Do different osmolar solutions change the epithelial surface of the healthy rabbit cornea?

BACKGROUND: We evaluated various osmolar solutions in use for ophthalmic treatment for their effect on the corneal surface. Healthy corneas were exposed to hypoosmolar balanced salt solution (BSS), an isoosmolar solution and hyperosmolar solution Previn. METHODS: Rinsing solutions--BSS from Opsia, and Previn from Prevor--were provided by the manufacturers. Our laboratory made an iso-corneal solution from an electrolytes and amino acid composition, based on our measurements for osmolarity of human corneas. During final anesthesia, each six healthy rabbit eyes were exposed to 1 drop of the above-mentioned solutions, every second for 120 min. Drops were applied from a height of 2 cm, wetting the corneal surface homogeneously. RESULTS: Surface changes compared to healthy corneas were visible in scanning-electron-microscope images. In grading such changes,we found that balanced salt solution caused changes within the surface appearance, with increased cell-shape changes and microvilli loss. Isoosmolar and Previn solution did not show slightly pronounced nuclei within an intact cellular membrane. CONCLUSION: Isoosmolar and hyperosmolar rising did not change the microvilli of the corneal-cell surface. Hypoosmolar rinsing changed the surfaces considerably. We believe that, contrary to prevalent opinion, application of hyperosmolar solutions to the healthy eye does not harm corneal surface integrity. Iso-corneal solution and Previn solution did not change the surface of the healthy rabbit cornea.

[Use of lavage fluid containing diphoterine for irrigation of eyes in first aid emergency treatment]. / Verätzungen des Auges Diphoterinhaltige Augenspüllösung in in der Erste-Hilfe-Therapie.

PURPOSE: Eye irrigation is a widely accepted therapeutic must in first aid treatment. The burning agent is removed, diluted, and if possible neutralized. Usually water, NaCl 0.9%, Ringer's lactate or phosphate buffer are the most accepted rinsing solutions. We present a relatively new substance called Previn (Diphoterine in countries other than Germany). It is a hypertonic, polyvalent, and amphoteric substance. Its binding energy for acids, bases, reducers, and oxidation is stronger than the binding energy of biological compounds for these burning agents. Concerning its compatibility with the eye and its efficacy, we compare Previn to the rinsing solutions in general use. MATERIAL AND METHODS: The first experiment (I) shows the effects of ocular rinsing with 500 ml Previn in ten healthy human subjects compared with phosphate buffer rinsing. Evaluation is done by slit lamp examination and confocal microscopy. An experimental study (II) compares in vitro buffering capacity (a) of Previn to other rinsing solutions and shows (b) in vivo efficacy of rinsing with Previn versus other rinsing solutions by pH measurements on the corneal surface and anterior chamber of rabbits after a 30-s burn with 1 N sodium hydroxide. RESULTS: (I) No harmful effect of irrigation with Previn could be found. Its compatibility with the eye is comparable to phosphate buffer rinsing. (II a) Buffering capacity was found to be stronger for Previn in acids and bases compared to phosphate buffer or Ringer's lactate. (II b) The in vivo study on rabbits proved Previn effect onaqueous pH comparable to phosphate buffer in buffering 1 N NaOH, whereas NaCl showed no buffering effect at all. CONCLUSION: The above studies have shown that Previn (Diphoterine) is comparable to other rinsing solutions concerning its compatibility with the human eye. Its buffering capacity is comparable to phosphate buffer. Previn and phosphate buffer should only be used in first aid treatment and not for continued rinsing therapy.

Phosphate buffer in alkali eye burns as an inducer of experimental corneal calcification.

Corneal calcification is a common problem in severe inflammation, chronic glaucoma, renal disorders and other diseases with disturbed calcium and phosphorus metabolism. The pathogenesis of corneal calcifications in ocular diseases is not yet completely understood. We present a model of an induced corneal calcification by local treatment. In a double-masked experiment 16 rabbits underwent eye burn of one cornea followed by immediate rinsing (160 ml) with isotonic phosphate buffer (n=8) or saline solution (n=8) three time a day for 16 days. Tissues were excised, shock frozen and cut into 10 microm slices, freeze dried and coated with evaporated carbon. In the phosphate buffer group an early onset of corneal opacification occurred resulting in completely white corneas after 16 days, combined with corneoscleral ulceration. The other group showed similar corneal erosion and a little corneal ulceration, but no opacifications. The opacifications of the phosphate buffer group could be identified as calcifications by direct measurements of calcium and phosphate (by energy dispersive X-ray analysis on corneal samples). In conclusion, inappropriate application of phosphate leads to uncontrolled calcifications of the cornea after severe burns to the eye. This reflects clinically observed calcifications after eye burns and possibly the adverse side effects of phosphate buffered eye drops being applied in ophthalmology.

