Optical coherence tomography based microangiography for quantitative monitoring of structural and vascular changes in a rat model of acute uveitis in vivo: a preliminary study

Uveitis models in rodents are important in the investigation of pathogenesis in human uveitis and the development of appropriate therapeutic strategies for treatment. Quantitative monitoring of ocular inflammation in small animal models provides an objective metric to assess uveitis progression and/or therapeutic effects. We present a new application of optical coherence tomography (OCT) and OCT-based microangiography (OMAG) to a rat model of acute anterior uveitis induced by intravitreal injection of a killed mycobacterial extract. OCT/OMAG is used to provide noninvasive three-dimensional imaging of the anterior segment of the eyes prior to injection (baseline) and two days post-injection (peak inflammation) in rats with and without steroid treatments. OCT imaging identifies characteristic structural and vascular changes in the anterior segment of the inflamed animals when compared to baseline images. Characteristics of inflammation identified include anterior chamber cells, corneal edema, pupillary membranes, and iris vasodilation. In contrast, no significant difference from the control is observed for the steroid-treated eye. These findings are compared with the histology assessment of the same eyes. In addition, quantitative measurements of central corneal thickness and iris vessel diameter are determined. This pilot study demonstrates that OCT-based microangiography promises to be a useful tool for the assessment and management of uveitis in vivo.

Therapeutic efficacy of intravitreal bevacizumab on posterior uveitis complicated by neovascularization

PURPOSE

To evaluate the therapeutic effect of intravitreal bevacizumab in patients with uveitis-associated choroidal/retinal neovascularization.

METHODS

Two female patients (40 years, 15 years) with posterior uveitis, (one presumed ocular sarcoidosis, one lupus) were evaluated for neovascularization of the posterior segment. Both patients were given a single dose of 1.25 mg intravitreal bevacizumab.

RESULTS

Significant anatomical and functional recovery was evident in both patients within a few weeks.

CONCLUSION

In selected uveitic patients, bevacizumab may be an option for managing neovascularization.

[The specific features of delivery in women with gestosis and myopia]

The treatment option for retinal degeneration, including peripheral vitreochorioretinal degenerations, was performed in 415 pregnant females (including 25 healthy pregnant females); it differed in patients with myopia and gestosis at labor and in the postpartum period in the fact that regularity was first revealed at labor: increases in cardiac output and cerebral circulation index and a decrease in uveal tract blood filling (rheographic quotient, Rq) from 1.78 to 0.5-0.7 per thousand. This results in retinal tissue hypoxia and dystrophy to give rise to free radical oxidation products. The treatment is that vasodilators increasing uveal tract blood filling by 0.9 per thousand are intravenously injected. Prolonged epidural anesthesia used during administrations of spasmolytics and vasodilators additionally shows a 0.9 per thousand increase in Rq in parturients with myopia and gestosis. Antioxidants that inhibit free radical oxidation products are used in the lipoprotein complexes of retinal cells and retinal degeneration are prevented and treated.

[An application of Color Doppler ultrasonography in evaluate of brachytherapy in patients with uveal melanomas]

Uveal melanomas, even those of big size, are recently more readily treated conservatively, with radiotherapy, though the efficiency of this treatment has not been yet established.

PURPOSE

Of the study was the assessment of the usefulness of Color Doppler (CD) or Power Doppler (PD) examination in monitoring the effectiveness of brachytherapy in the management of melanomas.

MATERIAL AND METHODS

Examination was performed in 15 patients, who were treated because of medium size or large uveal melanomas, with plaque radiation (brachytherapy). CD/PD examination of blood flow within the tumor, with the use of SonoVue contrast agent in several cases, was performed before institution of the therapy and two times after the treatment, as follow-up.

RESULTS

Regression of the tumor and gradual atrophy of its neovascularisation was observed in all the examined patients. The enhancement of Color Doppler imaging with contrast agent helps in making decision to further therapeutic options as complex situation.

CONCLUSIONS

Color and Power Doppler ultrasonography is a helpful method in monitoring the effectiveness of brachytherapy in patients with uveal melanomas.

Human endothelial cells express NOD2/CARD15 and increase IL-6 secretion in response to muramyl dipeptide

Mutations in the human NOD2/CARD15 gene cause Blau syndrome, an autoinflammatory disorder involving the joints, skin and eyes. Insights into the mechanism of this association may be gained by a further understanding of where NOD2 is expressed. The objective of this study was to analyze ocular endothelial cells for NOD2 expression. Human ocular tissue was analyzed by immunohistology using anti-NOD2 antisera. RNA isolated from iris, choroid and endothelial cell lines was analyzed by reverse transcription-PCR and real-time quantitative PCR. Gene regulation was studied by treating endothelial cells with TNF-alpha and IFN-gamma. Functional responses were assessed by measuring IL-6 release from endothelial cells treated with muramyl dipeptide (MDP), synthetic lipopeptide (Pam3CSK4) and lipopolysaccharide (LPS). Immunohistological analysis revealed staining of endothelial cells in the uveal tract. NOD2 expression was detected in primary ocular endothelial cell cultures, and levels increased in response to inflammatory cytokines. Endothelial cells from choroid demonstrated enhanced release of IL-6 in response to MDP, and synergy was observed following treatment with MDP and either Pam3CSK4 or LPS. The observations that endothelial cells express NOD2, upregulate NOD2 in response to stimuli known to promote NOD2 expression and show synergistic cytokine responses to MDP and TLR ligands previously shown to be mediated by NOD2 are informative since they may be relevant to pathogenic mechanisms leading to the spectrum of inflammation seen in Blau syndrome.

[Clinicopathological study on suprachoroidal and supraciliary hemorrhage during enucleation]

PURPOSE

To investigate the pathogenesis of suprachoroidal and supraciliary hemorrhage that might have been induced during enucleation.

METHODS

A histopathological examination of 392 enucleated eyeballs was carried out and 8 eyeballs with suprachoroidal and supraciliary hemorrhage were selected for further clinicopathological examination.

