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Biomedical subjects

Peter Koch Jensen

Publications and source records attributed to Peter Koch Jensen.

7 recordsLinked to original sources
PubMed2006

Determinants of bleb morphology in minimally invasive, clear-cornea micropenetrating glaucoma surgery with mitomycin C.

PURPOSE: Antimetabolites, especially mitomycin C (MMC), increase the incidence of late bleb-related endophthalmitis in trabeculectomy. This is related to a higher incidence of avascular, thin, cystic, translucent blebs, which may be caused by a toxic effect on conjunctival tissue. An MMC dose-response study was carried out focusing on bleb morphology and function. PATIENTS AND METHODS: In a retrospective, comparative case series study, 2 successive groups of patients with complicated glaucoma were compared 2 years after a special, minimally invasive, filtering procedure (intrastromal holmium laser keratostomy). Preoperative local subconjunctival injections of a fixed MMC dose (4 microg) were used in group A, and lower MMC doses, calculated individually (1 or 2 microg), were used in group B. Bleb vascularity and morphology were evaluated by masked grading of photomicrographs. Bleb function was evaluated by intraocular pressure (IOP). RESULTS: Total bleb avascularity occurred in 63% of the blebs in group A and 0% in group B (P < 0.01). In eyes with IOP < or = 20 mmHg without medical treatment, the mean IOP was significantly lower in group 1 (8 vs 15 mm Hg, P < 0.002). A translucent cystic bleb without conjunctival stroma was observed in only 1 eye in group A. An optimal spongy stromal bleb was observed in all other eyes (96%) despite the different MMC doses. The numbers of complications in the 2 groups were nearly equal. CONCLUSIONS: Bleb avascularity after 4 microg MMC could be avoided by the use of 1 or 2 microg MMC on the basis of preoperative prognosticators for failure, but at the expense of some of the IOP-lowering effect. This indicates that the therapeutic index (clinical safety margin) of MMC seems to be narrow. An MMC dose-response relation was not observed for the thin, cystic, and translucent bleb. The low incidence of this bleb (4%) indicates that the operative technique, apart from the vascularity, may be the most essential determinant of bleb morphology.

Adolescent↗
PubMed2006

Automatic retinal oximetry.

PURPOSE: To measure hemoglobin oxygen saturation (SO(2)) in retinal vessels and to test the reproducibility and sensitivity of an automatic spectrophotometric oximeter. METHODS: Specialized software automatically identifies the retinal blood vessels on fundus images, which are obtained with four different wavelengths of light. The software calculates optical density ratios (ODRs) for each vessel. The reproducibility was evaluated by analyzing five repeated measurements of the same vessels. A linear relationship between SO(2) and ODR was assumed and a linear model derived. After calibration, reproducibility and sensitivity were calculated in terms of SO(2). Systemic hyperoxia (n = 16) was induced in healthy volunteers by changing the O(2) concentration in inhaled air from 21% to 100%. RESULTS: The automatic software enhanced reproducibility, and the mean SD for repeated measurements was 3.7% for arterioles and 5.3% venules, in terms of percentage of SO(2) (five repeats, 10 individuals). The model derived for calibration was SO(2) = 125 - 142 . ODR. The arterial SO(2) measured 96% +/- 9% (mean +/- SD) during normoxia and 101% +/- 8% during hyperoxia (n = 16). The difference between normoxia and hyperoxia was significant (P = 0.0027, paired t-test). Corresponding numbers for venules were 55% +/- 14% and 78% +/- 15% (P < 0.0001). SO(2) is displayed as a pseudocolor map drawn on fundus images. CONCLUSIONS: The retinal oximeter is reliable, easy to use, and sensitive to changes in SO(2) when concentration of O(2) in inhaled air is changed.

Humans↗
PubMed2005

A comparison of colour micrographs obtained with a charged couple device (CCD) camera and a 35-mm camera.

PURPOSE: The purpose of this study was to determine if micrographs produced with a colour charged couple device (CCD) camera were comparable in quality to micrographs obtained with a 35-mm colour film camera. The Axiocam (Zeiss, Jena, Germany) CCD camera produced images of 3900 x 3090 pixels. METHODS: Each picture in a series of 50 pairs of film and digital micrographs was rated independently by each of three observers on the categories of colour, detail and overall impression. A total of 28 of the 50 pairs of micrographs were discarded due to colour differences. RESULTS: Digital micrographs were rated lower on colour and higher on detail compared to film micrographs. The film and digital micrographs were rated equally on overall impression. The difference in colour between film and digital micrographs can be compensated for using image processing software on the digital image. However, such manipulation was not carried out as part of the present study. The study originally included 50 digital micrographs and 50 film micrographs. The micrographs were paired and 22 of the 50 pairs of micrographs were assessed. Thus 28 pairs were not evaluated due to colour differences in the non-manipulated pictures. The interobserver difference on colour in the remaining 22 pairs given as mean square +/- standard error of the mean was - 0.27 +/- 0.10, 0.62 +/- 0.10 and 0.90 +/- 0.11. The interobserver difference on detail was - 0.48 +/- 0.10, 0.95 +/- 0.10 and 1.43 +/- 0.10. The interobserver difference on overall impression was - 0.70 +/- 0.10, 0.57 +/- 0.10 and 1.27 +/- 0.10. All the results differed significantly (p < 0.001). CONCLUSION: Digital micrographs are sufficient in detail, colour and overall impression to replace the traditional 35-mm film recordings for use in histopathology.

