Biomedical subjects

C Kreiner

Publications and source records attributed to C Kreiner.

6 recordsLinked to original sources

PubMed2001

[Accommodative lens implant].

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.

Accommodation, Ocular↗

PubMed1997

[Reduction of cataract by plasma etching of intraocular lenses. An animal experiment study].

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.

Animals↗

PubMed1993

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)

Adult↗

PubMed1991

[Eliminating reflection of intraocular lenses].

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.

Humans↗

PubMed1991

[Lens epithelium necrosis factor for prevention lens opacity].

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.

Biological Factors↗

PubMed1987

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.

Elasticity↗