Uveal Tissue: The Anatomy, its structures, Physiology

This presentation provides a comprehensive overview of the uveal tissue of the eye, which includes the iris, ciliary body, and choroid. It covers the anatomy, vascular supply, and physiological functions, along with its role in ocular health. The PPT is designed for optometry and ophthalmology students, educators, and eye care professionals, offering a clear understanding of the structure, function, and clinical relevance of the uveal tract.

1. UVEA Reshu Yadav Assistant Professor SHS CSJMU

2. UVEAL TISSUE Uveal tissue constitutes the middle vascular part of the eyeball. From anterior to posterior, it can be divided into three parts, namely, iris, ciliary body and choroid.

3. IRIS It is the anterior most part of the uveal tract. It is a thin circular disc corresponding to the diaphragm of a camera. Its average diameter is 12 mm and thickness is about 0.5 mm. In its center (slightly nasal), is an aperture of about 3-4 mm called the pupil, which regularizes the amount of light reaching the retina. At the periphery, the iris is attached to the middle of anterior surface of the ciliary body. It divides the space between the cornea and lens into anterior and posterior chambers.

4. Microscopic appearance Anterior surface of the iris Anterior surface of the iris – It can be divided into a ciliary zone and a pupillary zone by a zigzag line called the collarette (which represents the attachment of pupillary membrane). The collarette, which lies about 2 mm from the pupil margin, is the thickest region of the iris.

5. Ciliary zone- It is characterized by- Radial streake Crypts Contraction furrows Pupillary zone- This part of the iris (about 1.6 mm wide) lies between the collarette and pigmented pupillary frill

6. Posterior surface of the iris It is dark brown or black in color. It looks smooth with naked eye. However, when seen under magnification, it presents following radial and circular furrows and folds- Schwalbe's contraction folds Schwalbe's structural furrows The circular furrows

7. Microscopic structure The iris consists of four layers, which from anterior to posterior are as follows- Anterior limiting layer Iris stroma Anterior epithelial layer Posterior pigmented epithelial layer

8. Anterior limiting layer It is the anterior most condensed part of the stroma. It consists of melanocytes and fibroblasts. The definitive color of the iris depends upon this layer. In blue iris, this layer is thin and contains few pigment cells. While in brown iris, it is thick and doubly pigmented.

9. Iris stroma It forms the main bulk of the iris tissue and consists of loosely arranged collagenous network with mucopolysaccharide ground substance. In it, are embedded the sphincter pupillae muscle, dilator pupillae muscle, blood vessels, nerves, pigment cells and other cells which include lymphocytes, fibroblasts and macrophages.

10. Sphincter pupillae muscle- It forms one-millimeter broad circular band in the pupillary part of iris. It is supplied by the para-sympathetic fibers through the third nerve( Oculomotor nerve). It constricts the pupil. 2. Dilator pupillae muscle- It lies in the posterior part of the stroma of ciliary zone of the iris It is supplied by the cervical sympathetic. It dilates the pupil.

11. Anterior epithelial layer It is the anterior continuation of the pigment epithelium of retina and ciliary body.

12. Posterior pigmented epithelial layer It is the anterior continuation of the non-pigmented epithelium of the ciliary body which in turn is the continuation of the sensory retina.

13. CILIARY BODY It is the forward continuation of the choroid at ora serrata. In cut section, it is triangular in shape. The anterior side of triangle forms the part of the angle of anterior and posterior chamber. In its middle, it is attached to the iris. The ciliary body is divided into two parts- The anterior part (about 2-2.5 mm) having finger-like ciliary processes is called pars plicata (corona ciliaris) and the posterior smooth part (about 5 mm wide temporally and 3 mm wide nasally) is called pars plana

14. Microscopic structure Ciliary body consists of following five layers- Supraciliary lamina Stroma of the ciliary body Layer of pigmented epithelium Layer of non-pigmented epithelium Internal limiting membrane

15. Supraciliary lamina It is the outermost condensed part of stroma and consists of pigmented collagen fibers. Posteriorly, it is a continuation of the suprachoroidal lamina and anteriorly it becomes continuous with the anterior limiting membrane of the iris.

16. Stroma of the ciliary body It consists of connective tissue of collagen and fibroblasts. Embedded in the stroma are ciliary muscle, vascular stroma, nerves, pigment cells and other cells. Ciliary muscle- It is a non-striated muscle which occupies most of the outer part of the ciliary body. It consists of three parts: The longitudinal or meridional fibres The circular fibres Radial fibres

17. Actions of ciliary muscle - Main action of all the parts of the ciliary muscle is to slacken the suspensory ligaments of the lens and thus help in accommodation. Radial fibers also help in aqueous outflow.

