Comparative microvascular anatomy of mammalian ciliary processes

Methylmethacrylate lumenal castings of the ciliary body microvasculature were prepared from eight mammalian species and studied with the scanning electron microscope. In all of these species, the ciliary body is supplied by the major arterial circle, which originates solely from the long posterior ciliary arteries without contribution from the anterior ciliary circulation. In contrast to primates and rabbits, the ciliary processes of the eight species we studied are supplied by only one type of arteriole, which travels posteriorly from the major arterial circle to the iris root, where it gives rise to ciliary process arterioles. Using precise microdissection techniques, we found marked interspecies variations in ciliary process angioarchitecture among the mammalian eyes examined. Rodents (rat and guinea pig) demonstrated several interesting similarities to primates, with extensive interprocess connections and irregularly dilated, concentrically parallel capillaries traveling posteriorly to empty into the choroidal veins. In addition, rat ciliary process arterioles displayed marked focal constrictions suggestive of precapillary "sphincter" agonal activity. The carnivore ciliary process (cat and dog) is supplied by a single arteriole traveling posteriorly throughout its length and sending capillary arcades to its margin from where they drain outward into venous sinuses at the base of the process. Ungulate processes (sheep, goat, pig and cow) receive blood from multiple arterioles that occupy the process core along with veins that empty into the choroidal circulation. These vessels serve delicate capillaries lying on the sides, margin and head of each process. The anatomic variations described here should be considered in the design and interpretation of physiologic and immunohistochemical studies of ciliary body vascular perfusion in non-primate animal models.     

Cytochemical localization of adenyl cyclase in the rabbit ciliary body

The cytochemical localization of adenyl cyclase was investigated in the rabbit ciliary process by electron microscopy. The specificity of histochemical procedure was enhanced by the use of adenylyl imidodiphosphate (AMP-PNP) as a reaction substrate.The methodological problems are discussed regarding the fixation and the concentration of lead nitrate in the incubation medium. It was concluded that 0·5% glutaraldehyde and 4 mm-lead nitrate were appropriate for histochemical demonstration of adenyl cyclase activity in the rabbit ciliary body.The detectable enzymatic activity was distributed almost exclusively on the plasma membrane of non-pigmented epithelial cells, the boundary between non-pigmented and pigmented epithelial cells and capillary endothelial cells of the ciliary process. No reaction product was found on the plasma membrane of pigmented epithelial cells, nor in the epithelial cells of the iridial portion of the ciliary process.These findings strongly suggest that adenyl cyclase activity which is distributed predominantly on the plasma membrane of non-pigmented epithelial cells plays an important role in the regulation of aqueous humor formation.     

Isolation of non-pigmented epithelial cells from rabbit ciliary body

We describe a new technique for the separation and isolation of nonpigmented ciliary body epithelial cells from rabbit. Excised ciliary body is incubated in a medium buffered with EGTA to a free-Ca2+ concentration of 10(-8) M, and the nonpigmented cell layer is separated from the pigmented layer by microdissection under direct visualization. This technique yields intact cells which are greater than 99% nonpigmented. It can be used to produce preparations of nonpigmented cell plasma membrane and of viable whole cells, which may be useful for biochemistry, pharmacology, cell transport studies and tissue culture.     

Bicarbonate transport mechanisms in rabbit ciliary body epithelium.

Sections of whole ciliary body dissected from Dutch belted rabbits were incubated with the cell entrappable pH probe BCECEF-AM. This led to a highly specific localization of epifluorescence emission at the exposed, non-pigmented cell layer (npe) of the dual layered epithelium that covers this organ. The BCECF-loaded tissue sections were superfused in a flow-through chamber and the intracellular pH (pHi) of small groups (10-20) of cells was derived from the ratio of the emission intensities derived from excitations at 490 and 440 nm. In CO2/HCO3- Ringer's, npe pHi = 7.09 +/- 0.11. Replacement of CO2/HCO3- by Hepes increased pHi by 0.22 +/- 0.02, indicating alkali secretory activity under the bicarbonate-rich conditions. Replacement of Cl- by gluconate elicited a rapid, 0.6-U increase in pHi. This effect exhibited little dependence on Na+ and was inhibited by 0.5 mM dihydro-4,4'-diisothiocyanatostilbene -2,2'-disulfonate (H2DIDS). These results indicate the presence of an electroneutral Cl-/base exchange activity. Elevation of [K-] (by partial replacement of Na+) also elicited increases in pHi. In Cl(-)-free media pHi reached 7.8-8.0, a condition under which intracellular [HCO3-] is at least twice as high as its extracellular value. This effect did not occur in the absence of Na+. The Na(+)-dependent high [K+]-induced pHi increase was inhibited by H2DIDS. The effects of Ba2+ on pHi, alone and in combination with high [K+], as well as that of full K+ removal, suggested that the link between high [K+] and pHi increase was mainly due to the effect of cell depolarization on an electronegative Na+ dependent HCO3- transporter. Under normal physiological conditions, the two acid/base transport systems are the main determinants of npe pHi.     

