▃Anatomy and Physiology

Uveal tract is the middle and highly vascular coat of eyeball. It consists of the following three parts: iris, ciliary body, and choroid.

Iris is the anterior most part of the uveal tract. Ciliary body extends from the scleral spur anteriorly up to ora serrata posteriorly. Choroid extends from the ora serrata anteriorly up to optic disc posteriorly. Ciliary body and choroid line the sclera. These anatomically distinct parts of the uveal tract are closely related; hence, the inflammatory processes affecting one part often involve the other part too.

■Iris

It forms a free circular diaphragm in the coronal plane which contains an aperture in the center called pupil (diameter 2.5–4 mm). The iris is attached with the ciliary body. This attachment is called root. The root is the thinnest part; hence, prone to tear on trauma. Collarette divides the anterior surface of iris into the pupillary and ciliary zones. Crypts (minute depressions) are mainly found in the ciliary zone (Fig. 8.1).

Microscopically, iris is composed of four layers (anterior to posterior, Fig. 8.2):

•Anterior limiting layer: It covers the anterior surface of the iris and is deficient in areas of crypts; this allows easy transfer of fluid between iris and anterior chamber.

•Iris stroma: It consists of loosely arranged collagenous network and also contains–

♢Blood vessels which run in a radial direction.

♢Nerves.

♢Pigment cells.

♢Two unstriped muscles: sphincter pupillae and dilator pupillae (Fig. 8.3 and Table 8.1).

•Anterior pigmented epithelium consists of flattened cells.

•Posterior pigmented epithelium consists of cuboidal cells. These two layers of pigmented epithelium, developmentally, are derived from retina and are continuous with each other at the pupillary margin.

The sensory nerve supply of the iris is derived from the trigeminal (Vth) nerve.

■Ciliary Body

It is triangular in cross-section with the base forward. The iris is attached at the middle of the base, so the base forms part of the angle of the anterior and posterior chambers. The outer surface of the ciliary body lies against the sclera. The stroma of the ciliary body is composed of collagen fibers as well as ciliary muscle, vessels and nerves. The inner surface of the ciliary body is divided into two regions:

Anterior part: It is called pars plicata and has approximately 40 villi which form ridges around the circumference called which are known as ciliary processes.

Posterior part: It is smooth and called pars plana (Fig. 8.4).

Ciliary Processes

The core of ciliary processes contains blood vessels embedded in loose connective tissue. These are the site of aqueous production. The inner surface is lined by epithelium which is two layered (Fig. 8.5):

Outer pigmented layer: It is a continuation of the retinal pigment epithelium; in forward direction, it is continuous with anterior pigmented epithelium of iris.

Inner nonpigmented layer: It represents forward continuation of sensory retina and is continuous with posterior pigmented epithelium of iris.

Ciliary Muscle (AN41.3)

It is an unstriped muscle and forms the chief mass of the ciliary body. Ciliary processes contain no part of the ciliary muscle. It is composed of three types of fibers with a common origin.

1.Meridional (longitudinal) fibers: These are inserted at the scleral spur and run anteroposteriorly on the inner aspect of sclera. These are involved in regulation of aqueous outflow.

2.Radial (oblique) fibers: These are inserted in the root of iris in close relation to the dilator muscle.

3.Circular fibers: These help in accommodation.

Nerve supply of ciliary muscle: It is supplied by the oculomotor nerve (through short ciliary nerves). Its sensory nerve supply is derived from the trigeminal (Vth) nerve.

Functions of Ciliary Body

The ciliary body serves the following functions:

•Formation of aqueous humor (by ciliary processes).

•Accommodation (through circular fibers of the ciliary muscle).

•Regulation of aqueous outflow (through insertion of the meridional fibers of ciliary muscle at the scleral spur).

■Choroid

It is an extremely vascular part of the uveal tract. Outer surfaces (suprachoroidal lamina) lie in contact with sclera, with a potential space between the two structures, the suprachoroidal space, which contains long and short posterior ciliary arteries and nerves. The inner surface is in contact with Bruch’s membrane, a thin elastic membrane. The stroma of choroid is largely composed of blood vessels which increase in size from within outward . Thus, the innermost (immediately beneath Bruch’s membrane) zone comprises ciliary plexus formed by fenestrated vessels called choriocapillaris which nourish the outer layer of retina (Fig. 8.6).

Nerve supply of choroid: The sensory fibers are derived from the trigeminal (V) nerve, and the vasomotor function is regulated by autonomic nerves (Table 8.2).