Choroid Neoplasms↗
PubMed2004

Optic nerve oxygenation.

The oxygen tension of the optic nerve is regulated by the intraocular pressure and systemic blood pressure, the resistance in the blood vessels and oxygen consumption of the tissue. The oxygen tension is autoregulated and moderate changes in intraocular pressure or blood pressure do not affect the optic nerve oxygen tension. If the intraocular pressure is increased above 40 mmHg or the ocular perfusion pressure decreased below 50 mmHg the autoregulation is overwhelmed and the optic nerve becomes hypoxic. A disturbance in oxidative metabolism in the cytochromes of the optic nerve can be seen at similar levels of perfusion pressure. The levels of perfusion pressure that lead to optic nerve hypoxia in the laboratory correspond remarkably well to the levels that increase the risk of glaucomatous optic nerve atrophy in human glaucoma patients. The risk for progressive optic nerve atrophy in human glaucoma patients is six times higher at a perfusion pressure of 30 mmHg, which corresponds to a level where the optic nerve is hypoxic in experimental animals, as compared to perfusion pressure levels above 50 mmHg where the optic nerve is normoxic. Medical intervention can affect optic nerve oxygen tension. Lowering the intraocular pressure tends to increase the optic nerve oxygen tension, even though this effect may be masked by the autoregulation when the optic nerve oxygen tension and perfusion pressure is in the normal range. Carbonic anhydrase inhibitors increase the optic nerve oxygen tension through a mechanism of vasodilatation and lowering of the intraocular pressure. Carbonic anhydrase inhibition reduces the removal of CO2 from the tissue and the CO2 accumulation induces vasodilatation resulting in increased blood flow and improved oxygen supply. This effect is inhibited by the cyclo-oxygenase inhibitor, indomethacin, which indicates that prostaglandin metabolism plays a role. Laboratory studies suggest that carbonic anhydrase inhibitors might be useful for medical treatment of optic nerve and retinal ischemia, potentially in diseases such as glaucoma and diabetic retinopathy. However, clinical trials and needed to test this hypotheses.

Animals↗
PubMed2004

Carbonic anhydrase inhibition increases retinal oxygen tension and dilates retinal vessels.

BACKGROUND: Carbonic anhydrase inhibitors (CAIs) increase blood flow in the brain and probably also in the optic nerve and retina. Additionally they elevate the oxygen tension in the optic nerve in the pig. We propose that they also raise the oxygen tension in the retina. We studied the oxygen tension in the pig retina and optic nerve before and after dorzolamide injection. Also the retinal vessel diameters during carbonic anhydrase inhibition were studied. METHODS: A polarographic oxygen electrode was placed transvitreally immediately over the retina or the optic disc in anaesthetised pigs. The oxygen tension was recorded continually and 500 mg dorzolamide was injected intravenously. Retinal vessel diameters were analysed from monochromatic fundus photographs taken before and after injection of dorzolamide. RESULTS: Baseline retinal oxygen tension (RPO2) was 3.34+/-0.50 kPa (mean +/- SD, n=6) and baseline optic nerve oxygen tension (ONPO2) was 3.63+/-1.00 kPa. RPO2 was increased by 0.36+/-0.11 kPa (n=6, P=0.025) and ONPO2 by 0.73+/-0.34 kPa (n=6, P=0.003) 30 min after dorzolamide administration. The retinal arterioles was significantly dilated by 13+/-7% (n=5, P=0.016) and the retinal venules by 12+/-8% (n=5, P=0.030) 30 min after injection of dorzolamide. CONCLUSION: Retinal and optic nerve oxygen tension increased with systemic administration of dorzolamide. The retinal vessels dilated, probably causing increased blood flow inducing the observed increase in RPO2. The increased oxygenation of retina by CAI may offer therapeutic possibilities in ischaemic diseases of the retina and optic nerve.

Animals↗
PubMed2002

Uveal effusion and ultrasonic imaging: a clinical series.

PURPOSE: To establish the diagnostic role of imaging by ultrasound for the diagnosis of uveal effusion syndrome. METHODS: Using ultrasonic imaging features as the main criteria for evaluation, the recorded data from 16 patients with presumed uveal effusion seen between 1994 and 2000 were reviewed and analysed for clinical manifestations and current diagnostic suggestions. Eventually, as cumulating experience suggested that ultrasound is capable of indicating uveal effusion, the study set-up became in part more prospective. RESULTS: The two main ultrasonic features found were: (1) extended multi-layered detachment patterns by B-scan, often kinetically mobile; (2) a spongy oedematous ciliary body region, often with interstitial lacunae, as demonstrated by high-resolution ultrasound biomicroscopy (50 Mhz). CONCLUSIONS: In patients with visual loss and ambiguous detachment-like fundus pathology, ultrasonic features are often of practical guidance for diagnosing uveal effusion syndrome.

Adolescent↗