The Type II Aachen-Keratoprosthesis in humans: case report of the first prolonged application.

PURPOSE: To improve the prognosis of corneal grafts in silicone-oil filled eyes of patients with severe ocular trauma by a prolonged application of the Type II Aachen-Keratoprosthesis (KPro). This application endeavors to improve post-keratoplasty prognosis by avoiding corneal endothelial dystrophy in the aphakic eye due to contact with silicone oil. PATIENT AND PROCEDURES: The Aachen-Keratoprosthesis' haptic was modified to allow tight contact with cells. The Type II Aachen-Keratoprosthesis was then implanted in an 18-year-old male, with previous management of bilateral corneal rupture. Rather than utilize the device as a temporary intraoperative tool, we extended the device's lifespan in the eye. MAIN FINDINGS: Following implantation, the patient could see hand movements up to 0.1 with best correction. After 8 weeks, vision decreased and a retroprosthetic membrane proliferated. Upon conjunctival retraction, 3 months after the initial surgery, we excised the prosthesis and performed a re-vitrectomy and corneal grafting. The silicone oil was removed. After eighteen postoperative months, the graft remained clear, the retina was completely attached, and the vision was stable: 0.1 best corrected. CONCLUSION: This case reports the prolonged implantation and prospect of the Type II Aachen-Keratoprosthesis to be utilized as a permanent device to restore vision in the near future.

Functionalization of silicone rubber for the covalent immobilization of fibronectin.

Surface modification techniques were employed in order to provide functionalized silicone rubber with enhanced cytocompatibility. Acrylic acid (AAc), methacrylic acid (MAAc) and glycidylmethacrylate (GMA) were graft-co-polymerized onto the surface of silicone induced by an argon plasma and thermal initiation. The polymerizations were carried out in solution, in the case of acrylic acid a vapor phase graft-co-polymerization subsequent to argon plasma activation was carried out as well. Human fibronectin (hFn), which acts as a cell adhesion mediator for fibroblasts, was immobilized by making use of the generated carboxylic or epoxy groups, respectively. Surface analysis was accomplished by means of X-ray photoelectron spectroscopy (XPS), infrared spectroscopy in attenuated total reflection mode (IR-ATR), scanning electron microscopy (SEM), atomic force microscopy (AFM) and dynamic contact angle measurements using the Wilhelmy-plate method. The amount of immobilized active hFn was semiquantified by enzyme-linked immunosorbent assay (ELISA) using a structure-specific antibody against the cell-binding domain of hFn. In vitro testing showed a remarkable difference between surfaces exposing adsorbed-only and surfaces with covalently immobilized hFn.

Eye burns: an emergency and continuing problem.

Adequate treatment of eye burns is an essential task of rescue teams. Clinical and occupational medicine studies have shown that efficient emergency treatment can prevent severe eye damage, but therapy is frequently delayed or inadequate. When initial therapy has been delayed or missed, several treatment strategies, including surgery, are available that may improve the outcome of an injury with poor visual prognosis. Discussed in this review are common accident mechanisms, causative agents and biophysical/pathogenetic aspects of eye burns, together with emergency and long-term treatment strategies including surgical procedures, and factors influencing outcome.

Aachen keratoprosthesis as temporary implant for combined vitreoretinal surgery and keratoplasty: report on 10 clinical applications.