RESULTS

Among 14 eyeballs with severe acute intraocular inflammation, 7 eyeballs with suprachoroidal and supraciliary hemorrhage were found and one other such eyeball was seen among 53 with neovascular glaucoma. Among these 8, there was one case of prolapse of intraocular tissue with severe hemorrhage into the suprachoroidal and supraciliary spaces; 4 cases of severe hemorrhage into the suprachoroidal and supraciliary spaces without prolapse of intraocular tissue; and 3 cases of mild hemorrhage into the suprachoroidal or supraciliary spaces.

CONCLUSIONS

In the eyeballs with severe acute intraocular inflammation, intraocular pressure was elevated and the blood vessels were weakened by inflammatory cell infiltration. During enucleation external forces affected the blood vessel wall of the ciliary arteries and vortex veins, and the breakdown of vessel walls might have been the cause of the suprachoroidal and supraciliary hemorrhage.

Visualization of uveal perfusion by contrast-enhanced harmonic ultrasonography at a low mechanical index: a pilot animal study

OBJECTIVE

To evaluate contrast-enhanced harmonic ultrasonography at a low mechanical index for its usefulness in visualizing uveal perfusion.

METHODS

The study was performed with 9 rabbits, 6 intact and 3 with focal impaired blood flow in the uvea. Ultrasonography was performed by harmonic imaging (transmit, 5 MHz; receive, 10 MHz) with a contrast agent. The agent was administered at a dose of 50 microL/kg. Transmission power was at a mechanical index of 0.2, which is below the US Food and Drug Administration guideline. The images were compared between the impaired and intact eyes. For uveal measurements, video signal intensity-versus-time plots were generated in all cases. The plots were analyzed to obtain the rate of signal intensity increase and peak signal intensity.

RESULTS

A clear increase of signal intensity was observed after contrast agent administration. The signal intensity of the uvea was lower in the impaired eye than in the intact eye. In the impaired eye, the intensity was lower on the side with impaired flow than on the other side. The differences were significant.

CONCLUSIONS

Our findings suggest that uveal perfusion can be visualized by contrast-enhanced harmonic ultrasonography in the harmonic imaging mode at a low mechanical index.

Ocular neovascularization in patients with uveitis

Neovascularization is an infrequent but serious complication of uveitis. The retina and optic disk appear to be affected most often, although new blood vessels may arise from the iris, ciliary body, and choroid as well. Although neovascularization can usually be identified on careful clinical examination, some patients may require fluorescein angiography or UBM. Numerous neovascular growth and inhibitory factors have been identified experimentally. Clinically, however, uveitic neovascularization appears to be determined most directly by the severity of the inflammation and the presence of retinal nonperfusion. Virtually all patients with uveitic neovascularization deserve a trial of local or systemic corticosteroids. Laser photocoagulation can be considered in those patients who fail to respond to corticosteroid therapy, but only when retinal nonperfusion has been demonstrated on fluorescein angiography. Surgical excision of newly formed vessels is reserved for selected patients with CNV and uveitis, but should only be considered when corticosteroids and focal photocoagulation are ineffective or are otherwise contraindicated.

Regulation of uveal and retinal blood flow in STZ-diabetic and non-diabetic rats; involvement of nitric oxide

PURPOSE

In experimental and human diabetes mellitus evidence for an impaired function of the vascular endothelial cells has been found. The purpose of the present experiments was to measure uveal and retinal blood flow and vascular resistance at an early stage of experimental diabetes mellitus and to evaluate the effects of acetylcholine and L-arginine in control and L-NAME-pretreated animals.

METHOD

The radioactively labelled microsphere method was applied to normal Sprague-Dawley rats and rats with STZ-induced diabetes of three weeks duration.

RESULTS

In the present study, similar blood flow and vascular resistance were observed in the uvea of normal and STZ-diabetic rats. Evidence for a basal vasodilating NO-tone was found both in the uvea and in the retina of both groups. In the normal rats as well as in the diabetic animals, acetylcholine induced choroidal vasodilation. Local blood flow increased from 54 +/- 17 to 142 +/- 32 mg x min(-1) in normal rats and from 57 +/- 18 to 112 +/- 23 mg x min(-1) in diabetic rats (P < 0.05 respectively). No hemodynamic changes were observed in the anterior uvea, demonstrating a difference in reactivity between these vascular beds. In animals pretreated with the NO-synthase inhibitor L-NAME, acetylcholine did not significantly affect local blood flow in the choroid, suggesting NO as a mediator of the vasodilation.

CONCLUSION

The results indicate a normal action of NO in the ocular vascular beds at this stage of experimental diabetes mellitus in the rat.

Sympathetic vasoconstriction in the rat anterior choroid is mediated by alpha1-adrenoceptors

These experiments were undertaken in an attempt to use laser-Doppler flowmetry to measure anterior choroidal blood flow in the anesthetized rat and to study the mechanism by which sympathetic nerve stimulation might produce vasoconstriction in this vascular bed. Electrical stimulation of the preganglionic cervical sympathetic nerve produced reproducible, frequency-related ocular vasoconstrictor responses with maximal vasoconstriction seen at about 32 Hz. Ocular vasoconstrictor responses were blocked by intravenous treatment with the nonselective alpha-adrenoceptor antagonists, phentolamine (5 mg kg(-1)) and phenoxybenzamine (2 mg kg(-1)), as well as with the selective alpha1-adrenoceptor antagonist, prazosin (0.3 mg kg(-1)). In contrast, the selective alpha2-adrenoceptor blocker, rauwolscine (0.5 mg kg(-1)), only potentiated the vasoconstriction. Neither intravenous atropine (1 mg kg(-1)) nor propranolol (1 mg kg(-1)) altered the magnitude of neurally evoked vasoconstriction. These results demonstrate the usefulness of laser-Doppler flowmetry in studies of the rat anterior choroidal circulation and suggest that adrenergic neurogenic vasoconstriction in the anterior segment of the rat eye is mediated almost exclusively by alpha1-adrenoceptor mechanisms.

