Vascular Layer of the Eyeball That is Continuous With the Iris

Anatomy of the Uvea

Myron Yanoff MD , in Ophthalmology , 2019

Choroid

The choroid is the principal vascular and pigmented tissue that forms the middle coat of the posterior part of the eye. It extends from the ora serrata to the optic nerve. ⁷ The choroid is the most vascular tissue in the eye, and it has been implicated in the pathophysiology of a variety of ocular diseases. ⁸ It is attached to the sclera by connective tissue strands and especially posteriorly by numerous blood vessels and nerves that enter the choroid from the sclera. Small amounts of choroidal tissue may extend into the scleral canals through which ciliary vessels and nerves enter the eye. It varies in thickness from 0.1 mm anteriorly to 0.22 mm posteriorly. Choroidal thickness maps using a spectral-domain optical coherence tomographic instrument show that thinner choroidal area spreads around the optic disc and the peripapillary choroid increases in thickness the farther it is away from the optic nerve. The peripapillary choroid in the inferior quadrant is significantly thinner compared with all other quadrants. ^9,10

Histologically, the choroid reveals four layers: the lamina fusca, the stroma, the choriocapillaris, and Bruch's membrane. Bruch's membrane can be divided into five components: the basement membrane of the retinal pigment epithelium, an inner collagenous zone, an elastic layer, the outer collagenous zone, and the basement membrane of the endothelium of the choriocapillaris. The choriocapillaris, a highly vascularized layer, is the capillary layer of the choroid and provides nutrition to the retinal pigment epithelium and outer retinal layers (photoreceptor cell and outer plexiform layers and the outer aspect of the inner nuclear layer). It appears to have a finely spotted appearance and to be arranged in polygonal structures that might be associated with clusters of choriocapillaris lobules of 200- to 250-µm diameter and approximately 20-µm thickness with a central arteriolar feeder and an array of draining venuoles. ^11,12 The endothelial cells lining the choriocapillaris are fenestrated and are joined by gap junctions. The stroma of the choroid contains larger arteries and veins. These vessels are not fenestrated. The lamina fusca is the transition zone between sclera and choroid. It consists of a delicate meshwork of elastic fibers, fibrocytes, and melanocytes, traversed by long posterior ciliary nerves and vessels.

There are various studies that can be used to visualize the choroid vascular structures. Fluorescein angiography (FA) and indocyanine green angiography (ICGA) are both invasive tests that require intravenous administration of dye and imaging for 10–30 minutes. Fluorescein is typically used to visualize the retinal vasculature, whereas ICGA is used to see the choroidal vasculature. ¹³ Optical coherence tomography angiography (OCTA) is a new noninvasive imaging technique that employs motion contrast imaging to high-resolution volumetric blood flow information, generating angiographic images in a matter of seconds. OCTA can show images from the internal limiting membrane (ILM) to the choroid to visualize the individual vascular plexus and segment the inner retina, outer retina, choriocapillaris, or other area of interest. ⁸

Uvea

Myron Yanoff MD , Joseph W. Sassani MD MHA , in Ocular Pathology (Eighth Edition), 2020

Normal Anatomy

I.

The uvea is composed of three parts: iris, ciliary body, and choroid ( Figs. 9.1 and 9.2).

A.

The iris is a circular, extremely thin diaphragm separating the anterior or aqueous compartment of the eye into anterior and posterior chambers.

1.

The iris can be subdivided from pupil to ciliary body into three zones—pupillary, mid, and root—and from anterior to posterior into four zones—anterior border layer, stroma (the bulk of the iris), partially pigmented anterior pigment epithelium (which contains the dilator muscle in its anterior cytoplasm and pigment in its posterior cytoplasm), and completely pigmented posterior pigment epithelium.

2.

The sphincter muscle, neuroectodermally derived like the dilator muscle and pigment epithelium, lies as a ring in the pupillary stroma.

B.

