topical dexamethasone 0.1% qid was prescribed. One week after presentation, the PIOL was relocated. Postoperatively, endothelial cell count analysis was performed in both eyes.

CONCLUSIONS

A decrease in the hexagonality of the endothelial cells was noted in both eyes, which was substantially lower in the injured eye.

Corneal endothelial cells' protection against thermal injury: influence of ophthalmic viscoelastic substances in experimental study on rabbits

PURPOSE

To quantify the maximal level of temperature and the time the maximal temperature is achieved and correlate the temperature parameters to the mean rate of endothelial cell loss after standardized ultrasound delivery assisted with four viscoelastic substances or different temperature of balanced salt solution (BSS).

METHODS

Thirty rabbits (60 eyes) were divided into six groups in which different viscoelastic substances or different temperature of BSS were used: Group 1, Viscoat; 2, Provisc; 3, soft shell technique; 4, Celoftal; 5, BSS 22 degrees C; and 6, BSS 4 degrees C. The same parameters of ultrasound energy were delivered by standard phaco tip introduced into pupillary plane. Thermocamera was employed for measurements of temperature parameters. Endothelium cell count was measured before surgery and 1 month postoperatively.

RESULTS

Maximal level of temperature was measured as follows: Group 5, 27.85 +/- 0.52 degrees C; Group 2, 27.75 +/- 0.54 degrees C; Group 3, 27.74 +/- 0.46 degrees C; Group 4, 27.25 +/- 0.60 degrees C; Group 6, 26.81 +/- 0.34 degrees C; Group 1, 26.52 +/- 0.48 degrees C (p<0.05). The time the maximal temperature is achieved was statistically shorter in Groups 5 and 6: 4 seconds, 5 seconds, respectively, p<0.0001, as compared with Group 2 (30 seconds), Group 3 (40 seconds), Group 1 (45 seconds), and Group 4 (50 seconds). The mean rate of endothelial cell loss was calculated as follows: Group 1, 4.35%+/-2.55%; Group 2, 8.43%+/-5.2%; Group 3, 6.25%+/-4.20%; Group 4, 6.53%+/-4.65%; Group 5, 14.3%+/-3.85%; and Group 6, 8.78%+/-4.45%.

CONCLUSIONS

Viscoelastic substances offer different levels of endothelial cell protection against temperature increase during phacoemulsification. The mean rate of endothelial cell loss correlates with the time the maximal temperature is achieved rather than with the value of maximal level of temperature. This implicates that surgical strategy should consider the choice of the most effective viscoelastic substances, particularly in difficult cases, e.g., hard nucleus, shallow anterior chamber, primary endothelial abnormality.

Effects of SV40 T antigen transduction on human corneal endothelial cell wound healing in vitro

OBJECTIVE

The aim of this study was to investigate the endothelial wound healing effects of SV40 large T and small t antigen transduction on cultured human corneal endothelial cells (HCEC).

METHODS

Human corneal endothelial cells were infected with either mock solution, Ad green fluorescent protein (GFP), or Ad SV40 T/t antigen/GFP, then mechanically wounded 48 h later. The endothelial wound healing rate was quantified by an analysis of the photographs taken every 12 h after wounding. The characteristics of Ad SV40 T/t Ag/GFP-infected human corneal endothelial cells were evaluated with cell morphology, cell density, contact inhibition, and cytoskeletal features using rhodamine phalloidin to stain F-actin. DNA synthesis was assessed using 5-Bromo-2'-deoxy-uridine (BrdU) labeling.

RESULTS

Wound healing rates in the first 12 and 24 h after wounding were significantly faster in the Ad SV40 T/t antigen/GFP-infected group than the other two groups. In all three groups, the morphology, cell density, and cytoskeletal features of cells at confluency was similar and contact inhibition retained. There were no differences in the pattern of F-actin and endothelial cell density 4 d after wound closure. However, during the process of wound healing, prominent stress fibers in migrating cells near the wound edge were noted in normal cells at 36 h after wounding, whereas the Ad SV40 T/t Ag/GFP-infected cells showed similar changes as early as 12 h after wounding. BrdU staining results revealed that the Ad SV40 T/t antigen/GFP-infected group had labeled cells showing DNA synthesis in the wound area at 12 h after wounding, while no labeled cells were found in the other two groups.

CONCLUSIONS

In an in vitro model, transduction of human corneal endothelial cells using a recombinant adenoviral vector expressing SV40 T/t antigen enhanced both the wound healing rate and proliferative capacity, especially in the first 12 h after wounding, and the characteristic morphologic features of the infected cells were maintained.