Nitric oxide modulation of retinal, choroidal, and anterior uveal blood flow in newborn piglets

The purpose of the present study was to investigate the role of nitric oxide (NO) in modulating the resting vascular tone of the choroidal and anterior uveal circulations and the autoregulatory gain of the retina. Blood flow (ml/min/100 gm dry weight) to tissues was determined in 23 anesthetized piglets (3-4 kg) using radiolabelled microspheres. Ocular Perfusion Pressure (OPP) was defined as mean arterial pressure minus intraocular pressure (IOP) which was manipulated hydrostatically by cannulation of the anterior eye chamber. The OPP was decreased during intravenous infusion (30 mg/kg/hr) of either the NO-synthase inhibitor L-NAME or the inactive enantiomer D-NAME. Blood flows were determined at OPP of 60, 50, 40, 30, and 20 mmHg following initial ocular blood flow measurements. Mean initial choroidal and anterior uveal blood flows with L-NAME showed a 47+/-12% and a 43+/-6% reduction (p <.001), respectively. Mean choroidal blood flows were significantly reduced (p<.01) in the L-NAME treated animals at an OPP of 60 and 50 when compared to D-NAME. Uveal blood flows were linearly correlated with OPP in the L-NAME and D-NAME treated groups. Uveal blood flow was greater following exogenous administration of L-arginine (180 mg/kg). Mean initial retinal blood flow did not differ significantly in either group. Retinal blood flow with L-NAME was reduced at OPP of 60 mmHg and below compared to D-NAME (p<.05). The degree of compensation in the autoregulatory gain of the retinal vasculature was reduced in the presence of L-NAME at an OPP of 50 mmHg and below compared to D-NAME. These data support the hypothesis that NO may be a primary mediator in maintaining resting vascular tone to the choroid and anterior uvea in vivo and that NO blockade reduces the degree of compensation in the autoregulatory gain of the retinal vasculature within a specific range of ocular perfusion pressures.

Light microscopy of uveoscleral drainage routes after gelatine injections into the suprachoroidal space

PURPOSE

To visualize the suprachoroidal space and to study the morphology of possible uveoscleral drainage routes in the human eye.

METHODS

Indian ink stained gelatine was injected directly into the suprachoroidal space of 7 human donor eyes. Those quadrants where gelatine appeared in the episcleral venous network were cut in their entirety in consecutive sections and examined by light microscopy.

RESULTS

Gelatine was observed in the connective tissue surrounding scleral vessels and nerves. Gelatine was also traceable in fine, endothelium-lined channels at the inner aspect of the anterior sclera. These channels seemed to originate at the inner surface of the sclera, close behind the scleral spur, and communicate with the intrascleral venous plexus.

CONCLUSION

Fluid is drained from the suprachoroidal space through the perivascular and perineural spaces of scleral blood vessels and nerves. In addition, this study indicates that there are preformed channels at the inner aspect of the anterior sclera, capable of draining fluid directly into scleral veins.

Effects of topical nipradilol, a beta-blocking agent with alpha-blocking and nitroglycerin-like activities, on aqueous humor dynamics and fundus circulation

PURPOSE

To study the effects of nipradilol, a nonselective beta-blocker with alpha 1-blocking activity and nitroglycerin-like activity, on aqueous humor dynamics and optic nerve head (ONH) circulation in albino rabbits.

METHODS

Experiments were carried out during the dark phase, in conscious rabbits conditioned to a schedule of alternating 12-hour periods of light and dark. The blood-aqueous barrier permeability and the aqueous flow rate were determined fluorophotometrically. The effect on outflow to general blood circulation and uveoscleral outflow were determined by using the fluorophotometric Diamox technique, and the effect on the uveoscleral outflow was further assessed by using the anterior chamber perfusion method. The ONH circulation was estimated by using the laser speckle method.

RESULTS

Unilateral topical administration of 0.25% nipradilol solution lowered intraocular pressure (IOP) with relatively weak contralateral effects in a dose-dependent manner with a maximum reduction of 6 mm Hg and an effect duration of 6 hours. Twice-daily instillation for 14 days showed no attenuation of the effects. Single instillation of 0.25% nipradilol showed no significant effect on blood-aqueous barrier permeability and decreased aqueous flow rate in the treated eye (17%; P < 0.01) and in the contralateral eye (9%, P < 0.05). Nipradilol produced no significant effect on outflow facility to general blood circulation, whereas it substantially increased uveoscleral outflow. Twice-daily 0.25% nipradilol instillation increased ONH tissue blood velocity by 13% (P < 0.01), which was probably attributable to locally penetrating drug.

CONCLUSIONS

Because of its ability to lower IOP and to increase uveoscleral outflow and optic nerve head circulation in rabbits, further studies are warranted to determine whether nipradilol has potential as an antiglaucoma agent in humans.

Endothelium-dependent vasodilation in the uvea of hypertensive and normotensive rats

PURPOSE

The effects of endothelium-related substances such as acetylcholine, a stimulator of endogenous NO-production, the NO-synthesis inhibitor L-NMMA, the exogenous NO-donor sodium nitroprusside and the endothelin (ET)A-receptor antagonist BQ123, on uveal blood flow were investigated in normotensive and hypertensive SHR rats.

METHOD

The radioactively-labelled microsphere method was applied for the measurement of regional blood flow in the uvea.

RESULTS

Under resting conditions, local blood flow was lower in the hypertensive animals. The increase in choroidal blood flow (145 +/- 50%; P < 0.01) and reduction in vascular resistance (-58 +/- 7%; P < 0.01) observed in the WKY after i.v. infusion of acetylcholine, 2 micrograms x kg bw-1 x min-1, were significantly less pronounced in animals pretreated with L-NMMA, indicating local formation of NO as a vasodilator mechanism. In contrast, acetylcholine did not induce significant vasodilation in the choroid of SHR rats. In the anterior uvea of both strains, acetylcholine did not affect local blood flow. L-NMMA, 20 mg x kg bw-1, alone reduced blood flow in the entire uvea of both strains. Intravenous injection of BQ123, 1 mg x kg bw-1, did not affect regional blood flow in the uvea of WKY or SHR animals. Infusion of acetylcholine following ETA-receptor blockade induced vasodilation in both the choroid and anterior uvea in the WKY but not in the SHR.

CONCLUSIONS

Acetylcholine-stimulated NO-mediated vasodilation, but not basal NO-formation, was impaired in the choroid of the SHR. Furthermore, an interaction between vasoconstricting ET and acetylcholine was found in the anterior uvea of normotensive but not hypertensive rats.