The ciliary body, contiguous with the iris anteriorly and the choroid posteriorly, is divisible into an anterior ring, the pars plicata (approximately 1.5 mm wide in meridional sections), containing 70–75 meridional folds or processes, and a posterior ring, the pars plana (approximately 3.5–4 mm wide in meridional sections).

1.

The ciliary body is wider on the temporal side (approximately 6 mm) than on the nasal side (approximately 5 mm).

2.

From the scleral side inward, the ciliary body can be divided into the suprachoroidal (potential) space, the ciliary muscles (an external longitudinal, meridional, or Brücke's; a middle radial or oblique; and an internal circular or Müller's), a layer of vessels, the external basement membrane, the outer pigmented and inner nonpigmented ciliary epithelium, and the internal basement membrane.

C.

The largest part of the uvea, the choroid, extends from the ora serrata to the optic nerve.

1.

The choroid nourishes the outer half of the retina through its choriocapillaris and acts as a conduit for major arteries, veins, and nerves.

2.

From the scleral side inward, the choroid is divided into the suprachoroidal (potential) space and lamina fusca; the choroidal stroma, which contains uveal melanocytes, fibrocytes, occasional ganglion cells, collagen, blood vessels (outer or Haller's large vessels and inner or Sattler's small vessels), and nerves; the choriocapillaris (the largest-caliber capillaries in the body); and the outer aspect of Bruch's membrane.

3.

The choriocapillaris in the posterior region of the eye has a lobular structure, with each lobule fed by a central arteriole and drained by peripheral venules.

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Ophthalmology

Basil J. Zitelli MD , in Zitelli and Davis' Atlas of Pediatric Physical Diagnosis , 2018

Uvea

Inflammation of the uveal tract (iris, ciliary body, and choroid) has many potential causes, including infections (toxoplasmosis, herpes zoster and simplex, and Lyme disease), collagen vascular disease (most frequently juvenile rheumatoid arthritis and sarcoidosis), and trauma. In the majority of children, the etiologic agent cannot be determined. Advanced retinoblastoma is also in the differential diagnosis for a patient with signs that suggest uveitis.

Involvement of the anterior segment alone (iritis or anterior uveitis) may produce pain, ciliary injection (conjunctival injection most prominent at the corneal-scleral limbus), tearing, photophobia, and decreased vision. Synechiae, adhesions between the iris and lens or peripheral cornea, may produce corectopia, which is an abnormally shaped pupil. Inflammatory reaction in the anterior chamber may be viewed with the aid of a slit lamp as inflammatory cells and fibrin or protein (flare) in the aqueous fluid. With the high magnification of the slit lamp, inflammatory cells may be seen floating in the aqueous fluid much like dust is seen in bright sunlight shining through a window. If severe, iritis may make the eye appear dull or glassy as the cells and fibrin make the aqueous fluid less transparent (Fig. 20.82). Clumps of inflammatory cells may adhere to the posterior corneal surface, forming keratic precipitates. Inflammatory nodules may also be seen on the surface of the iris or at the iris border (Busacca and Koeppe nodules) in chronic uveitis.

Iritis, which is milder in degree, may be present without signs or symptoms while causing damage to the eye. Children with juvenile idiopathic arthritis must have periodic screening examinations. Patients with polyarticular disease should be examined annually, and those with positive anti-nuclear antibodies and pauciarticular disease, particularly females, who are more likely to develop ocular complications, should be examined three or four times per year to detect and treat the uveitis before complications of synechiae, cataracts, glaucoma, and macular edema develop (seeChapter 7).

Pars planitis, or intermediate uveitis, is an idiopathic, bilateral inflammation of the pars plana or pars ciliaris portions of the ciliary body. Symptoms include "floaters," and blurring of vision produced by the inflammatory debris floating in the vitreous. There may be some complaint of photophobia. Inflammatory cells in the anterior vitreous can make visualization of the retina with the direct ophthalmoscope difficult. If the inflammation is severe, it may produce leukocoria. Pars planitis is a diagnosis of exclusion made on the basis of characteristic findings and absence of laboratory results suggesting other causes of uveitis. Most cases are self-limited; however, chronic courses with exacerbations and remissions may produce visual loss resulting from cataracts, glaucoma, optic nerve inflammation, and cystoid macular edema. Retinal detachment because of membrane formation and phthisis bulbi may occur in advanced cases (Fig. 20.83).