P2 purinergic receptor-coupled signaling in the rabbit ciliary body epithelium

PURPOSE: To identify and characterize P2 purinergic receptors and their signaling pathways in the epithelial cells of the rabbit ciliary body. METHODS: Real-time fluorescence ratio imaging of the intact fura-2-loaded nonpigmented ciliary body epithelial (NPE) cells of rabbit were used to record changes in the intracellular free calcium concentration ([Ca(2+)](i)), in response to a number of purinergic agonists and antagonists. The effects of some of these drugs on the inositol phosphate (IP) levels in ciliary processes were also examined. RESULTS: Adenosine diphosphate (ADP), adenosine triphosphate (ATP), and uridine triphosphate (UTP) dose dependently increased the [Ca(2+)](i) and IP levels. The [Ca(2+)](i) increases induced by ADP and UTP were distinguishable, both kinetically and pharmacologically. The effect of ADP on [Ca(2+)](i) was mimicked by a number of P2Y(1)-selective agonists, and was blocked by three P2Y(1)-receptor-specific antagonists. The [Ca(2+)](i) increases elicited by ADP (or its analogs) and UTP were additive. CONCLUSIONS: Rabbit ciliary body epithelium possesses both P2Y(1) and P2Y(2) metabotropic purinergic receptor subtypes, which differentially use the IP(3)/Ca(2+) second-messenger pathway.     

Topographical anatomy of the ciliary sulcus

The topography of the ciliary sulcus area in humans was examined by slitlamp biomicroscopy and scanning electron microscopy. Characteristics of this area included the following: the sulcus was angulated anteriorly; the ciliary processes were of unequal length; the zonules did not insert on the tips of the ciliary processes but, instead, inserted slightly posteriorly; the contour of the sulcus area was irregular; bands stretched from the base of the ciliary processes to the posterior surface of the iris, making the sulcus a potential space in some areas of the eye. Effects of this topography on IOL implantation are postulated.     

Characterization of human and rabbit pigmented and nonpigmented ciliary body epithelium

Nonpigmented epithelial (NPE) and pigmented epithelial (PE) cells were carefully dissected from both human and rabbit ciliary processes and have been maintained in vitro and partially characterized by morphology and immunocytochemical techniques using polyclonal and monoclonal antibodies against S-100 proteins, collagen type I and type III. The tissue distribution of these proteins was studied in formalin fixed deparaffinized tissue sections of human and rabbit eyes by immunoperoxidase staining techniques. Both NPE and PE cell lines from human and rabbit showed hexagonal morphology by light microscopy; distinct granules containing pigment could be visualized in the PE cell lines, but not in the NPE cells. Antibodies against S-100 proteins stained NPE layer intensely and PE layer slightly in the human tissue sections. The staining was less intense in rabbit tissues than human tissues. The ciliary body stroma was positive for collagen type III and negative for collagen type I or S-100.     

The effect of transscleral laser cyclophotocoagulation on rabbit ciliary body vascularization

Long-term changes in the vascular network of rabbit ciliary processes induced by Nd:YAG laser cyclophotocoagulation were examined both from a morphological viewpoint and with respect to three-dimensional organization (in vascular casts). Relative changes in intraocular pressure (IOP), monitored within eyes irradiated across one-quarter, one-half, three-quarters, or all of the ciliary body circumference, are discussed in relation to morphological changes. The clinical implications of these findings are considered.This work was supported by the Swiss National Science Foundation, grant number 3.844.-0.86, by the Swiss Commission for the Promotion of Scientific Research, and in part by Alcon LaboratoriesDedicated to T.H. Schiebler, MD, Professor of Anatomy at the University of Würzburg, Federal Republic of Germany, on the occasion of his 65th birthday     

Characterization of serotonin receptors in the iris + ciliary body of the albino rabbit

