Uvea II PDF

Uvea II Karen Gil MD, MHSN Iris Histology Four layers: – Anterior border layer – Stroma and sphincter muscle – Anterior epithelium and dilator muscle – Posterior epithelium Ciliary Body – Pars Plana Ora serrata: – Dentate process or teeth – Oral bays Zonule fibers insertion – Pars Plicata Valleys of...

Uvea II Karen Gil MD, MHSN Iris Histology Four layers: – Anterior border layer – Stroma and sphincter muscle – Anterior epithelium and dilator muscle – Posterior epithelium Ciliary Body – Pars Plana Ora serrata: – Dentate process or teeth – Oral bays Zonule fibers insertion – Pars Plicata Valleys of Kuhnt Ciliary Body Ciliary Muscle Composed of smooth muscle fibers Longitudinal muscle fibers of Brücke Radial Annular Ciliary Body Choroid Choroid Suprachoroid Lamina Choroid Stroma – Haller’s layer – Sattler’s layer – Choriocapillaris Bruch’s membrane Functions of the Iris Acts as a diaphragm to regulate the amount of light entering the eye Iris muscles innervated separately – Parasympathetically – sphincter muscle – constriction of the pupil – Sympathetically – dilatator muscle – pupillary enlargement Functions of the Ciliary Body Production and secretion of the aqueous humor Muscles causes accommodation and can affect aqueous outflow – some longitudinal fibers of the trabecular meshwork are attached to the ciliary muscle so the configuration of the TM changes and facilitate aqueous movement through the anterior chamber angle structures Function of the Ciliary Body Accommodation – – Ability of the eye to change power and bring near objects into focus on the retina – Accomplished by increasing the power of the lens Contraction of the longitudinal fibers of the ciliary muscle pulls the choroid forward Contraction of the circular fibers draws the ciliary body closer to the lens – decreasing the diameter of the ring formed by the ciliary body – release the tension of the zonule fibers – lens capsule adopt a more spherical shape The lens thickens and the anterior surface curve increase – When the ciliary body relax the ciliary body is “at rest” – distance vision Functions of the Ciliary Body Aqueous Humor Production Ciliary body capillaries and the ciliary epithelial layers are significant factors in the production and secretion of AH Stroma of the ciliary processes contains a dense network of fenestrated capillaries the number and shape of the processes provides a large surface for secretion into the posterior chamber Functions of the Ciliary Body Aqueous Humor Production AH is produced from the nonpigmented ciliary epithelium Three mechanisms contribute in to the production and secretion 1. Diffusion 2. Ultrafiltration 3. Active secretion Functions of the Ciliary Body Aqueous Humor Production Diffusion – Passive movement of ions across a membrane related to size and solubility – the molecules move from the higher concentration to the lower concentration Functions of the Ciliary Body Aqueous Humor Production Ultrafiltration – Passive flow of blood plasma from the capillaries into the ciliary stroma – Caused by increased hydrostatic pressure Substances leave the blood thru diffusion and ultrafiltration, but must be actively secreted across the nonpigmented ciliary epithelium to become Aqueous Humor Fig. 6. Ultrafiltration. This process is similar to dialysis, but with the addition of a hydrostatic pressure that increases the rate of net movement of water and salt molecules across the semipermeable membrane. The final equilibrium concentrations on either side of the membrane are the same as in dialysis. The hydrostatic pressure merely increases the rate at which equilibrium is achieved. (Courtesy of RL Stamper, MD.) Functions of the Ciliary Body Aqueous Humor Production Active secretion – Molecules are transported across the membrane against a concentration gradient in an energy-utilizing process – 80-90% of the AH production Functions of the Ciliary Body Aqueous Humor Production Nonpigmented ciliary epithelium has two enzymes that catalyze reactions that are both essential for aqueous formation 1. Na/K ATPase – utilized ATP to pump Na+ - water follows 2. Na+ is highly dependent on bicarbonate for movement into the posterior chamber Carbonic anhydrase – catalyzes this reaction CO2 +H2O HCO3 Yielding bicarbonate (carbonic anhydrase inhibitors used in glaucoma therapy decrease significantly aqueous secretion) Fig. 8. Diagram of possible secretory pathways in the ciliary processes. AA, ascorbic acid; CA carbonic anhydrase. (From Wiederholt M, Helbig H, Korbmacher C. Ion transport across the ciliary epithelium: Lessons from cultured cells and proposed role of the carbonic anhydrase. In Carbonic Anhydrase. Basel: Verlag-Chemie, 1991:232–244, with permission.) Functions of the Ciliary Body Aqueous Humor Production Active secretion utilizes ATP and both enzymes (Na/K ATPase and carbonic anhydrase) to move sodium and bicarbonate into the posterior chamber for aqueous production Movement of Na+ and Clprimarily drives secretion into the posterior chamber with bicarbonate ions having an indirect role by moderating Cl- flux Fig. 8. Diagram of possible secretory pathways in the ciliary processes. AA, ascorbic acid; CA carbonic anhydrase. (From Wiederholt M, Helbig H, Korbmacher C. Ion transport across the ciliary epithelium: Lessons from cultured cells and proposed role of the carbonic anhydrase. In Carbonic Anhydrase. Basel: Verlag-Chemie, 1991:232–244, with permission.) Functions of the Ciliary Body Aqueous Humor Function Maintains pressure and shape of the eye Provides a transparent colorless refractive index Provides nutrition for the avascular cornea, lens, anterior vitreous and TM Serves as a collection bin for metabolic waste products of surrounding tissues and clears out inflammatory products and blood from the globe Functions of the Ciliary Body Aqueous Humor Composition AH has 20 times greater ascorbate concentrations than plasma Ascorbate (Vit. C) acts as an antioxidant to protect cornea and lens against oxidative damage – higher concentration in the lens 1.6mM compared to the aqueous 1.06mM Functions of the Ciliary Body