Bifocal ultra thin intraocular lens--optical properties and clinical results.

The therapy of the cataract with the implantation of intraocular lenses is a great success story over the last 20 years. However cataract patients cannot accommodate anymore and need additional glasses for the far and near view. In the last 10 years bifocal concepts for intraocular lenses have been investigated with little success. Our new bifocal diffractive bifocal lens showed in clinical trials with 150 Patients an excellent visual performance. Less than 10% of the patients still use additional glasses. Due to the diffractive principle the lens can be manufactured very thin. Therefore the lens can be easily implanted through very small incisions. The lens shows the potential for the replacement of multifocal glasses.

Effects of an external exposure to 200 ppm methyl ethyl ketone on nasal mucosa in healthy volunteers.

OBJECTIVES: To investigate the effects of an acute exposure to 200 ppm methyl ethyl ketone on the nasal mucosa of healthy volunteers. METHODS: Nineteen healthy non-smoking men were exposed to 200 ppm methyl ethyl ketone and to a sham exposure in an exposure chamber, using a cross-over design. Mucociliary transport time was determined with the saccharine test. Interleukin (IL)-1beta, IL-6, IL-8, and tumor necrosis factor-alpha (TNFalpha) were measured in nasal secretions. Subjective symptoms were assessed by questionnaire. RESULTS: Mucociliary transport time was significantly higher (660 vs. 600 s (medians), P = 0.01) after solvent exposure. Concentrations of IL-1beta and IL-8 were insignificantly elevated after exposure (IL-1beta: 83.8 pg/ml vs. 48.1 pg/ml, medians, P = 0.11; IL-8: 14471 pg/ml vs. 11080 pg/ml, P = 0.12), whereas those of IL-6 and TNFalpha remained unchanged. Subjects did not feel any irritation of nasal mucosa. CONCLUSION: Concentrations of organic solvents not exceeding their MAK values can cause subclinical rhinitis. The secretion of proinflammatory cytokines and impairment of mucociliary transport can explain the development of clinical rhinitis in highly exposed subjects.

[Accommodative lens implant]. / Akkommodatives Linsenimplantat.

PROBLEM: To date, approaches to restore accommodation following cataract surgery have been based on the principle of a liquid or solid implant that moves within the capsular bag and thereby changes the optical characteristics of the eye. However, these implants have been associated with shrinking and fibrosis of the capsular bag, a problem that will not be solved in the foreseeable future. APPROACH: If accommodation is effected by shifting the whole capsule including its contents on the optical axis, capsular fibrosis will virtually no longer play a role. In order to execute this shift via the neuronal feedback mechanisms of the ciliary muscle in a controlled way, radial zonular forces or movements must be transformed into axial ones, which is possible by means of tiny permanent magnets. This paper describes the basic aspects of such an implant. The dependence of accommodation on all relevant parameters is quantified in a computer simulation. CONCLUSION: The implant described appears to be practicable with justifiable technical and surgical efforts.

Determining the imaging quality of intraocular lenses.

PURPOSE: To validate the proposed optical requirements of a draft international standard for intraocular lenses (IOLs). SETTING: Eight optical testing laboratories in the United States, Germany, Japan, and The Netherlands. METHODS: The testing laboratories performed modulation transfer function (MTF) tests on various IOLs using a model eye and visual resolution tests in air. Each laboratory performed duplicate measurements on a set of 43 lenses that was circulated among the testing laboratories. RESULTS: The interlaboratory tests showed that the MTF measurements using a model eye had better repeatability and reproducibility than the more common industry practice of resolution testing in air with parallel light and the United States Air Force three-bar target. However, the two methods correlated well. The commonly applied criterion that an IOL resolve in air at least 60% of the Rayleigh cutoff spatial frequency corresponded to a minimum requirement of 0.43 MTF units at 100 mm-1 in a model eye. CONCLUSIONS: Either criterion may be applied in accordance with a proposed international standard for IOLs. The model eye method can be applied over a broader range of dioptric powers and is relevant for materials that interact with aqueous. Both tests appear to have a greater ability to detect unwanted surface aberrations than resolution testing of IOLs in a water cell using parallel light, a method described in the current American National Standards Institute standard.