Nitric oxide as a mediator of parasympathetic vasodilation in ocular and extraocular tissues in the rabbit

PURPOSE

The aim of this study was to investigate in rabbits the relationship between nitric oxide and the noncholinergic vasodilation caused by facial nerve stimulation in the eye and some extraocular tissues.

METHODS

Uveal vascular resistance was determined by measuring simultaneously the flow from a cannulated vortex vein with intraocular pressure and arterial blood pressure recordings. The local blood flow in different parts of the eye (iris, ciliary body, choroid, and retina), eyelids, nictitating membrane, Harderian gland, and lacrimal gland was determined using radioactive microspheres. The effects of facial nerve stimulation, at different frequencies, were examined before and after the administration of nitric oxide synthase (NOS) inhibitors.

RESULTS

In the experiments with direct determination of uveal blood flow, stimulation of the facial nerve caused a frequency-dependent decrease in uveal vascular resistance, indicating vasodilation. This effect was reduced or abolished by NOS inhibition at low frequencies but was unaffected at high frequencies. Determination of regional blood flow, with radioactive microspheres, showed that the stimulation increased local blood flow in all parts of the uvea. Compared to the nonstimulated control side, stimulation at 2 Hz increased choroidal blood flow by 89% +/- 12% before NOS inhibition and by 45% +/- 10% after NOS inhibition, a difference of 44% +/- 77% (n = 9; P < or = 0.05). Iris and ciliary body vasodilation appeared to be equally reduced. In eyelids, Harderian gland, and lacrimal gland, the vasodilation elicited by stimulation at 2 Hz was abolished almost completely by NOS inhibition. The vasodilation in most of the extraocular tissues was reduced significantly by NOS inhibition at 5 Hz, with only a slight reduction in the choroid, iris, and ciliary body. Retinal blood flow also was significantly increased by facial nerve stimulation at 2 Hz and 5 Hz. The increase in retinal blood flow appeared to be more sensitive to NOS inhibition than the increase in uveal blood flow.

CONCLUSIONS

These results suggest that the formation of nitric oxide plays an important role in the uveal, retinal, and extraocular vasodilation brought about by facial nerve stimulation at low frequencies. At high frequencies, other neurotransmitters also seem to be involved.

Ipsilateral facial and uveal arteriovenous and capillary angioma, microphthalmos, heterochromia of the iris, and hypotony: an oculocutaneous syndrome simulating Sturge-Weber syndrome

Sturge-Weber syndrome is a disorder characterized by ipsilateral cavernous hemangioma of the face, uvea, and brain in patients who may present with an enlarged eye, exudative retinal detachment, glaucoma, and seizures. This report presents the clinicopathologic findings of an otherwise healthy infant with ipsilateral arteriovenous and capillary hemangiomas of the face and uveal tract, microphthalmos, iris heterochromia, hypotony, and absence of central nervous system involvement. The association of an arteriovenous-capillary angioma of the ocular adnexa and ipsilateral uveal tract is a syndrome that is distinct from Sturge-Weber syndrome.

Effect of nitric oxide synthase inhibition on blood flow after retinal ischemia in cats

PURPOSE

To determine the effect of nitric oxide synthase inhibition on blood flow in the cat retina and on changes in the electroretinogram after 1 hour of ocular ischemia.

METHODS

After the induction of general anesthesia, one eye in each of 18 cats was subjected to 60 minutes of ischemia by raising intraocular pressure above systolic arterial pressure. One group (n = 9) was administered 30 mg/kg L-NG-nitro-arginine-methylester (L-NAME) intravenously 60 minutes before ischemia. The other group (n = 9) was administered an equivalent volume of saline intravenously. Five minutes after the end of ischemia, blood flow in the retina, choroid, and iris-ciliary body was measured using injections of radioactively labeled microspheres. Electroretinographic studies were carried out before, during, and 1, 2, 3, and 4 hours after ischemia ended. Arterial blood gas tension, systemic arterial pressure, hematocrit, and anesthetic levels were controlled in each experiment.

RESULTS

Basal blood flow in iris-ciliary body was decreased by L-NAME, whereas retinal and choroidal blood flow was unchanged. Postischemic hyperemia was unaltered in the choroid and reduced in the retina. There was enhancement of postischemic hyperemia in the iris-ciliary body, but this effect may have resulted from a decrease in basal flow in the L-NAME group. Electroretinographic a- and b-wave recoveries were not altered by L-NAME; L-NAME infusion significantly decreased b-wave amplitude.

CONCLUSIONS

Nitric oxide appears to be a significant factor in the regulation of uveal circulation and may contribute to the regulation of retinal, but not choroidal, blood flow after ischemia. The authors could not detect a difference in outcome by electroretinography with or without nitric oxide synthase inhibition.

[Nitrergic reactivity in endothelial cells of human uveal blood vessels]

BACKGROUND

We investigated the presence of Nicotinamid-adenin-dinucleotid-phosphat (NADPH)-diaphorase activity in endothelial cells of the human uveal vessels, using a histochemical procedure which presumably localizes the reaction product nitric oxide.

MATERIAL AND METHODS

11 donor eyes destined for corneal transplantation (male: 6; female: 5; age: 56 +/- 8 years) were used within 14 +/- 7 h postmorten. After removal of the cornea and retinal pigment epithelium, flat mounts of the choroid were made. Serial sections, 12-16 microns in thickness were cut from the ciliary body and iris using a cryomicrotome. Sections mounted on chromalaun-gelatine-coated glass slides, treated according the standard NADPH-diaphorase reaction and finally mounted in Kayser's glycerol-gelatine prior to examination in the light microscope.

RESULTS

Human choroidal vascular endothelial cells revealed positive NADPH-diaphorase activity, which was detected by the presence of punctate blue staining in the cytoplasm. No significant difference in distribution pattern or area density was seen amongst small and large vessels in either choroid, ciliary body or iris. Ganglion cells in the choroid and ciliary body also exhibited NADPH-diaphorase reactivity.

CONCLUSION

The presence of NADPH-diaphorase reactivity in vascular endothelial and ganglion cells of the human choroid suggests a possible nitrergic relaxation mechanism in human uveal vasculature.

