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Biomedical subjects

O Hockwin

Publications and source records attributed to O Hockwin.

213 records · Page 12Linked to original sources
PubMedDate not supplied

Cataract classification.

Opacifications of the eye lens--generally defined as cataracts--develop in various different parts of the lens. Therefore, one has to differentiate the types of opacities. For epidemiological studies it is prerequisite to classify the cataracts according to their localization within the lens as well as to the size and intensity of the opacified area. Two approaches have been used in the past: 1) subjective methods of lens observation (based on slit lamp microscopy) and 2) objective methods with measurements of lens transparency or lens opacity respectively based on slit image documentation according to the Scheimpflug principle combined with the retroillumination technique. With ageing, the light transparency of the lens is subjected to considerable changes. Even without the formation of an opacity the transmission of the wavelengths in the UV-B/UV-A and the visible range is diminished. The single lens layers are affected by this phenomenon to different degrees. These changes which might also indicate an early stage of 'cataract formation' cannot be discerned by subjective methods. The densitometric image analysis of Scheimpflug slit images, however, allows the exact measurement of the light scatter in the single lens layers and enables the early recognition of disturbances in transparency which is of crucial importance particularly in cataract epidemiology. In view of our present knowledge the evaluation of risk factors which might be of importance in multifactorial cataract processes will hardly be possible by carrying out prevalence and/or incidence studies involving a single examination of the population. In this case follow-up studies (cohort studies) with repeated examinations are prerequisite. The 'objective methods' for classification alone are able to ensure the necessary reproducibility and the possibility to measure transparency changes in the lens before visible (and therefore subjectively recognizable) opacifications occurred. The methodical procedure with respect to an epidemiological study on the involvement of UV-B radiation in the processes of cataract formation in man requires the application of objective methods for cataract classification.

Adult↗
PubMedDate not supplied

Postsynthetic changes of glutathione peroxidase (EC 1.11.1.9) and glutathione reductase (EC 1.6.4.2) in the ageing bovine lens.

Postsynthetic changes in the enzyme and structural proteins play an important role in the mechanisms of ageing of the lens, when development of protein aggregates and -S-S- linking occurs. Protection of the free -SH groups through the glutathione peroxidase and glutathione reductase system is a prerequisite to avoid these phenomena. Investigations on these two enzymes in young and old bovine lens tissues showed that they are themselves subjected to age-dependent modifications. With increasing age, the specific activity decreases while a simultaneous increase in heat lability occurs. This means that in the course of postsynthetic processes the stability of the conformation decreases and that finally the catalytic properties are lost.

Aging↗
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Location and severity of UVB irradiation damage in the rat lens.

We investigated the location and severity of lens opacities and epithelial alterations following ultraviolet-B (UVB) irradiation in vivo, using Brown Norway rats. A group of 9 rats received 65 mJ/cm2 UVB irradiation from overhead lamps every 6 days. Lens changes were documented and evaluated by an anterior eye segment analysis system. Lens epithelial cells were examined postmortem in flat preparations. After 8 weeks of the irradiation schedule (total dose: 0.6 J/cm2), an anterior polar opacity was apparent; at 16 weeks, the opacities had progressed more deeply into the cortex. At postmortem examination, cells in the central region displayed disorganization, clumping, some pyknotic nuclei and mitosis. There were deeper opacities and cell damage was more severe above the central horizontal plane than below it. This present study demonstrated that UVB damage differed in the superior and inferior parts divided by a horizontal plane through the lens anterior pole, when the UVB source was above and there was no reflection from below or laterally. The lens epithelial cells, and associated lens fibers, are the first target of UVB irradiation.

Animals↗
PubMedDate not supplied

In vivo evaluation of epikeratophakia lenses by means of Scheimpflug photography.

The recovery of clarity in frozen, lyophilized human tissue lenticules used for epikeratophakia has been a matter of controversy. According to some authors, several months are necessary for the lenticules to resume normal transparency; others report clinical experience of much shorter times. Up to now, objective documentation of such findings has not been substantiated. We used a Topcon LS-45 camera to photograph four eyes that underwent epikeratophakia, preoperatively and at 2, 4, 6, and 8 weeks after surgery, and analyzed the film negatives by linear microdensitometry. The degree of film blackening, that is the density of the tissue, was expressed graphically by peaks of various height measured in millimeters. Best spectacle corrected Snellen visual acuity was also recorded. Similar measurements of corneal transparency were performed in 20 healthy adult volunteers whose best corrected spectacle visual acuity was 20/20. In the four operated eyes, (two keratoconus, one aphakia, and one myopia), the light scattering was increased in both the host cornea and the donor lenticule. The lenticule had a considerably increased light scattering in all patients at both 2 and 4 weeks after surgery, but was comparable to that of unoperated corneas in three of four patients at 6 weeks.

Adult↗
PubMedDate not supplied

Investigations on the heat lability of enzyme activities in bovine lenses following incubation under various culture conditions.

The quality of different culture media and incubation procedures has occasionally been tested by measurements of the specific enzyme activities in incubated lenses. New methodology developments in the field of enzymology, such as partial heat denaturation of enzyme activities have so far rarely been used in the investigations on the physiologic conditions of incubated lenses. Investigations with bovine lenses separated into cortex and nucleus, involving different media and incubation periods, indicate that tests on the heat lability of the enzyme phosphofructokinase (PFK) allow early recognition of intra-molecular alterations which lead to changes in the stability. The method is based on the fact that the PFK in the lens nucleus forms a metastable component (metazyme) during aging, which is more susceptible to heat (50 degrees C) than the native PFK component.

Animals↗