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Biomedical subjects

A Midelfart

Publications and source records attributed to A Midelfart.

At least 19 recordsLinked to original sources
PubMed2006

Differences in activities of antioxidant superoxide dismutase, glutathione peroxidase and prooxidant xanthine oxidoreductase/xanthine oxidase in the normal corneal epithelium of various mammals.

Under normal conditions, antioxidants at the corneal surface are balanced with the production of reactive oxygen species without any toxic effects. Danger from oxidative stress appears when natural antioxidants are overwhelmed leading to antioxidant/prooxidant imbalance. The aim of the present study was to examine the activities of enzymes contributing to the antioxidant/prooxidant balance in normal corneal epithelium of various mammals. The enzyme activities of antioxidant superoxide dismutase and glutathione peroxidase, as well as prooxidant xanthine oxidoreductase/xanthine oxidase were examined using biochemical methods. Results show that superoxide dismutase activity is high in rabbits and guinea pigs, whereas in pigs the activity is low and in cows it is nearly absent. In contrast, glutathione peroxidase activity is high in cows, pigs and rabbits, whereas in guinea pigs the activity is low. As far as prooxidant enzymes are concerned, elevated xanthine oxidoreductase/xanthine oxidase activities were found in rabbits, lower activities in guinea pigs, very low activity in cows and no activity in pigs. In conclusion, the above results demonstrate inter-species variations in activities of enzymes participating in antioxidant/prooxidant balance in the corneal epithelium. It is suggested that the levels of antioxidant and prooxidant enzymes studied in the corneal epithelium might be associated with the diurnal or nocturnal activity of animals. UV rays decompose hydrogen peroxide to damaging hydroxyl radicals and perhaps for this reason large animals with diurnal activity (cow, pig) require more effective peroxide removal (high glutathione peroxidase activity) together with the suppression of peroxide production (low superoxide dismutase activity, low xanthine oxidoreductase activity).

Animals↗
PubMed2004

UV Rays, the prooxidant/antioxidant imbalance in the cornea and oxidative eye damage.

In this minireview, the factors involved in the development of corneal injury due to an increased amount of UVB rays are summarized. Experimental studies have shown that an increased number of UVB rays leads to a profound decrease in corneal antioxidants (high molecular weight, antioxidant enzymes as well as low molecular weight, mainly ascorbic acid) so that a prooxidant/antioxidant imbalance appears. The decrease of corneal antioxidant protective mechanisms results in oxidative injury of the cornea and causes damage of the inner parts of the eye by UVB rays and by reactive oxygen species generated by them.

Animals↗
PubMed2002

Xanthine oxidoreductase and xanthine oxidase in human cornea.

Xanthine oxidoreductase (xanthine dehydrogenase + xanthine oxidase) is a complex enzyme that catalyzes the oxidation of hypoxanthine to xanthine, subsequently producing uric acid. The enzyme complex exists in separate but interconvertible forms, xanthine dehydrogenase and xanthine oxidase, which generate reactive oxygen species (ROS), a well known causative factor in ischemia/reperfusion injury and also in some other pathological states and diseases. Because the enzymes had not been localized in human corneas until now, the aim of this study was to detect xanthine oxidoreductase and xanthine oxidase in the corneas of normal post-mortem human eyes using histochemical and immunohistochemical methods. Xanthine oxidoreductase activity was demonstrated by the tetrazolium salt reduction method and xanthine oxidase activity was detected by methods based on cerium ion capture of hydrogen peroxide. For immunohistochemical studies. we used rabbit antibovine xanthine oxidase antibody, rabbit antihuman xanthine oxidase antibody and monoclonal mouse antihuman xanthine oxidase/xanthine dehydrogenase/aldehyde oxidase antibody. The results show that the enzymes are present in the corneal epithelium and endothelium. The activity of xanthine oxidoreductase is higher than that of xanthine oxidase, as clearly seen in the epithelium. Further studies are necessary to elucidate the role of these enzymes in the diseased human cornea. Based on the findings obtained in this study (xanthine oxidoreductase/xanthine oxidase activities are present in normal human corneas), we hypothesize that during various pathological states, xanthine oxidase-generated ROS might be involved in oxidative eye injury.

Adult↗
PubMed2001

Reactive oxygen species (ROS)-generating oxidases in the normal rabbit cornea and their involvement in the corneal damage evoked by UVB rays.

