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Eye
- 1. Anatomy of Eyeball Dr. Ayshah Hashimi
- 2. EYEBALL • Highly specialized sensory organ • Located within the bony orbit • Surrounded by the adipose tissue • Enveloped in a thin fascial sheath called the tenon’s capsule. • Function as photoreceptor • See around 100 different shades of color • The eyeball consists of three layers:  Fibrous  Vascular pigmented/Uvea  Nervous (retina) • Refractive structures of the eye includes- Cornea, Aqueous humor, the Lens and vitreous body • Two chambers- anterior and posterior
- 3. Fascial sheath (Tenon’s capsule) • Anteriorly, it attaches to the sclera, while posteriorly it fuses with the meninges that wrap the optic nerve • Space between sclera and tenon capsule is episcleral space • Inner surface is smooth while outer surface provides attachment to the extraocular muscles • Function- protect the eyeball, position it within the orbit and allow the actions of the extraocular muscles
- 4. Fibrous Layer Consist of 2 parts • Sclera • Cornea Sclera • Outermost, opaque, white layer covering 5/6th of the eyeball • Thickest posteriorly • Posterior scleral foramen site of perforation by the optic nerve • Lamina cribrosa- sieve-like structure formed by numerous piercing of inner 1/3 of sclera by fibres of optic nerve while outer 2/3 of the sclera is continuous with the dural sheath of the optic nerve • Apertures  Anteriorly 4 apertures at recti muscles attachment that transmit anterior ciliary arteries  In middle, i.e. behind the equator there are 4-5 apertures allowing the passage of vorticose vein  Posteriorly there are numerous openings for short ciliary vessels and nerves
- 5. • Anteriorly, it is continuous with cornea and the junction is called as sclerocorneal junction or Limbus • Internal scleral sulcus that contains the scleral venous sinus (canal of Schlemm) • Sclera is 3 layered structure- episcleral, sclera proper, lamina fusca CANAL OF SCHLEMM
- 6. Cornea • Circular transparent layer that covers the pupil, iris and anterior chamber of the eye • Thickest at its periphery, becoming gradually thinner towards its center • Composed of proteins and cells organized in five layers  Stratified corneal epithelium (5 layers of cells centrally, while on the periphery it contains up to 10 layers) contains pain receptors  Bowman’s membrane (meshwork of irregularly arranged collagen fibrils)  Substantia propria (corneal stroma)- thickest corneal layer  Descemet’s membrane  Corneal endothelium • Functions  Refraction of light  Protective role
- 7. Vascular or pigmented layer or Uvea or uveal tract It consists of the three layers-choroid, ciliary body and iris. The iris features an opening anteriorly called the pupil, while the choroid is deficient on the posterior pole of the eye where the optic nerve exits the eyeball Choroid Highly vascular layer accounting for almost 90% of the total blood flow in the eye The choroid is divided into three layers: • Vessel layer • Capillary layer • Bruch’s membrane Function Provide the blood supply to the outer layers of the retina, and in front of eye
- 8. Ciliary body • It is continuous with the choroid posteriorly and with the iris anteriorly • Forms a complete ring around the iris and on cross section it is triangular in shape • Narrow base faces the periphery of the iris while apex faces postero-laterally and is continuous with the choroid • The base of the ciliary body is rough and it is called the pars plicata, while its posterior surface is smooth and it is called the pars plana. The pars plicata gives off the thin projections called the ciliary processes • The intervals between the ciliary processes serve as the attaching sites of the zonular fibers of the lens
- 9. The ciliary body consists of three parts: • Ciliary epithelium • Ciliary stroma • Ciliary muscle Functions • The ciliary muscle enables the accommodation of the eye • The ciliary processes produce the aqueous humor into the posterior chamber eye. The humor flows through the pupil into the anterior chamber of the eye, where it is absorbed into the scleral venous sinus (the canal of Schlemm) • Its posterior surface faces the vitreous body and provides it with glycosaminoglycans
- 10. Iris • Contractile, heavily pigmented, circular diaphragm • Contains numerous melanocytes • Border between the anterior and posterior chambers of the eye • Located anterior to the lens and posterior to the cornea, being immersed in the aqueous humor • Periphery of the iris is marked as its root or the ciliary margin • Acute angle formed by the root of iris and the cornea is called the iridocorneal angle (filtration angle) • Contains two smooth muscles that enable its contractile property- Sphincter pupillae muscle & Dilator pupillae muscle • Circular opening is visible in the center called the pupil.
- 11. Sphincter pupillae muscle Dilator pupillae muscle
- 12. Aqueous Humor • Transparent watery fluid with low protein concentration • Maintains the intraocular pressure • Keep eye distended • Provides nutrition for the avascular ocular tissues and also removes waste products formed • For refractive index • Prevents eye dryness
- 13. Formation and Circulation • Aqueous humor is secreted in the posterior chamber by ciliary processes of Pars Plicata • Ciliary processes epithelium releases actively Na ion that brings with it Cl and HCO3 ions. This increases osmotic pressure within the posterior chamber that pulls water from vessels. Glucose, Amino acids, lactic acid, ascorbic acid and some immunoglobulins also comes out of it • It leaves the eye through the porous trabecular meshwork and • Flows into Schlemm’s canal and finally drains into episcleral vein • The 2° route is the uveoscleral drainage, and is independent of the intraocular pressure. Approx. 10% drainage occurs at this level Vitreous body • Transparent, colourless, gelatinous mass that fills the space between the lens and the retina of the eyeball
Editor's Notes
- Episclera- outermost connective tissue layer Sclera proper/scleral stroma- dense irregular connective tissue gives the sclera its distinctive white color. Change in color is pathological. Red indicated congestion and inflammation, yellow indicates jaundice Lamina fusca- pigmented layer. Space between choroid and Lamina fusca is perichoroidal space, that contains long and short posterior ciliary arteries and nerves.
- Corneal transplant is done coz of its avascularity and thus has no immune cells The corneal endothelial cells don’t undergo mitosis, so if they get injured, the corneal surface can become permanently opaque.
- vessel layer which contains numerous melanocytes as well as many blood vessels. capillary layer which consists of the numerous melanocytes and the smaller branches of the vessels from the vessel layer. Bruch’s membrane which consists of five distinctive components; the basement membrane of the endothelium of the capillaries of the capillary layer, collagen and elastic fibers, and the basement membrane of the pigmented layer of the retina
- Ciliary epithelium- double-layered Ciliary stroma rich in blood vessels (ciliary vessels) Ciliary muscle- When this muscle contracts, it pulls the ciliary body anteriorly. This leads to the loosening of the zonular fibers of the lens, allowing the lens to shrink and become more convex. This process enhances the refractive power of the lens and plays an important role in the process of accommodation.
- Change in pupil size is to control the amount of light that enters the eye
- Mydriasis (dilatation of pupil) Miosis (contraction of pupil)