Osmotic tolerance of rabbit and human corneal endothelium

Safety of intracameral injection of levofloxacin 0.5% eye drops single dose 0.6 ml preservative free on rabbit eye

Background

This was an experimental, parallel, and randomized study to evaluate the safety of single intracameral injection of 0.6 ml 0.5% preservative-free levofloxacin eye drops on rabbit eye.

Methods

In total, 24 eyes of 12 New Zealand white rabbits were divided into three groups. The first group (LFX) was treated with 0.1 ml intracameral injection of levofloxacin 0.5% eye drops of 0.6 ml preservative-free (n = 6), the second group (CRAV) was treated with 0.1 ml intracameral injection of levofloxacin 0.5% eye drops 5 ml commercially available eye drops preservative-free (n = 6), and the third group (BSS) were treated with 0.1 ml intracameral injection of balanced salt solution (n = 12). All groups received a single dose. The clinical evaluation was performed on the 1 st, 3 rd, 5 th, and 7 th day after injection. Each eye was enucleated on the 7 th day and underwent a histopathology examination.

Results

The clinical scores among the three groups did not show any significant difference on days 1 st, 2 nd, 3 rd, and 7 th (p>0.05). The only ones noted in clinical scores were mild corneal opacity, mild cells, and flares in the anterior chamber. The histopathology score demonstrated no statistically significant difference between the three groups (p>0.05). Vacuolization of corneal endothelial cells was noted in all groups but was not statistically significant.

Conclusions

A single intracameral injection of 0.6 ml 0.5% preservative-free levofloxacin eye drops was safe for rabbit eye, according to clinical and histopathology scores, similar to levofloxacin 0.5% eye drops in 5 ml bottle preservative free.

Scaffold-Free Strategy Using a PEG-Dextran Aqueous Two-Phase-System for Corneal Tissue Repair

Forming thin tissue constructs with minimal extracellular matrix surrounding them is important for tissue engineering applications. Here, we explore and optimize a strategy that enables rapid fabrication of scaffold-free corneal tissue constructs using the liquid-liquid interface of an aqueous two-phase system (ATPS) that is based on biocompatible polymers, dextran and polyethylene glycol. Intact tissue-like constructs, made of corneal epithelial or endothelial cells, can be formed on the interface between the two liquid phases of ATPS within hours and subsequently collected simply by removing the liquid phases. The formed corneal cell constructs express essential physiological markers and have preserved viability and proliferative ability in vitro. The corneal epithelial cell constructs are also able to re-epithelialize the corneal epithelial wound in vitro. The results suggest the promise of our reported strategy in corneal repair.

[Establishing Evidence for Use of Appropriate Medicines in the Operating Room]

Various issues related to clinical use of medicines remain unclear, and pharmacists are expected to establish evidence for appropriate use of medicines. The present review summarizes our findings from three areas of research regarding the use of medicines in the operating room: 1) We evaluated the extent of extravasation injury due to thiopental (2.5 mg/100 μL) and propofol (1.0 mg/100 μL) at the macroscopic and histopathologic levels in a rat model. Thiopental, which causes tissue necrosis, can be classified as a "vesicant", and propofol can be classified as an "irritant". Moreover, warming strongly exacerbated the degeneration or necrosis induced by extravasation of thiopental. 2) The cytotoxicity of povidone-iodine solution (PVP-I) for ophthalmic use and that of polyvinyl alcohol-iodine solution (PAI) was compared using a human corneal epithelial cell line. Despite exhibiting equivalent antiseptic effects, the cytotoxicity of PVP-I diluted 16-fold was greater than that of PAI diluted 6-fold. After inactivation of iodine, the cytotoxicity of PVP-I persisted; therefore, to avoid corneal damage, antisepsis should be achieved with PAI. 3) The stability of 1 μg/mL adrenaline when used as an intraocular irrigating solution to maintain pupil dilation was evaluated. After mixing for 6 h, the adrenaline concentration was 65.2% (pH 8.0) of the initial concentration. Moreover, the low concentration of sodium bisulfite in the irrigating solution could have caused adrenaline reduction. Our results strongly suggest that intraocular irrigation solution containing adrenaline should be prepared just prior to use in surgery.

Acute corneal edema without epithelium compromise. A case report and literature review

El edema de córnea es una entidad que se produce por un gran número de causas y tiene diversas formas de presentación y diferentes grados de afección. En este artículo se reporta el caso de un hombre con edema de córnea agudo sin compromiso epitelial, en el que el cuadro clínico, el examen oftalmológico y los estudios de extensión no lograron establecer su etiología. Además, se hace una revisión de la literatura disponible respecto a todas las posibles causas de edema de córnea agudo, agrupándolas en aquellas que ocasionan el edema por lesión o inflamación epitelial o estromal, por disfunción endotelial o por un aumento en la presión intraocular.

