Search PubMed⌕ Search

Biomedical subjects

S Orgül

Publications and source records attributed to S Orgül.

At least 19 recordsLinked to original sources
PubMed1999

Relationship between corneal temperature and finger temperature.

BACKGROUND: Because the temperature of the body surface depends largely on local blood flow, temperature measurements might provide information on the latter. OBJECTIVE: To evaluate the relationship between corneal temperature and finger temperature. METHODS: Corneal, finger, and body core temperatures were measured in a relatively unselected population of 266 white persons. Excluded were persons taking topical eye medication or with corneal inflammatory signs. Corneal and finger temperatures were measured on 1 randomly selected side of the body by means of a noncontact infrared thermometer. As a measure of body temperature, the tympanic temperature was measured by means of a noncontact infrared ear thermometer. A total of 124 females and 142 males were examined. RESULTS: A correlation analysis in a least squares regression model was highly significant (R = 0.67; P<.001), with corneal temperature as the dependent variable and environmental, tympanic, and finger temperatures and age and sex as predicting variables. All variables contributed significantly to prediction of the corneal temperature. The corrected mean corneal temperature after adjusting for environmental, tympanic, and finger temperatures and for age of participants was 0.16 degrees C higher in male participants (P = .002). CONCLUSIONS: Corneal temperature correlates with finger temperature even after adjusting for environmental and tympanic temperatures and for the age and sex of participants. A possible cause for these findings are some parallelisms in blood-flow regulation in the finger and the eye.

Adolescent↗
PubMed1999

Physiology of perfusion as it relates to the optic nerve head.

Blood flow in the optic nerve has been demonstrated to be autoregulated, and, thus, within certain limits, to be independent of the local perfusion pressure. As in the brain, a close coupling of neuronal activity and optic nerve head blood flow has been demonstrated. A number of regulatory systems and factors participate in the regulation of vascular tone in various organs, including the optic nerve. Metabolic and myogenic mechanisms keep local perfusion constant or adapted to the local metabolic needs. Such mechanisms seem to be involved in the regulation of optic nerve blood flow as well. In contrast, neuronal blood flow regulation is of minor importance in the optic nerve. Many of the regulatory modalities induce a response of vascular smooth muscle cells through stimulation of factors produced by the endothelial cell layer. Indeed, endothelial factors are of utmost importance in the regulation of optic nerve blood flow. The facts that there is a basal formation of nitric oxide, which leads to an active dilation of the ocular vasculature, and that endothelin-1 decreases blood flow to the anterior optic nerve in a dose-dependent manner suggest that alterations in these regulatory mechanisms might be relevant for optic nerve blood flow alterations as they relate to glaucomatous optic neuropathy. It is hoped that a detailed knowledge of blood flow regulation in the optic nerve might initiate new treatment modalities in optic neuropathies that are hemodynamic and vascular in nature.

Animals↗
PubMed1999

Relationship between blood flow velocities in retrobulbar vessels and laser Doppler flowmetry at the optic disk in glaucoma patients.

The relationship between blood flow velocities in retrobulbar vessels and blood flow at the optic nerve in glaucoma patients was assessed in a prospective study. The Heidelberg retina flowmeter (HRF) was used to assess optic nerve head blood flow in 13 open-angle glaucoma patients. In the same patients, color Doppler imaging (CDI) measurements were obtained from the ophthalmic artery, the central retinal artery and the posterior ciliary arteries. Using data for one randomly selected eye per subject, correlations between HRF recordings and CDI measurements were evaluated by means of Spearman's rank correlation factor. All three HRF parameters correlated with CDI measurements obtained from retrobulbar vessels. The most marked correlations were those of the HRF parameter 'volume' with the end-diastolic velocity in the ophthalmic artery and the medial posterior ciliary artery (R = 0.79, p = 0.0012 and R = 0.81, p = 0.0007, respectively), and the peak systolic velocity in the lateral posterior ciliary artery (R = 0.82, p = 0.0006). The present study suggests that glaucoma patients with altered blood flow in retrobulbar vessels are likely to show an alteration in optic nerve blood flow as measured with the HRF.

Aged↗
PubMed1999

Asymmetry in intraocular pressure and retinal nerve fiber layer thickness in normal-tension glaucoma.

