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Biomedical subjects

S Orgül

Publications and source records attributed to S Orgül.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1995

An in vivo model of chronic optic nerve ischemia: the dose-dependent effects of endothelin-1 on the optic nerve microvasculature.

The purpose of this study was to evaluate the effects induced by chronic microapplication of endothelin-1 on the anterior optic nerve microvasculature and to determine the dose-response characteristics of endothelin-1 on this vascular bed. Daily dosages between 4.69 x 10(-4) and 9.0 x 10(-1) micrograms/day of endothelin-1 were delivered continually over 3 days, and at a constant flow rate, to the perineural region of the anterior optic nerve of 15 albino rabbits via osmotically-driven minipumps. The vasomotor effect of local endothelin-1 on the microvasculature of the optic nerve was examined using intraluminal microvascular corrosion casting technique. The vasomotor effects were quantified by measuring the relative amount of vasoconstriction of the arterioles supplying the anterior optic nerve (primary and secondary branches of the short posterior ciliary arteries). The average constriction was calculated for the endothelin-treated eyes and the untreated, contralateral eyes. The mean vasoconstriction in the endothelin treated eyes ranged from 14.7% to 30.0% and was highly correlated with the logarithmic value of the daily dose of endothelin-1 (R2 = 0.59, p = 0.00083). The interocular difference (between treated and untreated eyes) of the optic nerve vasoconstriction ranged from 0-19% (mean +/- SD: 7.23 +/- 5.7%). This interocular difference also correlated highly with the log of the daily endothelin-1 dosage (R2 = 0.80; p < 0.0001). By additionally accounting for the weight and sex in a multiple linear regression function, the correlation was markedly improved (R2 = 0.92; p < 0.0001). In conclusion, the microvasculature supplying the anterior optic nerve of the rabbit demonstrates a dose-dependent vasoconstriction with chronic local application of endothelin-1. This in vivo, experimental model offers a titratable method with which the effects of chronic vasoconstriction and vascular insufficiency on the optic nerve can be examined.

Animals↗
PubMed1995

Perilimbal aneurysms of conjunctival vessels in glaucoma patients.

Aneurysms of the conjunctival vessels occur frequently. Such aneurysms have even been described in glaucomatous patients but their significance in this condition is not clear. Because they may be of clinical value in some conditions, the extent of perilimbal aneurysms of the conjunctiva was evaluated in 20 normal-tension-glaucoma patients, 20 primary open-angle-glaucoma patients, and 60 controls. The extent of these aneurysms was graded as follows: none (0), faint (1-2), moderate (3-5), and copious (> or = 6). The group frequencies of these categories were 5%, 25%, 10%, and 60% in normal-tension-glaucoma patients; 40%, 40%, 20%, and in primary open-angle-glaucoma patients; and 43%, 32%, 12%, and 13% in control patients, respectively. The incidence of copious perilimbal aneurysms of the conjunctiva was significantly higher in normal-tension-glaucoma patients than in primary open-angle-glaucoma patients and controls (P < 0.0001). Because local medication cannot account for the differences in relation to the control group and because glaucoma patients differed mainly in that normal-tension-glaucoma patients had vascular risk factors, the reason for our finding might be related to circulation problems.

Aged↗
PubMed1995

Reproducibility of topometric data with a scanning laser ophthalmoscope in rabbits.

The Heidelberg Retina Tomograph is a confocal scanning laser ophthalmoscope which obtains three-dimensional images of the optic nerve head and the retina in the human eye. Because of its potential investigative uses in experimental animal models of glaucoma, we examined its variability with optic nerve head measurements in the rabbit eye. Three topographic images, recorded on different days, were acquired from the right eye of 5 New Zealand white rabbits over 3 weeks. To estimate the lowest possible variability, a second series of three images was recorded in a single setting without displacement of the rabbits. The average coefficient of variability (standard deviation/mean) for the estimate of the optic nerve head cup volume (volume below surface) was 11.1% in the independent series and was decreased to 3.0% in the sequentially recorded series without displacement of the rabbits (P < 0.001). These values indicate a comparable variability for the estimate of the optic nerve head cup volume in the rabbit compared with those reported for the human eye. This variability is considerably decreased by maximally standardizing the image acquisition position, suggesting that variability largely depends on the alignment between the subject and the laser-scanner.