Experiments were undertaken to determine if serotonin (5-HT) radioligand binding sites were present in a membrane fraction of iris + ciliary body from adult, albino rabbits. The total binding of 3H-5-HT, 3H-spiroperidol (SPI) and 3H-ketanserin (KET), all at 2 nM, was determined in the absence and in the presence of ketanserin, mianserin, methysergide or 5-methoxytryptamine (5-MT), all at 1 microM. Except for ketanserin, which displaced 15% of 3H-KET binding, none of the agents altered 3H-SPI or 3H-KET binding. Reductions of 12% and 14% in 3H-5-HT binding were achieved by ketanserin and mianserin, respectively. In contrast, methysergide and 5-MT displaced 3H-5-HT binding by 57% and 56%, respectively. 5-HT (1 microM) also displaced 3H-5-HT binding by approximately 60% and this was used to measure nonspecific binding. Specific binding of 3H-5-HT was saturable and of high affinity with one population of binding sites being labelled. Kd and Bmax values of 1.1 nM and 57.8 fmoles/mg protein were obtained. Seven 5-HT antagonists possessing various affinities for 5-HT1 and 5-HT2 binding sites were assessed for their ability to displace specific 3H-5-HT binding. Ketanserin was the least potent (Ki greater than 3 microM). In contrast, the respective Ki values for metergoline and methysergide were 13 nM and 20 nM. These observations indicate the presence of 5-HT1 binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spontaneous fluid transport across isolated rabbit and bovine ciliary body preparations

PURPOSE: To quantify spontaneous fluid transport across the isolated ciliary bodies of rabbit and bovine and to determine their osmotic permeabilities. METHODS: A complete annulus of ciliary body was mounted in a custom-designed chamber appropriate for detecting net fluid movement across the in vitro preparation. RESULTS: A net fluid flow in the blood-to-aqueous direction was measured. It was generally observed that tissue freshness is a critical parameter for detection of such flow. The spontaneous, baseline fluid transport rate lasted, on average, approximately 4 hours. This flow solely reflects the secretory activity of the isolated ciliary epithelium, since the in vitro arrangement precludes contributions from ultrafiltration. Both the isolated rabbit and bovine ciliary body epithelia transported fluid in the absence of an external osmotic or pressure gradient. After corrections for area and possible collapse of the processes, a total flux rate of approximately 23 microL/hour or 13% of the in vivo flow in rabbit was estimated. This value agrees with predictions of ionic fluxes and short-circuit current measurements, which are also obtained in vitro. The fluid flow is bicarbonate dependent in rabbit and chloride dependent in bovine, consistent with ionic transport mechanisms described in these species. Ouabain inhibited the fluid flow across both species, indicating dependence on active ionic transport. Irrespective of the spontaneous fluid transport, a flow elicited by an osmotic gradient allowed for a calculation of the osmotic permeability coefficient (P(f); approximately 10(-3) cm/s) in line with reports in other epithelia. In addition, mannitol permeability (5.6 x 10(-6) cm/sec) was similar to that measured in "tight" epithelia, as determined by measurements of radiolabeled fluxes of the sugar across rabbit ciliary bodies mounted in the chambers used for the present fluid transport study. CONCLUSIONS: This work demonstrates that isolated ciliary epithelial preparations transport fluid in the blood-to-aqueous direction. The present observations suggest that mounting arrangements for measuring volumetric fluid flow across the ciliary epithelium is suitable for future studies directed toward the pharmacological control of secretion.     

Medulloepithelioma of the ciliary body

A rare case of medulloepithelioma of the ciliary body is described. The tumour necessitated enucleation of the eye; histopathological diagnosis was benign nonteratoid medulloepithelioma of the ciliary body.     

Medulloepithelioma of the ciliary body

Neuroepithelial tumors of the ciliary body occur more seldom than retinoblastoma. The congenital form is called medulloepithelioma, the adult-acquired adenoma or adenocarcinoma. Medulloepitheliomas consist of organoid epithelial structures developing anteriorly along surfaces such as the iris. The authors report on a congenital type unusually growing not only anteriorly along the lens, but also posteriorly along the retina's surface causing retinal detachment.     

Melanocytoma of the ciliary body

CLINICAL CASE: We report the case of a 25 year old woman who attended our Hospital with a pigmented lesion in anterior chamber angle of her right eye. She complained of reduced visual acuity on the same eye. On examination, and once complementary tests were performed, a pigmented lesion located on the iris root and ciliary body of her right eye was confirmed. A decision to perform a local resection was made and there were no surgical complication. Histology results confirmed the diagnosis of ciliary body melanocytoma. DISCUSSION: Ciliary body melanocytoma is a benign rare lesion with only 40 cases described in the literature. A local resection of this benign lesion should be considered as alternative to enucleation, even though differential diagnosis with malignant melanoma must also be considered.