Evidence suggesting the existence of stem cells for the human corneal endothelium

PURPOSE

The well-known reluctance of human corneal endothelial cells (HCECs) to divide has continually intrigued investigators. Related to this, the discovery of an increased endothelial cell population in the periphery of the human cornea has prompted an investigation for evidence of the existence of stem-like cells in the endothelial periphery. Showing that stem cells or transient amplifying cells may exist in the periphery might explain the origin of HCECs and indicate a source for these cells in wound repair. In addition, these cells might be of value in culturing or as a source for the synthesis of artificial corneas.

METHODS

Human corneas with attached scleral rims were obtained from eye banks and were assayed for telomerase activity and BrdU (bromodeoxyridine) incorporation to determine, respectively, the presence of a stem-like cell marker and replicative activity. In the case of telomerase activity, the tissues were divided into central, intermediate and peripheral areas by the use of trephines. BrdU staining (using alkaline phosphatase bound secondary antibody) was performed on whole corneas plus scleral rims exposed to BrdU antibodies on the endothelial side whereas BrdU fluorescence (using fluorescein bound secondary antibody) was obtained from transverse sections of the these tissues by the same procedure. Some corneas were wounded to determine whether the wounded areas stimulated BrdU (by staining or fluorescence) followed by the synthesis of transforming growth factor beta (TGFbeta). The latter was determined by quantitative ELISA. Rabbit corneas were also assayed for BrdU incorporation to compare their evidence of cell division with that of humans.

RESULTS

After dividing corneas into central, intermediate, and peripheral sections, the dissected endothelial tissues exhibited positive telomerase activity in the peripheral and intermediate sections. No activity was observed in the central endothelial tissues or the limbus between the trabecular meshwork and Schwalbe's line. BrdU staining with alkaline phosphatase was occasionally observed in the wounded area's human corneal endothelial cells after wounding. When BrdU fluorescence assays were made on corneal transverse sections with fluorescein, fluorescence occurred in an area just at and adjacent to the trabecular meshwork, but was not seen at the corneal endothelium. After wounding, BrdU fluorescence extended into the corneal endothelium. TGF-beta levels were increased in fluids bathing the endothelium following wounding, but the increases lagged behind the wounding event.

CONCLUSIONS

It is suggested stem-like cells may be sequestered in a niche at the junctional region where the corneal endothelial cells and the trabecular meshwork come together. These putative stem cells may supply new cells for both the corneal endothelium and the trabeculae. Evidence suggests that cells from this area migrate (perhaps as transient amplifying cells) to the endothelial periphery and, perhaps, to wounded areas of the corneal endothelium when needed. The migration may not be constant and may be age dependent.

The response of healing corneal epithelium to grooved polymer surfaces

Corneal epithelial wounds heal rapidly by the inwards growth of tissue with a contracting wound front. A synthetic polymer lens to correct refractive error (an implantable contact lens) could be incorporated into the cornea using this wound healing process. Topographical cues on the polymer surface may facilitate epithelial tissue migration over the anterior device surface. Here, silicone discs with a defined surface geometry of parallel grooves (groove and ridge widths of 1, 2, 5 and 10 microm; groove depths of 1 and 5 microm) were implanted into corneas and maintained in organ culture. The nature and rate of epithelial tissue migration over the test surfaces was monitored for 8 days and evaluated using microscopy and histology. Irrespective of the pitch, deep groove geometries directed tissue migration laterally along the grooves but this prevented contraction of the wound front and retarded migration rates. No guidance occurred on any of the shallow groove geometries but these allowed inwards radial migration with a contracting wound front and supported migration rates equivalent to a flat surface. None of the geometries tested promoted tissue migration above a flat polymer surface and data suggested that parallel grooves may not be optimal for this application.

Surgical detachment of Descemet's membrane and endothelium imaged over time by in vivo confocal microscopy

A 90-year-old woman developed a large circular capsulorhexis-like defect in Descemet's membrane as a complication of small incision cataract surgery. Nine months post-surgery, in vivo confocal microscopic examination of the temporal mid-peripheral cornea revealed an endothelial cell density of 934 +/- 69 cells/mm2 (normal range 1566-3088 cells/mm2). Endothelial pigmented deposits were visible as scattered hyper-reflective areas on the posterior endothelial surface. Descemet's folds were also noted. In vivo confocal microscopy performed 3 years later showed the temporal mid-peripheral corneal endothelial density (in the region of the break) was 948 +/- 66 cells/mm2. A reduction of endothelial polymegathism and pleomorphism was observed. Imaging in the region of the temporal portion of the original Descemet's defect showed well-defined linear structures with hyper-reflective edges. Compared to 3 years previously, the cornea at the level of Descemet's membrane appeared to have greater reflectivity. This case demonstrates how microstructural changes in the cornea can be described and analysed over time with the assistance of in vivo confocal microscopy.

