Ultrastructural Organization of Uveal Melanoma Stromal Cells.

Typical blood capillaries and vessels in uveal melanoma were shown and different types of uveal melanoma stromal cells were determined by electron microscopy and immunohistochemical analysis. Macrophages, fibroblasts of varying degrees of differentiation and endothelial-like cells with numerous caveolae in the cytoplasm were found in the channels of the extracellular matrix surrounding accumulations of tumor cells. The presence local structures positively stained for markers of the blood and lymphatic vessels (CD31 and podoplanin) in channels of the extracellular matrix suggests that the described endothelial-like cells can be the structural basis for blood and lymphatic vessels of the tumor.

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.

Histological findings of uveal capillaries in rabbit eyes after multiple intravitreal injections of bevacizumab.

PURPOSE: To evaluate the potential toxicity of multiple intravitreal injections of bevacizumab on the uveal capillaries of rabbit eyes. MATERIALS AND METHODS: Nine eyes of nine rabbits that received single intravitreal injections of bevacizumab (IVB) constituted the single IVB group, while nine eyes of nine rabbits that received three injections of IVB, with an interval of 28 days between injections, constituted the repeat IVB group. Seven eyes of seven rabbits constituted the control group. The rabbits in the single and repeat IVB groups were sacrificed 7 and 28 d after the single and third IVB injection, respectively. Uveal specimens were compared between groups after immunohistochemical staining. Ultrastructural findings were evaluated by electron microscopy. Control group rabbits were sacrificed 7 d after saline injection. Clinical examination and fundus fluorescein angiography were performed at baseline, 7 d after the first injection, and after the last injection. RESULTS: Differences in the CD31-positive areas of the iris, ciliary body and choroid 7 d after IVB were not statistically significant among the single IVB, repeat IVB and control groups (p = 0.0749, p = 0.7237 and p = 0.7346, respectively; analysis of variance). Endothelial cell fenestrations (ECFs) in the choriocapillaris and ciliary body observed by electron microscopy on day 7 in the single and repeat IVB groups were decreased by 50% (p < 0.0001) and 33% (p < 0.0001), respectively, in both IVB groups compared with those in the control group. However, ECFs observed on day 28 in both groups were comparable to those observed in the control group. CONCLUSIONS: Single IVB and repeated IVB did not have any effect on normal vessel endothelium density as per immunohistochemical findings. Ultrastructural findings revealed that IVB transiently decreased the ECFs in the choriocapillaris and ciliary body.

Microanatomy of the anterior uveoscleral outflow pathway in normal and primary open-angle glaucomatous dogs.

OBJECTIVE: To compare the morphology of the uveoscleral (US) outflow pathway in normal and glaucomatous canines. ANIMALS STUDIED: 10 normal beagles, 10 beagles with inherited primary open-angle glaucoma, 4 cocker spaniels with spontaneous glaucoma. PROCEDURES: Formalin-preserved globes were sectioned tangentially and sagittally and treated with H&E, Masson's trichrome, or elastin stains or analyzed by immunohistochemistry to visualize smooth muscle actin. Tissues associated with the US pathway were observed and compared using light microscopy. RESULTS: Tangentially oriented sections clearly revealed spaces for the transport of aqueous humor at the junction of the posterior iridocorneal angle (ICA) and anterior ciliary body musculature (CBM). Within the external anterior-most of the US pathway, the supraciliary space, distinct connective tissue cords and smooth muscle pegs fastened the ciliary body to the adjacent sclera. Compared to normal controls, glaucomatous eyes developed a robust scleral elastic sheath at the junction between the posterior ICA and the anterior CBM. In advanced glaucomatous beagles and cocker spaniels, a large amount of melanophores were seen in the US pathway and surrounding vasculature. Within the C8M of glaucomatous specimens, the smooth muscle bundles appeared fewer and separated by elastic-rich ECM. Structures of the US pathway changed little with age. CONCLUSIONS: The anterior portion of the canine US pathway is well defined and appears to be altered little with age. However with glaucoma, changes of the US pathway were associated with its the elastic components, as well as the accumulation of melanophores. Collectively, these changes may have an effect on US outflow and, subsequently, aqueous humor dynamics.

Aqueous humor dynamics during the day and night in volunteers with ocular hypertension.

OBJECTIVE: To evaluate the differences in aqueous humor dynamics between nighttime and daytime in participants with ocular hypertension. METHODS: Thirty participants (mean [SD] age, 59.2 [11.1] years) with ocular hypertension were enrolled in the study, which included 1 daytime and 1 nighttime visit. During each visit, measurements included central cornea thickness by ultrasound pachymetry, intraocular pressure (IOP) by pneumatonometry, aqueous flow by fluorophotometry, outflow facility by tonography, and blood pressure by sphygmomanometry. Uveoscleral outflow was calculated using the Goldmann equation. Daytime measurements were made only of episcleral venous pressure by venomanometry, anterior chamber depth by A-scan, and outflow facility by fluorophotometry. Repeated-measures analysis of variance and 2-tailed t tests were used for statistical comparisons. RESULTS: Compared with daytime seated IOP (21.3 [3.5] mm Hg), nighttime seated IOP (17.2 [3.7] mm Hg) was reduced (P < .001) and nighttime supine IOP (22.7 [4.6] mm Hg) was increased (P = .03). Central cornea thickness was increased at night from 570 (39) µm to 585 (46) µm (P < .001). There was a 48% nocturnal reduction in aqueous flow from 2.13 (0.71) µL/min during the day to 1.11 (0.38) µL/min at night (P < .001). Uveoscleral outflow was significantly reduced (P = .03) by 0.61 µL/min at night when using supine IOP, tonographic outflow facility, and episcleral venous pressure adjusted for postural changes in the Goldmann equation. All other measurements had no significant changes. CONCLUSIONS: Significant ocular changes occur at night in individuals with ocular hypertension, including a reduction in seated IOP but an increase in habitual IOP, thickening of the cornea, and decreases in aqueous flow and uveoscleral outflow. Outflow facility does not change significantly at nighttime.

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]. / Zastosowanie kolorowej ultrasonografii dopplerowskiej do oceny skutecznosci brachyterapii u pacjentów z czerniakiem blony naczyniowej.

UNLABELLED: 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.

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.

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.

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.

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 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.