UNLABELLED: A new keratoprosthesis was used during pars plana vitrectomy in order to test the optical quality, watertightness, short-term biocompatibility and handling of the new device. The implantability was also tested, given that this keratoprosthesis might in future be left in place for several months. This Aachen keratoprosthesis (Aachen-KPro) is developed to be used as permanent implant to restore vision in corneal blind patients. PATIENT AND METHODS: The Aachen-KPro was used during pars plana vitrectomy in 10 patients with opaque corneas. In four cases, trauma precipitated the ocular disease. Eye burn was the cause of corneal and retinal disorders in another four cases. One patient had a history of congenital glaucoma with myopia, and one of uveitis with corneal dystrophy. After trephination of 6.5 mm in diameter, the Aachen-KPro, composed of soft silicone rubber, was temporarily placed in the trephination hole. After completion of the vitrectomy, the Aachen-KPro was replaced by a 7 mm corneal graft. RESULTS: Intraoperative use of the Aachen-KPro allowed uncomplicated intraoperative handling, smooth adaptation to the corneal rim in the trephination hole, and an undistorted view of the central and peripheral retina. Leakage, even during scleral depression, could be avoided by individual suturing of the scleral rim. After a follow-up period of 1-10 months, the retina was still attached in all cases. The corneal graft was clear after surgery in four eyes, and edema was found in three cases. Amnion or conjunctiva was placed over three patients' transplants. CONCLUSION: We report the first temporary implantations of a new keratoprosthesis in 10 patients. Its flexibility and good optical qualities allowed control of intraoperative procedures. The outcome and prognosis of the vitreoretinal surgery and keratoplasty were related to the primary diagnosis. The Aachen-KPro has shown advantages, especially in eyes where the anterior eye segment is severely damaged by eye burn or previous surgical interventions. In the future, prolonged use of the Aa-chen-KPro is planned for selected eyes.

Aachen-Keratoprosthesis as temporary implant. Case report on first clinical application.

BACKGROUND: The Aachen-Keratoprosthesis was designed to serve as a permanent keratoprosthesis, modeling natural corneal physical properties as closely as possible. Prior to permanent application in patients, keratoprostheses are commonly tested in animal models to assess biochemical and biomechanical compatibility. However, immune and inflammatory responses acquired through animal experimentation are difficult to extrapolate in order to develop a predictable and generalized outcome in humans. Therefore, this preliminary report includes results following a temporary implantation of the Aachen-Keratoprosthesis in a patient during vitreoretinal surgery to assess the long-term prospect of application as a permanent artificial cornea. PATIENT AND METHODS: A 43 year old man presented with a ruptured right eye resulting in an opaque cornea and retinal detachment. A soft silicone rubber keratoprosthesis, the Aachen-Keratoprosthesis, was temporarily implanted. Subretinal membranes were removed and the total retinal detachment was reattached. Liquid perfluorocarbon and silicone oil were used. The temporary keratoprosthesis was replaced by a 7 mm corneal graft after completion of surgery. RESULTS: The Aachen-Keratoprosthesis was securely positioned into the trephined hole. It allowed complete visualisation of vitreous, retina and thus controlled manipulations in the vitreous cavity up to the extreme periphery. Leakage across the trephination-prosthesis interface was minimal. CONCLUSION: We report the first temporary application of an innovative keratoprosthesis. Its flexibility and good optical qualities allow visualisation and control of intraoperative procedures. This temporary pilot study of the Aachen KPro encourages further investigation of the Aachen KPro as a permanent replacement for a diseased cornea.

Corneal biopsy in keratitis performed with the microtrephine.

BACKGROUND: The aetiology of most cases of keratitis remains unclear because the causative agents respond to broad-spectrum antibiotics. Problems occur when they become resistant to local therapies. Further diagnostic measures such as corneal scrapings or biopsies are then necessary. In order to ensure early and gentle biopsy followed by effective diagnosis within 24 h, corneal biopsy specimens were obtained with a microtrephine. PATIENTS AND METHODS: Microbiopsies were obtained from 28 patients suffering from corneal infiltrates or ulcerative keratitis. Different stainings were used to identify the pathogens. Photographs of the clinical healing process were taken immediately after biopsy and during the follow-up. RESULTS: One hundred and ten microbiopsies were performed. One hundred and eighteen specimens could be obtained. No perforation occurred. In 5 of 10 cases in which herpetic keratitis was predicted, herpes DNA could be confirmed. The other five cases were found to be caused by other microbes. In 15 of 18 cases, the bacterial pathogen could be confirmed by Gram's stain diagnosis after microtrephination. Corneal smear was positive in only 7 of these cases. In 2 of 6 cases, predicted to be caused by fungi, lactophenol-blue staining of the microbiopsies showed positive results. Corneal smear was positive in only 1 of these 2 fungal cases. No intraoperative or postoperative complications occurred. No worsening of the disease as a result of treatment could be observed. CONCLUSIONS: The confirmation of microbial cause of keratitis is more effective using microbiopsy than with corneal smears. As a result of the effective treatment after biopsy diagnosis, the majority of cases of keratitis healed. Local therapy seems to have been optimised due to the unroofing of infection during biopsy as well. Therefore microbiopsy in combination with laboratory diagnosis may prove to be a very useful diagnostic and possibly therapeutic method in the clinical routine.

