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THE ANATOMY OF THE UVEAL TRACT PRESENTATION
- 1. THE UVEAL TRACT FESTUSBOAMPONG KWAKYE BSc Med Sci, MBChB, MWACS, FICO (Ghana)
- 2. INTRODUCTION • The uvealtract: • Middle vascular pigmented layer of the eye, consists of the iris, ciliary body and choroid. • Continuous with one another with opening anteriorly, the pupil • Posteriorly the choroid is deficient at the optic nerve canal.
- 3. The eye has3 basic layers, or “coats” 1. Outer fibrous coat (the walls and window) Sclera & cornea 2. Middle vascular coat iris, ciliary body & choroid 3. Inner neural coat (essentially part of the brain) retina
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- 5. THE IRIS • Thin,heavily pigmented, contractile circular disk • Suspended in the frontal or coronal plane anterior to the lens and ciliary body. • The iris separates the anterior and posterior chambers • The iris is attached by its root at the angle (iridocorneal) of the anterior chamber where it merges with the ciliary body and trabecular meshwork.
- 6. THE IRIS • 12mmin diameter • Circumference of 37mm. • Pupil regulates amount of light entering the eye • The pupil may vary from 1 to 8 mm in diameter. • Normal size 3-4mm • Iridonesis
- 7. Structure • The pupilmargin and iris root are thin, and hence more susceptible to tearing (iridodialysis). • Anterior surface divided into two zones by collarette. • ciliary zone and pupil zone • The anterior surface has radial streaks (straight when the pupil is contracted and wavy when dilated) and contraction furrows (more noticeable in dilated irides).
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- 9. MICROSCOPIC STRUCTURE • 1.Anterior limiting layer • 2. Iris stroma • 3. Anterior epithelial layer • 4. Posterior pigmented epithelial layer
- 10. MICROSCOPIC ANATOMY Anterior borderlayer • consisting of a dense collection of fibroblasts, melanocytes and a few interspersed collagen fibres. • Determines the colour of the iris • Deficiencies in the anterior border layer are evident macroscopically as crypts.
- 11. MICROSCOPIC ANATOMY Stroma • Looseconnective tissue containing fibroblasts, melanocytes and collagen fibres • Contains mast cells and macrophages • Lying within the stroma close to the pupil margin is the sphincter pupillae muscle, a circumferential ring of smooth muscle fibres about 1mm in width. • The sphincter muscle consists of smooth muscle cells • Innervation by parasympathetic nerve fibres from the oculomotor nerve (postganglionic fibres from the ciliary ganglion travel via the short ciliary nerves)
- 12. MICROSCOPIC ANATOMY Dilator pupillaemuscle • Filled with myofilaments • Extend from iris root towards pupil • When the muscle contract, it pulls the pupillary margin towards the ciliary body, dilating the pupil • Innervated by sympathetics via long ciliary nerve
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- 14. MICROSCOPIC ANATOMY Posterior pigmentepithelium • Heavily pigmented • large cuboidal epithelial cells that appear black macroscopically
- 15. MICROSCOPIC ANATOMY 3. AnteriorEpithelial Layer • Anterior continuation of pigment epithelium of ciliary body • Lacks melanocytes Posterior pigmented epithelial layer • Anterior continuation of non pigmented epithelium of ciliary body which in turn is the continuation of sensory retina • Contain abundant columnar type pigment cells • It curves around the pupillary margin and extends for a short distance onto anterior border layer of iris stroma as the pigment ruff
- 16. PUPIL MOVEMENTS • Mydriasis(dilation) occurs in • low light intensity • states of excitement • fear. • action of the dilator pupillae muscle. • Miosis (contraction) occurs in • illuminated conditions • during convergence • while sleeping. • As a result of the action of the sphincter pupillae.
- 17. BLOOD SUPPLY OFTHE IRIS • Form bulk of iris stroma • They arise mainly from major arterial circle • Some also arise directly from anterior ciliary arteries • Veins drain into the ciliary body and eventually the vortex veins • Responsible for radial streaks seen on anterior surface of iris
- 18. NERVE SUPPLY OFTHE IRIS • The sensory nerves are branches of the long and short ciliary nerves, themselves branches of the nasociliary nerve (ophthalmic division of the trigeminal). • The autonomic innervation of the iris muscles is discussed under stroma.