■Blood Supply of Uveal Tract

Arterial supply: Uveal tract is supplied by three groups of ciliary arteries:

•Short posterior ciliary arteries.

•Long posterior ciliary arteries.

•Anterior ciliary arteries.

The choroid is supplied by short posterior arteries, reinforced anteriorly by anastomosed recurrent branches from the major arterial circle of iris. Ciliary body and iris are supplied by long posterior ciliary arteries and anterior ciliary arteries via the major arterial circle.

Venous drainage: Uveal tract is drained by the following three groups of ciliary veins:

•Short posterior ciliary veins.

•Vortex veins (venae vorticosae).

•Anterior ciliary veins.

Short posterior ciliary veins receive blood only from the sclera. Vortex veins (four in number) receive blood from the uveal tract with the exception of the outer part of ciliary muscle. These open into ophthalmic veins. Anterior ciliary veins receive blood from the outer part of ciliary muscle.

The high vascularity of the uveal tract makes it vulnerable for its frequent involvement in various infections as well as systemic vascular and immune diseases.

▃Inflammation (Uveitis) (OP6.1, 6.2, 6.3, 6.8)

The inflammation of the uveal tract is generally not confined to a single part of the uvea and tends to involve uvea as a whole. The inflammation of iris (iritis) is almost always associated with some amount of inflammation of the ciliary body (cyclitis) and vice versa.

■Classification

Uveitis may be classified anatomically, clinically, etiologically, and pathologically as follows:

•Anatomical classification (

♢Anterior uveitis.

♢Intermediate uveitis.

♢Posterior uveitis.

♢Panuveitis.

•Clinical classification:

♢Acute uveitis.

♢Chronic uveitis.

♢Recurrent uveitis.

•Etiological classification:

♢Infective uveitis.

♢Secondary to systemic diseases.

♢Neoplastic uveitis.

♢Traumatic uveitis.

♢Idiopathic uveitis.

•Pathological classification:

♢Granulomatous.

♢Nongranulomatous.

The “International Uveitis study group” has recommended to follow anatomical classification.

Anatomical Classification of Uveitis

Based on the anatomical site of involvement, uveitis can be:

•Anterior uveitis: It is the inflammation of the anterior uvea (iris and pars plicata of ciliary body). It is further subdivided into–

♢Iritis: Inflammation predominantly involves iris.

♢Anterior cyclitis: Inflammation predominantly involves the anterior part of ciliary body (pars plicata)

♢Iridocyclitis: Both iris and pars plicata of the ciliary body are equally involved in this condition.

•Intermediate uveitis is subdivided into:

♢Pars planitis: There is predominant involvement of pars plana (the posterior part of ciliary body).

♢Basal retinochoroiditis: There is predominant involvement of the extreme periphery of retina.

•Posterior uveitis: It is the inflammation of the uveal tract posterior to vitreous base. It can be subdivided into:

♢Choroiditis: It is the primary involvement of choroid which may be focal, multifocal, or diffuse.

♢Chorioretinitis: Choroiditis associated with retinitis is known as chorioretinitis.

♢Retinochoroiditis: Here, retina is primarily involved with associated choroidal involvement.

•Panuveitis: It is the inflammation involving the entire uveal tract.

Clinical Classification of Uveitis

Uveitis is classified according to the mode of onset and duration:

•Acute: It is sudden in onset and symptomatic too. It persists for ≤6 weeks.

•Chronic: It has insidious onset and asymptomatic. It persists for months/years, or if inflammation recurs in less than 3 months after cessation of therapy.

•Recurrent: When there are repeated episodes of uveitis with period of inactivity (without treatment) between the episodes lasting at least 3 months, it is called recurrent uveitis.

Etiological Classification of Uveitis

•Infective uveitis: It may be due to:

♢Bacterial infections, for example, tuberculosis, leprosy, gonorrhea and brucellosis.

♢Spirochaetal infections, for example, syphilis, leptospirosis and Lyme disease.

♢Viral infections, for example, herpes simplex, herpes zoster, cytomegalovirus (CMV) and acquired immune deficiency syndrome (AIDS).

♢Fungal infections, for example, presumed ocular histoplasmosis syndrome (POHS), candidiasis and cryptococcosis.

♢Parasitic infections, for example, toxoplasmosis, toxocariasis and onchocerciasis.

•Secondary to systemic diseases: Uveitis is found in association with the following diseases:

♢Auto immune disorders

–Ankylosing spondylitis.

–Reiter’s disease (or syndrome).

–Psoriatic arthritis.

–Juvenile chronic arthritis (JCA).