The etiology of glaucoma is most probably multifactorial. This study intended to investigate the asymmetry in intraocular pressure (IOP) and that in retinal nerve fiber layer (RNFL) thickness in normal-tension glaucoma patients. Two diurnal tension curves, obtained within 3 months and counting at least five IOP readings each, including an early morning IOP measurement upon awaking, were obtained in 15 normal-tension glaucoma patients. None of the patients received IOP-lowering therapy. IOP asymmetry was present in at least three readings and was always in the same direction. The optic nerve was imaged in both eyes in each patient by means of confocal scanning laser ophthalmoscopy (Heidelberg Retina Tomograph). The interocular difference in RNFL thickness and the RNFL cross-sectional area were correlated with the interocular difference in IOP by means of Spearman's rank correlation factor. Nine female and 6 male normal-tension glaucoma patients (mean +/- SD age was 62. 4 +/- 16.9 years) were included in this study. Interocular IOP asymmetry varied between 0.30 and 4 mm Hg. Strong negative correlations were found between interocular asymmetry in IOP and interocular asymmetry in RNFL thickness asymmetry (R = -0.652, p = 0. 0083) and interocular asymmetry in RNFL cross-sectional area (R = -0. 702, p = 0.0034). The present results demonstrate for the first time a more marked thinning of the neuroretinal nerve fiber layer in the eye with the higher IOP in normal-tension glaucoma patients.

Chronic Disease↗
PubMed1999

Vascular dysregulation: a principal risk factor for glaucomatous damage?

Both intraocular pressure (IOP) and vascular factors appear to play an important role in the pathogenesis of glaucomatous optic neuropathy (GON). Arteriosclerosis and its risk factors are of minor importance, whereas vasospastic syndrome clearly is associated with GON. A vascular endotheliopathy seems to be involved in the diathetic hyperresponsiveness to stimuli, such as coldness or emotional stress. This in turn leads to a compromised autoregulation, and thereby renders the eye more sensitive to IOP or to a decrease in blood pressure. A variation in ocular perfusion may lead to an increase in free oxygen radicals. This may finally lead to apoptosis.

Animals↗
PubMed1998

Optic nerve blood-flow abnormalities in glaucoma.

Glaucoma can be defined as an optic nerve disease with typical morphological and functional changes. There are many risk factors associated with this neuropathy. The best known factor is an increased intraocular pressure. There are, however, many other risk factors. Among them, vascular factors play a major role. Although such vascular factors have been postulated more than hundred years ago, it is only recently that the physiology and pathophysiology of the optic nerve head circulation is, to some extent, understood. New instruments have been developed to measure ocular blood flow including blood flow in the optic nerve head. Although most of the studies indicate that circulation is changed in glaucoma patients, there is little association between glaucoma and arteriosclerosis. The main cause for the circulation disturbance in glaucoma seems rather to be a vascular dysregulation leading to local vasospasm and to systemic hypotension.

Animals↗
PubMed1998

Abnormalities of microcirculation in glaucoma: facts and hints.

Many risk factors associated with glaucoma have been identified recently. The best known of these is increased intraocular pressure (IOP). Among the others, however, vascular risk factors play a major role. Although such vascular factors were already postulated more than 100 years ago, only recent technical developments have afforded systematic investigations of associated microcirculatory disturbances and basic principles of blood flow regulation. In glaucoma, besides IOP, vascular dysregulation (such as local vasospasm and systemic hypotension, resulting in impaired autoregulation of blood flow in the optic nerve head, the choroid, and other ocular tissues) seems to be a major risk factor. However, multiple coacting factors, which are not limited to the eye but are, rather, symptoms of a systemic disease, seem to be involved in the damaging process.

Choroid↗
PubMed1998

Endothelium-derived vasoactive substances relevant to normal-tension glaucoma.

Glaucoma is a progressive optic neuropathy that has a multi-factorial etiology. The most important risk factor is certainly an increased intraocular pressure. However, clinical observations have indicated that factors other than increased intraocular pressure also damage the neural tissue in glaucomatous optic neuropathy. The most prominent of these to be vascular dysregulation. Vascular tone is permanently regulated by a number of regulatory systems and factors, and the endothelial cell layer acts as an important mediator for the response to these factors. According to recent evidence, glaucomatous optic neuropathy may be associated with changes in endothelium-dependent vascular regulation. Consequently, therapeutic approaches based on vasodilator drugs acting via endothelium-derived substances are being developed. Although promising preliminary studies have been performed, the clinical relevance of such treatment remains to be clarified.

Animals↗
PubMed1998

Effect of carbogen, oxygen and intraocular pressure on Heidelberg retina flowmeter parameter 'flow' measured at the papilla.