Poloxamines for deswelling of organ-cultured corneas

BACKGROUND

Poloxamines are amphiphilic tetrofunctional block copolymers composed of four polyoxyethylene-polyoxypropylene arms joined to a central ethylene diamine bridge. Their safe profile allows diverse pharmaceutical and biomedical applications.

AIM

To assess their use for corneal deswelling using a porcine model of organ culture (OC).

METHODS

Five poloxamines (T90R4, T904, T908, T1107 and T1307) were dissolved in a standard commercial OC medium (control) to reach 350 mosm kg(-1). In vitro cytotoxicity was tested using MTT assay on human corneal epithelial and endothelial cell (EC) lines and on primary human corneal fibroblasts. Paired porcine corneas stored in OC for 3 days were assigned for 48 h to a poloxamine medium or to a standard deswelling medium containing 5% dextran T500. Corneal EC density, morphometry, mortality, stromal thickness and transparency were evaluated before and after deswelling. Post-deswelling, EC viability/mortality was determined using a fluorescent live/dead assay.

RESULTS

Besides similar corneal thickness reduction and transparency improvement, T908, T1107 and T1307 decreased EC loss (5.4 ± 1.7% vs. 9.9 ± 2.6% in controls (p < 0.001)) and mortality, improved EC morphometry and reduced endothelial lesions compared to dextran.

CONCLUSION

On this porcine model, poloxamines T908, T1107 and T1307 appear as good candidates to replace dextran for the deswelling. Experiments on human corneas are now necessary to confirm their efficiency and safety profile in OC.

Safety of prophylactic intracameral moxifloxacin 0.5% ophthalmic solution in cataract surgery patients

PURPOSE

To determine the safety of prophylactic intracameral moxifloxacin 0.5% ophthalmic solution (Vigamox) in patients having cataract surgery.

SETTING

American Eye Center, Manila, Philippines.

METHODS

Preoperative and 1-month postoperative anterior chamber reaction, corneal endothelial cell density, and corneal thickness were assessed in 65 eyes that had cataract surgery with intracameral moxifloxacin. All eyes received 0.1 mL intracameral moxifloxacin 0.5% ophthalmic solution containing 500 mug of moxifloxacin as the last step of phacoemulsification. Different ophthalmologists conducted the postoperative evaluation in an observer-masked fashion. A P value less than 0.05 was considered significant.

RESULTS

All 65 eyes completed the study. The mean age was 69.5 years +/- 9.13 (SD) (range 48 to 84 years). All eyes had a postoperative best corrected visual acuity of 20/30 or better. All eyes had trace to +2 cells and flare anterior chamber reaction only on the first day after surgery. The mean endothelial cell count was 2491.52 cells/mm(2) preoperatively and 2421.58 cells/mm(2) postoperatively. The mean difference was 70 cells/mm(2), which not statistically significant (P = .737). The increase of 17.80 microm in postoperative pachymetry 1 month after surgery was not statistically significant (P>.65).

CONCLUSION

Intracameral Vigamox 0.5 mg/mL appeared to be nontoxic in terms of visual rehabilitation, anterior chamber reaction, pachymetry, and corneal endothelial cell density.

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.

Toxic anterior segment syndrome

Toxic anterior segment syndrome (TASS) is a sterile postoperative inflammatory reaction caused by a noninfectious substance that enters the anterior segment, resulting in toxic damage to intraocular tissues. The process typically starts 12 to 48 hours after cataract/anterior segment surgery, is limited to the anterior segment of the eye, is always Gram stain and culture negative, and usually improves with steroid treatment. The primary differential diagnosis is infectious endophthalmitis. Review of the literature indicates that possible causes of TASS include intraocular solutions with inappropriate chemical composition, concentration, pH, or osmolality; preservatives; denatured ophthalmic viscosurgical devices; enzymatic detergents; bacterial endotoxin; oxidized metal deposits and residues; and factors related to intraocular lenses such as residues from polishing or sterilizing compounds. An outbreak of TASS is an environmental and toxic control issue that requires complete analysis of all medications and fluids used during surgery, as well as complete review of operating room and sterilization protocols.

Effect of ophthalmic viscosurgical devices on lens epithelial cells

PURPOSE

To investigate the morphological effects of Viscoat (sodium hyaluronate 3.0%-chondroitin sulfate 4.0%) on lens epithelial cells (LECs).

SETTING

Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, USA, and the Laboratory of Ultrastructural Morphology, Zoological Institute, University of Liège, Liège, Belgium.