–Behcet’s syndrome.

–Rheumatoid arthritis.

–Systemic lupus erythematosus (SLE).

–Polyarteritis nodosa.

–Vogt–Koyanagi–Harada (VKH) syndrome.

♢Sarcoidosis

♢Metabolic disorder: Diabetes mellitus.

♢Gastrointestinal disorders

–Whipple’s disease.

–Ulcerative colitis.

–Crohn disease.

•Neoplastic uveitis: May be associated with

♢Acute leukemia.

♢Iris melanoma.

♢Reticulum cell sarcoma of brain.

♢Large cell lymphoma.

♢Histiocytic cell sarcoma.

All these can present features of uveitis and are termed “masquerade syndromes.”

•Traumatic—trauma to the eye may be:

♢Blunt trauma: It may cause uveitis due to mechanical or irritative effect to intraocular blood.

♢Penetrating injury.

♢Surgical trauma.

•Idiopathic (uveitis of unknown etiology):

♢Pars planitis.

♢Sympathetic ophthalmitis.

♢Glaucomatocyclitic crisis (Posner–Schlossman syndrome).

♢Uveitis-glaucoma-hyphema (UGH) syndrome.

♢Geographical choroidopathy.

•Miscellaneous:

♢Lens-induced uveitis: It may be phacolytic or phacoanaphylactic.

♢Fuch’s heterochromic iridocyclitis.

♢Uveitis associated with ocular ischemia: Ischemia alters permeability of vessels, leading to leakage of cells and proteins which, in turn, result in uveitis.

Pathological Classification of Uveitis

Pathologically, uveitis can be of two types: nongranulomatous and granulomatous (Table 8.3).

Nongranulomatous uveitis: In this type, the reaction is exudative (or allergic). Exudation of protein-rich fluid results in aqueous flare. Outpouring of lymphocytes and polymorphs which adhere to corneal endothelium results in fine keratic precipitates (KPs). It tends to be of acute onset and short duration.

Granulomatous uveitis: It is usually due to invasion of eye by living organisms, but it can also be of immunological etiology. So, hypersensitivity reaction is common in granulomatous uveitis and exudative type of reaction is not encountered. This type of inflammation tends to be of insidious onset and chronic course with minimal aqueous flare. It is common in tuberculosis, leprosy, sarcoidosis, syphilis, etc. Granulomatous uveitis is characterized by dense nodular infiltration of the uveal tissue (Flowchart 8.1).

■Investigations

The investigations are ordered after assessing the type of uveitis suspected on clinical examination. If there is single attack of mild, unilateral, acute anterior uveitis without specific features of underlying disease, investigations are not necessary. Indications for investigations are recurrent uveitis, bilateral uveitis, and posterior uveitis. Table 8.4 lists the investigations performed for uveitis along with the rationale behind those investigations.

▃Anterior Uveitis (Iridocyclitis) (OP6.1, 6.2, 6.3, 6.8) (OP6.6)

Clinically, anterior uveitis (iridocyclitis) may present in two forms: acute and chronic, as explained in Table 8.5.

■Clinical Features

Symptoms

The main symptoms of acute anterior uveitis are pain, photophobia, blurred vision, redness, and reflex lacrimation through fifth nerve stimulation supplying iris. Pain is of sudden onset, worse at night, and radiates along distribution of 1st (ophthalmic) division of 5th nerve to forehead, scalp and cheek. Causes of blurring of vision are depicted in Fig. 8.8.

Signs

Anterior uveitis is characterized by signs, as depicted in Fig. 8.9.

1.Circum corneal (ciliary) congestion: It is deep and has a violaceous hue (Fig. 8.10).

2.Corneal signs:

•Endothelial dusting: It is the deposition of small inflammatory cells on corneal endothelium in the early stages of uveitis. It gives rise to a dirty appearance.

•KPs: These are the clusters of inflammatory cells on corneal endothelium. These appear only after a few days. They are seldom present in simple iritis but are characteristics of cyclitis and iridocyclitis (Fig. 8.11).

3.Anterior chamber signs:

•Aqueous cells: Presence of circulating cells is a strong indication of an active inflammation of uvea.

•Aqueous flare: It is due to leakage of proteins into aqueous and not necessarily a sign of active uveitis (Fig. 8.12a).

•Hypopyon (OP6.4): It is a feature of intense inflammation where poured polymorphs settle down at the bottom of anterior chamber to form hypopyon with a horizontal level (Fig. 8.12b).