Functionally adapted surfaces on a silicone keratoprosthesis.

BACKGROUND: Silicone intraocular lenses as well as silicone sponges and encircling bands on the bulbar surface are widely used and are well tolerated. The aim of this project is a new one-piece silicone keratoprosthesis with enhanced cell adhesion in the haptic region to optimize the keratoprosthesis stability. These investigations show how enhanced profileration of conjunctival fibroblasts and, therefore, improved tissue compatibility can be achieved by hydrophilizing and by protein immobilisation on a hydrophobic silicone surface. This allows a combination of desired chemical and mechanical properties of the silicone bulk material with surfaces of improved tissue compatibility. METHODS: Silicone foils with surface modifications of different kinds were tested. Experiments were done using cell cultures with murine fibroblasts L-929 and human conjuctival fibroblasts. Cytotoxicity assays were carried out with cells grown on the material in direct contact, as well as in indirect contact, with extracts (EN 30993-5). Viability stains by means of fluoresceindiacetate and ethidiumbromide together with morphology analyses by hemalaun-staining were performed. RESULTS: For the unmodified and modified foils themselves and their extracts any negative influence on cell cultures of murine and human cells could be excluded. There was a gradual improvement of cell morphology, spreading and proliferation dependent on the degree of surface modification. Covalently immobilised fibronectin showed the best results in contrast to adsorptive binding. CONCLUSIONS: Silicone surfaces can be modified chemically with bioactive proteins. These modifications are cell compatible and do not result in toxic reactions. The degree and type of silicone hydrophilization results in improved development of cell morphology, spreading and proliferation. Even better results are obtained after covalent binding of bioactive proteins like fibronectin. Improved biocompatibility with enhanced cellular overgrowth has been demonstrated in vitro for the modified silicone of the haptic region. We believe that this type of modification will help in reducing extrusion problems observed with former keratoprostheses.

A new way of removing silicone oil from the surface of silicone intraocular lenses.

PURPOSE: This study was performed to ascertain the efficacy of Perfluorhexyl-octan, C14F13H17 (F6H8), in dissolving silicone oil from the surface of silicone intraocular lenses. So far F6H8 is the only solvent of silicone oil that is tolerated by intraocular tissues. MATERIALS AND METHODS: Intraocular silicone lenses (Domilens) were examined after application of small droplets of silicone oil of two different viscosities (AdatoSIL-OL 1000 and 5000) followed by rinsing with F6H8. To allow distinction between silicone oil and F6H8 the silicone oil was stained. Microscopic examination was carried out under video control. RESULTS: One hundred microliters of AdatoSIL-OL 1000 could be easily removed with about 800 microl of F6H8; 50 microl of AdatoSIL-OL 5000 also disappeared after 800 microl of F6H8. A larger drop of the latter oil could not be removed even after application of 2 ml of F6H8. CONCLUSION: Silicone oil 1000 can be easily dissolved by F6H8, whereas silicone oil 5000 is more difficult to remove because of its higher viscosity.

[Biocompatibility of flexible intraocular lenses in vivo]. / Zur Biokompatibilität von faltbaren Intraokularlinsen in vivo.

PURPOSE: One aspect of biocompatibility of IOLs can be tested using specular microscopy of the anterior and posterior surface of the lens in vivo. METHODS: We examined 45 patients after implantation of a "Memory lens" and 31 patients after the implantation of an "Acrysof" lens 3-6 months after surgery. RESULTS: Typical deposits (Lens epithelial cells, spindle-shaped macrophages, giant cells, pigment, Wolter membrane) were rarely seen on both types of lenses. There were fewer lens epithelial cells on the posterior capsule and less secondary cataract after implantation of the "Acrysof" lens. CONCLUSIONS: We did not find any indication of reduced biocompatibility in any of the lenses examined. The reduced rate of secondary cataract after implantation of the "memory lens" may be explained by the fact that this lens type sticks to the posterior capsule better.