Ocular Infections

Carlos Franco-Paredes MD, MPH , in Core Concepts in Clinical Infectious Diseases (CCCID), 2016

Infectious Causes of Uveitis

The uvea comprises the iris, ciliary body, and choroid. The iris regulates light that reaches the retina, the ciliary body produces aqueous humor, and the choroid nourishes the retina. The uvea is the pigmented, middle layer of the eye. The uvea may become infected and given its location, particularly when the choroid is involved, there is an associated retinitis (chorioretinitis). ³ The classification of uveitis includes: anterior (iritis, cyclitis, iridocyclitis), intermediate (pars plana), and posterior (choroiditis, chorioretinitis, retinitis) (Table 4.3). Uveitis may involve the cornea (keratouveitis) or the sclera (sclerouveitis), and when it involves all three parts of the uvea is termed pan-uveitis. The most common infectious cause of anterior uveitis is herpes simplex infection, followed by leprosy, and Lyme's disease. Posterior uveitis is often caused by toxoplasmosis, toxocariasis, syphilis or caused by CMV. Pan-uveitis may be associated with syphilis, tuberculosis, and invasive candidiasis. ⁴

Table 4.3. Infectious Etiologies of Uveitis (Including Retinitis)

Category a	Etiology	Core concepts
Viral	Rubella Chikungunya virus Zika virus Parvovirus B19	May produce anterior and posterior uveitis
	Anterior uveitis	Hypertensive anterior uveitis
	Varicella–Zoster virus (VZV)	Acute hypertensive anterior uveitis with granulomatous or nongranulomatous keratic precipitates (bilateral). Corneal scars maybe present and patchy or sectoral iris atrophy and vitritis. Can be seen during trigeminal zoster or associated with VZV vasculopathies
	Cytomegalovirus (CMV)	Acute anterior uveitis (Posner-Schlossman syndrome) bilateral Chronic CMV uveitis (eye discomfort and blurring)
	Herpes simplex (HSV-1 HSV-2) b	Presents with an injected eye and raised intraocular pressure with presence of corneal scars; unilateral HSV-1 causes keratouveitis and anterior uveitis HSV-1 and HSV-2 may cause acute retinal necrosis c
	Posterior uveitis	Acute Retinal Necrosis Syndrome
	VZV   HSV-1, HSV-2   EBV, CMV	Rapid onset of pan-uveitis dominated by vitritis, vasculitis, and retinitis involving the peripheral retina (Progressive Outer Retinal Necrosis – PORN)
	Measles (subacute sclerosing panencephalitis)	Bilateral necrotizing retinitis
	CMV	CMV retinal exudates, hemorrhage, vascular sheathing, and choroidal inflammation
	West Nile virus   Chikungunya	Chorioretinitis (chikungunya may also cause anterior uveitis)
Bacterial	Anterior uveitis
	Neisseria meningitidis	In patients with meningococcal meningitis
	Leptospira (leptospirosis)	Weil's disease is associated with anterior uveitis10–44% of cases
	Mycobacterium leprae (leprosy)	Bilateral acute or chronic anterior uveitis
	Brucella mellitensis –Brucella abortus	Bilateral acute anterior uveitis
	T. pallidum (syphilis)	Argyll Robertson pupil is a small irregular pupil associated with anterior uveitis
	Intermediate uveitis
	Borrelia burdorgferi (Lyme's disease)	Significant anterior segment inflammation secondary stages of Lyme's disease
	Tropheryma whippleii (Whipple's disease)	Associated with vitreous opacities and retinal-choroidal vasculitis
	Posterior uveitis
	Bartonella hensellae	Exudative focal necrotic retinitis
Protozoan	Posterior uveitis	Retinitis with optic disk edema and a macular star
	Toxoplasma gondii	Exudative focal necrotic retinitis
Mycobacterial	Posterior uveitis or Pan-uveitis Mycobacterium tuberculosis	Posterior uveitis is manifested as a bilateral multifocal choroiditis with our without retinal necrosis
Fungal	Cryptococcus neoformans	Retrobulbar neuritis of the optic nerve produces gradual loss of vision
	Candida	May produce a chronic endophtalmitis that mimics posterior uveitis d
Helminthic	Toxocara cati or Toxocara cani (toxocariasis)	Three different clinical presentations: (1) peripheral chorioretinal granuloma; (2) posterior pole chorioretinal granuloma; and (3) pan-uveitis