Grading of aqueous flare and cells is performed with 2 mm long and 1 mm wide slit beam of slit lamp biomicroscope. Cells are graded by counting cells per field, while aqueous flare is graded by degree of obscuration of iris details (Table 8.6).

4.Four iris signs:

•Iris pattern becomes blurred and indistinct as exudation in iris stroma causes filling of crypts on the anterior surface of iris (muddy iris).

•Iris nodules: These are of two types: Koeppe’s nodules, found at pupillary margin, and Busacca nodules, found on anterior surface of iris. These nodules typically occur in granulomatous uveitis.

•Posterior synechiae: These are the adhesions between anterior lens surface and posterior surface of iris. Posterior synechiae show predilection for lower part of pupil in early stages due to the gravitation of exudates. These must not be allowed to become organized. These may be segmental (adhesions at some points) or annular, that is, ring synechiae (extending for 360 degree). The condition is called seclusio pupillae.

•Iris atrophy: It is an important feature of Fuchs heterochromic iridocyclitis and uveitis due to herpes virus.

5.Pupillary signs:

•Size—miosis: Due to spasm of sphincter pupillae.

•Shape—irregular shape: When pupil with segmental posterior synechiae is dilated with mydriatic (atropine and homatropine), intervening portion of pupillary margin (between posterior synechiae) dilate and pupil assumes a festooned appearance (festooned pupil, Fig. 8.13).

•Reaction—sluggish pupillary reaction (due to edema of iris).

If exudation from iris and ciliary body is profuse, it may cover the surface of iris as well as the pupillary area. This type of uveitis is called plastic iridocyclitis. Exudates upon iris surface may become organized and contract, resulting in eversion of pupillary margin (ectropion pupillae). Exudates may block the pupil and get organized. The condition is called occlusio pupillae.

6.Lenticular sign: Pigment dispersal on anterior capsule of lens.

7.Anterior vitreous sign: Vitreous cells (inflammatory cells in anterior vitreous).

In iritis, aqueous cells are more than vitreous cells.

In iridocyclitis, cells are equally distributed in aqueous and vitreous humor.

In cyclitis, exudates in vitreous are more. When they organize, they form cyclitic membrane behind the lens.

To understand the development of signs in anterior uveitis, it is necessary to remember the anatomy and pathological changes occurring in the iris (Fig. 8.14 and Flowchart 8.2).

Anatomy of Iris

1.Iris has crypts on the anterior surface of ciliary zone.

2.Iris has blood vessels running in the radial direction.

3.Iris has spongy stroma consisting of loosely arranged collagenous network.

4.Iris has unstriped muscle fibers.

■Investigations

•Hematological investigations (total leucocyte count [TLC], differential leucocyte count [DLC], erythrocyte sedimentation rate [ESR], blood sugar).

•Serological test (antinuclear antibody [ANA], rheumatoid factor, human leucocyte antigen [HLA] typing, venereal disease research laboratory [VDRL], fluorescent treponemal antibody absorption test [FTA-ABS], enzyme-linked immunosorbent assay [ELISA], etc.).

•Radiological investigations (X-ray chest and sacroiliac joints, CT scan).

•Skin test (Mantoux test and Kveim test) .

•Urine examination to rule out urethritis.

•Anterior chamber paracentesis for polymerase chain reaction (PCR) to diagnose organisms and cellular analysis.

■Differential Diagnosis (OP3.1)

Acute iridocyclitis must be differentiated from acute conjunctivitis and acute angle closure glaucoma (Table 8.7). Dilatation of pupil is urgently required in acute anterior uveitis (iridocyclitis), but it may worsen acute angle closure glaucoma, so it is a must to differentiate between the two.

■Treatment

It includes general treatment of uveitis with cycloplegics and mydriatics, corticosteroids and immunosuppressives; specific treatment of underlying cause; and treatment of sequelae and complications.

General Treatment (OP6.9)

Cycloplegics and Mydriatics

Short-acting preparations are Tropicamide 0.5% or 1% drops and Cyclopentolate 1% drops, while long-acting preparations are Homatropine 2% drops and Atropine 1% drops or ointment (most powerful cycloplegic).

Mode of Action

These relieve the spasms of ciliary muscle and sphincter pupillae so, give comfort and rest to the eye. These prevent formation of posterior synechiae. It is best achieved by short-acting cycloplegics which keep the pupil mobile. Pupil should not be kept constantly dilated in chronic anterior uveitis, as posterior synechiae can still form in dilated position. These break down recently formed posterior synechiae. Once synechiae have formed, topical Atropine 1% drop or ointment is used.

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