METHODS

Human LECs collected via capsulorhexis were examined by light microscopy (LM) and transmission electron microscopy (TEM). Lens epithelial cells from rabbit capsulorhexis samples were studied by LM and TEM following exposure to Provisc (sodium hyaluronate 1.0%) or Viscoat ophthalmic viscoelastic device (OVD). Since Viscoat is hypertonic (340 mOsm), hypertonic, isotonic, and hypotonic solutions were compared to investigate a possible mechanism for the observed effects. The effects of Provisc and Viscoat on rabbit LECs in the intact lens were also compared.

RESULTS

Human LECs gathered via capsulorhexis following exposure to Viscoat were generally thinner than control samples and often had condensed nuclei and increased intracellular vacuolization. Rabbit capsular tissue exposed in situ to Viscoat demonstrated changes similar to those seen in humans. Cells exposed to Provisc were similar to cells in untreated controls in humans and rabbits. Corneal endothelial cells exposed to either agent were unaffected. Experiments with hypertonic and hypotonic buffers induced some of the changes noted with Viscoat, but the effects were less severe. Lens epithelial cells in intact rabbit lenses exposed to Viscoat appeared similar to LECs in the control samples.

CONCLUSIONS

Light microscopy and TEM of human lens capsule tissue suggest that Viscoat induces significant morphological changes in LECs during cataract surgery. The changes may underlie the improved visualization of these cells that has been reported during cataract surgery. Corneal endothelial cells were unaffected by exposure to Viscoat. Studies in a rabbit model suggest that the hyperosmolarity of Viscoat may play a partial role in the LEC changes.

Observation of the Posterior Endothelial Surface of the Rabbit Cornea Using Atomic Force Microscopy

PURPOSE

To study the surface of normal corneal endothelium by means of atomic force microscopy (AFM).

METHODS

The central corneal endothelial posterior surface of New Zealand white rabbits was examined. Specimens were observed in Balanced Salt Solution using the contact mode of the AFM either fresh or after fixation in cacodylate-buffered glutaraldehyde solution. Removal of sialic acid residues and hyaluronic acid was achieved by means of enzymatic treatment with neuraminidase and hyaluronidase.

RESULTS

Observation of the fresh specimens revealed the presence of an apical endothelial surface coating material (glycocalyx). Removal of sialic acid residues and hyaluronic acid after enzymatic treatment using neuraminidase and hyaluronidase, respectively, permitted the elucidation of the structure of the nondigested coating material. Fixation of the samples resulted in removal of the surface coating material. The imaging of the fixed endothelium surface revealed the mosaic of polygonal cells with the apical flaps of cell junctions emerging over the cell surface. The cell shape and the other characteristics of the posterior surface fixed endothelium were comparable to those described in the literature using scanning electron microscopy. The scanning of very small ranges has provided high-resolution images at the nanometer level in fixed and fresh corneal endothelial surfaces.

CONCLUSION

The atomic force microscope represents a new powerful imaging tool permitting high-resolution observation of corneal endothelium surface in fresh and minimally prepared fixed specimens.

Ocular surgical pharmacology: corneal endothelial safety and toxicity

The purpose of this review is to discuss the recently published literature related to corneal endothelial toxicity and safety. We discuss postoperative complications, such as toxic endothelial cell destruction syndrome and toxic anterior segment syndrome, that cause significant injury to the patient and anxiety to the physician. Additionally, we review recent papers related to intraocular medications, preservatives, and devices, including antibiotics, anesthetics, viscoelastics, and enzymatic sterilization detergents, that have potentially toxic effects on the corneal endothelium.

Prophylactic intracameral cefuroxime. Evaluation of safety and kinetics in cataract surgery

PURPOSE

To evaluate the safety and kinetics of prophylactic intracameral cefuroxime in cataract surgery.

SETTING

Department of Ophthalmology, St. Eriks Hospital, Stockholm, Sweden.

METHODS

In a nonrandomized observer-masked best-case trial, the visual rehabilitation and the evolution of laser flare intensity and corneal endothelial cell density after cataract surgery were assessed in 45 patients receiving intracameral cefuroxime and in 45 control patients. Immunoglobulin E-mediated sensitivity was evaluated using a skin prick test to cefuroxime in a screening program comprising all cataract patients operated on in 1997. Intracameral concentrations of cefuroxime in samples retrieved 30 seconds (n = 10) and 1 hour (n = 9) postoperatively were evaluated in an observer-masked fashion with a microbiological assay.

