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1. ANATOMY OF THE EYE BALL

2. LECTURE OUTLINE INTRODUCTION DIMENSIONS OF THE EYEBALL SEGMENTS AND CHAMBERS OF THE EYEBALL THE LAYERS OF THE EYE BALL EXTRAOCULAR MUSCLES APPENDAGES OF THE EYEBALL BLOOD SUPPLY TO THE EYEBALL NERVE SUPPLY TO THE EYEBALL VISION

3. INTRODUCTION The eye is a sense organ. It is an organ of sight it is actually an extension of the brain. its a cystic oblate spheroid structure kept distended by the intraocular pressure. A normal human being has 2 eyes, one right and one left. The eyeballs are located within the bony socket of the face and this socket is called orbit . In the orbit are other organs and tissue that help the eye to stay healthy and function normally

4. DIMENSIONS OF THE EYEBALL Anterior-posterior diameter......................................24mm horizontal diameter....................................................23.5mm vertical diameter........................................................23mm circumference.............................................................75mm volume.........................................................................6.5ml weight..........................................................................7grams

5. SEGMENTS AND CHAMBERS OF THE EYEBALL Anterior segment : this segment includes the lens and the structures anterior to it( the iris and cornea). it is sub divided into the anterior chamber and the posterior chamber . the anterior chamber is about 2.5mm deep in normal adult and contains about 0.25mls of aquoeus humour . Posterior segment : this segment includes the choroid, ciliary body, vitreous humour , retina, optic disc and macula.

6. LAYERS/COATS OF THE EYEBALL The eyeball is basically divided into three layers; Fibrous layer : this is the layer that includes the sclera and the cornea. 1/6 of the eyeball is covered by the cornea and 5/6 of the eyeball is covered by the sclera. It is also called the corneo-scleral layer. The vascular layer : this layer include the iris, ciliary body and the choroid. It is also called the uveal layer. The nervous layer : This is the layer that includes the retina.

7. Fibrous layer It is the toughest layer. It is made up of the clear and transparent cornea in front ie anterior 1/6 of the globe. The remainder is the opaque sclera. The thickness of the cornea at the centre is about 0.5mm and at the limbus it is 1.0mm thick.

8. Cornea The cornea is divided in five parts; 1. The epitherlium 2. The bowman’s membrane 3. The stroma 4. The descemete membrane 5. The endothelium

9. Reasons why the cornea is transparent It has no blood vessels It has no pigments It is not keratinised The corneal fibres in the stroma are well arranged to allow light to pass through without any interference. The cornea is relatively dehydrated i.e. relative deturgescence

10. Sclera The sclera is opaque and is perforated at the back (behind) by the fibres of the optic nerve as they pass through on their way to the brain. The area or perforation is the region of the optic nerve head and is called lamina cribrosa . The sclera is tough to prevent easy rupture of the eye and to provide an attachment for the extraocular muscles The sclera is opaque because it is more fibrous and has more water content than the cornea that is why it appears white.

11. The junction between the cornea and the sclera is a transitional zone measuring about 1.0 to 2.0 mm and is known as the limbus . Here the cornea blends with the sclera and it also marks the region of the anterior chamber angle. The anterior chamber angle is where the aqueous humour drains through. An anterior chamber angle contains the insertion of the iris to the sclera spur, the canal of Schlemm, the trabecular meshwork, and the Schwalbe's line

12. The vascular layer This layer is also known as the uvea. it is divided in three parts; the choroid the ciliary body the iris

13. the choroid The choroids: this portion of the uvea is located towards the back of the eyeball. It is made up of a network of blood vessels arising from short ciliary arteries. The choroid supplies blood to the outer retina. The choroid is drained by four vortex veins.

