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.

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.

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.

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.

[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.

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.