RESULTS

Intracameral cefuroxime did not have a statistically significant effect on postoperative visual acuity, induced laser flare intensity, or endothelial cell loss compared with nonadministration of intracameral antibiotic prophylaxis. Three positive skin prick tests to cefuroxime were found in the 5813 screened cataract patients. The median aqueous humor concentration of cefuroxime at 30 seconds was 2742 mg/L, declining to 756 mg/L 1 hour after drug instillation.

CONCLUSIONS

Intracameral cefuroxime 1 mg appears safe in terms of local toxicity. Immunoglobulin E-mediated allergy to cefuroxime is rare in the cataract population. The treatment achieved high aqueous concentrations even 1 hour after surgery.

Corneal toxicity secondary to inadvertent use of benzalkonium chloride preserved viscoelastic material in cataract surgery

AIMS

To study the long term toxic effects of intraocular benzalkonium chloride (BAC).

METHODS

19 patients exposed to intraocular BAC preserved viscoelastic during cataract surgery in February 1999 developed severe striate keratopathy immediately postoperatively. 16 patients, including two who underwent penetrating keratoplasty, were studied in the period April to June 2000. Ocular symptoms, visual acuity, biomicroscopy, intraocular pressure, dilated funduscopy, specular endothelial microscopy, and corneal pachymetry findings were recorded. The corneal and iris specimens of the two patients who underwent keratoplasty were studied by light, transmission, and scanning electron microscopy.

RESULTS

Six males and 10 females, aged 64-98 years, were studied 14-16 months postoperatively. All patients were symptomatic. 12 patients had best corrected visual acuity of 6/12 or better and four patients of between 6/18 and 6/60. Five patients had corneal epithelial oedema and 11 had Descemet's membrane folds. The central corneal thickness, 620 (SD 71) microm, in affected eyes was significantly higher (p<0.005, two tailed paired t test) than that of the contralateral eyes, 563 (SD 48) microm. The endothelial cell density was significantly lower (p<0.0001, two tailed paired t test) in affected eyes: 830 (SD 280) cells/mm2 v 2017 (SD 446) cells/mm2. The mean average cell area was significantly higher in the BAC treated eyes: 1317 (SD 385) microm2 v 521 (SD 132) microm2. There was no significant difference in the coefficient of variation of cell size between the two eyes (p=0.3, two tailed paired t test). Two corneal specimens displayed morphological features of bullous keratopathy and other non-specific abnormalities. Extracellular melanosomes were present in a portion of the iris of one case.

CONCLUSION

BAC is toxic to the corneal endothelium when used intraocularly, leading to severe striate keratopathy. This cleared in most cases but left varying degrees of residual stromal thickening in all eyes. If penetrating keratoplasty is required the results are excellent.

Corneal toxicity of intraocular hyaluronidase

The purpose of this study was to examine the corneal toxicity of different preparations of intraocular hyaluronidase. SDS-PAGE analysis of bovine testicular hyaluronidase (Wydase) and chromatographically purified hyaluronidase (Sigma) was performed. These two preparations were injected into the anterior chamber of rabbits in amounts ranging from 1.5-150 IU (Wydase) and 1.5-300 IU (Sigma). A third set of rabbit eyes received Wydase vehicle alone or in combination with Sigma hyaluronidase. Treated control eyes were injected with saline. Slit lamp examination and indirect ophthalmoscopy were performed preoperatively and on postoperative days 1 and 7. Light microscopy of the corneas was performed. SDS-PAGE of Wydase revealed numerous protein impurities, while Sigma demonstrated one protein band consistent with mammalian hyaluronidase. Persistent corneal edema, severe anterior chamber fibrin, and endothelial necrosis, were seen in the majority of eyes injected with Wydase in amounts of 50 IU and greater (n = 11). Thirty percent (30%) of the eyes injected with the Sigma preparation (n = 11) had localized corneal opacity similar to 50% of eyes injected with saline (n = 2). Of the rabbit eyes injected with the Wydase vehicle (n = 19), 68% had toxic changes. Intracameral injection of Wydase is toxic to the rabbit cornea in amounts of 50 IU and greater. A chromatographically purified preparation showed only transient local toxicity. Toxicity of Wydase may be due to protein impurities and the thimerosal-containing vehicle.

Toxic endothelial cell destruction from intraocular benzalkonium chloride

PURPOSE

To present a cluster of cases of corneal edema occurring after phacoemulsification.

SETTING

Regional hospital in rural Australia.

METHODS

This retrospective case series comprised 12 patients from a single surgical list comprising 19 cases who developed persistent corneal edema after having phacoemulsification.

RESULTS

After 6 months, the edema improved in 1 patient. Inadvertent intraocular use of balanced salt solution (BSS) preserved with benzalkonium chloride was found to be the cause of this serious complication.