Aqueous Humor Composition AH has 200 times less protein than plasma Consequence of the tight junctional barrier Low concentration of proteins – causes minimal light scatter and thus maximum light transmission flare Functions of the Ciliary Body Aqueous Humor Composition Waste products from the cornea and lens – Cl-, aminoacids, lactate High concentration of lactate- metabolic waste product of the anaerobic glycolysis of the lens and cornea Functions of the Ciliary Body Aqueous Humor Production 2.5 μl AH produced per minute AH production follows the circadian rhythm with a higher rate during the day, rate decrease 50% during night The osmolarity of AH is slightly hyperosmotic to the plasma AH viscosity is relative to water (1.025-1.040) Blood Aqueous Barrier Controls the secreted AH Fenestrated capillaries permit large molecules to exit the blood Tight zonular junctions of the NPE prevent the molecules from passing between the cells Forcing the molecules to pass thorough the cell to enter the posterior chamber Blood Aqueous Barrier Protein is well controlled Small content in the AH Proteins pass easily out the ciliary vessels fenestrations but do not pass into de posterior chamber because of the tight junction barrier of the NPE Iris is freely permeated by the AH Iris capillaries are not fenestrated so prevent large molecules leak out of the iris blood vessels and the zonula occludens junction in the endothelial cell maintain the barrier function Functions of Choroid Provides nutrients to the outer retina Is an egress for catabolites from the retina passing though Bruch’s membrane into the choriocapillaris Dark pigmented to absorb excess of light (as de RPE layer) Suprachoroidal space provides a pathway for the posterior vessels and nerves that supply the anterior segment Blood Supply to the Uvea Short posterior ciliary arteries enter around the optic nerve – their branches form the choroidal vessels Blood Supply to the Uvea Long posterior ciliary arteries and anterior ciliary arteries join – major circle of the iris – supply iris and ciliary body Venous return for most of the uvea is through the vortex veins Uveal Innervation Sensory innervation – the nasociliary branch form the trigeminal nerve Sympathetic fibers form the superior cervical ganglion via the ophthalmic and short ciliary nerves innervate – the choroidal blood vessels (vasoconstriction) Sympathetic fibers from the superior cervical ganglion via the long ciliary nerves innervate – iris dilator (contraction) – ciliary muscle (relaxation) Uveal Innervation Parasympathetic fibers from the ciliary ganglion innervate – the ciliary muscle (contraction) – Iris sphincter muscle (contraction) – Choroidal vessels (vasodilatation) Normal Iris Images courtesy by Drew Patterson Aging Changes Iris Loss of pigment form the epithelium is evident at the pupillary margin on transillumination Pigment deposition can be seen – – – – Iris surface Anterior lens surface Posterior cornea Trabecular meshwork Dilator muscle atrophies Sphincter muscle becomes sclerotic – (difficult to dilate with pharms) Age Changes Ciliary Body Connective tissue within the layers of the ciliary muscle increase (become sclerotic) Ciliary muscle contraction diminish with age AH formation decreases about by age 80 is approximately 25% of what is was Age Changes Choroid Drusen – – excessive membrane basement (basal lamina) material is deposited in the inner collagenous zones of Bruch’s membrane – Seen as small, pinheadsized, yellow –white spots in the fundus – contain cellular fragments and accumulation of basal laminar material Age Changes Choroid Choriocapillaris decrease in density and diameter- resulting in a decrease choroidal blood flow Also choroidal thickness decrease in the normal aging macula Clinical Applications Iridodialysis – Blunt trauma to the eye or head – Thin iris root tear away from the ciliary body – Result in damaged blood vessels and nerves – Blood can be seen in the anterior and posterior chambers – Damage may cause sector paralysis of the iris muscles Clinical Applications Iris Synechiae – Abnormal attachment between the iris surface and another structure – Posterior Synechiae Iris adherent to the anterior lens surface Can increase IOP if AH can’t pass to the anterior chamber – Anterior Synechiae Anterior iris surface is adherent to the corneal endothelium or the TM Clinical Applications Pigmentary Dispersion Syndrome – Pigment granules are shed form the posterior iris surface – Dispersed into the anterior chamber – Can be deposited on the iris, lens, corneal endothelium and the TM – Compromise aqueous outflow – Pigment loss will be evident on transillumination of the iris Clinical Applications Presbyopia – Loss of the ability to accommodate – Normal age-related change – Loss of elasticity restricts muscle movement and hampers accommodation Clinical Applications Thyndall Phenomenon – Usually beam of light in the anterior chamber is dark, with the presence of particles will be visible – Uvea inflammation – flare and cells – Cause: disruption of the zonula occludens between the nonpigmented ciliary cells causes a breakdown of the blood aqueous barrier allowing immune factors and leucocytes enter the AH – Hypopion – significant accumulation of cells – Hyphema – blood at the anterior chamber (trauma) Clinical Applications Age Related Macular Degeneration – Degenerative process involves choroid and retina – Presence of multiple or confluent drusen – Drusen – tick layer of basal laminar cells deposit – Detachment or atrophy of the RPE with subsequent formation of disciform scars, loss of photoreceptors and neovascularization Clinical Applications Age Related Macular Degeneration – Metabolites products of the choriocapillaris and waste products of the retina must pass though Bruch’s membrane – With age phospholipids accumulate in the membrane (lipofuscin) – Bruch’s membrane becomes hydrophobic, impedes passage of water and may result in RPE detachment Clinical Applications Iris Melanoma vs Iris Mole Clinical Applications Persistent Pupillary Membrane Remnants (PPM) Image courtesy from Ashley Houdek