18. Layer of pigmented epithelium It is a forward continuation of the retinal pigment epithelium. Anteriorly, it is continuous with the anterior pigmented epithelium of the iris.

19. Layer of non-pigmented epithelium It consists mainly of low columnar or cuboidal cells, and is a forward continuation of the sensory retina which stops at the ora serrata. It continues anteriorly with the posterior (internal) pigmented epithelium of the iris.

20. Internal limiting membrane It lines the nonpigmented epithelium and is the forward continuations of the internal limiting membrane of the retina.

21. Ciliary processes Ciliary processes are whitish finger-like projections from the pars plicata part of the ciliary body. They are about 70-80 in number and form the site of aqueous production. Each process is about 2 mm long and 0.5 mm in diameter.

22. Ultrastructure of the ciliary process Each ciliary process is composed of three basic components: the network of capillaries, stroma and two layers of the epithelium. Network of capillaries- It occupies the center of each process. Each capillary consists of a very thin endothelium with fenestrae or false pores which is lined by a basement membrane.

23. 2 . Stroma of ciliary processes- It is very thin and separates the capillary network from the epithelial layers. It consists of ground substance (containing mucopolysaccharides, proteins and solute of plasma), a few collagen connective tissue fibres and wandering cells.

24. 3. Two layers of epithelium- These are arranged with their apical surfaces in apposition to each other. The tide junction between the cells of this layer creates part of the blood aqueous barrier.

25. CHOROID Choroid is the posterior most part of the vascular coat of the eyeball. It extends from the optic disc to ora serrata. Its inner surface is smooth, brown and lies in contact with pigment epithelium of the retina. The outer surface is rough and lies in contact with the sclera. It is thicker posteriorly (0.22 mm) than anteriorly (0.1 mm).

26. Microscopic structure The choroid consists of the following four layers- Suprachoroidal lamina (lamina Fusca) Stroma of the choroid Choriocapillaris Basal lamina (Bruch's membrane or lamina vitrae)

27. Suprachoroidal lamina (lamina fusca ) It is a thin (10-34 mm) membrane of condensed collagen fibres, melanocytes and fibroblasts It is continuous anteriorly with the supraciliary lamina of the ciliary body & posteriorly with suprachoroidal space which contains long and short posterior ciliary arteries and nerves.

28. Stroma of the choroid It consists of loose collagenous tissue with some elastic and reticular fibres. It contains plenty of pigment cells and other cells like macrophages, mast cells, plasma cells and lymphocytes The outer layer of large vessels (Haller's layer) and the inner layer of medium vessels (Sattler's layer)

29. Choriocapillaris It consists of a rich capillary network which receives most of its blood from the medium and large vessels of the stroma. It nourishes the pigment epithelium and the outer layers of sensory retina

30. Basal lamina (Bruch's membrane) Bruch's membrane is the innermost layer of choroid and is approximately 2-4 mm in thickness It is a multilayered structure which lies between the choriocapillaris and RPE.

31. BLOOD SUPPLY OF UVEAL TRACT Arterial supply- The uveal tract is supplied by three sets of arteries- Short posterior ciliary arteries- These arise as two trunks from the ophthalmic artery. Each trunk divides into 10-20 branches which pierce the sclera around the optic nerve and supply the choroid in a segmental manner.

32. 2. Long posterior ciliary arteries- These are two in number (nasal and temporal). These pierce the sclera obliquely on medial and lateral side of the optic nerve and run forward in the suprachoroidal space to reach the ciliary muscle, without giving any branch.

33. 3. Anterior ciliary arteries- These are 7 in number: 2 each from the arteries of superior rectus, inferior rectus and medial rectus muscles and one from that of lateral rectus muscle. These arteries pass anteriorly in the episcleral, give branches to sclera, limbus and conjunctiva, and ultimately pierce the sclera near the limbus to enter the ciliary muscle.

34. Venous drainage Veins draining uveal blood are- Anterior ciliary veins - They carry blood only from the ciliary muscle, they are smaller than the corresponding arteries. Smaller veins from the sclera- They only carry blood from the sclera and not from the choroid. These are smaller than the corresponding arteries.

35. 3. Venae verticosae (vortex veins or posterior ciliary veins)- These are usually 4 in number (superior temporal, inferior temporal, superior nasal and inferior nasal). They pierce the sclera obliquely on each side of the superior rectus and inferior rectus muscles, about 6 mm behind the equator. At their choroidal end, the vortex veins have an ampulliform dilatation. Drain blood from whole of the choroid Receive small veins from optic nerve head & also receive small veins from the retina.