CONCLUSIONS

Benzalkonium chloride in concentrations commonly used extraocularly is highly toxic to the corneal endothelium. Every possible safeguard should be taken to prevent inadvertent intraocular use of such preserved solutions.

Osmolality of various viscoelastic substances: comparative study

PURPOSE

To determine the osmolality of various viscoelastic substances.

SETTING

Department of Ophthalmology, Johannes Gutenberg-University, Mainz, and Institute for Medical Device Testing, Memmingen, Germany.

METHODS

The analysis was carried out according to the European Pharmacopoeia by means of a calibrated osmometer using the freezing-point depression method. Each syringe was analyzed as a duplicate analysis.

RESULTS

Mean osmolalities (mOsmol/kg) of the sodium hyaluronate viscoelastic substances were Allervisc 299; Allervisc Plus 307; Amvisc Plus 335; AMO Vitrax 284; Biolon 279; Dispasan 311; Dispasan Plus 314; Healon 295; Healon GV 312; Healon5 322; HYA-Ophtal 376; Microvisc 313; Microvisc Plus 341; Provisc 307; Rayvisc 312; Viscoat 340; Visko 296; Visko Plus 319. Mean osmolarities of the hydroxypropyl methylcellulose viscoeslatic substances were Adatocel 278; HPMC Ophtal L 358; HPMC Ophtal H 360; La Gel 317; OcuCoat 309; Visco Shield 376.

CONCLUSIONS

There were significant differences in osmolality among viscoelastic substances, which may explain the differences in corneal thickness after cataract surgery. A viscoelastic substance with an osmolality of 305 mOsmol/kg or slightly higher is preferable, especially in patients with a compromised corneal endothelium.

Changes in cell surface primary cilia and microvilli concurrent with measurements of fluid flow across the rabbit corneal endothelium ex vivo

Primary cilia and microvilli have been reported on the mammalian rabbit corneal endothelium but their relationship to cell function is undefined. Six corneas from healthy 2 kg female albino rabbits were glutaraldehyde-fixed post mortem (15:00 h) or twelve corneal stroma-endothelial preparations incubated at 37 degrees C under an applied hydrostatic pressure of 20 cm H2O for 4 h prior to fixation. The corneal endothelium was assessed by quantitative scanning electron microscopy. Cells fixed immediately post mortem were decorated with small stubby microvilli (average 21 +/- 13/100 micron 2), and only 25% of the cells were decorated with primary cilia having an average length of 2.44 +/- 1.56 microns. Following 4 h ex vivo incubation with a phosphate-buffered Ringer solution, conspicuous microvilli developed to an average density of 40 +/- 19/100 micron 2 and primary cilia were found on 12% of the cells, having on average length of 2.27 +/- 1.38 microns. Following 4 h incubation in a bicarbonate-buffered Ringer solution, small stubby microvilli developed to a density of 49 +/- 18/100 micron 2, and 40% of the cells showed primary cilia with an average length of 4.31 +/- 1.93 microns; the net trans-endothelial fluid flow in the latter set was 60% greater. These studies indicate that the primary cilia on corneal endothelial cells might be responsive to fluid flow, but that mild mechanical and/or chemical stress could also be the cause of the change since the elaboration of primary cilia can be accompanied by microvilli as well.

Effect of bicarbonate-free balanced salt solutions on fluid pump and endothelial morphology of rabbit corneas in-vitro

Corneas from young adult albino rabbits were exposed, in-vitro, to various bicarbonate-free balanced salt solutions under an applied hydrostatic pressure of 20 cmH2O at 35 degrees C for up to 4.5 h. The solutions were buffered with a HEPES-MOPS mixture, phosphate salts or acetate-citrate salts (pH 7.1-7.4). All of these solutions support a net fluid pump activity attributed to the corneal endothelium although the net fluid pump rates were less than those measurable with a bicarbonate-buffered, CO2-equilibrated Ringer solution. Evaluation of the endothelia by scanning electron microscopy revealed no evidence of any acute toxic effect of the balanced salt solutions. Morphometric analyses of cell size and shape revealed a normal mosaic for endothelia exposed to commercial balanced salt solution for 5 h. The results further indicate that exogenous bicarbonate is not required for the net fluid pump function of the mammalian corneal endothelium.