Cryoinjury in endothelial cell monolayers

Developing successful cryopreservation strategies for corneas have proven to be more difficult than anticipated, because of the resulting loss of viability and detachment of endothelial cells from Descemet's membrane following cryopreservation of corneas. The objectives of this study are to develop a more detailed understanding of cryoinjury in human corneal endothelial cell (HCEC) monolayers and to examine the effects of storage temperature, cryoprotectant type and concentration, and cooling/warming rates on HCEC monolayers. Monolayers of endothelial cells attached to collagen-coated glass, immersed in an experimental solution (with and without cryoprotectant) were cooled at 1 degrees C/min to various temperatures (-5 to -40 degrees C), then thawed directly or cooled rapidly to -196 or to -80 degrees C before thawing. Cryoprotectants used were dimethyl sulfoxide and propylene glycol in concentrations of 1 and 2M. Monolayers were assessed for membrane integrity and detachment using SYTO/ethidium bromide fluorescent stain. The presence of cryoprotectants resulted in high recovery of membrane integrity and low monolayer detachment in monolayers thawed directly from temperatures down to -40 degrees C. In contrast, there was excessive detachment and loss of membrane integrity in monolayers cooled to -196 degrees C compared to monolayers cooled to -80 degrees C. Also, increasing cryoprotectant concentrations did not improve recovery of the monolayers. The higher recovery and lower detachment after storage at -80 degrees C compared to storage at -196 degrees C suggest that storage temperatures for corneas should be re-evaluated.

Retained IOL fragment and corneal decompensation after pseudophakic IOL exchange

A 72-year-old man had exchange of a foldable silicone multifocal intraocular lens (IOL) by transection, removal, and monofocal IOL replacement. One month after the exchange, irreversible corneal edema developed and penetrating keratoplasty was performed. At the time of the corneal transplant, a small silicone fragment was discovered in and removed from the anterior chamber. Histologic evaluation of the patient's cornea demonstrated an absence of corneal endothelium, suggesting the fragment was the etiology of the corneal decompensation.

Endothelial cell integrity after phacoemulsification with 2 different handpieces

PURPOSE

To investigate corneal endothelial cell loss in fresh phakic human autopsy cadaver eyes after phacoemulsification (PE) with a conventional handpiece or a new oscillatory handpiece.

SETTING

Department of Ophthalmology, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA.

METHODS

Twenty fresh phakic human autopsy globes were randomized to PE with a conventional handpiece (n = 10) or an oscillatory handpiece (n = 10). The main parameters evaluated were age, nucleus density, amount of ophthalmic viscosurgical device (OVD) used, and mean PE time and ultrasound (US) power. After surgery, the corneas were excised and the endothelia were vitally stained with trypan blue and alizarin red. Light microscopy was used to assess the endothelial cell loss.

RESULTS

The mean age, density of the nucleus, OVD used, and US power were similar between the groups. The mean PE time was less with the NeoSoniX handpiece (0.71 minutes +/- 0.39 [SD]) than with the conventional handpiece (1.05 +/- 0.53 minutes). The mean number of dead endothelial cells was significantly lower in the oscillatory handpiece group (31.3 +/- 24.2 cells/mm(2)) than in the conventional handpiece group (60.4 +/- 46.8 cells/mm(2)) (P<.001, Mann-Whitney rank sum test).

CONCLUSIONS

Less corneal endothelial cell loss occurred after PE with an oscillatory handpiece than with a conventional handpiece. Further randomized clinical trials are recommended to validate this study.

Aquaporin-1 expression is decreased in human and mouse corneal endothelial dysfunction

PURPOSE

To determine if aquaporin-1 expression is decreased in human and mouse corneal endothelial dysfunction.

METHODS

Immunohistochemistry with anti-aquaporin 1 antibody and confocal microscopy were used to study a case series of human corneal specimens, and a mouse model of corneal endothelial injury was created with injection of sterile hot water into the anterior chamber with a 33 gauge needle. Western blotting of mouse and human corneas was used to provide confirmatory evidence.

RESULTS

Aquaporin-1 was found to be expressed in normal human cornea and decreased in human corneas with endothelial disease but not in human corneas with non-endothelial corneal disease. Aquaporin-1 was also found to be reduced in mouse corneas subjected to corneal endothelial injury. Both results were confirmed by western blot analysis.