Animals↗
PubMed1994

Anterior chamber depth and pigment dispersion syndrome.

Pigment dispersion syndrome is thought to be the result of iris pigment abrasion by zonular packets. This condition primarily affects young males with myopia, perhaps because of deeper anterior chambers that make such pigment abrasion more likely. Males have been described to have larger eyes and deeper anterior chambers. This constellation, however, does not explain conclusively the predominance of males who have pigment dispersion syndrome. We, therefore, studied whether anterior chambers in males are deeper than those in females, not only in absolute measures but also relative to the axial length. Our results of 60 patients disclosed that men had not only significantly deeper mean absolute anterior chambers (men, 3.22 +/- 0.42 mm; women, 2.88 +/- 0.38 mm; P = .002) but also deeper mean relative anterior chambers (men, 13.54% +/- 1.66%; women, 12.45% +/- 1.2%; P = .013). No significant differences existed between genders with regard to lens thickness, extent of ametropia, and visual acuity. Thus, normal developmental differences between genders may predispose males for deeper anterior chambers and, consequently, for pigment dispersion syndrome.

Adult↗
PubMed1994

Moderate exertion lasting only seconds reduces intraocular pressure.

Intense physical exertion is known to reduce intraocular pressure (IOP). However, the effect of physical exertion on IOP in the first few seconds after beginning exertion has not been studied previously. IOP was determined twice within 15 s in 32 healthy, young men. Seventeen performed six deep knee bends within 8-10 s preceding the second IOP measurement, while 15 did not. The mean reduction in IOP immediately after such brief and moderate exertion was 1.9 +/- 0.3 mmHg, compared with 0.8 +/- 0.2 mmHg in the control group. The difference between both groups was statistically significant. Thus, even moderate physical exertion may reduce IOP. As the relative decrease in IOP correlated with the relative increase in heart rate, the observed reduction in IOP after brief, moderate physical exertion may be due to sympathetic activity.

Adult↗
PubMed1994

[Experiences with mitomycin C].

BACKGROUND: Recently, encouraging results with the use of Mitomycin C in trabeculectomy have been reported. PATIENTS: We used Mitomycin C (0.028%) during trabeculectomy in 72 eyes of 68 patients. Forty-one eyes have already been controlled during 6 months and 19 eyes during 9 months after the surgery. RESULTS: The mean intraocular pressure after 6 and 9 months was respectively 13 +/- 8 mm Hg and 13 +/- 10 mm Hg. The difference between these results and the preoperative values (27 +/- 9 mm Hg) were statistically significant after 6 and 9 months (p < 0.001). Despite frequent choroidal detachments (20 eyes), the visual acuity recovered during the follow-up to the preoperative values. CONCLUSIONS: In patients with uncertain prognosis for the intraocular pressure after trabeculectomy, the intraoperative application of Mitomycin C seems to improve considerably the operative success rate.

Adult↗
PubMed1994

Comparison of the severity of normal-tension glaucoma in men and women.

To determine whether damage in normal-tension glaucoma is more pronounced in men or in women, we analyzed visual-field damage, intraocular pressure, age, frequency of acral vasospastic reaction on local cooling, and frequency of headache in 28 consecutive patients with newly diagnosed normal-tension glaucoma. The difference between genders with regard to mean visual-field defect was significant (9.4 +/- 1.3 dB in men and 6.7 +/- 1.0 dB in women; p = 0.034). This difference could not be explained by other variables. Because the population tested was relatively young, this study suggests normal-tension glaucoma to be more severe in men, in an earlier stage of the condition.

Female↗
PubMed1994

Optic disc cupping in arteritic anterior ischemic optic neuropathy.

Patients with anterior ischemic optic neuropathy due to giant cell arteritis are thought to develop optic disc cupping, resembling that seen in glaucomatous eyes, while such cupping does not seem to occur in nonarteritic anterior ischemic optic neuropathy. However, this remains controversial. We describe a patient with arteritic anterior ischemic optic neuropathy (the clinical diagnosis was confirmed with a biopsy from the temporal artery) who developed disc cupping within 4 months after acute episode. This patient never had elevated intraocular pressure, and prior to the acute event the optic nerve heads had had a normal appearance with a physiologic cup.

Aged↗
PubMed1993

Osmotic stress in an in vitro model of the outer blood-retinal barrier.