A test for crystalline lens biocompatibility

The current use of monkeys for testing intraocular fluids and viscoelastic materials is being questioned because of the decreasing availability and increasing cost of these scarce animals. The rabbit is an inexpensive, readily available, and convenient animal which might provide an alternative model for this purpose. In this study we have outlined the lens changes (clefts or vacuoles) that are observed in the New Zealand white rabbit as a result of toxicity to intraocular test materials. We used two viscoelastic agents, 1% sodium hyaluronate-Healon and 2% carboxymethylcellulose, and balanced salt solution to evaluate the efficacy and reproducibility of lens changes in this test study. The lens changes in each case were reproducible and could easily be graded. When used in concert with other tests, this new test can help in the preliminary evaluation of an ophthalmic material before its final clinical use in humans.

The corneal endothelium

The endothelium is a monolayer of cells on the posterior corneal surface that transports water from the stroma into the anterior chamber. This movement of water counters a natural tendency for the stroma to swell and is necessary to maintain a transparent cornea. Embryologic studies, in particular the demonstration of the derivation of the endothelium from the neural crest, have provided insight into the factors that govern the response of this tissue to disease. In some species the endothelium can regenerate after injury, but in man cellular enlargement is the main mechanism of repair after cell loss. A clinical estimate of endothelial cell density and function is provided by specular microscopy, fluorophotometry and pachymetry. In this paper we review the development, structure and function of the corneal endothelium, and then consider the pathological processes that can affect this tissue.

Clinical evaluation of the effect of acetylcholine on the corneal endothelium

A transient corneal edema is often seen after the injection of acetylcholine solution in the anterior chamber during cataract surgery. Ninety eyes of 90 patients scheduled for extracapsular cataract extraction with posterior chamber intraocular lens implantation were randomly assigned to two groups: one which received acetylcholine solution in the anterior chamber and one, a control group, which received only external conjunctival pilocarpine drops as a miotic. At three days, endothelial folds (P = .04) and corneal edema (P = .01) were more pronounced in the acetylcholine group; at seven days, endothelial folds were more severe (P = .04) in the acetylcholine group. At 30 days, the acetylcholine group showed a 37.2% increase (P = .01) of the endothelial cell area, whereas the control group showed a 7.08% increase. The difference between the groups was statistically significant (P = .05). Anterior chamber fluorophotometry at 30 days showed an increase of the corneal transfer coefficient that was higher but not significant in the acetylcholine group. We suggest caution in the intraoperative use of acetylcholine solution, particularly in those eyes showing a preoperative compromise of the endothelium.

The assessment of endothelial integrity by scanning electron microscopy and fluorescein diacetate staining following treatment with cryoprotective additives

As part of the development of methods of corneal cryostorage for transplantation, a toxicity study was carried out on the rabbit corneal endothelium using four cryoprotective additives (CPA's) 1) dimethyl sulphoxide (Me2SO), 2) propane-1,2-diol (PG), 3) glycerol (GLY), 4) polyvinylpyrrolidone (PVP). A fifth group, based upon a CPA combination of Me2SO and PVP, was used to characterize both the assays, and the response of the endothelial layer to osmotic stress. The effect upon the cell membrane was assessed using scanning electron microscopy (SEM) and fluorescein diacetate with ethidium bromide staining (FDA/EB). Two sampling points were used, one immediately after treatment and the other following an incubation period. Calculations were performed to predict the maximum relative volume of cells during CPA exchange. Immediately following serial addition and removal of 2 or 3 mol/L (M) PG or GLY, the cells exhibited adverse morphological changes shown with SEM, and the proportion of intact cells judged by FDA/EB staining was significantly reduced when CPA equilibration was performed at 37 degrees C rather than at 20 degrees C. A 3M Me2SO concentration gave less morphological change than 3M PG or GLY, but even after treatment with 4M Me2SO more than 95% cells were judged intact by FDA/EB staining. PVP at 40% w/v showed minimal damage with both assays, and the fifth experimental group suggested that PVP may protect from injury during hypotonic stress. With all groups, the integrity of the cell layer recovered during incubation, so that for each sample the percentage of intact cells was high. However, although confluency was often restored following incubation, total cell density was usually reduced. The results indicate that serial addition and removal of 3M Me2SO is tolerated by the cornea, whereas PG or GLY cannot be used at 2 or 3M without inducing osmotic damage. There was low toxicity to PVP, and it was an effective osmotic buffer.

