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Biomedical subjects

O Hockwin

Publications and source records attributed to O Hockwin.

At least 37 records · Page 2Linked to original sources
PubMed1992

Comparison of the Nidek EAS 1000 system and the Topcon SL-45 in clinical application.

Some years ago, Nidek developed a new imaging system for the anterior eye segment, which offers the possibility of recording Scheimpflug and retroillumination images. The system consists of 2 different technical units, a camera unit for image recording and a computer unit for storage, system operation and image analysis. To evaluate the clinical use of the system and its reproducibility, a study with 31 volunteers/patients was performed that were photographed with the Nidek EAS 1000 at the meridians 0 degree, 45 degrees and 180 degrees. Two examinations with a 1-week interval were performed. In addition, a direct comparison of the EAS 1000 with the Topcon SL-45 was carried out with 32 volunteers that were photographed at 0 degree and 45 degrees; a retroillumination photo was additionally recorded. The video images were evaluated with the computer software, the SL-45 negatives were standardly measured with a Joyce-Loebl densitometer. The handling of the EAS 1000 in clinical use was found to be easy and comfortable for the patient, as the alignment is done with infrared light. Difficulties occur only with the retroillumination photography in that the infrared light for imaging may outshine the red fixation light during exposure. However, shadowing problems due to the eyelashes occur in oblique slit positions, especially in those patients with a pronounced front head. In studying the reproducibility, the mean values of the individual coefficients of variation for light scattering (density) were in a range between 3.6 and 5.06%, but more than 35% of the single values show a variation coefficient above 5% (maximum 20.3%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

A new approach to drug penetration study.

To investigate the route of drug penetration into the eye and drug distribution patterns in the lens, the distribution of aldose reductase inhibitor (AL-04114) in the lens was measured in short term bovine lens organ cultures and topical administration to rabbit eyes. A micro lens sectioning technique was applied to determine drug localization within the lens. Freshly enucleated bovine lenses were incubated with different concentrations of an ARI (AL-04114)-containing medium for 3 hours. For the in vivo study, 40 microliters of 0.3% AL-04114 (ophthalmic solution) were administered into the cul de sacs of rabbits 3 times at 3 hour intervals. After the incubation and final instillation, the lenses were divided into an equatorial ring and several layered sections. Drug concentration was measured by a reversed-phase HPLC system. The drug concentration was highest within the layer of the posterior shallow cortex > equator > anterior shallow cortex. No drug penetration was observed in the anterior/posterior deeper cortex or nucleus in vitro. The in vivo experiment revealed drug penetration in the equator and anterior shallow cortex, but not in any other lens layers. Drug penetration was detected within the serum and aqueous humor, but not in the vitreous.

Absorption↗
PubMed1992

[Aspects of physiology, pathology and epidemiology of cataract].

World Health Organization estimates that 23 million people have a visual acuity of 0.05 or less. For 12-15 million people cataract is the cause of poor visual acuity or blindness and the majority of those afflicted live in Third World countries. It is estimated that in the year 2025 around 40 million people will become blind due to cataract. The therapeutic procedure of choice is surgical removal of the lens. The high success rate of this procedure in highly industrialized countries has been achieved by the constant improvement in technology and operative technique. This, however, does not hold true for Third World countries. The etiology and pathogenesis of cataract are not yet completely understood. This paper reports on the clinical findings and epidemiology of cataract and deals with the physiology and pathology of the lens. The aim of the study was to recognize possible cataractogenic risk factors. A decrease in the blindness rate caused by cataract in Third World countries can best be achieved through prevention.

Cataract↗
PubMed1991

[Lens changes following pneumatic retinopexy: preliminary results of linear densitometry image analysis of Scheimpflug photographs two months after operation].

The small degree of morbidity and a better postoperative visual acuity are the advantages of pneumatic retinopexy in comparison to encircling procedures in the treatment of retinal detachment. The injection of air or gas into the vitreous cavity can theoretically induce a cataract postoperatively. Two months after pneumatic retinopexy (SF6-gas) Scheimpflug photography and microdensitometric evaluation of the negative were performed on 22 pairs of phacic eyes showing changes in the transparency of the lens. The deterioration of transparency in the operated eye was small but higher than that of the non-operated eye. Due to the short follow up period no prognosis is possible as to the future lens transparency changes.

Cataract↗
PubMed1991

[Lens changes following intraocular tamponade in vitrectomy. Linear densitometric image analysis of Scheimpflug photographs 6 months after operation].