The corneas of albino rabbits were irradiated (5 min exposure once a day) with UVB rays (312 nm) for 4 days (shorter procedure) or 8 days (longer procedure). The eyes were examined microbiologically and only the corneas of sterile eyes or eyes with non-pathogenic microbes were employed. Histochemically, the activities of reactive oxygen species (ROS)-generating oxidases (xanthine oxidase, D-amino acid oxidase and alpha-hydroxy acid oxidase) were examined in cryostat sections of the whole corneas. Biochemically, the activity of xanthine oxidoreductase/xanthine oxidase was investigated in the scraped corneal epithelium. UVB rays significantly changed enzyme activities in the corneas. In comparison to the normal cornea, where of ROS-generating oxidases only xanthine oxidase showed significant activity in the corneal epithelium and endothelium, D-amino acid oxidase was very low and alpha-hydroxy acid oxidase could not be detected at all, in the cornea repeatedly irradiated with UVB rays, increased activities of xanthine oxidase and D-amino acid oxidase were observed in all corneal layers. Only after the longer procedure the xanthine oxidase and D-amino acid oxidase activities were decreased in the thinned epithelium in parallel with its morphological disturbances. Further results show that the xanthine oxidase/xanthine oxidoreductase ratio increased in the epithelium together with the repeated irradiation with UVB rays. This might suggest that xanthine dehydrogenase is converted to xanthine oxidase. However, in comparison to the normal corneal epithelium, the total amount of xanthine oxidoredutase was decreased in the irradiated epithelium. It is presumed that xanthine oxidoreductase might be released extracellularly (into tears) or the enzyme molecules were denatured due to UVB rays (particulary after the longer procedure). Comparative histochemical and biochemical findings suggest that reactive oxygen species-generating oxidases (xanthine oxidase, D-amino acid oxidase) contribute to the corneal damage evoked by UVB rays.

Alcohol Oxidoreductases↗
PubMed2000

The influence of near-work on development of myopia among university students. A three-year longitudinal study among engineering students in Norway.

PURPOSE: The aim of this study was to investigate the effect of near-work on development and progression of myopia among adults exposed to high educational demands. METHODS: A three-year longitudinal refraction study was performed among 224 Norwegian engineering students (mean age 20.6 years, 117 females and 107 males) measuring their refraction at the beginning and the end of the period. The examinations included automated and clinical refraction in cycloplegia and a questionnaire regarding time spent on different kinds of near-work was filled in by the participants. A total of 192 students (100 females and 92 males) completed the study. RESULTS: The mean refractive change of -0.51+/-0.49 D (n=192) during the three-year period was statistically significant (p=0.0001). A significant relationship between refractive change towards myopia and time spent on reading scientific literature (p< or =0.001) and on practical near-work (p< or =0.05), respectively, was found. Also, a significant relationship between refractive change towards myopia and time spent at lectures was revealed (p< or =0.001). No relationship was found between refractive change and time spent at working with video display terminals (VDT) or watching television, respectively. CONCLUSIONS: The results indicate that intensive near-work could initiate myopia or lead to its progression in young adults. The time spent on near-work seems to play a significant role in that process.

Adult↗
PubMed2000

Visual field defects in patients taking vigabatrin.

PURPOSE: To investigate visual field loss in patients on long-term treatment with the antiepileptic drug vigabatrin, recently reported to cause visual disturbances. METHODS: Eighteen patients taking vigabatrin for 0.5-9.5 years were examined with automated perimetry up to 60 degrees from fixation using the Humphrey Field Analyser. Five patients with epilepsy receiving other medications served as controls. Patients found to have a visual field defect underwent ophthalmologic examination. RESULTS: Among the 18 patients in the vigabatrin group, visual field defects categorised as mild were revealed in 6 right eyes (33%) and 8 left eyes (44.4%), while defects categorised as severe were found in 9 right eyes (50%) and 8 left eyes (44.4%). The majority of the defects (66.7% in the right eye) were peripheral constriction with nasal predominance. The location of the defects was confirmed in 8 patients also tested with Kowa AP340 perimetry. CONCLUSION: According to our results, visual field defects among the patients on vigabatrin therapy may occur more frequently than previously recognised.

Adult↗
PubMed1999

[Spectacles--over and out? Past and future use of spectacles].

Spectacles are the most important optical aid and one of the most significant of inventions. History shows that ground rock crystals have been used for thousands of years. In Europe, eyeglasses were used from 13th century AD. Because of the loss of the eye's accommodation due to ageing--presbyopia--most people need eyeglasses for reading after the age of 50. Despite the developments of modern technology, it is still impossible to replace all use of eyeglasses.