[Hypothermic effects on uveal blood flow and postoperative inflammation in vitrectomy]

Hypothermic effects on uveal blood flow and postoperative inflammation were evaluated in experimental vitrectomy on albino rabbits. Solutions used for intraocular perfusion were maintained at 9 degrees C and 22 degrees C. Following the vitrectomy, the rabbits' intraocular spaces were irrigated for 60 minutes. The temperature at various sites and the uveal blood flow were measured before and during the procedure. Aqueous protein concentrations were checked on postoperative days 1, 7, and 14. Another solution maintained at 37 degrees C was used as a control. There was a larger decrease in temperature at the retina than there was at the choroid and the ciliary body. Blood flow at the ciliary body decreased to 76.0% and 77.0% at the choroid after 60 minutes of irrigation at 9 degrees C. The decrease at 22 degrees C were 91.0% and 88.3%, respectively. Aqueous protein concentrations at both 9 degrees C and 22 degrees C were significantly lower than at 37 degrees C on the first postoperative day in the eyes irrigated for 60 minutes. In the eyes irrigated for 30 minutes, however, no significant differences were seen. Hypothermia during a prolonged vitrectomy operation seems to decrease inflammation in early postoperative stages.

Ocular macro- and microcirculation after topical application of clonidine and metipranolol

We investigated the effect of clonidine (Isoglaucon, an alpha-agonist) and metipranolol (Betamann, a beta-antagonist) on the blood flow in the ophthalmic artery and the anterior uvea of 40 young, healthy volunteers (mean age, 23.5 +/- 2 years) in a prospective, randomized simple blind study. The blood flow in the iris and ciliary body was detected by laser-Doppler flowmetry (bpm, 403a; TSI; wavelength, 780 nm; power, < 1.6 mW). The blood flow in the ophthalmic artery was measured by pulsed Doppler sonography (4 MHz, EME). The blood pressure, pulse respiration, and intraocular pressure (IOP) were recorded. Vascular resistance (RF) was calculated by the equation RF = (RRmean--IOP)/blood flow. Group 1 was treated with a single drop of Betamann (3 mg/ml) applied topically, and group 2 was treated with Isoglaucon (2.5 mg/ml). Measurements were made before and 30 min after application. Both drugs significantly lowered the IOP by about 7% (P = 0.01). Clonidine did not affect the blood velocity in the ophthalmic artery. In group 2 (metipranolol) we found a significant increase in the blood velocity in the ophthalmic artery during the diastolic period (from 11.0 +/- 3.7 to 11.9 +/- 2.2 cm/s, P = 0.05). Both clonidine and metipranolol decreased the iridal blood flow [clonidine, from 9.3 +/- 3.9 to 7.6 +/- 3.1 (flux), P = 0.05; metipranolol, from 7.5 +/- 2.9 to 6.5 +/- 2.6 (flux), P = 0.05]. Vascular resistance in the iris increased under the effect of clonidine (P = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of a tapered, blunt, bipolar cautery tip for trabeculectomy

A bipolar cautery instrument with a tapered, blunt tip has been developed for glaucoma filtering surgery. Evaluated in 30 consecutive trabeculectomy procedures, the instrument proved suitable for all aspects of the operation. The narrow, 23-gauge shaft and tapered, blunt tip allowed gentle, pin-point coagulation of individual bleeders, as well as cauterization of tracks of tissue in a continuous motion. The unit was effective for external cauterization of conjunctival and scleral vessels, as well as for internal cauterization of anterior uveal tissue.

L-arginine-derived nitric oxide: a major determinant of uveal blood flow

The effect of inhibition of the L-arginine-nitric oxide pathway on regional ocular blood flow was studied in anaesthetized Beagle dogs. Under control conditions (mean arterial blood pressure 105 +/- 6 mmHg) trapping of 11 and 15-microns-diameter tracer microspheres revealed the following regional blood flows (ml min-1 g-1): retina 0.065 +/- 0.016, choroid 5.72 +/- 0.32, ciliary body 0.77 +/- 0.11, iris 0.18 +/- 0.04. After i.v. infusion of nitro-L-arginine methylester (20 mg kg-1), a potent inhibitor of nitric oxide production from L-arginine, mean arterial blood pressure increased from 105 +/- 6 mmHg by 19% to a new steady-state level of 125 +/- 7 mmHg. This increase of arterial blood pressure extended over 3 hr and was reversible after i.v. infusion of L-arginine (100 mg kg-1 over 10 min). Despite the increase in blood pressure following infusion of nitro-L-arginine methylester blood flow of choroid, ciliary body, and iris were significantly decreased by 40, 40 and 48%, respectively. Retinal blood flow did not change significantly (-12%). These results suggest that the L-arginine-nitric oxide pathway is of major importance for the adjustment of uveal blood flow under resting physiological conditions.

The bovine arterially-perfused eye: an in vitro method for the study of drug mechanisms on IOP, aqueous humour formation and uveal vasculature

A method is reported in which the isolated bovine eye is perfused through a long posterior ciliary artery with buffered physiological saline, to provide simultaneous monitoring of drug effects on intraocular pressure (IOP), vascular resistance and the condition of the blood-aqueous barrier. With perfusion under constant pressure of 45 mm Hg, perfusate flows at 1.64 +/- 0.12 ml.min-1 (mean +/- SEM) and IOP is 7.26 +/- 0.16 mm Hg. Applying a constant flow rate of 2.25 ml.min-1, IOP averages 10.19 +/- 0.32 mm Hg and in both cases this can be maintained for around 2h. Increasing the perfusion flow rate from 1.5 to 3.5 ml.min-1 produces a 76% rise in perfusion pressure but IOP increases only insignificantly (< 10%). The inclusion in the perfusion fluid of dextran and albumin to maintain oncotic pressure similar to that of plasma makes no difference to the IOP achieved and does not affect the leakiness of the barrier. The preparation shows a net consumption of oxygen, supporting the hypothesis that the aqueous humour formed is secreted by active transport processes. Timolol (in bolus doses of 1-300 nmol) injected into the perfusing fluid is shown to induce a dose-dependent fall in IOP within 5 min, reaching a steady state within 40 min. Timolol, however, causes no significant change in vascular resistance, whether this is measured as perfusion flow rate under constant pressure or as perfusion pressure at constant flow rate, nor does it alter the permeability of the barrier. Other beta-blockers such as oxprenolol and betaxolol also induce dose-dependent decreases in IOP. By applying a fluorescein dilution technique, it is found that the aqueous formation rate (K(out) = 0.0046 min-1, or 12.9 microliters.min-1) is also reduced by timolol and, in a dose-dependent manner, by the new carbonic anhydrase inhibitor, MK-927. The bovine perfused eye offers a useful method for studying the mechanisms of action of drugs on IOP and aqueous humour formation, in isolation from the complicating influences of the CNS and the cardiovascular system and without the necessity to kill animals for experimental purposes.