CONCLUSIONS

Corneal endothelial injury is associated with decreased aquaporin-1 expression.

Endothelial trauma in the surgery of cataract

Cataract surgery is most common in human surgery and comprises 80% of eye surgery programs. Owing to sophisticated technologies, it has become a routine surgery with lowered complications rate; hence, the functional outcome is more conditioned by operative trauma. The aim of this study was to demonstrate the significance of specular microscopy in the evaluation of operative trauma during extra-capsular cataract extraction (ECCE) and phacoemulsification (P), in a controlled environment. The study included 100 consecutive patients who met the established criteria, and groups were formed according to the type of surgery by the assignment of successive numbers from a random number table. Examination and photographs of the corneal endothelium, as well as pachymetry were performed on Keeler-Konan Poclington Specular Microscope (KSP). The obtained results revealed significant dissimilarity in endothelial cell reduction (9.17% in group E, and 4.72% in group P), which generated statistically significant correlation of pre-operative and post-operative pachymetry in the group E (p=0.0004). On the basis of the results obtained by specular microscopy, it was concluded that under the same conditions phacoemulsification caused reduced operative trauma of the corneal endothelium.

Corneal epithelial injury thresholds for multiple-pulse exposures to Tm:YAG laser radiation at 2.02 microm

Corneal epithelial damage thresholds for exposures to sequences of pulses of 2.02 microm infrared radiation produced by a Tm:YAG laser were investigated. Thresholds were determined for sequences of pulses at frequencies of 1, 10, 20, and 100 Hz. The duration of the individual pulses was 0.300 s at 1 Hz, 0.025 s at 10 and 20 Hz, and 0.005 s at 100 Hz. Threshold damage is correlated by an empirical power law of the form H(th) = CN(-alpha), in which H(th) is the threshold radiant exposure per pulse, and N is the number of pulses. The constant C differs depending on the pulse repetition frequency and individual pulse duration. The exponent alpha has values between 0.22 and 0.29. For some Tm:YAG exposures the empirical power law underestimates the damage threshold for small numbers of pulses. An empirical critical temperature model in which the critical damage temperature has a weak dependence on the duration of the single pulses or the entire train of pulses also correlates injury thresholds for both single and multiple pulses.

Nonmechanical Q-Switched Erbium:YAG Laser Trephination for Penetrating Keratoplasty

OBJECTIVE

To assess the alterations in human donor corneal tissue induced by Q-switched erbium (Er):YAG laser corneal trephination.

METHODS

Thirty human corneoscleral donor buttons unsuitable for transplantation were placed in an artificial chamber on an automated rotation device. Corneas were trephined with a Q-switched Er:YAG laser (wavelength, 2.94 microm; pulse duration, 400 nanoseconds) along (donor and recipient) aluminum silicate (ceramic) open masks. A spot diameter of 0.65 mm, energy setting of 50 mJ/pulse, and repetition rate of 5 Hz were used. Corneal thermal damage and cut regularity were quantitatively assessed in 24 corneas processed for light microscopy and by transmission and scanning electron microscopy.

RESULTS

The stromal thermal damage was the highest (mean [SD], 8.0 [2.7] microm) at a 150-microm cut depth and decreased downward. Cut regularity was very good and did not significantly differ between donors and recipients. Scanning electron microscopy confirmed that the cuts were highly regular; transmission electron microscopy revealed 2 distinctive subzones within the stromal thermal damage zone.

CONCLUSIONS

Thermal damage induced by Q-switched Er:YAG nonmechanical corneal trephination was low, and the regularity of the cuts was very good.

CLINICAL RELEVANCE

The Q-switched Er:YAG laser may have the potential to become an alternative to the excimer laser for nonmechanical penetrating keratoplasty.

Experimental study of viscoelastic in the prevention of corneal endothelial desiccation injury from vitreal fluid-air exchange

PURPOSE

To evaluate the usefulness of viscoelastic in protecting the corneal endothelium from desiccation injury associated with fluid-air exchange in a rabbit model.

DESIGN

Experimental study.

METHODS

Rabbit eyes undergoing pars plana lensectomy and vitrectomy were insufflated with either dry or humidified air for 20 minutes following introduction of either Opegan (sodium hyaluronate 1.0%; Santen, Osaka, Japan) or Viscoat (sodium hyaluronate 3%-chondroitin sulfate 4%; Alcon, Tokyo, Japan) into the anterior chamber. In two other groups of rabbit eyes, the same procedure was performed without using any viscoelastic agent. Corneas obtained from rabbits undergoing surgery were compared with corneas obtained from rabbits not undergoing surgery. Potential alterations in the corneal endothelium were investigated by scanning electron microscopy, by Phalloidin-FITC staining of actin and by in vitro measurements of corneal permeability for carboxyfluorescein using a diffusion chamber.