[Reduction of cataract by plasma etching of intraocular lenses. An animal experiment study]. / Verminderung des Nachstars durch Plasmaätzung von Intraokularlinsen. Eine tierexperimentelle Untersuchung.

BACKGROUND: We studied if a modification of the silicon intraocular lens (IOL) by plasma etching is able to promote a bonding of the IOL surface and the capsular bag which might inhibit proliferation and migration of lens epithelial cells. METHODS: Silicon-disc lenses (90D, Adatomed), as disposable for regular cataract surgery, were used. Their haptic surface was etched via the use of a SO2 plasma, leaving the optic unmodified. The experiments were done on dwarf rabbits to allow for tight apposition of IOL and bag. Nine rabbits underwent extracapsular lensectomy using propofol anaesthesia and phaco/clear cornea surgical technique. Six eyes each received either no, a regular or a modified IOL. After 11 weeks the eyes were enucleated. Capsular bag and IOL were digitized using a flatbed scanner with transparency adapter. The data obtained were calibrated against a densitometric standard. The densities of the various specimen were analyzed quantitatively using self designed software. RESULTS: In aphacic eyes no significant posterior capsule opacification (PCO) was detectable. In the same time-span the regular IOL had developed a dense, heterogenous PCO. The plasma-treated IOL showed, especially in the central areas, a significant reduction of PCO as compared to untreated IOL. CONCLUSION: The reduction of PCO could not be explained by adhesion of the IOL surface and the capsular bag, which would impair migration of lens epithelial cells and thereby PCO. Likewise, lower PCO may be related to improved hydrophilic properties of the surface-modified IOL.

Accuracy in determining intraocular lens dioptric power assessed by interlaboratory tests.

PURPOSE: To describe a testing program conducted by a standards group as a guide for setting international tolerances for intraocular lens (IOL) dioptric power. SETTING: Multicenter study. METHODS: Seven biconvex, poly(methyl methacrylate) IOLs ranging in power from 10.00 through 30.00 diopter (D) were circulated among nine participating laboratories experienced in IOL optical measurements. Each laboratory performed repeated optical tests to determine dioptric power. These results were analyzed for repeatability and reproducibility in accordance with methods specified by the International Organization for Standardization. RESULTS: Intralaboratory repeatability was less than 0.5% of the dioptric power, and interlaboratory reproducibility, when following a normalized procedure for correction and conversion, was less than 1.0% of the dioptric power. CONCLUSION: Tolerance limits of +/0 0.30 D in the range 0 to 15.00 D, +/- 0.40 D for 15.50 to 25.00 D, and +/- 0.50 D for 25.50 to 30.00 D have been proposed as an international standard for IOLs. The contribution of IOL power error within the limits of the standard are estimated to contribute less than 1.0% to the total error in postoperative refractive prediction.

Chemical and physical stability of perfluorocarbons with laser treatment.

Physical and toxicological aspects of different perfluorocarbons and semifluorinated compounds are discussed. The urgent need for ultrapurification of perfluorocarbons is demonstrated. In vitro laser treatment simulating physiological conditions of two ultrapurified perfluorocarbons used for temporary tamponade and mechanical fixation of unfolded retina in case of giant tears, and one semifluorinated diether resulted in no detectable chemical alteration. Cytotoxic examinations of both laser treated and untreated probes showed no difference in cell proliferation.

[The growth behavior of mouse fibroblasts on intraocular lens surface of various silicone and PMMA materials]. / Wachstumsverhalten von Mausfibroblasten auf Intraokularlinsenoberflächen aus verschiedenen Silikon- und PMMA-Materialien.

Experience with intraocular lenses (IOL) made of PMMA dates back ca. 40 years, while silicone IOLs have been in use for only about 10 years. The biocompatibility of PMMA and silicone caoutchouc was tested in a comparative study investigating the growth of mouse fibroblasts on different IOL materials. Spectrophotometric determination of protein synthesis and liquid scintillation counting of DNA synthesis were carried out. The spreading of cells was planimetrically determined, and the DNA synthesis of individual cells in direct contact with the test sample was tested. The results showed that the biocompatibility of silicone lenses made of purified caoutchouc is comparable with that of PMMA lenses; there is no statistically significant difference. However, impurities arising during material synthesis result in a statistically significant inhibition of cell growth on the IOL surfaces.