The aim of the study was to evaluate whether the Heidelberg retina flowmeter (HRF), a new device for retinal and anterior optic nerve blood flow assessment, can gauge, at least semiquantitatively, a known effect such as an increase in optic nerve blood flow by hypercapnia or a decrease in optic nerve blood flow by hyperoxia or high intraocular pressure (IOP). Measurements with the HRF were obtained at the papilla of three groups of 5 young healthy subjects (1) at baseline and after breathing 5% carbogen, (2) at baseline and after breathing 100% oxygen and (3) at baseline and after increasing IOP to 20 and 50 mm Hg. The changes in the value of the HRF parameter 'flow' were analyzed by means of a paired Student's t test. Breathing 100% oxygen for 7 min resulted in a statistically significant decrease of 34.7+/-2.5% (mean+/-SEM) in HR parameter 'flow' (p < 0.01) at the papilla. Breathing 5% carbogen for 7 min resulted in a statistically significant increase of 18.3+/-2.6% in HRF parameter 'flow' (p = 0.024). Increasing IOP to 20 mm Hg did not result in a statistically significant change in HRF parameter 'flow' (-9.6+/-7.4%; p = 0.13). Increasing IOP from 20 to 50 mm Hg, however, resulted in a statistically significant decrease of 40.1+/-6.6% in HRF parameter 'flow' (p = 0.003). With the applied stimuli, the HRF parameter 'flow' changed in the expected direction, i.e. an increase with hypercapnia and a decrease with hyperoxia or high IOP. The simplicity of use of the HRF instrument suggests that it might be well suited for a non-invasive, at least semiquantitative, assessment of changes in blood flow at the papilla.

Adult↗
PubMed1998

Measurement of intraocular pressure with a modern noncontact tonometer.

PURPOSE: To evaluate the intraocular pressure (IOP) in a population without known glaucoma as measured by means of a noncontact tonometer (NCT). METHODS: IOP values of 842 persons, measured by means of a Pulsair 2000 NCT (Keeler Instruments, Inc., Broomhall, Pennsylvania) by 5 investigators were evaluated. Three consecutive measurements were taken first on the right eye and then on the left eye in each subject. Topical anesthesia was not used. RESULTS: The distribution of the measured IOP values was significantly different from a normal distribution. The median IOP was 15.0 mmHg (lower quartile/ upper quartile 12.5/17.2). There were no differences in IOP values between male and female subjects or between right and left eyes. There was no correlation between age and IOP values. Ninety percent of the subjects had an IOP within a range of 9-24 mmHg in both eyes. Among the examined subjects, the IOP was above 24 and 21 mmHg in 4,6 and 11%, respectively, in at least one eye. The median range of consecutive IOP measurements in one eye was 3 mmHg (lower quartile/upper quartile 2.0/4.0). The median interocular IOP difference was 1.7 mmHg (0.7/2.7). The median individual coefficient of variation (CV) values were 10.0% for the right eyes, -10.8% for the left eyes. Among the 5 different examiners, the IOP values, range of 3 consecutive IOP readings in one eye, interocular asymmetry and CV values were statistically comparable. CONCLUSION: The Pulsair 2000 NCT is very simple to use and its handling is mostly independent of the operator. The results of the present investigation might be of some value for future screening programs.

Adolescent↗
PubMed1998

Influence of acquisition parameters on hemodynamic measurements with the Heidelberg Retina Flowmeter at the optic disc.

PURPOSE: The Heidelberg Retina Flowmeter (HRF; Heidelberg Engineering GmbH, Heidelberg, Germany) is a new instrument that determines hemodynamic variables at discrete locations of the retina and the optic disc. The objective of this study was to evaluate the influence of various HRF recording settings on the long-term variability of the HRF parameter. "Flow," computed at the optic nerve head in healthy individuals. METHODS: The authors obtained 2 sets of 5 HRF recordings in 10 healthy individuals (age range, 23-60 years). The HRF recordings were obtained within a scan area of 10 degrees x 2.5 degrees (set 1) and 20 degrees x 5 degrees (set 2). For each set, the HRF recordings were obtained on 5 consecutive days. Respective HRF recordings for both sets were obtained on the same days. On these recordings, the HRF parameter, "Flow," was computed at 3 different regions of interest (temporal superior, temporal inferior, and temporal rim of the optic disc). At all three locations, Flow was computed within windows of measurement of 10 pixels x 10 pixels and 20 pixels x 20 pixels. The effect of larger windows (30 pixels x 30 pixels, 40 pixels x 40 pixels, and 50 pixels x 50 pixels) was tested at the temporal rim of the optic disc. RESULTS: The highest reliability coefficient was reached with a scan area of 20 degrees x 5 degrees at the temporal superior rim of the optic disc (r = 0.93). Within a scan area of 20 degrees x 5 degrees, the size of the user-defined measuring window did not influence the reliability. Two models of analysis of variance disclosed that the only effect on the computed value of Flow that reached statistical significance was that because of the scan area (F = 11.172; p = 0.001). The location of the window of measurement and its size had no statistically significant effect. CONCLUSION: The present results show that the location of the window of measurement has an important effect on the long-term variability of the HRF parameter, Flow. In addition, different scan areas influence significantly the computed values of this parameter.