Because of the difficulty involved in in vivo experimental manipulations of the outer blood-retinal barrier, we developed an in vitro model. Retinal pigment epithelium (RPE) from bovine eyes was grown on semipermeable membranes. A continuous monolayer of RPE developed a measurable transepithelial electrical resistance (TER). TER was used as a parameter of barrier function. The tightness of the cellular monolayer was also tested with fluorescein. The TER increased in confluent cultures by 60-70 ohms-cm2, and there was no fluorescein leakage. After exposure of the cultures to 0.2% trypsin or 1% ethylenediaminetetraacetic acid (ETDA), we detected a reversible breakdown of the epithelial barrier function. Under transmission electron microscopy, we detected no disassembly of the junctional components after breakdown of the barrier function with trypsin or EDTA. A hyperosmotic NaCl solution in the basal medium as well as a hypoosmotic NaCl solution in the apical medium induced a breakdown in the TER, whereas a hyperosmotic NaCl solution in the apical medium induced only a slight decrease in the TER. Under transmission electron microscopy, we detected an intracellular blistering and large intercellular widening. A hypo-osmolar NaCl solution in the basal medium induced a rise in the TER. With regard to these experiments, it seems, at least in vitro, that the function of occluding junctions in bovine RPE as permeability barriers depends on extracellular calcium. Furthermore, our results were such as if the outer blood-retinal barrier were designed to prevent subretinal inflow of free water.

Animals↗
PubMed1992

[Model experiments of the outer blood-retinal barrier in vitro].

Because of the difficulty in conducting experiments on the outer blood-retinal barrier in vivo, we developed an in vitro model. Bovine retinal pigment epithelial cells were grown on semipermeable membranes, enabling separate manipulation of the apical and basal medium. As a parameter of barrier function, we measured the transepithelial resistance (TER). Barrier function was also tested with fluorescein. The transepithelial resistance increased under optimal culture conditions, in confluent cultures, by 200 omega and there was no fluorescein leakage. After exposure to trypsin in Ca/Mg-less medium or EDTA or after application of argon laser, we were able to induce a breakdown of the TER and fluorescein leakage. This happened immediately after laser exposure, 1 min after EDTA, and 4 min after trypsin application. We observed no morphological differences after breakdown of the barrier function on the intercellular connections compared to normal confluent cultures following EDTA or trypsin exposure. In all experiments there was a recovery of barrier function after returning the cells to control conditions. These first results demonstrate that our in vitro model is a sensitive method for investigating barrier function in retinal pigment epithelium in cell culture.

Animals↗
PubMed1991

[Simultaneous corneal transplantation in mucopolysaccharidosis].

We report the case of a 14 year old girl who obtained simultaneous penetrating keratoplasty for corneal opacity with functional loss as a consequence of a mucopolysaccharidosis typ Hurler/Scheie. Postoperatively, the host cornea displayed partial clearing. We discuss mechanisms possibly involved.

Adolescent↗
PubMedDate not supplied

The influence of sex difference in measurements with the Langham Ocular Blood Flow System.

PURPOSE: To assess sex difference and parameters possibly accounting for such a difference in healthy subjects evaluated by means of the Langham Ocular Blood Flow (OBF) System. METHODS: Pulse amplitude of intraocular pressure (IOP) and pulsatile ocular blood flow (POBF) as measured with the Langham OBF System were assessed in 86 healthy men and 69 healthy women. RESULTS: Compared to men, women showed higher POBF (mean +/- SD: 722.6 +/- 152.8 versus 647.8 +/- 164.9 microL/min; P =.0056) and pulse amplitude (mean +/- SD: 2.3 +/- 0.7 versus 2.0 +/- 0.6 mm Hg; P =.0043) values. Sex difference was still significant after correcting for age, refraction, blood pressure, IOP, and pulse rate. Pulse amplitude correlated negatively with pulse rate, and POBF correlated negatively with IOP. Women had higher readings in pulse amplitude and POBF, even after correcting for age, refraction, IOP, blood pressure, and pulse rate. CONCLUSIONS: While using the Langham OBF System, one needs to be aware of sex difference that is independent of other hemodynamic parameters. How the observed difference in POBF is related to ocular blood flow, and how it might influence the preponderance of various ocular diseases in men or women remains to be clarified.

Adolescent↗