A complication arising from vitrectomy is the formation of cataract. As a result of an intra- and postoperative tamponade chosen (BSS, air, SF6-gas, silicon oil) the size and frequency of the cataract varies accordingly. 6 months after vitrectomy Scheimpflug photography and microdensitometric evaluation of the negatives were performed on 30 pairs of phacic eyes showing changes in the transparency of the lens. Following silicon oil tamponade a significant deterioration of transparency (t-test) was observed in the lens nucleus of the operated eye; in the area of the lens in front of the nucleus a marked but not significant deterioration of transparency was discovered following both silicon oil and SF6-gas tamponade. In the case of the area in front of the nucleus following SF6-gas tamponade as well as the whole of the lens following BSS or air tamponade a small but not at all significant difference in lens transparency was apparent after comparison of the operated to the non-operated eyes.

Cataract↗
PubMed1991

[Inhibition of cholesterol synthesis and cataract].

The cholesterol requirements of the lens for the formation of plasma membranes are met by self-synthesis only until early postnatal life. This ability subsequently decreases with increasing age and probably ceases altogether. The cholesterol supply then has to come from exogenous sources. These findings are of great importance for the qualitative assessment of extrahepatic side effects of HMG-CoA-reductase inhibitors given for disturbances of lens transparency. The observation of cataracts in chronic toxicity tests with high doses in beagle dogs suggested that the lens enzyme was also affected by the inhibitor, thus causing cataracts. In contrast to other workers' results, we did not find any activity of HMG-CoA-reductase in our experiments with calf, bovine, dog and rat lenses. Preliminary studies with bovine eyes demonstrate a direct correlation between the cholesterol serum level and the content of the aqueous humor. This shows the importance of the exogenous supply for the lens requirements. A further strong argument is that the use of HMG-CoA-reductase inhibitors in patients with pathologically increased cholesterol level is safe as far as the lens transparency is concerned, as demonstrated in clinical trials.

Animals↗
PubMed1991

[The HMG-CoA reductase inhibitors simvastatin and pravastatin. No indication for side effects in use on humans].

During the last few years an increased interest has been directed towards the application of a new class of cholesterol lowering substances, the HMG-CoA reductase inhibitors. Since preclinical trials with beagle dogs revealed lens opacifications, the necessity of drug safety studies arose. The paper presents the results of two drug safety studies concerning Simvastatin (45 patients) and Pravastatin (35 patients) after an application period of two years in patients with primary hypercholesterolemia type II. Besides ophthalmological examinations (every 6 month) Scheimpflug photographs of the anterior eye segment have been taken and the negatives subjected to microdensitometric image analysis. Neither the clinical parameters nor the results of Scheimpflug measurement showed drug induced changes at the eye until now. Based on these results cataractogenic side effects of the substances in question could not be proven.

Adult↗
PubMed1991

[Development of lens opacities in a period of 6 months after pneumatic retinopexy].

When performing a pneumatic retinopexy, air or gas is injected into the vitreous cavity to reattach a primary, rhegmatogenous retinal detachment. SF6 gas, for examples, remains in the vitreous cavity for up to 2 weeks before it is completely absorbed. It is conceivable that the injection of SF6 gas into the vitreous cavity interferes with lens metabolism, thus causing opacities of the lens. Even minor early changes in lens transparency can be monitored by Scheimpflug photography. Two months after performing a pneumatic retinopexy, 31 out of 100 consecutive eyes showed a loss of lens transparency, which was not pronounced or statistically significant. Six months after surgery the loss of transparency was more pronounced in all lens layers, increasing from the front to the back. The increment was statistically significant for the anterior lens cortex. Further investigations are needed to determine whether lens changes are the result of the intraocular tamponade with SF6 gas or are related to other factors, such as the surgical maneuver itself.

Cataract↗
PubMed1991

Regional enzyme profiles in rabbit lenses with early stages of naphthalene cataract.

The naphthalene cataract in the pigmented rabbit, in contrast to the corresponding model in the pigmented rat, is characterized by a rather unstable cataract development during the later stages. Some animals rapidly develop mature cataracts, others develop cortical cataracts with almost no further progression inspite of a continued naphthalene treatment. To get more insight into this phenomenon, a study with pigmented rabbits (8 weeks old) was designed and at different stages of cataract development lenses were separated in single layers with the Bonn freeze-sectioning device. The key enzymes of the carbohydrate metabolism and the redox potential were determined in those layers. The results of the biochemistry failed however to explain the prominent differences of cataract development in-vivo. We conclude from these findings that the naphthalene cataract model in the pigmented rabbit shall no longer be used in drug side-effect or efficacy studies.