Europe↗
PubMed1999

Detection of dexamethasone in the cornea and lens by NMR spectroscopy.

BACKGROUND: To study the penetration and metabolism of dexamethasone phosphate in the cornea and lens from rabbit following topical administration. METHODS: After topical administration of 0.1, 1 and 10% dexamethasone phosphate solutions, respectively, the cornea and lens were removed and extracted with either perchloric acid (PCA) or with chloroform/methanol to study the lipophilic and hydrophilic metabolites of the drug. The extracts were analyzed with 1H and 19F NMR spectroscopy. RESULTS: Using 19F NMR spectroscopy, both dexamethasone and dexamethasone phosphate were detected simultaneously in the extract of the cornea and lens obtained from the eyes denuded of the epithelium before the treatment. Using 10 and 1% drug solutions, the signals from dexamethasone were also detectable in the 1H NMR spectra among many endogenous metabolites. CONCLUSION: 1H and 19F NMR spectroscopy was shown to be a useful method in the study of penetration and metabolism of dexamethasone in the eye, particularly because both the lipophilic and hydrophilic metabolites of the drug could be detected simultaneously.

Animals↗
PubMed1999

Refractive changes among Norwegian university students--a three-year longitudinal study.

PURPOSE: The aim of this study was to investigate the changes in refractive error during a three-year period among university students exposed to high educational demands. METHODS: A three-year longitudinal cohort study was performed among 224 Norwegian engineering students (mean age 20.6 years, 117 females and 107 males) measuring their refraction at the beginning and the end of the period. The examinations included automated and clinical refraction in cycloplegia. A total of 192 students (100 females and 92 males) completed the study. RESULTS: In the student population under study the prevalence of myopia increased significantly from 48% to 65% (p<0.001, right eye) and the mean refractive error increased significantly from -0.64+/-2.18 D (n=224) to -1.21+/-2.30 D (n=192) (p<0.001, right eye) during the period. Of eyes emmetropic at the start of the study (n=49, right eye), 59% became myopic. Among the eyes initially myopic (n=92, right eye), 73% progressed further into myopia, with at least -0.37 D during the three-year period. Of eyes initially hyperopic (n=51, right eye), 8% became myopic, while 14% became emmetropic. CONCLUSIONS: A shift in refraction towards myopia is frequent among university students during their study period.

Adult↗
PubMed1999

Biometric changes in the eyes of Norwegian university students--a three-year longitudinal study.

PURPOSE: The aim of this study was to investigate the changes in biometric measurements and corresponding refractive errors during a three-year period among university students exposed to high educational demands. METHODS: A three-year longitudinal cohort study was performed among 149 Norwegian engineering students (79 females and 70 males, mean age 20.6+/-1.2 years) measuring their refraction and ocular dimensions at the beginning and at the end of the period. The examinations included refraction, keratometry, and A-scan ultrasonographic measurements of the ocular components, all made in cycloplegia. RESULTS: After three years the mean refractive change was -0.52+/-0.45 D (p<0.05), which was accompanied by a change in lens thickness of 0.07+/-0.10 mm (p<0.05), and a vitreous chamber elongation of 0.27+/-0.30 mm (p<0.05). The results refer to the right eye. Stratification of the sample based on their initial refraction (myopes, emmetropes, and hyperopes) showed refractive change towards myopia for all subgroups as well as a significant increase in lens thickness and vitreous chamber depth. No significant three-year change in anterior chamber depth or corneal curvature was found in any of the groups. For all groups, vitreous chamber elongation gave a notable dioptric change in myopic direction. CONCLUSIONS: A shift in refraction towards myopia after puberty is accompanied by vitreous chamber elongation which can explain the dioptric change in myopic direction.

Adult↗
PubMed1998

Dexamethasone and dexamethasone phosphate detected by 1H and 19F NMR spectroscopy in the aqueous humour.