[Experimental study on local cooling of the eyeball in ocular surgery (4). The local cooling effect on uveal blood circulation, intraocular pressure, and intravitreous pressure]

The effects of local cooling on the uveal blood circulation, intraocular pressure, and intravitreous pressure were evaluated. Saline solutions maintained at 10 degrees C and 35 degrees C were dripped on the rabbit ocular surface. After 5-minute dripping of 10 degrees C saline solution, the temperature decreased by 10.6 degrees C at the ciliary body, 7.7 degrees C at the choroid and 2.9 degrees C at the central region of the vitreous. Hydrogen clearance with electrolytically generated hydrogen gas was employed to measure the tissue blood flow, which fell to 82.9% of normo-thermal value at the ciliary body and 86.3% at the choroid. The intravitreous pressure dropped by 2.8 mmHg. After 30-minute dripping of 10 degrees C saline solution, the intraocular pressure dropped by 3.0 mmHg. We consider that the reduction of intraocular and intravitreous pressure during local cooling of the ocular surface is related to decrease in the uveal blood flow.

[Prostaglandins as ocular hypotensive drugs]

Prostaglandins can lower intraocular pressure when they are applied topically to the eye. This pressure-lowering effect is mediated by enhancement of uveoscleral outflow. Human ciliary muscle has binding sites (receptors) for prostaglandins and the EP2 receptor subtype is the predominant prostanoid receptor found in this muscle. Prostaglandins are thought to bind to these receptors located on the ciliary muscle, induce its relaxation, and promote the uveoscleral outflow. It is important to know the receptor type involved in the pressure reduction to design a new drug with less adverse effect and more potency.

Glibenclamide and L-NG-nitro-arginine methyl ester modulate the ocular and hypotensive effects of calcitonin gene-related peptide

Calcitonin gene-related peptide (CGRP) given i.v. to rabbits induced hypotension and a breakdown of the blood-aqueous barrier. Glibenclamide, a blocker of ATP-sensitive K+ (K+ATP) channels antagonized both these effects. The K+ATP channel opener diazoxide reduced blood pressure but did not damage the blood-aqueous barrier. Inhibition of nitric oxide synthase antagonized the effects of CGRP on the blood-aqueous barrier but did not attenuate the hypotensive response. The results suggest that vasodilatation induced by the opening of K+ATP channels is a prerequisite for the effect of CGRP on the blood-aqueous barrier.

Calculation of the pulsatile ocular blood flow

Based on reasonable assumptions, it is theoretically possible to determine the pulsatile ocular blood flow. The pertinent parameter is not the pulse amplitude but the steepest decay value of record (ie, the minimum of dV(t)/dt). Some advantages of developing the record in Fourier series are discussed. The importance of careful analysis of the recording system is stressed.

An ocular renin-angiotensin system. Immunohistochemistry of angiotensinogen

The circulating renin-angiotensin system (RAS) is an important determinant in maintaining adequate systemic blood pressure, and it also may modify organ-specific blood flow. All recognized RAS components have been identified in the eye. In this study, angiotensinogen (ANG) was localized using an affinity-purified antibody and paraffin sections of seven human eyes. An antibody for human serum albumin was used for comparison. The ANG was present selectively in the cytoplasm of the nonpigmented ciliary epithelium (NPCE), more prominently in the pars plana than in the pars plicata. Both ANG and albumin were present in the blood vessel lumina of the uvea and retina. Both antibodies also stained perivascular tissue in the uvea, but not in the retina, reflecting the relative tightness of blood-tissue barriers. The detection of ANG in the NPCE may be significant in view of previous descriptions localizing prorenin and angiotensin-converting enzyme in the same cell layer.

Effects of Lofexidine, an α2-adrenoreceptor Agonist, on Ocular Blood Flow and Ion Transport of Rabbit Iris-ciliary Body

The effect of topical unilateral application of lofexidine, an alpha 2-agonist, on ocular regional blood flow was tested in anesthetized rabbits using radiolabeled microspheres. A significant reduction in blood flow was found only in the ciliary body of the treated eye at 1 hr after lofexidine treatment. However, the IOP of both eyes was decreased significantly at 30 and 60 min post lofexidine treatment. Yohimbine (i.v.) blocked this IOP lowering effect, but only partially prevented the blood flow response. In addition, no significant difference was found in either basal or amphotericin-B stimulated short-circuit current or potential difference of the isolated rabbit iris-ciliary body after 30 minutes of lofexidine treatment. These observations suggest that the IOP lowering effect of lofexidine appears to be mediated by alpha 2-receptors but unrelated to the reduction in the ocular blood flow and net electrogenic ion transport.

Neuropeptide Y (NPY): a vasoconstrictor in the eye, brain and other tissues in the rabbit

The effect of neuropeptide Y (NPY) on uveal vascular resistance was studied in rabbits by direct determination of uveal blood flow from a cannulated vortex vein. Regional blood flows, in the eye, the brain and several other tissues, were measured, with radioactive microspheres, during neuropeptide Y-infusion in rabbits with and without alpha-adrenoceptor blockade. Intravenous infusion of increasing doses of neuropeptide Y caused a dose-dependent increase in the total uveal vascular resistance. Maximal effect, a 70% increase, was achieved with 120 pmol kg-1 min-1. In the microsphere experiments, this dose rate was given i.v. over 10 minutes and blood flow determinations were made before and at 2 and 10 minutes after the start of the infusion. After 2 minutes of neuropeptide Y, there were marked blood flow reductions in the spleen, kidneys, adrenal glands, gastro-intestinal tract, choroid plexus and pineal and pituitary gland. The effect in the eye was small at 2 minutes, but at 10 minutes local blood flows in the choroid and the ciliary body were decreased by 50% and the iridal blood flow by 30%. Retinal blood flow was not affected by neuropeptide Y. At 10 minutes there were also significant blood flow reductions in the brain, tongue, masseter muscle and several glandular tissues. The effects of neuropeptide Y on local blood flow in rabbits that had been subjected to alpha-adrenoceptor blockade were very similar to the effects in the animals without alpha-adrenoceptor blockade. The results show that, in the rabbit, neuropeptide Y has marked effects on local blood flows in several tissues, including the eye, and suggest that neuropeptide Y may significantly contribute to the uveal vasoconstriction during sympathetic nerve stimulation.

