Biomedical subjects

Michael Georgopoulos

Publications and source records attributed to Michael Georgopoulos.

25 records · Page 2Linked to original sources

PubMed2003

Effects of sildenafil on retinal blood flow and flicker-induced retinal vasodilatation in healthy subjects.

PURPOSE: Sildenafil is a specific inhibitor of phosphodiesterase V, which is widely used for the treatment of erectile dysfunction. Sildenafil has been shown to induce vasodilation in several vascular beds by inhibiting the cGMP breakdown. The present study was conducted to investigate whether sildenafil increases blood flow in the human retina. METHODS: In a randomized, double-masked, placebo-controlled, two-way crossover study in 12 healthy male volunteers the effects of a single dose of 100 mg sildenafil were studied. Subjects received sildenafil or placebo on two different study days. After administration, retinal hemodynamic parameters were measured every 20 minutes. Retinal vessel diameters and retinal blood velocity were assessed with the retinal vessel analyzer and bidirectional laser Doppler flowmetry, respectively. In addition, the response of retinal vessel diameters to stimulation with diffuse flicker light was studied. Blood pressure and intraocular pressure were measured with noninvasive techniques. RESULTS: Sildenafil had no effect on mean arterial pressure, pulse rate, intraocular pressure, retinal blood velocity, or retinal arterial diameter. However, a significant increase in retinal venous diameters (4.7% +/- 3.2%; P=0.0028 versus placebo) and retinal blood flow 15.7% +/- 18.0%; P=0.029 versus placebo) was observed. Sildenafil had no effect on flicker-induced vasodilation in retinal arteries or veins. CONCLUSIONS: The data indicate that sildenafil increases retinal venous diameters and retinal blood flow in healthy subjects. By contrast, it does not affect intraocular pressure and flicker-induced retinal vasodilation. Further studies are needed to elucidate whether this drug may be therapeutically used in retinal ischemic disease.

3',5'-Cyclic-GMP Phosphodiesterases↗

PubMed2002

Reproducibility of standardized retroillumination photography for quantification of posterior capsule opacification.

PURPOSE: To determine the short-term reproducibility of standardized digital retroillumination images of regeneratory posterior capsule opacification (PCO) using the photographic setup at 1 institution. SETTING: Department of Ophthalmology, University of Vienna, Vienna, Austria. METHODS: In this prospective study, 60 retroillumination images of 30 eyes with varying degrees of PCO and different types of intraocular lenses were acquired with a standardized digital coaxial retroillumination system. Two images were taken per eye with a 1-minute interval between images. Ten other eyes were photographed in the same way but with a 5-day interval between the 2 images. All images were evaluated with a fully automated, objective PCO analysis software in which the PCO score was from 0 to 100. The 2 results (A, B) in each eye were compared, and the differences were calculated. RESULTS: There was a high correlation between the A and B results (r = 0.99). The mean absolute difference was 3.7%. The repeatability coefficient was 8.8%. CONCLUSION: Digital coaxial retroillumination photography provided quick acquisition of regeneratory PCO images. It provided excellent image quality and high reproducibility. The technique forms a good basis for automated quantification of PCO with new software systems.

Cataract↗

PubMed2002

Assessment of anterior capsule opacification: photographic technique and quantification.

PURPOSE: To develop and evaluate a standardized slitlamp photographic technique to document and quantify anterior capsule opacification (ACO) in the pseudophakic eye. SETTING: University of Vienna, Medical School, Department of Ophthalmology, Vienna, Austria. METHODS: In this prospective study, slitlamp photographs were taken in 29 eyes of 19 patients with ACO of varying degrees and intraocular lenses of different materials. Digital slitlamp photographs were taken by 2 examiners using a standardized protocol. The intensity of anterior fibrosis was evaluated using subjective grading by 2 masked examiners and by image analysis. RESULTS: A standardized protocol was developed for documentation of ACO. The intraexaminer (or short-term) reproducibility (r = 0.96, P < .01) and interexaminer reproducibility (r = 0.93, P < .01) were excellent. The results of image analysis used to objectively quantify ACO correlated with the subjective grading (r = 0.95, P < .01). CONCLUSION: This standardized technique of slitlamp photography and image analysis provided reproducible documentation and can therefore serve as a basis for the quantification of ACO.

Anterior Chamber↗

PubMed2002

Refractive outcome of cataract surgery using partial coherence interferometry and ultrasound biometry: clinical feasibility study of a commercial prototype II.

PURPOSE: To evaluate the refractive outcome of cataract patients 3 months postoperatively using optical biometry obtained with a prototype version (axial length measurement, ALM, Carl Zeiss Jena) of the commercial partial coherence interferometry (PCI) instrument (IOLMaster, Carl Zeiss Jena). SETTING: Department of Ophthalmology, Vienna General Hospital, and Institute of Medical Physics, University of Vienna, Austria. METHODS: Forty-five patients with age-related cataract in both eyes were scheduled for bilateral cataract surgery. Axial length was measured preoperatively with a prototype (ALM) of the commercial PCI instrument as well as with immersion ultrasound (IUS). Immersion US was performed by a single experienced investigator. In each patient, the first eye was randomly assigned to receive an intraocular lens (IOL) using the Holladay IOL power formula based on ALM or IUS biometry. The other biometric technique was used in the contralateral eye. Subjective refractive outcome was assessed 3 months postoperatively. RESULTS: Refractive outcomes with the 2 techniques did not differ significantly (P = .28). The mean numerical error (MNE) (the difference between the refractive outcome 3 months postoperatively and the predicted spherical equivalent) was 0.13 diopter (D) and 0.03 D for the ALM and IUS, respectively. The mean absolute error (MAE) (the absolute value of MNE) was 0.48 D (range 0.00 to 1.58 D) and 0.46 D (range 0.01 to 1.92 D) with the ALM and IUS, respectively. By recalculating the surgeon factor retrospectively to correct the Holladay formula to obtain a postoperative MNE of zero, a theoretical MAE of 0.46 D was obtained with both biometry techniques. CONCLUSIONS: Refractive outcome in cataract patients using PCI biometry was as good as that achieved with optimized IUS. However, the difference in axial length measured by the ALM compared to that measured by IUS must be considered when using the IOL A-constants supplied by the manufacturers.