a

Many patients with anterior uveitis have inflammatory origin associated with the HLA-B27 haplotype. Other inflammatory conditions that may produce uveitis in association with other neurologic syndromes include: Behcet's disease, Sarcoidosis, Vogt–Koyanagi–Harada syndrome, Kawasaki's disease, inflammatory bowel disease, Cogan's syndrome, Wegener's granulomatosis, relapsing polychondritis, or multiple sclerosis.

b

HSV can cause Posner-Schlossman syndrome, Fuchs uveitis syndrome, or acute iris depigmentation and pigmentary glaucoma.

c

Acute retinal necrosis syndrome is a serious progressive ocular condition characterized by retinal necrosis, retinal vasculitis and intraocular inflammation caused by VZV, HSV-1, HSV-2, and rarely, CMV or EBV.

d

Also, chronic infection following cataract surgery caused by Propionibacterium acnes can be associated with a a chronic pseudophakic endophtalmitis that mimics anterior uveitis.

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Trauma

John F. Salmon MD, FRCS, FRCOphth , in Kanski's Clinical Ophthalmology , 2020

Anterior uvea

•

Pupil. The iris may momentarily be compressed against the anterior surface of the lens by severe anteroposterior force, with resultant imprinting of pigment from the pupillary margin. Transient miosis accompanies the compression, evidenced by the pattern of pigment corresponding to the size of the constricted pupil (Vossius ring –Fig. 22.16A). Damage to the iris sphincter may result in traumatic mydriasis, which can be temporary or permanent. The pupil reacts sluggishly or not at all to both light and accommodation. Radial tears in the pupillary margin are common (Fig. 22.16B).

•

Iridodialysis is a dehiscence of the iris from the ciliary body at its root. The pupil is typically D-shaped and the dialysis is seen as a dark biconvex area near the limbus (Fig. 22.16C). Retroillumination shows the extent of the injury (Fig. 22.16D). An iridodialysis may be asymptomatic if it is covered by the upper lid. However, monocular diplopia and glare sometimes ensue if the dehiscence is exposed in the palpebral aperture. Traumatic aniridia (360° iridodialysis) is rare. In a pseudophakic eye, the detached iris may be ejected through the cataract surgical incision (Fig. 22.17).

•

Ciliary body (see below).

Anatomy of the eye and orbit

John V. Forrester MB ChB MD FRCS(Ed) FRCP(Glasg) (Hon) FRCOphth(Hon) FMedSci FRSE FARVO , ... Eric Pearlman BSc PhD , in The Eye (Fourth Edition), 2016

Uveal tract or uvea

The uveal tract (L. uva = grape), the middle vascular pigmented layer of the eye, consists of the iris, ciliary body and choroid (see Fig. 1-10). These three components are continuous with one another and have an opening anteriorly, the pupil, and posteriorly the choroid is deficient at the optic nerve canal. The uveal tract is analogous to the vascular pia-arachnoid of the brain and optic nerve, with which it anastomoses at the optic nerve head. The choroid is described on p. 55; the iris and ciliary body are described below.