Adult↗
PubMed1998

Descriptive information of topographic parameters computed at the optic nerve head with the Heidelberg retina tomograph.

PURPOSE: To analyze the frequency distribution and descriptive information of topometric data obtained with the Heidelberg Retina Tomograph (HRT) in a normal population. METHODS: Topographic measurements of the optic disc were acquired and evaluated using the HRT in 225 subjects between 12 and 90 years of age. After randomly selecting one eye per subject, the frequency distributions, mean values, minima, maxima, and first, fifth, fiftieth, ninety-fifth, and ninety-ninth percentiles were evaluated for topographic parameters computed by the HRT. The influence of age, intraocular pressure (IOP), disc size, and disc shape on optic disc topometric data was analyzed. A principal component analysis of the topometric parameters was performed. The frequency distributions, mean values, minima, maxima, and first, fifth, fiftieth, ninety-fifth, and ninety-ninth percentiles of the interocular difference in topographic parameters were evaluated. RESULTS: All topographic parameters showed a unimodal but not necessarily normal distribution. None of the parameters showed a relevant correlation with age, IOP (in the normal range), and overall shape of the anterior optic nerve, but a few parameters showed a clinically significant correlation with disc size. A principal component analysis identified four relevant factors (optic nerve cup, retinal nerve fiber layer, optic disc size, and optic nerve cup shape) in the entire data set of optic nerve topometric data. The absolute value of all interocular differences in topographic parameters showed an asymmetric but unimodal distribution. CONCLUSION: The mathematical description of the optic nerve cup shape provides information on optic nerve head topography independently from cupping, nerve fiber layer thickness, and disc size. Potentially, quantification of further aspects in optic nerve head topography might improve the discriminatory power of computerized quantitative optic nerve head analysis.

Adolescent↗
PubMed1997

Variability of contour line alignment on sequential images with the Heidelberg Retina Tomograph.

BACKGROUND: The influence of the contour line alignment software algorithm on the variability of the Heidelberg Retina Tomograph (HRT) parameters remains unclear. METHODS: Nine discrete topographic images were acquired with the HRT from the right eye in six healthy, emmetropic subjects. The variability of topometric data obtained from the same topographic image, analyzed within different samples of images, was evaluated. A total of four mean topographic images was computed for each subject from: all nine discrete images (A), the first six of those images (B), the last six of those nine images (C), and the first three combined with the last three images (D). A contour line was computed on the mean topographic image generated from the nine discrete topographic images (A). This contour line was then applied to the three other mean topographic images (B, C, and D), using the contour line alignment in the HRT software. Subsequently, the contour line on the mean topographic images was applied to each of the discrete members of the particular images subsets used to compute the mean topographic image, and the topometric data for these discrete topographic images was computed successively for each subset. Prior to processing each subset, the contour line on the discrete topographic images was deleted. This strategy provided a total of three analyses on each discrete topographic image: as a member of the nine images (mean topographic image A), and as a member of two subsets of images (mean topographic image B, C, and/or D). The coefficient of variation (100 x SD/mean) of the topographic parameters within those three analyses was calculated for each discrete topographic image in each subject ("intraimage" coefficient of variation). In addition, a coefficient of variation between the nine discrete topographic images ("interimage" coefficient of variation) was calculated. RESULTS: The "intraimage" and "interimage" variability for the various topographic parameters ranged between 0.03% and 3.10% and between 0.03% and 24.07% respectively. The "intraimage" coefficients of variation and "interimage" coefficients of variation correlated significant (r2 = 0.77; P < 0.0001). CONCLUSION: A high "intraimage" variability, i.e. a high variability in contour line alignment between sequential images, might be an important source of test re-test variability between sequential images.