RESULTS

Scanning electron microscopy displayed less distortion of corneal endothelium with Opegan and Viscoat compared with the dry air-only exposed corneas. Using humidified air in Opegan and Viscoat coated corneas maintained the normal actin cytoskeleton during fluid-air exchange. Paracellular leakage was much less with Opegan and Viscoat use following infusion of dry air comparing to that of dry air-only group (P =.026 and P =.041). The difference was much more striking following humidified air infusion in Opegan or Viscoat coated corneas comparing to dry air-only infused corneas (P <.002 and P <.002).

CONCLUSIONS

Coating of rabbit corneal endothelium with Opegan or Viscoat before fluid-air exchange largely prevents dry air damage to the endothelium. Infusion of humidified air further protects corneal endothelium during fluid-air exchange in aphakic rabbit eyes.

Acoustic cavitation in phacoemulsification: chemical effects, modes of action and cavitation index

High-intensity ultrasound (US) energy (HIUE) has been extensively used in the last 3 decades in a wide range of surgical procedures, including phacoemulsification. The generation of radicals and sonoluminescence (SL) by application of continuous-wave (CW) HIUE to an aqueous medium under conditions simulating cataract phacoemulsification surgery is demonstrated by electron paramagnetic resonance (EPR) spectroscopy and a sensitive photon-detecting system. The findings provide direct evidence for the generation of acoustic cavitation in the simulated intraocular environment, pointing out that generation of acoustic cavitation in clinical phacoemulsification and other surgical applications of US is possible. The findings imply that the effects of acoustic cavitation in aqueous medium may contribute to the endothelial damage observed clinically following phacoemulsification cataract surgery. Saturation of the irrigating solution with various gases modifies the acoustic cavitation. Saturation of the irrigating solution with CO2 practically eliminates acoustic cavitation, with the concomitant elimination of radicals and SonL. CO2 may be utilized clinically to suppress acoustic cavitation in phacoemulsification and other medical applications. A cavitation index (CI) is introduced for the purpose of standardizing phacoemulsification instrumentation and other medical US devices that employ HIUE.

Viscoelastic protection from endothelial damage by air bubbles

PURPOSE

To determine whether viscoelastic materials effectively protect the corneal endothelium from air bubbles.

SETTING

Department of Ophthalmology, Yonsei University College of Medicine, Seoul, Korea.

METHODS

Human eye-bank and rabbit eyes had a standardized phacoemulsification procedure with or without viscoelastic material (Healon [sodium hyaluronate 1.0%], Healon GV [sodium hyaluronate 1.4%], or Viscoat [chondroitin sulfate 4.0%-sodium hyaluronate 3.0%]). The integrity of the endothelium was examined after the procedure with F-actin staining and scanning electron microscopy. Rabbit eyes with and without viscoelastic material (Healon or Viscoat) had a standardized irrigation/aspiration (I/A) procedure. The mucinous layer of the endothelium was examined after the procedure with transmission electron microscopy.

RESULTS

In the phacoemulsification experiment without viscoelastic material, with Healon, and with Healon GV, the endothelium of human and rabbit corneas had many areas of cell loss in a pattern consistent with air-bubble damage. With Viscoat, endothelial cells remained intact. In the I/A experiment, the mucinous layer of Viscoat-exposed rabbit endothelium appeared thinner. In the same experiments without viscoelastic material or with Healon, the mucinous layer of the endothelium appeared normal.

CONCLUSIONS

Viscoat effectively protected the endothelium from air-bubble damage. Viscoat appears to protect the endothelium by acting as a physical barrier. Its adherence is probably related to the way it interacts with the mucinous layer of the endothelium.

Endothelial protection: avoiding air bubble formation at the phacoemulsification tip

PURPOSE

To investigate the conditions under which bubbles form during phacoemulsification.

SETTING

Department of Ophthalmology, Yonsei University College of Medicine, Seoul, Korea.

METHODS

In the first part of the study, the partial pressure of oxygen (pO(2)) was used as a surrogate measure for the partial pressure of air. Irrigation solutions packaged in glass and plastic containers were studied. A directly vented glass bottle was also tested. The pO(2) of the various irrigation solutions was measured as the containers were emptied. In the second part, phacoemulsification procedures were performed in rabbit eyes with different power settings and different irrigation solutions. Intracameral bubble formation during the procedure was recorded. Following the phacoemulsification procedures, the corneas were stained for F-actin and examined for endothelial injury.