Aged↗

PubMed2002

Effect of an acrylic intraocular lens with a sharp posterior optic edge on posterior capsule opacification.

PURPOSE: To compare the posterior capsule opacification (PCO) inhibiting effect of the sharp posterior optic edge design of the Sensar OptiEdge AR40e intraocular lens (IOL) (Allergan Surgical) with that of the round-edged design of the Sensar AR40 IOL. Setting Department of Ophthalmology, University of Vienna, Vienna, Austria. METHODS: This prospective randomized patient- and examiner-masked study comprised 106 eyes of 53 patients with bilateral age-related cataract. Each patient had cataract surgery in both eyes and received an AR40 IOL in 1 eye and an AR40e IOL in the other eye. Postoperative examinations were at 1 week, 2 and 6 months, and 1 year. Digital slitlamp and digital retroillumination images of each eye were taken. The amount of PCO was assessed subjectively at the slitlamp and objectively using automated image-analysis software. RESULTS: The AR40e group had significantly less regeneratory and fibrotic PCO 1 year after surgery. The mean automated image-analysis software PCO score (scale 0 to 10) was 2.19 in the AR40 group and 1.10 in the AR40e group (P <.001). The AR40e group had less peripheral fibrotic PCO. There was no significant difference in patient-reported edge glare between the 2 IOL groups. CONCLUSIONS: The sharp-edged design of the Sensar OptiEdge AR40e IOL led to significantly less PCO than the round-edged AR40 IOL 1 year postoperatively.

Acrylic Resins↗

PubMed2002

Impact of irrigation in a new model for in vitro diffusion of mitomycin-C after episcleral application.

PURPOSE: Episcleral application of mitomycin-C (MMC) during glaucoma surgery hinders the post-operative wound healing but may lead to side effects to the ciliary body. We present an experimental model to investigate the influence of irrigation on diffusion of MMC through the sclera and into subscleral compartments. MATERIALS AND METHODS: Scleral quadrants of 10 human donor eyes were mounted on PMMA tubes filled with saline imitating the intraocular fluid. Beneath the sclera a subscleral sponge was fixed to mimic the ciliary body. The episcleral sides of the scleral quadrants were exposed to sponges soaked with 0.2 mg/ml MMC and thereafter irrigated with 0, 40, 100 and 200 ml saline. Mitomycin-C concentrations of the sclera and the subscleral compartments were analyzed by means of high-performance liquid chromatography. In a second experiment, after the application time of one minute, different times of free diffusion until analysis were allowed, to evaluate the time-course of MMC penetration. RESULTS: MMC concentrations declined from the scleral layers (1-13 microg/ml, depending on depth and irrigation) to the subscleral sponge (0.17-0.27 microg/ml) and to the subscleral fluid (0.002-0.05 microg/ml). Irrigation significantly reduced MMC concentrations in the superficial scleral layers and in the subscleral fluid to 10-30% of the no irrigation value. No effect was noted in the deep scleral layers and subscleral sponges. In the second experiment, the subscleral compartments showed higher MMC concentrations with longer diffusion times, whereas no effect on intrascleral MMC concentrations was observed. CONCLUSION: Irrigation reduced MMC concentrations in the superficial scleral layers and in the subscleral fluid by the same amount. The clinical value of irrigation should be reconsidered; a lower dose MMC application without irrigation might be a more rationale approach.

Analysis of Variance↗

PubMedDate not supplied

Tumour regression of uveal melanoma after ruthenium-106 brachytherapy or stereotactic radiotherapy with gamma knife or linear accelerator.

PURPOSE: This study assesses differences in relative tumour regression and internal acoustic reflectivity after 3 methods of radiotherapy for uveal melanoma: (1) brachytherapy with ruthenium-106 radioactive plaques (RU), (2) fractionated high-dose gamma knife stereotactic irradiation in 2-3 fractions (GK) or (3) fractionated linear-accelerator-based stereotactic teletherapy in 5 fractions (Linac). METHODS: Ultrasound measurements of tumour thickness and internal reflectivity were performed with standardised A scan pre-operatively and 3, 6, 9, 12, 18, 24 and 36 months postoperatively. Of 211 patients included in the study, 111 had a complete 3-year follow-up (RU: 41, GK: 37, Linac: 33). Differences in tumour thickness and internal reflectivity were assessed with analysis of variance, and post hoc multiple comparisons were calculated with Tukey's honestly significant difference test. RESULTS: Local tumour control was excellent with all 3 methods (>93%). At 36 months, relative tumour height reduction was 69, 50 and 30% after RU, GK and Linac, respectively. In all 3 treatment groups, internal reflectivity increased from about 30% initially to 60-70% 3 years after treatment. CONCLUSION: Brachytherapy with ruthenium-106 plaques results in a faster tumour regression as compared to teletherapy with gamma knife or Linac. Internal reflectivity increases comparably in all 3 groups. Besides tumour growth arrest, increasing internal reflectivity is considered as an important factor indicating successful treatment.

Adult↗