In vitro characterization of the mechanical properties of canine ophthalmociliary artery

The form and magnitude of K+ Krebs-induced contractures has been measured for the dog ophthalmociliary artery. Ring segments of the vessel were mounted in a myograph after the method of Hogestatt, Andersson and Edvinsson (1983, Acta Physiol. Scand. 117, 49-61). For low passive tensions the K(-)-induced contractures show both a phasic and tonic component, with the tonic tension component being the smaller. As passive tension is increased, the phasic component grows and plateaus whilst the tonic component continues to increase. For high passive tensions the phasic component disappears and the tonic component reduces in magnitude and the contracture is not fully reversible. Comparison of the length tension curves measured during K+ Krebs-induced contractures and Ca2(+)-free Krebs-induced relaxation shows that the active tension generated by this vessel increases with increasing passive tension until a peak active tension of 3.1 mN mm-1 is reached at an effective radius of 357 microns. For greater values of passive tension the active tension decreases. The calculated transmural pressure required to maintain the vessel at this optimal radius is 51.9 mmHg, which is very similar to the only available measurements of ophthalmic artery pressure, viz. 51.8 mmHg (Grunwald, Sinclair and Riva, 1981, Invest. Ophthalmol. Vis. Sci. 20, 564-6). The optimal passive stretch to apply to these ring segments for further pharmacological or physiological work is discussed.

Scanning electron microscopic study on the vasculature of the human anterior eye segment, especially with respect to the ciliary processes

The architecture of the vasculature of the human anterior eye segment was studied by scanning electron microscopy of vascular resin casts. Regarding the major vessels it was found that the perforating branches of the anterior ciliary arteries (ACA) form an anastomozing circle which lies in the posterior portion of the ciliary muscle (intramuscular circle). The ACAs supply the outer and posterior parts of the ciliary muscle, partly the iris, and the peripheral choroid by recurrent ACA branches. The major arterial circle of iris (MACI) which lies more anteriorly is formed mainly by the long posterior ciliary arteries and supplies the inner and anterior portion of the ciliary muscle, the iris and the ciliary processes. The ciliary process vasculature consists of three different vascular territories with discrete arterioles and venules. The first vascular territory which is located at the anterior end of the major processes, is drained posteriorly by venules which pass the ciliary body without greater connections to the venules of the major ciliary processes. The second and third territories comprise the vasculature of the major and minor ciliary processes drained posteriorly by venules which are located at the margin of the ciliary processes. In supravital experiments with human autopsy eyes, a characteristic segment of arterioles supplying the first and second territory was found to be constricted after immersion with epinephrine in a similar way as in cynomolgus monkeys in vivo. Although the general arrangement of the ciliary process vessels is similar to that of the cynomolgus monkey, there are characteristic differences in the size of the territories and in the pattern of the capillary networks. The division of the ciliary process vasculature into three vascular territories may reflect a functional differentiation in the process of aqueous humour production.

Non-adrenergic sympathetic vasoconstriction in the eye and some other facial tissues in the rabbit

The effects of unilateral sympathetic nerve stimulation (SNS) on regional blood flow in the rabbit were studied with radioactive microspheres. SNS at 10 or 4 Hz caused an approximately 60% reduction in choroidal blood flow, which was partly resistant to alpha-adrenoceptor blockade with phenoxybenzamine. The vasoconstriction evoked by SNS at 2 Hz was completely abolished by alpha-adrenoceptor blockade. A similar response was seen in the iris, ciliary body, masseter muscle and lacrimal gland. In the harderian gland, however, SNS (2 Hz) after alpha-adrenoceptor blockade caused a significant reduction in blood flow. In the salivary glands, combined beta- and alpha-adrenoceptor blockade with propranolol and phenoxybenzamine revealed a slight non-adrenergic vasoconstriction during SNS at 10 Hz; however, the blood flow was significantly increased during SNS at 4 and 2 Hz following alpha-adrenoceptor blockade. These results indicate that there is a frequency-dependent, non-adrenergic component in the sympathetic vasoconstriction of the eye and several facial tissues. In the salivary glands, beta-adrenoceptor-mediated vasodilatation tends to mask a non-adrenergic vasoconstriction.

Posterior axial corneal malformation and uveoretinal angiodysgenesis--a neurocristopathy?

This clinicopathological report describes an unusual combination of axial corneal malformation and angiodysgenesis in the uvea, retina and optic nerve in three eyes. In each specimen there was hypocellularity in the posterior axial stroma, with corresponding loss of the corneal endothelium. The vascular malformation consisted of numerous telangiectatic endothelium-lined tubes with inconspicuous or absent media. One globe was obtained from a stillborn fetus (36 weeks) in which renal agenesis and a sireniform malformation (mermaid fetus) occurred in conjunction with a Fallot's tetralogy, pulmonary hypoplasia and atresia of the trachea and duodenum. Eyes with almost identical malformations were obtained from a 39-week female neonate who died after 5 h as a consequence of renal agenesis and pulmonary hypoplasia. This combination of ocular tissue malformations can be explained by embryological studies, which have shown that the corneal stroma and endothelium and the ocular periendothelial vascular tissues are derived from the neural crest.