RESULTS

The initial pO(2) in irrigation solutions packaged in glass bottles was about half that at atmospheric levels; in solutions packaged in plastic, it was at atmospheric levels. As irrigation solutions were drained from the container, the pO(2) of the solution tended to rise toward atmospheric levels. The rate of pO(2) increase was markedly reduced by using a directly vented glass bottle. In the phacoemulsification procedures, bubble formation was most likely to occur with higher pO(2) and higher power settings. Observation of bubbles by the surgeon was highly correlated with endothelial damage.

CONCLUSIONS

Keeping the pO(2) low reduced the risk of endothelial damage, especially at higher phacoemulsification powers. The packaging of irrigation solutions was the most important factor in controlling the initial pO(2) of the solution. The pO(2) can be minimized throughout a phacoemulsification procedure by using a directly vented glass bottle.

The optimal molecular weight of dispersive type sodium hyaluronate for the reduction of corneal endothelial damage induced by sonication, irrigation, and aspiration

PURPOSE

The purpose of this study was to investigate the optimal molecular weight of dispersive sodium hyaluronate (Na-HA) for the reduction of corneal endothelial damage induced by sonication, irrigation, and aspiration, using enucleated pig eyes.

METHOD

The phaco-needle of phacoemulsification and aspiration (PEA) equipment was inserted into the anterior chamber after aqueous humor replacement with a 1% Na-HA solution of various molecular weights (2420 x 10(3), 1460 x 10(3), 1100 x 10(3), 520 x 10(3) or 290 x 10(3)). Then sonication, irrigation, and aspiration were conducted for 60 seconds. The residual rate of Na-HA in the anterior chamber and the damaged area of corneal endothelium were determined using an image analyzer.

RESULTS

Na-HA with a molecular weight of 1100 x 10(3) gradually disappeared from the anterior chamber after mixing with the irrigating solution, and the damaged area in only the 1100 x 10(3) group was significantly smaller compared with that in the control group.

CONCLUSION

These results suggest that an optimal molecular weight exists for dispersive hyaluronate applied for the protection of intraocular tissues during PEA. Under the conditions of this study, Na-HA with a molecular weight of 1100 x 10(3) displayed the highest protective efficacy.

Organization of junctional proteins in proliferating cat corneal endothelium during wound healing

PURPOSE

To evaluate for the first time cell junctional protein organization in proliferating corneal endothelial cells during in vivo wound healing.

METHODS

A total of 16 cats (32 eyes) were used in this study. A single 3-mm diameter (n = 24) or 1- to 2-mm diameter (n = 8) scrape injury was created in the central corneal endothelium of each eye. Twenty-four, 48, 72 hours or 5 days after scrape injury, eyes were collected for in situ double- or triple-labeling with phalloidin, anti-ZO-1, alpha-catenin, beta-catenin, and MIB-1 (monoclonal antibody to Ki67, a marker for actively cycling cells) and were imaged using confocal laser microscopy.

RESULTS

In 3-mm diameter injuries, endothelial cells completely resurfaced the wound 48 to 72 hours after scrape injury; smaller wounds resurfaced by 48 hours. Ki67 staining was negative 24 hours after scrape injury in all cases. Ki67-positive cells were observed in the central region of the wounds after 48 and 72 hours, and mitotic figures and pairs of postmitotic cells were observed. On day 5, Ki67-positive cells were rarely detected, and no mitotic figures were observed. In the wound area, a significant increase in cell area and a reduction in hexagonality were observed in cycling cells after 48 and 72 hours. Normal apical, pericellular staining of f-actin, ZO-1, alpha-catenin, and beta-catenin was partially maintained at all times during wound healing of small and large wounds. Double-labeling confirmed that these proteins were also present along the apical cell border in Ki67-positive cells.

CONCLUSIONS

After in vivo scrape injury, proliferation is limited temporally and spatially to spreading endothelial cells within the wound. Cell junctional connections appear to be maintained in actively cycling cells during healing.

Corneal endothelial damage after neodymium:YAG laser iridotomy

BACKGROUND AND OBJECTIVE

This study examined the long-term effect of neodynium:YAG (Nd:YAG) laser iridotomy on the corneal endothelium.