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Special Senses

Piper M. Treuting , ... Isabella Phan , in Comparative Anatomy and Histology, 2012

Gross Anatomy

The uvea consists of three components: iris, ciliary body, and choroid. The iris is a ring of tissue with a central opening forming the pupil; it separates the anterior and posterior chambers. The outer edge of the iris, known as the iris root, inserts into the ciliary body. The ciliary body is a band of tissue approximately 6 or 7  mm wide (in adult humans) located between the iris and sclera. It is divided into two parts: a thicker body (pars plicata) anterior to a flatter body (pars plana). The pars plana of the ciliary body is then continuous with the most posterior component of uvea, the choroid. The choroid extends from termination of the pars plana at the ora serrata to the optic nerve.

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Uveitis

TERRY KIM , DOUGLAS M. BLACKMON , in Primary Care Ophthalmology (Second Edition), 2005

Related Anatomy

The uveal tract is a heavily pigmented and highly vascular structure composed of three distinct anatomic components: the iris, ciliary body, and choroid (Fig. 9-1). The iris represents the most anterior portion of the uveal tract and is the only portion that is directly visible by external or slit lamp examination. It is located behind the cornea (with the space between the cornea and iris known as the anterior chamber) and is responsible for giving the eye its color. The central opening of the iris is the pupil, which constricts or dilates, depending on the amount of light entering the eye. The ciliary body is contiguous with the iris and has numerous functions, including aqueous humor production and accommodation. The choroid has a posterior location and lies between the retina and the sclera. Its main role is to provide a blood supply to the outer retina. These three components together form a continuous uveal lining that can be affected by inflammatory conditions within the eye.

Uveitis is a general term used to describe any inflammatory condition involving the uveal tract. Different classifications and terminology are used to denote the specific sites of the uveal tract primarily involved. For the anterior segment of the eye the terms iritis and iridocyclitis describe inflammation of the iris and of the iris–ciliary body complex, respectively. The terms vitritis, retinitis, and choroiditis designate inflammation in the relevant parts of the posterior segment of the eye. In this book, the term anterior uveitis means any inflammation of the iris and/or ciliary body, and the term posterior uveitis denotes any inflammation of the vitreous, retina, and/or choroid.

Identification of the segment of the eye primarily affected by uveitis guides formulation of a differential diagnosis, workup, and treatment. Some disorders appear exclusively as an anterior or a posterior uveitis, although in a few such disorders (e.g., sarcoidosis, Behçet syndrome, syphilis, tuberculosis), the inflammation can be either anterior or posterior. Because of the close anatomic and functional relationships of the vitreous, retina, and choroid, pinpointing the principal site of involvement, especially in the posterior segment, often is difficult. Classification of a uveitis as anterior or posterior may be difficult, because both segments may be involved. A severe anterior uveitis may result in anterior vitreous changes, whereas a vitritis may manifest with signs in the anterior chamber. When both segments of the uveal tract are definitely involved, the condition is called panuveitis. The term endophthalmitis is reserved for cases in which the inflammation is predominantly centered within the vitreous—a special type of posterior uveitis remarkable for its severity, necessitating prompt diagnostic workup and treatment (see Chapter 10).

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Ocular Tumors

N.V. Laver , ... N.A. Farhat , in Pathobiology of Human Disease, 2014

Background information

The uveal tract is a vascular intraocular coat composed of the iris, the ciliary body, and the choroid. The iris and ciliary body are located anterior to the ora serrata, the site that marks the beginning of the retina. The ciliary body is contiguous with the iris anteriorly and the choroid posteriorly. It can be divided into an anterior ring, or the pars plicata, and a posterior ring, or the pars plana. The vascular layer of the ciliary body is located between its muscle layer and the two layers of ciliary epithelium. The choroid is the largest and most posterior portion of the uvea, located between the retinal pigment epithelium and the sclera and extending from the ora serrata to the optic nerve. It consists mainly of blood vessels, nerve fibers, and pigmented melanocytic cells in a loose connective tissue matrix ( Figure 35 ). The choroid's prime function is to nourish the outer half of the retina. It is supplied by branches of the posterior and anterior ciliary vessels derived from the ophthalmic artery and drained by tributaries of the four or more vortex veins into the orbital ophthalmic veins and through the superior orbital fissure into the cavernous sinus.