Adult↗
PubMed1996

Sources of variability of topometric data with a scanning laser ophthalmoscope.

OBJECTIVE: To determine in a two-part study whether misalignment between the patient and the laser scanner is a major source of variability with the Heidelberg Retina Tomograph (Heidelberg [Germany] Engineering). METHODS: Three topographic images of the right optic nerve were acquired with the Heidelberg Retina Tomograph in eight patients with glaucoma. The correlations between average cup volume, variability of cup volume estimates, and direction of imaging were evaluated. Furthermore, the correlations between average rim volume, variability of rim volume estimates, and direction of imaging were evaluated. Next, the optic nerve cup volume and rim volume estimates of a rabbit's left eye were compared between three series of five topographic images acquired from three slightly different directions. RESULTS: Average cup volume, variability of cup volume estimates, and variability in the direction of imaging correlated significantly among the patients with glaucoma (multiple R2 = .95; P < .001). Average rim volume, variability of rim volume estimates, variability in the direction of imaging, and variability in the mean height of the contour line also correlated significantly (multiple R2 = .88; P = .03). In the rabbit eye, the cup volume and the rim volume differed significantly among the three image series (analysis of variance, P < .001 and P = .04, respectively). CONCLUSION: Misalignment between the patient and the laser scanner may account for significant variability with the Heidelberg Retina Tomograph.

Animals↗
PubMed1996

Measurement of optic nerve blood flow with nonradioactive colored microspheres in rabbits.

The objective of this study was to establish a nonradioactive technique to accurately assess blood flow in a small tissue such as the anterior optic nerve. Colored microspheres, 10.2 +/- 0.23 microns in diameter, were injected into the left atrium in each of 17 anesthetized rabbits. The rabbits were divided into four groups injected, respectively, with 5, 10, 50, or 100 million microspheres. Microsphere quantification in the tissue was performed after postmortem dissection and alkaline corrosion of the anterior optic nerve. Blood flow was evaluated by means of reference sample comparison method. While the relative interocular difference (range, 15.3-162.8%) was not significantly different between the rabbits injected with 5, 10, or 50 million microspheres (Kruskal-Wallis test, P = 0.11), injection with 100 million microspheres yielded a significantly lower relative interocular differences (range 2.3-12.8%) compared to the other three groups (Kruskal-Wallis test, P = 0.0048). In addition, reproducibility of microsphere counts was evaluated by ranking the difference between right and left optic nerve in percentage of the average number of microspheres per milligram of tissue in both optic nerves. The correlation between the relative interocular difference (range, 2.3-162.8%) and the average number of microspheres per milligram of tissue (1.2-78.7 microspheres/mg optic nerve tissue) was statistically significant (Spearman R, -0.90; P < 0.0001). The interocular variability in microsphere counts and interocular difference in intraocular pressure did not correlate (Spearman R, 0.33; P = 0.20). The rabbits injected with 100 million microspheres showed the highest average number of microspheres (range, 31.8-78.7 microspheres/mg optic nerve tissue). The optic nerve blood flow ranged between 0.14 and 0.24 microliters/mg/min among the rabbits injected with 100 million microspheres. The present experimental technique of optic nerve blood flow measurement is relatively inexpensive, highly reproducible, and obviates disposal of radioactive materials.

Animals↗
PubMed1996

Optic nerve vasomotor effects of topical apraclonidine hydrochloride.

AIMS: To examine, in vivo, the anterior optic nerve vasomotor effects of chronic apraclonidine hydrochloride in rabbits. METHODS: After local treatment in one randomly chosen eye with apraclonidine hydrochloride 0.5% over 21 days, the microvasculature of the optic nerve was examined in five rabbits using an intraluminal microvascular corrosion casting technique. The investigators were masked as to which eye was treated. The vasoconstriction near the branching point of arterioles supplying the optic nerve was calculated as a percentage of the downstream vessel calibre. An average constriction was calculated and compared between the treated and the contralateral, untreated, eyes by means of a two tailed t test for paired variables. Constriction values of a total of 72 arterioles supplying the optic nerve were obtained for the five rabbits. RESULTS: The average constriction in the treated and the control eyes was comparable (p = 0.96). CONCLUSION: Chronic administration of apraclonidine hydrochloride 0.5% produces no observable optic nerve vasomotor effects in the rabbit eye.

Administration, Topical↗