PATIENTS AND METHODS

A prospective study was designed. Patients with narrow and occludable angles or fellow eye of acute angle closure glaucoma attack were treated with Nd:YAG laser iridotomy. For one year, 31 eyes of 21 patients underwent complete follow-up. Corneal endothelial specular microscopy was performed before and after laser iridotomy at 1, 3, 6, and 12 months.

RESULTS

The decrease of endothelial cell density after YAG laser iridotomy was statistically significant at 1 month (P = 0.036), 6 months (P = 0.004), and 12 months (P = 0.000), respectively. The decrease was not statistically significant at 3 months (P = 0.467). Linear regression analysis indicated no statistical correlation between the percentage change in endothelial cell density and the total energy used during the treatment (1 month: P=0.08, 3 months: P= 0.3, 6 months: P=0.9, 12 months: P=0.2).

CONCLUSION

This study demonstrated significant endothelial cell loss in the 1-year follow-up. The result suggested that Nd:YAG laser iridotomy may pose a long-term hazard to the corneal endothelium.

Some observations on the use of cultured corneal endothelial cells as a model for intact corneal endothelium

Major differences have been identified between corneal endothelial cells in situ and those grown in culture. Cells in intact porcine corneal endothelium were studied and compared with primary cultures of the same cells either in suspension or in monolayers which had been grown on plastic (Nunc, Permonax). Differences were identified in the organization of the cytoskeleton (filamentous actin) between the cells in situ and in monolayer culture. The ability to withstand exposure to cryoprotective concentrations of Me(2)SO also varied substantially depending on whether the cells were in situ or in culture. These results underline the need for caution in the use of cells in culture as a model for studying the nature of injury to cells during the freezing of whole tissues.

Protection of corneal endothelium from irrigation damage: a comparison of sodium hyaluronate and hydroxypropylmethylcellulose

PURPOSE

To compare the endothelial protection of sodium hyaluronate and hydroxypropylmethylcellulose against endothelial damage induced by irrigation.

METHODS

An in vitro assay with freshly excised porcine eyes was developed using the Janus green photometry technique. Irrigation and aspiration technique was standardised. Forty pairs of porcine eyes were used. One randomly chosen eye was filled with sodium hyaluronate (SH) and the other with hydroxypropylmethylcellulose (HPMC). Irrigation and aspiration was carried out with balanced salt solution for 5 min. Twenty additional pairs of porcine eyes served as controls. Student's t-test was used for statistical analysis.

RESULTS

Both viscoelastic agents protected the endothelium as compared with controls. The endothelial protection, determined with the Janus green photometric technique, was significantly greater with HPMC than with SH.

CONCLUSIONS

Viscoelastic agents are effective in protecting the endothelium from irrigation damage in porcine eyes in vitro. HPMC provided greater protection than SH in this particular model.

[Photorefractive keratectomy. Free-running vs. q-switched Er:YAG laser (scanning mode)]

BACKGROUND

Examination of morphology in plane corneal ablation (in vitro) induced by an Er:YAG-laser (2.94 microns) in two modes: free-running (50 microseconds) and q-switched (200 ns).

METHODS

Sequences of different fluences in each mode were applied to freshly enucleated swine eyes. Parameters of free-running mode: fluences 1.21-4.77 J/cm2, frequency 80 Hz, spot size 500 microns FWHM, hexagonal spot shape. Parameters of q-switched mode: fluences 0.79-2.33 J/cm2, frequency 20 Hz, spot size 500 microns FWHM, round spot shape.

RESULTS

Histology showed thermal damage of 10-25 microns in depth caused by the free-running mode compared with 4.5-7.5 microns by the q-switched mode. In both gross photography and scanning electron microscopic examination, the surface was found to be more homogeneous and smoother in the q-switched mode.

CONCLUSIONS

Depending on the different application modes, both laser systems could be used for a defined corneal ablation in photorefractive keratectomy. However, at the moment, results using the Er:YAG laser are not as favorable as with the excimer laser.

[Thermal damage to the corneal endothelium in diode laser thermokeratoplasty]

Laser thermokeratoplasty (LTK) can be applied for correction of hyperopia and astigmatism by means of concentrically placed coagulations. Because of the temperature rise during coagulation, damage of the endothelial cells directly below the irradiated areas is possible. In this study, we examined the extent of the thermally denatured zones for different laser parameters and the threshold of thermal endothelial damage as a function of of temperature and duration of elevated temperatures. The threshold for thermal damage of endothelial cells was determined in isotonic NaCl solution for temperature exposures of 10 s and 1 min in a water bath. To determine the damage zones, corneas were irradiated under standardized conditions with a continuously emitting infrared (cw-IR) laser diode at various wave-lengths and different power values and were stained after preparation with trypan blue and alizarine red. The extensions of the damage zones were compared with calculated isotherms. Fifty percent cell damage was found at temperatures of 65 degrees C for heating times of 10 s and at 59 degrees C for 1 min. With thicker corneas, less laser power and higher absorption coefficients, the damage zone was reduced. The damage range determined corresponded to the calculated isotherms of 60 degrees C and 70 degrees C. Regarding clinical LTK, a loss of endothelial cells can be predicted and minimized or totally avoided by choosing the appropriate irradiation parameters.