Intracameral thrombin and the corneal endothelium

We perfused the endothelia of isolated human corneas mounted in the specular microscope with BSS Plus containing 1,000-U/ml or 100-U/ml dilutions of two commercially available topical thrombin preparations. Corneas perfused with thrombin at 1,000 U/ml showed intracellular and intercellular vacuole formation and altered junctional complexes. As listed on the package inserts, the thrombin preparations contained preservatives and other additives that present a significant osmotic load in 1,000-U/ml preparations. Corneas perfused with 100-U/ml thrombin solutions showed a significant attenuation in their deswelling rate but no ultrastructural alterations. One available thrombin preparation when diluted to 100 U/ml had a glycine concentration associated with previous retinal electroretinography changes. Polyacrylamide gel electrophoresis of one manufacturer's thrombin solution showed multiple high and low molecular weight constituents. Analysis of particulate contamination showed one 100-U/ml thrombin preparation to have a large quantity of particulates. Although thrombin may be useful when applied topically as an aid in surgical hemostasis, its use intraocularly presents substantial concern regarding the preparation's purity, additives, contaminants, and adverse effects on ocular tissues.

Effects of osmotic stress on rabbit corneal endothelium

The effects of osmotic stress on corneal endothelium were investigated by exposing rabbit corneas to anisosmotic conditions, and then perfusing the corneas with isosmotic glutathione bicarbonate Ringer solution for 4 hr at 35 degrees C. During the perfusion, endothelial function was assessed by measuring corneal thickness with a specular microscope. After perfusion, the corneas were prepared for scanning and transmission electron microscopy. Endothelial ultrastructure and function were well maintained after exposure to a wide range of osmolality (0.12-2.7 osmol/kg), but this tolerance of osmotic stress was dependent both on the duration and the temperature of exposure to the anisosmotic conditions. Exposure to an osmolality of 2.7 osmol/kg for 15 min at 23 or 37 degrees C resulted in gross damage to the endothelium when the hyperosmotic agent was sodium chloride. This damage was not the result of increased osmolality per se nor cellular shrinkage because the endothelium tolerated exposure to a sucrose solution of the same osmolality for 15 min at 37 degrees C. The detrimental effect of sodium chloride, however, was mitigated by reducing the temperature of exposure to 0 degrees C or reducing the duration of exposure to 5 min. These results suggest that endothelial cells become more tolerant of high electrolyte concentrations with reducing temperature, and this could be an important factor in the survival of the endothelium in corneal cryopreservation. The results also help to define the limits of osmotic shrinkage and swelling tolerated by endothelial cells. This will be of value in overcoming the detrimental osmotic effects associated with the addition and, in particular, the removal of cryoprotectants.

Osmotic properties of the rabbit corneal endothelium and their relevance to cryopreservation

The process of cryopreservation subjects cells to gross changes in the composition of the solution that surrounds them, changes that cause the cells first to shrink and then to swell by an osmotic mechanism. Empirical methods have been developed that permit many cells to survive freezing and thawing, but the cornea, which is crucially dependent upon the function of its endothelial monolayer, has proved quite refractory. In this paper we explore the osmotic response of the corneal endothelium of the rabbit to solutions ranging in osmolality from 0.25 to 8.6 X isotonic. Boyle van't Hoff behavior was observed between 0.43 and 8.6 X isotonic, and there was an apparent nonosmotic volume of 33.6%. However, ultrastructural damage was observed at the limits of this range, and it appeared that the tolerated range was 0.64-4.4 X isotonic. We show the extent to which dimethyl sulfoxide (Me2SO) would be expected to moderate changes in volume during freezing and suggest that its initial concentration should be at least 2M to prevent excessive shrinkage. We also show that cell swelling during removal of Me2SO is especially likely to be hazardous.

Comparison of K-Sol and M-K medium for cornea storage: results of penetrating keratoplasty in rabbits

Five pairs of rabbit corneas were stored for two weeks at 4 degrees C, one of each pair in K-Sol medium, and one in McCarey-/Kaufman (M-K) medium. After transplantation all penetrating keratoplasty grafts became clear and thin. Endothelial cell loss was significantly less in the K-Sol stored corneas. Another five pairs of corneas were stored for two weeks in K-Sol or three days in M-K medium. After penetrating keratoplasty there were no significant differences in clarity, thickness, or endothelial cell loss. The results indicate that K-Sol provides satisfactory medium-term corneal storage compared with short-term storage in M-K medium at refrigerator temperatures.

Corneal epithelial Cl-dependent pump quantified

Pairs of rabbit corneas were perfused and corneal thickness monitored. The epithelial side of the preparation, and after stabilization also the endothelial side, was covered with silicone oil. A constant thinning of the cornea was observed at a rate of 11.1 microns hr-1 (= 1.0 micron L h-1 cm-2) S.D. 2.1, n = 9. This thinning was also present after endothelial removal: 12.3 microns hr-1, S.D. 1.6 (n = 5). Epithelial abrasion virtually abolished the thinning (2.5 microns hr-1, S.D. 1.89, n = 4), as did cooling from 34 to 0 degrees C. When the preparation was perfused with a Cl-free solution (SO4(2-) instead of Cl-, corrected for osmolarity with sucrose) no significant thinning of the preparation was observed (2.4 microns hr-1, S.D. 2.49, n = 4) after covering both surfaces with silicone oil. This simple set of experiments quantified the epithelial pump mechanism. The epithelial pump rate of about 1.2 microns L hr-1 cm-2 has to be taken into account when endothelial pump rates are measured in the in vitro preparation with intact epithelium.

