Microendoscopy of the anterior segment vasculature in the rabbit eye

Intraocular microendoscopy is introduced as a new method which allows a direct in vivo observation of the microvasculature of the eye. Using video equipment, a quantitative evaluation of changes in vessel diameters, e.g. after administration of vasoactive agents, and an estimation of blood oxygenation are possible. Experimental studies with fluorescent dyes can also be performed using special filters. In albino rabbits, no apparent vascular disturbances were observed under certain experimental conditions. Touching a ciliary process with the tip of the endoscope immediately resulted in a vasodilation and stoppage of blood flow, surprisingly in the affected area only. After epinephrine, the locally traumatized ciliary processes remained unchanged while the vessels of the neighboring ciliary processes constricted intensely. After reduction of the intraocular pressure the major ciliary processes began to swell. A leakage of fluorescein-dextran was only found in the iridial ciliary processes.     

Changes of the vasculature and innervation in the anterior segment of the RCS rat eye

Investigating the anterior eye segment vasculature and innervation of dystrophic RCS rats, two major unique findings were observed: in the iris, young adult animals with retinal dystrophy showed an increase in substance P nerve fibres and a dilation of arterioles and capillaries. This finding continued during ageing. In the pars plana region, the surface covered by venules decreased continuously with age. In older animals, this decrease was parallelled by a local decrease of sympathetic TH-positive nerve fibres supplying these venules. For both conditions, no comparable data exists so far in the literature. They might point to a unique situation in the anterior eye segment of the dystrophic RCS rat.     

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.     

Hydrolysis of enkephalins in homogenates of anterior segment tissues of the albino rabbit eye

The kinetics and pathways of hydrolysis of methionine enkephalin (TGGPM), leucine enkephalin (TGGPL), and [D-Ala2] met-enkephalinamide (TAGPM) in homogenates of anterior segment tissues of the albino rabbit eye were studied using reversed phase HPLC. Both TGGPM and TGGPL were equally susceptible to hydrolysis with a half-life ranging from 11-50 min and were 11-23 times more susceptible to hydrolysis than TAGPM. All three peptides were hydrolyzed most rapidly in the corneal epithelium, followed by the iris-ciliary body, conjunctiva, corneal stroma, lens, and tears. Aminopeptidases were responsible for over 90% of the hydrolysis of TGGPM and TGGPL, while dipeptidyl peptidase and dipeptidyl carboxylpeptidase were responsible for the remainder. In contrast, dipeptidyl carboxylpeptidase was principally responsible for the hydrolysis of TAGPM, which by design is resistant to aminopeptidase action. Overall, these findings suggest that, in order to deliver short chain peptides intraocularly from topical solution instillation, it will be necessary to control the ocular tissue activity of aminopeptidases principally and, to a lesser extent, the activity of dipeptidyl peptidase and dipeptidyl carboxylpeptidase.     

三维前房分析仪对40岁以上人群前房形态测量的初步研究

目的分析三维前房分析仪测量的40岁以上社区人群的前房形态参数。设计横断面调查研究。研究对象对10例受试者作三维前房分析仪重复性检验。连续选取社区40岁以上受试者共92例，分为40～49岁、50～59岁、60～69岁、70岁以上四个年龄组，每组男、女至少10例。方法对10例受试者进行3次重复性前房形态检查，评价前房测量的可重复性。社区受检人群检查包括视力、裂隙灯显微镜、数码眼底照像及前房分析仪检查。凡前房轴深小于2mm者到北京同仁医院接受进一步检查。主要指标前房轴深、前房夹角、前房容积。结果前房轴深、前房夹角、前房容积的平均变异系数分别为0．4％、3．9％、2．6％。前房轴深、前房容积与性别、年龄因素有显著相关性，女性前房轴深较男性浅(P=0．044)、前房容积小(P=0．002)。随年龄增长前房轴深变浅、容积变小。前房夹角与性别、年龄因素无显著相关性。筛查中前房轴深小于2mm者共8例，4例确诊为青光眼。结论前房轴深与前房容积测量的可重复性好，前房夹角检测的可重复性略差。前房轴深、前房容积号性别、年龄因素相关。     

Localization of beta-andrenoceptors in the anterior segment of the albino rabbit eye using a fluorescent analog of propranolol.

A fluorescent analog of propranolol, 9-amino-acridin-propranolol (9-AAP), was injected into the carotid arteries of albino rabbits in an attempt to localize β-adrenergic receptors (β-adrenoceptors) in the anterior segment of the eye. 9-AAP fluorescence was noted mainly in the ciliary epithelium, but also in the walls of the episcleral vessels. Only mild fluorescence was noted in the iris sphincter region. It is suggested that these findings are compatible with the distribution of β-receptor sites in the anterior segment of the rabbit eye.     