- 19. THE CILIARY BODY •5–6 mm wide ring of tissue that extends from the scleral spur anteriorly to the ora serrata posteriorly. • It is divided into two zones, an anterior pars plicata (corona ciliaris) and a posterior pars plana • Triangular in cross-section; its base faces the anterior chamber and the apex blends posteriorly with the vascular choroid
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- 21. THE CILIARY BODY 1)Pars plicata • Anterior part • About 2 to 2.5mm long • Contains ciliary muscles • Have finger like processes -ciliary processes 70 radially arranged 2) Pars plana • Posterior smooth part • 5mm wide temporally • 3 mm wide nasally
- 22. MICROSCOPIC STRUCTURE From withoutinwards, consists of five layers: • 1) Supraciliary lamina • 2) Stroma of the ciliary body • 3) Layer of pigmented epithelium • 4) Layer of non-pigmented epithelium • 5) Internal limiting membrane
- 23. THE CILIARY BODY Stromaof the ciliary body • Consists of connective tissue and fibroblasts • Embedded in it: a. Ciliary muscle b. Blood vessels c. Nerves d. Pigment cells and other cells
- 24. THE CILIARY BODY Ciliarymuscle • Non-striated muscle • Occupies most of the outer part of the ciliary body • Three main groups: • The longitudinal or meridional fibres • The oblique or radial fibres • The circular fibres
- 25. THE CILIARY BODY 1)Longitudinal or meridional fibres • Most external and closest to the sclera • Pass posteriorly into the stroma of ciliary body 2) Oblique or radial fibres • Radiate out from the scleral spur 3) Circular fibres • Occupy anterior and inner portion of the ciliary body • Nearest to the lens • Runs parallel to the limbus
- 26. THE CILIARY BODY •Main action of all parts of ciliary muscles is to slacken the suspensory ligament of the lens and thus helps in Accommodation. • Contraction of the ciliary muscle, especially longitudinal and circular fibres pulls the ciliary body forward in accommodation. • Longitudinal muscle fibres form tendinous attachment to the scleral spur: their contraction increases aqueous flow by opening up the spaces of trabecular meshwork.
- 27. THE CILIARY BODY Vascularstroma • Contains major arterial circle just in front of circular fibres • Arterial circle is formed by the anastomosis between the long posterior ciliary arteries and anterior ciliary arteries and send branches to iris and ciliary body
- 28. Ciliary processes • Whitishfinger-like projections from pars plicata part of the ciliary body • 70 to 80 in number • Each process is about 2mm long and 0.5mm in diameter • Are the site of aqueous production
- 29. Ultrastructure of ciliaryprocesses Consists of: • The network of capillaries • Stroma of ciliary processes • Two layers of epithelium
- 30. Ultrastructure of ciliaryprocesses The network of capillaries • Occupies the centre of each process • Each capillary consists of a very thin endothelium with fenestration Stroma of the ciliary process • Very thin • Separates capillary network from epithelial layers Two layers of epithelium • Their apical surfaces in apposition to each other • Outer pigmented epithelium: Contains numerous melanin granules • Inner non-pigmented epithelium: The tight junction between cells of this layer form blood aqueous barrier
- 31. Nerve supply ofthe ciliary body • The ciliary body has • Parasympathetic • Sympathetic • sensory innervations. • Parasympathetic innervation: via short ciliary nerves through the oculomotor (III) • Sympathetic innervation reach the orbit as either direct branches of the internal carotid plexus or by joining the ophthalmic division of the trigeminal and its main branch in the orbit, the nasociliary nerve. • Sensory innervation from the nasociliary nerve; however, the function of these fibres is unknown.
- 32. Accommodation • To bediscussed under lens physiology • During accommodation there is some degree of forward and inward shift of the ciliary body, which serves to slacken the tension on the zonules, thus increasing the refractive power of the lens
- 33. CHOROID • Posterior portionof the middle vascular coat • Extremely vascular • Extends from optic disc to ora serrata • The inner surface: smooth, brown and lies in contact with RPE • The outer surface: rough and attached to sclera • Posteriorly-0.22mm thick • Anteriorly-0.1mm
- 34. CHOROID • Firmly attachedto the margin of the optic disc • Loosely at points where vessels and nerves enter it • Attachment to sclera is strongest
- 35. Microscopic Structure • Fromwithout inwards, consists of four layers: • Suprachoroidal lamina • Stroma of the choroid • Choriocapillaries • Bruch’s membrane
- 36. Microscopic Structure 1) Suprachoroidallamina • Made of condensed collagen fibres, melanocytes and fibroblasts 2) Stroma of the choroid • Contains vessels, nerves, cells & connective tissue
- 37. Microscopic Structure 3) Choriocapillaries •Consists of a rich bed of wide bore fenestrated capillaries • Receives most of its blood from medium and large vessels of stroma • Nourishes RPE & outer layers of sensory retina • Density greatest at macula 4) Bruch’s membrane • Innermost layer of choroid
- 38. BLOOD SUPPLY OFTHE UVEAL TRACT • Uveal tract supplied by 3 sets of arteries: • 1) Short posterior ciliary arteries • 2) Long posterior ciliary arteries • 3) Anterior ciliary arteries
- 39. Venous Drainage Vortex veins •Four in number • Two superior vortex veins open into superior ophthalmic vein • Two inferior vortex veins open into inferior ophthalmic vein
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