Bioequivalence of allopurinol preparations: to be assessed by the parent drug or the active metabolite?

Allopurinol is converted almost completely into a single active metabolite, oxipurinol, which has the same therapeutic pattern but a much longer elimination half-life than the parent compound. Therefore both allopurinol and oxipurinol were evaluated in our bioequivalence study in healthy volunteers comparing two allopurinol brands. Bioequivalence determination was based on the 90% confidence intervals (CI) of the area under the plasma concentration time curve from time zero to infinity (AUC0-infinity), of the area from time zero to the last measurable plasma concentration (AUC0-t (last)), and Cmax. Because of the lack of compound-specific criteria we used conventional limits for the bioequivalence range. Under these conditions the brand chosen as test preparation was judged to be bioequivalent to the reference form with respect to the extent of bioavailability, AUC0-infinity, and AUC0-t (last) of the parent drug. The CI of Cmax of allopurinol slightly exceeded the upper limit of 130%, so that bioequivalence was not confirmed with regard to the rate of bioavailability of the parent compound. The CI values of both AUC and Cmax of the active metabolite were tighter than those of allopurinol. In addition, the CI values of Cmax of oxipurinol were smaller than those of the corresponding AUC. As a consequence the test drug can clearly be accepted as bioequivalent, based on metabolite data. Since the active metabolite is of greater therapeutic significance than the parent drug, assessment of the bioequivalence of allopurinol preparations needs to be based on oxipurinol rather than allopurinol.(ABSTRACT TRUNCATED AT 250 WORDS)

A method of lens extraction for the injection of liquid intraocular lenses.

A method for the injection of liquid intraocular lenses into the capsular bag would offer many benefits in the treatment of cataracts. The corneoscleral incision could be made even smaller, the lens diaphragm would be conserved more physiologically, and a method of therapy for presbyopia might eventually be possible. As a prerequisite, a method of endocapsular lens removal is needed. We have developed such a method for our experiments on the injection of liquid intraocular lenses in the enucleated pig eye. We use a bimanual technique through two opposing 1-mm corneoscleral incisions and two openings measuring 1 mm in diameter in the peripheral anterior capsule. By using curved needles and suction tips, we could remove the capsular contents completely. The injected material was polymerized in situ by exposure to blue light and resulted in an optically clear cast of the lens capsule of surprisingly good optical quality.

Light-induced endocapsular polymerization of injectable lens refilling materials.

The use of advanced phacoemulsification techniques enables the surgeon to remove opacified lens material while preserving a nearly complete capsular bag. For this reason, several groups are presently working on lens refilling techniques. We have developed a method for the injection of a liquid monomer into the lens capsule. The material can be polymerized by exposure to cold light (wavelength, 400-500 nm) within the capsular bag. Using cell-culture experiments, we selected an optically clear material that has cytotoxic properties when placed in direct contact with cells but does not release cytotoxic substances into the surrounding medium. We have shown that reflux of the liquid monomer into the anterior chamber can be avoided by using a material that can be polymerized within the capsule. Initial experiments in rabbits indicate that the technique can be used without inducing a significant postoperative inflammatory response or leading to morphological changes in the cornea or the retina.

[Eliminating reflection of intraocular lenses]. / Entspiegelung intraokularer Linsen.

Reflections on the refractive surfaces of intraocular lenses can be a nuisance when performing retinoscopy or refractometry. Some patients with IOLs also see reflections which disturb their vision. This article examines the conditions for coating IOLs. It also explains why conventional coating methods cannot be used for IOLs.

[Lens epithelium necrosis factor for prevention lens opacity]. / Linsen-Epithel-Nekrose-Faktor (LENF) zur Nachstarverhütung.