BSS Plus: a potential irrigating solution for neurosurgery

BSS Plus is a pH-stable balanced salt solution similar to glutathione bicarbonate Ringer's solution. Extensively used in ophthalmology, it is of potential value in neurosurgery. In comparative tests of its effectiveness, 28 cats underwent bilateral irrigation of the surface of the cerebral cortex with normal saline on one side and BSS Plus on the other. After 2 hours, a marked decrease was seen in the surface pH of the hemisphere irrigated with normal saline but not of the hemisphere treated with BSS Plus. Blood-brain barrier changes (measured with Evans blue dye techniques) were more evident following saline irrigation. Somatosensory evoked potentials and cerebral blood flow were not significantly altered. Conventional light microscopy using three standard stains did not reveal a significant difference. Transmission electron microscopy studies were performed in 14 animals and scanning electron microscopy in six. In five animals both transmission and scanning electron microscopy studies were conducted after irrigation with both agents without a cottonoid cover and with immediate harvest of superficial layers from the living brain and immersion-fixation in glutaraldehyde. Tissue preservation was superior on the BSS Plus side in all studies. This agent may represent an improved irrigation solution for neurosurgery, but further studies are required.

Comparison of intraocular acetylcholine and carbachol

Commercially available 1% acetylcholine chloride and 0.01% carbachol chloride, which are commonly used as miotics in intraocular surgery, have recently been reformulated. Comparative studies of these agents show similar miotic activity. However, in vitro perfusion of human corneas demonstrated that 1% acetylcholine chloride causes marked changes in endothelial function and ultrastructure as compared to carbachol or BSS Plus. This study showed that 0.01% carbachol chloride was less toxic to the corneal endothelium than 1% acetylcholine chloride and suggests that 1% acetylcholine should not be used in corneas with compromised endothelium as in primary corneal endotheliopathies.

The effects of sodium hyaluronate, chondroitin sulfate, and methylcellulose on the corneal endothelium and intraocular pressure

Sodium hyaluronate (Healon), chondroitin sulfate, and methylcellulose have been used to protect the corneal endothelium from intraocular lens trauma. A study of the efficacy and toxicity of these compounds showed that 1% sodium hyaluronate, 0.4% methylcellulose, and 20% chondroitin sulfate were nontoxic to the corneal endothelium, but that 20% chondroitin sulfate caused a marked decrease in corneal thickness because of its hypertonicity. Anterior chamber injection of these viscous substances resulted in an increase in intraocular pressure. Within one to four hours the maximum intraocular pressure with 1% sodium hyaluronate was 67 +/- 4.1 mm Hg and that with 20% chondroitin sulfate was 55 +/- 3.5 mm Hg. The intraocular pressure did not increase to these high levels with 10% chondroitin sulfate or 0.4% methylcellulose or when the test substances were washed out of the anterior chamber. The corneal endothelium was protected from injury with 1% sodium hyaluronate and 20% chondroitin sulfate, but 10% chondroitin sulfate and 0.4% methylcellulose provided only minimal protection.

Corneal edema and the intraocular use of epinephrine

Commercially prepared dilutions (1:10,000) of epinephrine can cause marked increases in corneal thickness and loss of corneal endothelial cells when injected into the anterior chamber of the eye. Endothelial toxicity is related to the buffer capacity of the epinephrine solution, which is in turn controlled by the concentration of the antioxidant (sodium bisulfite) as well as by the vehicle formulation and a low pH value.

Endothelial physiology and intraocular lens implantation

The endothelium is the cellular monolayer which lines the posterior surface of the cornea. This layer is important in clinical ophthalmology because it is vital to maintenance of the transparency of the cornea and vision through its pump and barrier functions which limit the ingress of fluid into the cornea from the aqueous. When the function of the corneal endothelium becomes compromised, the corneal stroma swells as it hydrates. Subsequently, epithelial bullae form with painful recurring epithelial erosions, and finally corneal scarring and blindness result. The relatively vulnerable position of the corneal endothelium renders it susceptible to iatrogenic injury during intraocular procedures, especially IOL implantation: the poor regenerative (mitotic) capacity of the human corneal endothelium limits its ability to recover normal function once it is injured.