Animals↗
PubMed1990

Protein profiles of microsections of the fetal and adult human lens during development and ageing.

The water-soluble proteins of the human fetal lens (175- and 285-day-old) contain HM-, pre-alpha-, alpha-, beta- and gamma-crystallins. Using the frozen-sectioning technique, it can be demonstrated that the fetal lens does not have an homogeneous distribution of crystallins, but there are gradual differences between the cortices and the nucleus. The frozen-sectioning technique shows for the adult lens significantly increasing amounts of beta-crystallins of pI 4.95-5.55, especially at the posterior supra-nuclear layer, increasing amounts of HM-crystallins and decreasing amounts of beta-crystallins of pI 5.80-7.05 in the nucleus. This microsectioning technique was correlated with Scheimpflug photographs of the fetal and adult lens. In the fetal lens, the anterior capsule and 2 peaks in the anterior and posterior supranuclear layers could be visualized after densitometry. In the adult lens 5 layers could be demonstrated, e.g. the anterior capsule, the anterior supranuclear layer, the nucleus, the posterior supranuclear layer and the anterior capsule.

Aging↗
PubMed1990

The mechanisms of cataract formation.

This review summarizes current knowledge concerning cataract formation. Metabolically induced forms of cataract are discussed, but mainly aspects of cataract formation in older patients are described, especially with respect to lens protein modifications and epidemiological results. In most cases, cataract in older people is a multifactorial process and therefore cataracts appear in a multitude of different morphological types. Only accurate documentation of lens disturbances and the use of reproducible methods can provide more detailed information about the complexity of the disease cataract.

Aged↗
PubMed1990

Evaluation of functional and morphologic parameters of the cornea after epikeratophakia using prelathed, lyophilized tissue.

Up to now, the attention of ophthalmic surgeons has been focused mainly on the clinical results of epikeratophakia, demonstrating its safety, relative predictability, and capability of correcting a wide range of refractive errors. However, no prospective study has ever been undertaken to evaluate the influence of epikeratophakia on various physiologic and morphologic parameters of the cornea. The authors investigated some of these parameters prospectively in eight consecutive patients undergoing epikeratophakia with prelathed, lyophilized tissue. Fluorophotometric evaluation of the epithelial barrier function, corneal densitometry by means of Scheimpflug photography, and endothelial specular microscopy were performed preoperatively and 2, 4, 8, 12, and 24 weeks after epikeratophakia. The epithelial barrier function was shown to return to normal 4 weeks after surgery. The optical density of both the epi-lenses and the host corneas increased early after surgery, but was comparable to that of unoperated corneas 6 weeks postoperatively in all cases but one. The endothelial cell density was not altered by surgery in any patient. Despite the limited number of patients, this study indicates that most functional and morphologic parameters of the cornea are normal as early as 6 weeks after epikeratophakia in most cases.

Aphakia↗
PubMed1990

Ultraviolet-induced changes in corneal transmission properties and influence on Scheimpflug photography.

The effects of ultraviolet B (UV-B) irradiation on transmission of the rat cornea were studied in combination with or without naphthalene feeding. UV irradiation as well as naphthalene feeding caused a decrease in transmission in the wavelength region from 315 to 450 nm, UV irradiation being thereby the more hazardous influence. The combination of both noxae did not lead to a pronounced decrease as compared with UV irradiation alone. Although the histological findings of the eye lens suggest a syncataractogenic action of UV-B and naphthalene feeding, a corresponding effect could not be found by means of Scheimpflug photography. This could be possibly due to the alteration in corneal transmission properties following UV-B irradiation.

Animals↗
PubMed1990

Comparison between Topcon SL-45 and SL-45B with different correction methods for factors influencing Scheimpflug examination.

Topcon Tokyo manufactured the first series of SL-45 in 1980 and a second in 1982/83, which were completed in Bonn with all technical improvements developed so far. In 1987, the SL-45B was manufactured which included all previously added improvements. To compare both camera types, we carried out a test with 10 volunteers and the following technical variables for the SL-45: (1) miosis; (2) mydriasis; (3) flashbulb 1; (4) flashbulb 2; (5) film batch 1; (6) film batch 2, and (7) different types of film. Afterwards, 5 of these volunteers were photographed with the SL-45B. Photographer and reader were identical in all cases. Based on microdensitometry it could be demonstrated that, with the exception of a different film type, all variables can be compensated for by using the corneal peak as an external standard.

Anterior Eye Segment↗