Figure 35. Normal histology of the choroid. The choroid is composed of vessels, melanocytes, and fibroblasts. The choroid (black hashed lines) feeds the outer retina including the outer segments of the photoreceptors (black asterisk) and the retinal pigment epithelium (white asterisk). Bruch's membrane (white arrow) is the basement membrane of the retinal pigment epithelium (H&E stain, original magnification 600   ×).

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Immunologic ocular disease

James T. Rosenbaum , Justine R. Smith , in Clinical Immunology (Fourth Edition), 2013

Uveitis as a diagnostic entity

The uveal tract is the middle layer of the eye, divided into the anterior uvea (iris, ciliary body) and posterior uvea (choroid). The uvea is sandwiched between an outer layer (sclera) and an inner layer (retina). The anterior segment is separated from the posterior segment by the lens. Uveitis is an extremely variable spectrum of different diseases that includes a variety of infections and immune-mediated diseases ( Table 73.1). It is the third leading cause of preventable blindness worldwide. Inflammatory disorders of the retina (retinitis) and sclera (scleritis) frequently involve the adjacent uveal tract. Many different immune mechanisms could result in uveitis, as evidenced in animal models. These mechanisms include an immune response to a sequestered self-antigen, molecular mimicry, immune complex deposition, and the response to a toxin.

The differential diagnosis of uveitis is facilitated by identifying characteristic clinical features. Uveitis can be classified by location: anterior (iritis, iridocyclitis), intermediate (pars planitis, vitritis), or posterior (retinitis, choroiditis, retinochoroiditis, chorioretinitis, retinal vasculitis). Some forms of uveitis involve all portions of the uveal tract (panuveitis). Uveitis can be classified by course (self-limited, chronic, or recurrent); by onset (sudden, insidious); by symmetry (unilateral, bilateral); by associated complications such as glaucoma, cystoid macular edema (Figs 73.2–73.4), synechiae (for example, adhesion of the iris to the lens) (Fig. 73.5), retinal detachment, or band keratopathy (the deposition of calcium in the epithelium of the cornea) (Fig. 73.6); and by the appearance of inflammatory keratic precipitates on the endothelium of the cornea within the eye (granulomatous, nongranulomatous) (Fig. 73.7). Granulomatous diseases with large cellular concretions on the cornea or nodules within the iris include tuberculosis, syphilis, sarcoidosis, Vogt–Koyanagi–Harada disease, and sympathetic ophthalmia. The group of nongranulomatous diseases includes ankylosing spondylitis, reactive arthritis, and juvenile idiopathic arthritis. Table 73.2 shows how these parameters contribute to the differential diagnosis. Additionally, ethnic and geographic considerations factor into the differential diagnosis. For example, sarcoidosis, Behçet's syndrome, and Vogt–Koyanagi–Harada disease have strong ethnic predispositions, whereas certain infections such as cytomegalovirus in association with AIDS, leprosy, or onchocerciasis vary in prevalence based on geographic area. Together with a medical history, gender, and age, these findings help to narrow the differential diagnosis of uveitis.

The following case vignettes illustrate how important a precise and critical history and examination are. A 22-year-old man with low back pain and a red painful eye due to episodic, unilateral, sudden onset anterior uveitis is highly likely to have a spondyloarthropathy (Chapter 57). A 6-year-old girl with no ocular complaints but biomicroscopic findings of bilateral band keratopathy and leukocytes in the anterior chamber is likely to suffer from the pauciarticular subset of juvenile idiopathic arthritis (Chapter 53).

The most obvious sign of uveal inflammation is the presence of biomicroscopically visible leukocytes in the anterior chamber or the vitreous humor of the eye. Most patients with anterior uveitis will experience pain, redness, photophobia, miosis, and a variable degree of visual loss. In contrast, many forms of uveitis that affect the posterior segment will cause no redness, no pain, no change in pupil size (no macroscopically apparent signs of an inflamed eye). Instead, disturbances in visual acuity may vary from normal vision to seeing floaters, to blurred vision to blindness.

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