Plasma membrane disruption underlies injury of the corneal endothelium by ultrasound

The nature and the extent of acute injury to corneal endothelial cells caused by exposure to ultrasound radiation were characterized, as well as the long-term reaction of these cells to this form of injury. It was found that the degree of lethal cell injury induced by ultrasound scaled with exposure intensity and duration. Immediate changes in plasma membrane permeability were induced by ultrasound exposure. This ultrasound-induced permeability change was, however, transient in many cells, allowing them to trap and retain a normally impermeant tracer, fluorescein dextran, in cytosol. Microvilli were present on ultrasound treated cells in far greater density than on control cells, characteristic of exocytosis-based resealing. Cultures containing a majority of transiently permeabilized endothelial cells were morphologically indistinguishable from untreated control cultures, and the fluorescein dextran-labeled cells in these populations locomoted and divided normally. We conclude that cell death due to ultrasound exposure can occur rapidly via a necrotic mechanism that can be attributed to mechanically induced damage to the plasma membrane. However, not all cells injured become necrotic: some survive and appear to behave normally after exposure. Conditions that favor plasma membrane disruption resealing, e.g. that result in sub-lethal rather than lethal cell injury, may mitigate the reduction in corneal endothelial cell density consequent on phacoemulsification and aspiration surgery.

A method for determining the cytoprotective effect of catalase in transiently transfected cell lines and in corneal tissue

Both when developing gene constructs for therapeutic purposes and when testing the biological function of proteins, it would be convenient to use cells or tissues that have been transiently transfected with the gene of interest. However, determining the protective effects of transient gene expression is complicated by a low transfection efficiency, resulting in only a minority of the cells expressing the introduced gene and consequently a reduced sensitivity of assays measuring the death of transfected cells. In this study we have developed a convenient technique for determining cell death in transiently transfected vascular endothelial cell monolayers and in corneal tissue. Vascular endothelial cells were cotransfected with human catalase cDNA and the lacZ gene encoding beta-galactosidase, under conditions in which cells expressing beta-galactosidase also expressed catalase. By assaying release of beta-galactosidase upon cell death, it was possible to show that catalase transfection led to significant protection against the cytotoxic effect of increasing concentrations of hydrogen peroxide. The assay was adapted to demonstrate the protective effects of catalase transfection on hydrogen peroxide-mediated injury of intact corneal endothelium under ex vivo culture conditions. This assay should also be useful for characterizing the cytoprotective effects of other genes in transient transfection systems.

Effect of topically applied 0.1% dexamethasone on endothelial healing and aqueous composition during the repair process of rabbit corneal alkali wounds

PURPOSE

The effects of topical dexamethasone on the endothelial healing and the change of aqueous compositions were investigated during the repair process of alkali-wounded rabbit cornea.

METHODS

A central corneal alkali wound was produced by a 60 sec application of a 5.5 mm round filter paper soaked in 1N NaOH onto one eye of each rabbit. The eyes subsequently were treated topically with either 0.1% dexamethasone or a balanced salt solution (BSS) 4 times per day for 8 weeks. Endothelial wound morphometry was performed after alizarin red and trypan blue staining. The concentrations of ascorbic acid, glucose, and the ions, Na+, K+, Ca2+ and Mg2+, were measured in the aqueous humor.

RESULTS

Endothelial healing in control (alkali-wounded but not treated with dexamethasone) corneas showed a biphasic pattern of healing: an initial short-term healing for the first week and then a late long-term healing following the secondary endothelial breakdown. Topical administration of 0.1% dexamethasone deterred endothelial healing during the early period and prevented the secondary endothelial breakdown. However, the total repair process of endothelium was accelerated by the dexamethasone-treatment. Among the various components of the aqueous humor examined, ascorbic acid seemed the most sensitive to change caused by the alkali injury and dexamethasone treatment.

CONCLUSIONS

The present data indicate that dexamethasone may have a therapeutic potential in the management of endothelial healing after corneal alkali injury.