[Increased episcleral venous pressure in uveal effusion]

This paper reports on two patients with bilateral, spontaneous choroidal and retinal detachment. One patient had scleritis, while in the other no underlying eye disease was found. No signs of orbital venous congestion were detected. Although the pathogenesis of this disease is not fully known, the findings of (1) dilated episcleral veins and (2) elevated episcleral venous pressure suggest an obstruction of venous outflow from the uveal tract. The authors believe that these two findings may have been caused by shunting of venous blood anteriorly from the uveal tract into the episcleral veins due to partial obstruction of the vortex veins.

Regional uveal response to increased nutritional needs in the retinal zone of the developing eye demonstrated in an eye with retinoblastoma

The outer layers of the normal retina depend on indirect nutrition originating in the choriocapillaris and supplied to the retina by way of the pigment epithelium. An eye with exophytic retinoblastoma is used to demonstrate increased vascularity and tissue substance in the adjacent choroid believed to be indirectly induced by a regional increase in nutritional requirements in the retinal zone of a developing eye.

Microvascular access to the uveal tract in the rabbit eye for ocular pharmacologic studies

Drug delivery to the eyes is quite inefficient regardless if the drugs are administered topically or intravenously. It is known that less than 1% of topically instilled drug can be absorbed into the eyes while even less of intravenously injected drugs reach the eyes. A research model has been developed in this study which allows delivery of drugs effectively to uveal and anterior structures of the eye. This experimental model allows drugs to be delivered to the eye via cannulation of and retrograde flow through the valveless vortex veins. In addition, the superficial branch of the vortex vein (draining the ciliary body and iris) or the deep branch (draining the choroid plexus of the retina) can be selectively cannulated to suit the researcher's needs. Finally, this procedure minimizes systemic drug actions which otherwise would complicate interpretation of experimental results. This model can be used for in vivo laboratory studies on (a) metabolic and physiological processes of the uveal tract in the eye, and (b) drug delivery to selective tissues of the uveal tract in the eye. Dose-response relationships of pilocarpine and timolol to lower intraocular pressure were demonstrated with this model.

Ocular blood flow in dogs using radiolabelled microspheres

We used radioactive microspheres of different sizes to determine the rate of blood flow through the various parts of the eye in dogs. The use of either 15 +/- 5 microns or 25 +/- 5 microns microspheres gave reproducible measurements of total ocular and uveal blood flows. Using these sphere sizes, retinal flow was found to be close to 1% of the total ocular blood flow and showed poor reproducibility due in part to the small number of spheres trapped in the retinal vessels.

Pilocarpine antagonizes prostaglandin F2 alpha-induced ocular hypotension in monkeys. Evidence for enhancement of Uveoscleral outflow by prostaglandin F2 alpha

Twice daily topical application of 50 micrograms of prostaglandin F2 alpha tromethamine to cynomolgus monkey eyes produced significant ocular hypotension lasting at least six hours, with the intraocular pressure (IOP) falling between 35% and 50%, ie, to about 8 to 10 mm Hg, following the seventh dose. A single topical application of 1 mg of pilocarpine hydrochloride produced a much smaller IOP reduction and strong, probably maximal accommodation, both of which lasted at least eight hours. When prostaglandin F2 alpha-treated eyes were given pilocarpine before the seventh dose of prostaglandin F2 alpha, accommodation and IOP responded as in eyes receiving pilocarpine only. Atropine sulfate pretreatment of eyes receiving pilocarpine and prostaglandin F2 alpha completely prevented pilocarpine-induced accommodation and inhibition of ocular hypotension induced by prostaglandin F2 alpha. We hypothesize that (1) prostaglandin F2 alpha reduces IOP by increasing uveoscleral drainage of aqueous humor, and (2) pilocarpine pretreatment contracts the ciliary muscle, obliterating the intramuscular spaces and closing off the uveoscleral drainage pathway and thus physiologically blocking the effect.

Increased vascular permeability in spontaneously diabetic BB/W rats and in rats with mild versus severe streptozocin-induced diabetes. Prevention by aldose reductase inhibitors and castration

125I-labeled albumin permeation (IAP) has been assessed in various tissues in spontaneously diabetic insulin-dependent female BB/W rats and in male Sprague-Dawley rats with severe or mild forms of streptozocin-induced diabetes (SS-D and MS-D, respectively). In BB/W diabetic rats and in rats with SS-D, indices of IAP were significantly increased in tissues and vessels predisposed to diabetic vascular disease in humans, including the eyes (anterior uvea, posterior uvea, and retina), sciatic nerve, aorta, kidney, and new vessels formed after induction of diabetes. No evidence of increased IAP was observed in heart, brain, testes, or skeletal muscle in BB/W or SS-D rats. In MS-D rats, indices of IAP were increased only in the kidney and in new vessels formed after the onset of diabetes. Marked tissue differences were observed in the effects of two structurally different aldose reductase inhibitors (sorbinil and tolrestat) and of castration on diabetes-induced increases in IAP and in tissue levels of polyols in SS-D rats. Both aldose reductase inhibitors and castration completely prevented diabetes-induced increases in IAP in new vessels and in sciatic nerve in BB/W and SS-D rats. Both aldose reductase inhibitors also markedly decreased IAP in the anterior uvea (approximately 85%), posterior uvea (approximately 65-75%), retina (approximately 65-70%), and kidney (approximately 70-100%); castration reduced IAP in the anterior uvea (approximately 55%), kidney (approximately 50%), and retina (approximately 30%) but had no effect on the posterior uvea. The diabetes-induced increases in IAP in the aorta were reduced only slightly (approximately 20%) by aldose reductase inhibitors and castration.(ABSTRACT TRUNCATED AT 250 WORDS)

Uveal neovascularization at the ora serrata and pars plana

Thirty-two eyes with uveal neovascularization at the ora serrata and pars plana were studied histopathologically. Chronic retinal detachment of various etiologies was the most frequently associated feature, present in 65% of the patients. In three eyes, the neovascularization took the form of an angiomatous lesion, whereas in the others, capillaries, arterioles, and venules were present. A history of glaucoma was found in 60% of the patients. Other associated findings included choroidal rupture, vitreous hemorrhage, and a history of cryotherapy. Uveal neovascularization at the ora serrata should be considered in the differential diagnosis of retinal angiomas, retinal telangiectasia, malignant melanoma, adult Coats's disease, peripheral proliferative retinopathies, and vitreous hemorrhage.