To apply nuclear magnetic resonance (NMR) spectroscopy to study the penetration of dexamethasone phosphate into the aqueous humour from rabbit following topical administration. After topical administration of 0.1%, 1.0% and 10% dexamethasone phosphate solutions, respectively, samples of aqueous humour were aspirated, freeze-dried, redissolved in deuterium oxide and analyzed by high resolution 1H and 19F NMR spectroscopy. In order to study the lipophilic and hydrophilic metabolites of the drug, samples obtained after application of 1% dexamethasone phosphate were extracted with methanol/chloroform, and then extracted with perchloric acid. In all samples obtained from eyes denuded of the corneal epithelium prior to administration of dexamethasone, signals corresponding to the chemical shifts of the drug were identified in 19F NMR spectra. In the experiments performed with 1% dexamethasone phosphate, both dexamethasone and dexamethasone phosphate were detected in the aqueous humour. Using 10% dexamethasone phosphate solutions, signals from the drug were detected in 1H NMR spectra simultaneously with signals from about twenty other substances present in the aqueous humour. NMR spectroscopy appears to be a valuable method for studying dexamethasone metabolism and penetration into ocular tissues. It provides simultaneous detection of both the drug metabolites and other substances in the sample and might offer a complementary approach to other analytical methods.

Administration, Topical↗
PubMed1998

Refractive errors among young adults and university students in Norway.

PURPOSE: This study was initiated to compare the refractive state in a population sample to that among university students in Norway and to that among the general population in other Nordic countries. METHODS: A population sample of 112 individuals and 224 engineering students were randomly selected and examined using automated and clinical refraction in cycloplegia. RESULTS: Statistically significant differences were found in prevalences of myopia (population sample: 33%, students: 47%, p: 0.016) and prevalences of hyperopia (population sample: 47%, students: 30%, p: 0.001) between the two groups. The mean refractive error among the population sample was -0.1+/-2.0 D compared to -0.6+/-2.2 D among the students (p=0.0013). CONCLUSIONS: The population sample had a significantly lower prevalence of myopia and a higher prevalence of hyperopia than the student population. The state of refraction in the population sample was found to be in agreement with results reported from other Nordic countries.

Adult↗
PubMed1996

Women and men--same eyes?

In ophthalmology, few studies have been designed to investigate possible differences between women and men in a consistent manner. Some evidence is, however, available showing significance male-female differences. The importance of gender in ophthalmological research is emphasized by focusing on some knowledge about sex differences in ocular components in relation to cataract surgery and on the influence of the female hormones on the cornea.

Cataract Extraction↗
PubMed1996

Clinical evaluation of the Allergan Humphrey 500 autorefractor and the Nidek AR-1000 autorefractor.

AIMS/BACKGROUND: The intentions of this study were to estimate agreement between two different autorefractors and standard subjective refraction techniques and to evaluate the clinical implications of relying on the autorefractor measurements. METHODS: Subjective refraction was carried out on 448 cycloplegic eyes and compared with cycloplegic readings with the Allergan Humphrey 500 autorefractor (448 eyes) and the Nidek AR-1000 autorefractor (160 eyes). Each refraction was followed by clinical visual acuity measurement. The study population comprised 224 healthy students, 107 men and 117 women, with a mean age of 20.6 (SD 1.1) years. RESULTS: Both the Nidek and Humphrey autorefractors measured more negative or less positive refractive values compared with subjective refraction and these biases were statistically significant (Humphrey right eye -0.23 D, p = 0.0001, left eye -0.20 D, p = 0.0001), (Nidek right eye -0.13 D, p = 0.0001, left eye -0.11 D, p = 0.0002). Comparing the results of autorefraction with subjective refraction, the Nidek was better than the Humphrey autorefractor in several ways: a smaller mean difference, better agreement between spherical equivalent values, narrower limits of agreements, and better visual acuity obtained with the autorefraction. On the other hand, the Humphrey autorefractor agreed better with subjective refraction concerning cylinder axis. CONCLUSION: The results show that both autorefractors represent a valuable complement to subjective refraction, but cannot be used as a replacement.

Adolescent↗
PubMed1996

Metabolic analysis of the rabbit cornea by proton nuclear magnetic resonance spectroscopy.

Perchloric acid extracts of the rabbit cornea were analyzed by high-resolution 1H NMR spectroscopy, including the two-dimensional shift-correlated (COSY) technique. Numerous metabolites including leucine/isoleucine, 3-hydroxybutyrate, valine, lactate, alanine, lysine, acetate, glutamate, creatine/phosphocreatine, taurine, glycine, inositol, glucose, tyrosine, phenylalanine, histidine, adenosine and formate have been simultaneously detected and identified in the NMR spectra. Concentrations of some of these were also determined. Of particular importance are the detection and identification of hypotaurine in the corneal tissue. Hypotaurine is a precursor of the synthesis of taurine and may act as an antioxidant. Moreover, the presence of choline, a precursor for acetylcholine, was established. This novel metabolite profile of the cornea obtained by high-resolution 1H NMR spectroscopy may be of value in the study of pathologic and toxic disorders.

Acetates↗