Posterior capsule opacification is a common postoperative complication after extracapsular cataract extraction and lens implantation. If the patient's visual acuity is reduced markedly, a capsulotomy with a Nd-YAG laser may become necessary. Various attempts have been made with the aim of developing an injectable solution capable of damaging the epithelial cells of the capsule bag irreversibly and thereby avoiding posterior capsule opacification. This solution should be applied for a short time during the operation. In tissue culture we tested the influence of two injectable solutions [lens epithelial necrosis factor (LENF)] and aqua bidest. on cellular growth. Balanced salt solution served as control. We used human epithelial carcinoma cells, type HEp-2. The results were evaluated by vital staining (ethidium bromide and acridin orange), hemotoxylin staining, autoradiography and measurement of protein and DNA synthesis. The results showed that LENF is capable of damaging 100% of the epithelial cells irreversibly if it is applied for 20 s or longer. The influence of each of these solutions was tested on 20 human capsular flaps, which were excised during the operation. The flaps were immersed for 30 s in the different solutions. Vital staining of these flaps led to the following results: LENF causes a 100% cell damage of all epithelial cells of the capsular flaps. No vital cells remained. On the other hand Aqua bidest. cannot guarantee 100% cell damage of the capsular flap epithelia. Sixty percent of the capsular flaps treated with aqua bidest, showed differing amounts of remaining vital cells.

[Biocompatibility and pharmacokinetics of hydroxypropyl methylcellulose (HPMC) in the anterior chamber of the rabbit eye]. / Biologische Verträglichkeit und Pharmakokinetik von Hydroxypropylmethylcellulose (HPMC) in der Vorderkammer des Kaninchenauges.

The biocompatibility and pharmacokinetics of hydroxypropylmethylcellulose (HPMC) 2% (Adatocel) and Tylose 2% (MH 1000) were investigated. A modified anterior chamber implantation test on the rabbit eye is suitable for testing both the biocompatibility and the pharmacokinetics of visco-surgical substances. Both substances were well tolerated. From the fourth day onward, HPMC was no longer detectable in the anterior chamber by infrared spectroscopy.

Comparative study of the elasticity and memory of intraocular lens loops.

The elasticity and memory of intraocular lens loops was tested by manufacturing lenses with matching physical properties but with loops of either polypropylene or VS-100 polymethylmethacrylate (PMMA). After establishing the reliability of measurements, these lenses were compressed under physiologic conditions for up to three years. The rates and extent of reexpansion of the loops were then measured. Given loops of equivalent initial flexibility, VS-100 PMMA has less long-term tendency to reexpand to its initial shape than polypropylene.

Chemical and physical aspects of clinically applied silicones.

In conclusion, one can state that silicones are one of the most inert materials available for use in medical field today. They meet all the requirements for implants, summarized in table V, and can be considered as the ideal material for intraocular use, provided that the polymer is absolutely pure and free of any kind of residues. For silicone rubbers the following specifications have to be fulfilled: the material has to be free of reactive prepolymers and of catalyzers, the filler should be of the same chemical nature as the basic material and should be chemically bound to the backbone of the polymer, to avoid any kind of migration out of the polymer. For silicone oils, the following criteria are desirable: the oil has to be practically free of low molecular components, mainly cyclohexanes, the molecular weight distribution should be as small as possible and the oil should be free of catalysts.

[Detection of HBsAg and HBeAg in cleaning, rinsing and storage solutions of contact lenses and in tear fluid of carriers of HBsAg (author's transl)]. / Zur Frage der Hepatitisübertragung durch Kontaktlinsen.

Hepatitis-B-surface antigen (HBsAg) was not detected by sensitive radioimmunoassays in the tear fluids of 6 HBsAg carriers with low and medium titers of HBsAg (less than 1:10,000) in the serum. However, HBsAg could be demonstrated in low concentrations in tear fluids of 5 of 6 HBsAg carriers with high serum titers (greater than 1:10,000). The concentration of HBsAg in the tear fluid was at least 100 times lower than in the sera of these 5 persons. Correspondingly HBsAg could be found in only 1 of the rinsing and in none of the storage solutions of the contact lenses of 7 persons with high titers of HBsAg in the serum (greater than 1:32,000). HBsAg was not adsorbed to smooth HEMA-lenses. Because of the low concentration of HBsAg in tear fluids and the dilution effect (about 5 x 10(-10)) the transmission of hepatitis B by multiple use of contact lenses by several persons during adaption is lighly unlikely. In addition, a special cleaning solution (Liprofin) can destroy nearly completely the antigenicity of HBsAg at 60 degrees C.