The "Aachen" keratoprosthesis: a new approach towards successful keratoprosthesis-surgery.

BACKGROUND: None of the keratoprostheses available today is absolutely successful in the long term, neither the problems of extrusion, retroprosthetic membrane formation and intraocular pressure rise are yet solved. A new type of keratoprosthesis is required which can show improved ingrowth characteristics and allow intraocular pressure measurements. In order to possibly meet the above mentioned requirements we developed a flexible silicone keratoprosthesis with scleral fixation and chemical surface modification. METHODS: The one-piece keratoprosthesis is made of silicone rubber. Its optical zone has a diameter of 11 mm and is 0.3 mm thick. The surface-modified haptic consists of a scleral rim and eight branches for scleral fixation. A ridge at the back of the keratoprosthesis fitting into the trephination hole shall avoid leakage and retroprosthetic membrane formation. Optical and mechanical qualities are characterised by tensile tests, spectrophotometry and topography. RESULTS: A method for keratoprosthesis-production was established. The optical quality of the device was improved by submicron lathing of the mould. Spectrophotometry showed high visible and ultraviolet light transmission of the silicone. Mechanical tests with silicone samples revealed high tensile strength and elongation at break. The mechanical properties were not impaired by surface modification. CONCLUSIONS: The production of a flexible silicone keratoprosthesis with high optical and mechanical properties was established. Its use both for the treatment of permanently opacified corneas and as temporary keratoprosthesis seems to be possible.

Development of a surface modified silicone-keratoprosthesis with scleral fixation.

BACKGROUND: Many attempts have been made to create artificial corneas. The keratoprostheses currently available do not allow measurements of the intraocular pressure (IOP) and restrict the visual field. The main problem is extrusion due to an insufficient connection between implant and surrounding tissue. It is our aim to create a flexible keratoprosthesis with a wide field optic allowing measurements of the IOP. Surface modification will improve cell adhesion and therefore stability between implant and tissue. METHODS: The keratoprosthesis is made of silicone rubber. The optical zone is 11 mm in diameter with a thickness of 0.3 mm. The surface modified haptic consists of a scleral rim and 8 branches for scleral fixation. Optical and mechanical qualities were tested by tensile tests, spectrophotometry and topography. RESULTS: A method to produce one-piece silicone keratoprostheses was established. Submicron lathing of the mould led to an excellent optical quality. Spectrophotometry showed high degree of visible and ultraviolet light transmission of the silicone. Mechanical tests revealed high tensile strength and elongation at break which were not impaired by surface modification. CONCLUSION: The production of a flexible silicone keratoprosthesis with high optical and mechanical properties was accomplished, with possible use as both permanent and temporary keratoprosthesis.

The corneal stroma: an inhomogeneous structure.

PURPOSE: This study was conducted to determine the elemental composition of the human cornea. Special attention was paid to corneal stroma inhomogeneity. METHODS: Seventy human corneas were examined by means of energy-dispersive X-ray analysis. Epithelium, subepithelium, middle stroma, sub-Descemet layer, Descemet's membrane and endothelium were subjected to repeated measurements. RESULTS: In the cellular layers the phosphorus concentrations were high [0.35 mol/kg dry weight (dw) in the epithelium and 0.403 mol/kg dw in the endothelium]. Similar concentrations were found for sulphur (0.38 mol/kg dw in the epithelium). Stromal layers showed high contents of sulphur: 0.26 mol/kg dw. The phosphorus concentration was found to be higher in the subepithelium than in the middle stroma. Sulphur concentrations were highest in Descemet's membrane, followed by the subepithelium and the middle stroma. DISCUSSION: Nucleic acids and energy-containing phosphates explain the high levels of phosphorus in the cellular layers. The high sulphur concentrations may be related to the phosphoadenosinphosphosulfate and protein turnover in the epithelium. We interpret the inhomogeneous distribution of phosphorus in the stroma as a function of the density of keratocytes. An evaluation of all known sulphur-containing biochemical components of the stroma (0.217 mol sulphur/kg dw) corresponds to our measurements. In contrast to former results we find the corneal stroma to be an inhomogeneous structure.