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Biomedical subjects

S Orgül

Publications and source records attributed to S Orgül.

At least 37 records · Page 2Linked to original sources
PubMed1999

Variability in the measurement of corneal temperature using a noncontact infrared thermometer.

PURPOSE: To assess the variability of corneal temperature and the reproducibility of its measurement by means of a noncontact infrared thermometer in healthy subjects. METHODS: The THI-500 noncontact infrared thermometer (Tasco Japan, Osaka, Japan) was used for the measurement of corneal temperature. The reproducibility of corneal temperature measurements was assessed for 5 consecutive temperature readings obtained within 45 min or within 5 days. In addition, the interocular difference in corneal temperature and the diurnal temperature changes of the cornea were assessed. For each experiment, 10 healthy subjects were recruited. RESULTS: The reliability of 5 consecutive corneal temperature measurements obtained within 45 min and within 5 days was 97.92 and 85.35%, respectively. Interocular differences in corneal temperature were not statistically significant (p = 0.70). Average corneal temperature varied significantly during the day (p < 0.0001), with lower corneal temperature readings during the morning hours compared to those obtained during the afternoon. CONCLUSION: The assessment of corneal temperature by means of noncontact infrared thermometry is highly reproducible. Corneal temperature varies throughout the day, and this variation is independent of variations in environmental temperature.

Adult↗
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↗
PubMed1996

An endothelin-1 induced model of optic nerve ischemia in the rabbit.

PURPOSE: To evaluate blood flow reduction and topographic optic nerve changes after the local administration of endothelin-1 in vivo, delivered to the perineural region of the anterior optic nerve in the rabbit. METHODS: Endothelin-1 (five rabbits) in a dosage of 0.1 microgram/day or balanced salt solution (two rabbits) was delivered to the perineural region of the anterior optic nerve with osmotically driven minipumps. Optic nerve blood flow was determined by the colored microspheres technique after 14 days of local endothelin-1 or balanced salt solution administration to the microvasculature of the optic nerve. In addition, optic nerve blood flow was determined in two rabbits that had no minipump implants. The morphologic changes induced by reduction of blood flow were assessed in five additional rabbits implanted with osmotically driven minipumps containing endothelin-1 (0.1 microgram/day). These rabbits were observed for 8 weeks, and the morphologic optic nerve changes were monitored with a confocal scanning laser ophthalmoscope. RESULTS: Independent of intraocular pressure, endothelin-1 induced a decrease in blood flow of approximately 38% in the experimental eye, compared to the decrease induced by balanced salt solution or to the decrease in rabbits without minipumps (analysis of covariance, P = 0.0092). Multivariate statistical analysis showed a significant change in topometric parameters (cup area, cup depth, rim volume) obtained with a confocal scanning laser ophthalmoscope, indicating an increase in optic nerve cupping and a decrease of the perineural rim volume in the experimental eyes (P = 0.017). CONCLUSIONS: The current results suggest that morphologic optic nerve alterations can be induced experimentally in the rabbit model after ischemia produced by the local administration of endothelin-1 to the perineural region of the anterior optic nerve.

Animals↗
PubMed1996

An endothelin-1-induced model of chronic optic nerve ischemia in rhesus monkeys.

PURPOSE: The purpose of this study was to evaluate flow reduction to the optic nerve after chronic administration of endothelin-1 in primates. MATERIALS AND METHODS: Endothelin-1 (three rhesus monkeys), in a dosage of 0.1 microgram/day, or balanced salt solution (three rhesus monkeys) was delivered to the perineural region of the anterior optic nerve via osmotically driven minipumps. Optic nerve blood flow was determined by means of a colored microspheres technique after 7 days of local endothelin-1 or balanced salt solution administration. The effect of endothelin-1 on optic nerve blood flow was analyzed by analysis of convariance (ANCOVA) in a 2 (between groups: endothelin-1, balanced salt solution) x 2 (within subject: blood flow minipump optic nerve, blood flow controls) design, with intraocular pressure as a changing covariate. RESULTS: The decrease of optic nerve blood flow in the endothelin-1 eyes was significant compared to the balanced salt solution eyes (ANCOVA p = 0.015). Among the monkeys implanted with endothelin-1 minipumps, the decrease in optic nerve blood flow in the experimental eye compared to the contralateral eye (mean +/- SD 35.7 +/- 9.1%) was significant (p = 0.01), while that among the monkeys implanted with balanced salt solution minipumps (mean +/- SD 0.7 +/- 5.5%) was not (p = 0.73). CONCLUSIONS: This new primate model of chronic optic nerve ischemia may represent a method to evaluate experimentally the implication of a local hemodynamic perturbation in various optic neuropathies.

Animals↗
PubMed1995

Intraocular pressure decrease after local ocular cooling is underestimated by applanation tonometry.

BACKGROUND: The effects of intense systemic or local cooling on aqueous humor dynamics in animals are an increased total outflow facility and a decreased aqueous flow. Few studies suggest that only vasoconstriction of arteriolar segments of the episcleral vasculature may be the cause for a decrease in intraocular pressure after local cooling in humans. Because corneal changes may have influenced such studies, the effect of local cooling was assessed in normal subjects. METHODS: Intraocular pressure and corneal thickness were measured in 18 healthy human subjects before and after exposure of the right eye to both, an air stream at 20 degrees C, and an air stream at 0 degrees C. RESULTS: No significant changes in IOP or corneal thickness occurred under 20 degrees C conditions. After local cooling, the mean corneal thickness increased from 0.52 +/- 0.01 mm to 0.57 +/- 0.02 mm (p < 0.001). Mean intraocular pressure decreased from 13.8 +/- 2.9 mmHg to 12.9 +/- 3.1 mmHg (p < 0.026). The observed decrease in IOP correlated significantly but negatively (R = -0.53; p = 0.024) with the increase in corneal thickness, indicating that the cooling effect on IOP may be rather underestimated. CONCLUSION: The eye is very sensitive to local cooling effects, which may, however, partially be masked by changes in corneal thickness.

Adult↗
PubMed1995

Optic nerve vasomotor effects of topical beta-adrenergic antagonists in rabbits.

PURPOSE: To examine the anterior optic nerve vasomotor effects of nonselective and relatively beta-1-selective beta-adrenergic antagonists in rabbits, because different influences on optic nerve blood flow with these medications have been suggested. METHODS: After topical therapy for 30 days with either timolol maleate 0.5% (six rabbits), betaxolol hydrochloride 0.5% (six rabbits), or placebo (two rabbits), the microvasculature of the optic nerve was examined with an intraluminal microvascular corrosion casting technique. The investigators were masked to both the medication group and the treated eye. The constriction, in percent of the downstream vessel caliber, was measured at the vascular branching point of arterioles supplying the anterior optic nerve. An average constriction was calculated and compared between the medication groups and between the treated and the contralateral, untreated eyes. RESULTS: Constriction values from a total of 218 arterioles supplying the anterior optic nerve were obtained for the 14 rabbits. The means of the average constriction on the treated side were comparable between the groups treated with timolol maleate, betaxolol hydrochloride, and placebo (one-way analysis of variance, P = .64), as well as between the treated and untreated eyes (two-tailed t-test for paired variables, P = .68 for timolol maleate and P = .42 for betaxolol hydrochloride). The statistical power to find a difference of 5% or more average constriction was at least 90%. CONCLUSIONS: Both relatively selective and nonselective beta-adrenergic antagonists produce no observable optic nerve vasomotor effects in the rabbit eye.

Administration, Topical↗