Qualitative fundus oximetry in the albino rabbit's eye

The principle of fundus oximetry, as used by Broadfoot, Gloster and Greaves (1961), has been modified and elaborated, using two monochromatic light bundles, one with minimal, the other with maximal difference in the extinction coefficient for Hb and HbO₂, a high chopping frequency, fibre optics and a Lovac contact lens. Anaesthetized albino rabbits were used with the light entering the dilated pupil. The returning light can be divided into a non-variable part, originating from various planes of transition, and a part that behaves as if passed through a blood film of twice the vascular laye thickness. Using differential recording—the difference made zero at the beginning of the experiment—a higher sensitivity of the system may be employed than in the case of direct recording of the intensity of the returning light. Changes in oxygenation gave reproducible qualitative measurements of the oxygen saturation of the blood in the vascular layer.     

Reactions of efferent venous segments in the ciliary process vasculature of albino rabbits

In albino rabbits, the reactions of a defined venous segment of the ciliary process vasculature to vasoactive agents were studied using our new technique of in vivo microendoscopy and using supravital specimens of the anterior eye. This segment is situated in the pars plana of the ciliary body and is the continuation of the venules at the inner edge of the minor and major ciliary processes which posteriorly drain the blood in the veins of the peripheral choroid. Three- to 4 min after administration of carbachol, a constriction of this efferent venous segment was seen in the in vivo microendoscopy as well as in supravital specimens. The adjacent vessel segments remained relatively unchanged. Two- to 3 min after intra-arterial administration of atriopeptin (ANP), an intense constriction of the efferent venous segment, followed by a reactive hyperaemia, was found by in vivo microendoscopy. The iris veins which collect the blood from the iris and the iridial ciliary processes pass the pars plana without touching the ciliary process vasculature. No reactions to the vasoactive agents tested were observed in these vessels. It has been concluded that the efferent venous segment of the ciliary process may play a role in the regulation of perfusion pressure within the ciliary process capillaries.     

Interendothelial junctions of the rabbit iris vasculature in anterior uveitis

Ultrastructural tracer techniques and freeze-fracture electron microscopy were used to evaluate the alterations present in the tight junctions of rabbit iris blood vessels in anterior uveitis. In control animals, the iris vascular endothelial cells were seen to be joined by both tight and gap junctions. Leakage of tracer from these vessels was not observed. Freeze-fracture replicas of the tight junctions in these vessels revealed two to eight branching and anastomosing strands, the particles of which tended to remain with the E fracture face. Experimental animals received intravitreal injections of 1.0 microgram of E. coli endotoxin. Twenty-four hours later, at peak severity of the inflammatory response, the animals were sacrificed. Iris vessels from uveitic eyes were observed to leak tracer, primarily through their interendothelial clefts. In freeze-fracture replicas, junctional changes took two major forms. In most cases, junctional simplification was observed. Only one or two continuous strands were evident, with very few interstrand anastomoses. In fewer instances, focal areas of profound junctional disruption were seen. In the latter case, short strands of tight junctional particles remained but the complementary ridge and groove system characteristic of tight junctions was lost. The loss of this system is interpreted to indicate that separation of adjacent endothelial cells, and an opening of the interendothelial cell cleft, has occurred at these locations. Both junctional simplification and junctional disruption likely result in increased vascular permeability. It is not possible to judge the relative contributions to increased vascular permeability which attend widespread junctional simplification as opposed to rare, focal junctional disruptions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intraocular microendoscopy of the ciliary-process vasculature in albino rabbits: effects of vasoactive agents

The reactions of the ciliary-process microvasculature following administration of various vasoactive substances were studied in the albino rabbit using a new method of intraocular microendoscopy. This technique allows an in vivo observation of arterioles, capillaries and venules of the ciliary body and iris. As long as these tissues are not traumatized, the newly described method of intraocular microendoscopy produces no reactive changes in the vasculature. The video images of microendoscopy were also evaluated quantitatively. Administration of substance P caused a short-term ischemic phase in the ciliary-process vasculature which preceded a long-term hyperaemia. After topical administration of epinephrine as well as intra-arterial administration of epinephrine, phenylephrine and isoproterenol, rapid and intense vasoconstrictory or vasodilatory reactions were seen in the terminal arterioles of the vascular territories in the ciliary processes. The terminal arterioles of the iridial ciliary processes responded faster and more intensely than those of the major ciliary processes. It is concluded that the terminal arterioles play an important role in blood-flow regulation of the ciliary processes and function as special afferent vessel segments which control the circulation within the ciliary-process capillaries.