14. the ciliary body The ciliary body: this is in front of the choroid but just behind the region of the limbus. This portion has some muscles called cilliary muscles, which help, in accommodation and in the outflow of aqueous humour. The cilliary body also has cilliary processes, which are finger like projections. These processes are lined by epithelium and the epithelium is responsible for the production of aqueous humour

15. the iris this is the portion of the uvea that is in front of the ciliary body and is seen in the anterior segment of the eyeball. It hangs behind the cornea like a curtain and has a central hole called the pupil . The pupil changes its size to regulate the amount of light that enters the eye. It increases in size by the contraction of the dilator muscles and constricts by the help of the splinter muscles. the iris forms an angle with the limbus from the inside. this angle is called the anterior chamber angle and it contains important structures called trabecular meshwork and canal of Schlemm . these structures are important in the drainage of aqueous.

16. The nervous layer The inner layer of the eye is the retina . This layer is made up of nerve tissues and is sensitive to light. The elements that receive the light and transform or translate it into electrical messages are known as rods and cones . The chemical substance involve in the process is known as retinol which is gotten from vitamin A. These rods and cones transmit their information to the brain through the ganglion cells of the retina. These ganglion cells have long connections called axons. The axons of all the ganglion cells come together to form the optic nerve and leave the eye through the optic nerve head (or the disc ) which is at the back of the eyeball.

17. The nervous layer cont. There is a part of the retina that is concentration with cones and is responsible for the sharpness of vision. This portion is located temporal to the optic disk and is called the macular . At the centre of the macular is a small depression known as fovea . Towards the front of the eye, the retinal photosensitive elements terminate at the ora serrata. This ora serrata is continuous with the pars plana and the ciliary epithelium The outer retina is supplied by the choroid and drained by the vortex veins. The inner retina is supplied by the central retina artery and its branches and drained by the central retinal vein.

18. layers of the retina Retinal pigment membrane Photoreceptor External limiting membrane Outer nuclear layer Outer plexiform layer Inner nuclear layer Inner plexiform layer Ganglion cell layer Nerve fibre layer Internal limiting membrane

19. EXTRA OCULAR MUSCLES AND NERVE SUPPLY MUSCLES ABREV NERVE SUPPLY Superior rectus (SR) CN III Inferior rectus (I R) CN III Medial rectus (MR) CN III Lateral rectus (LR ) CN VI Superior oblique (SO) CN IV Inferior oblique (IO) CN III

20. APPENDAGES OF THE EYE Eyelid eyebrows conjunctiva lacrimal apparatus

21. CONJUNCTIVA The anterior sclera with the extra-ocular muscles is covered with a thin and transparent membrane which has epithelium and stroma. It contains tiny blood vessels. This membrane is known as the conjunctiva . It is divided into three parts; the bulbar conjunctiva , the palpebral conjunctiva and the fornices . The conjunctiva is attached all round the limbus and it contains some special cells which are known as goblet cells . these goblet-cells are responsible for production and secret of mucin. mucin is part of the precorneal tear-film which helps to keep the cornea healthy and prevent it from drying. the conjunctiva superior and inferior is reflected back to the eye lids to form pouches known as the superior fornix and the inferior fornix respectively..

22. Medially, the conjunctiva becomes folded to form the curuncle . On the lateral aspect it blends with the lateral canthus. The conjunctiva also contains at the region of the fornix and close to the tarsal plate some accessory lacrimal glands known as glands of krause and wolfring Underneath the conjunctiva is a loose fibrous tissue known as the Tenons Capsule which is also attached at the limbus but about 1.0 mm behind (posterior to) the attachment of the conjunctiva.

23. LENS Immediately behind the iris is a biconvex disc-like structure called crystalline lens . It is transparent to allow light to pass to the retina. This lens is attached to the ciliary body by fibrous stands known as Zonules of Zinn (or suspensory ligament). The lens has five different layers from the front to the back. These are; Anterior capsule Anterior cortex Nucleons Posterior cortex Posterior capsule

24. LENS cont. The lens helps in the process of accommodation in young people. Accommodation is the process by which the eye is able to focus to see clearly objects moved from a far distance to near position. This ability begins to fail at about the age of 38 years and becomes almost a complete failure by age 60years. The lens can become opaque and this condition is known as cataract .

25. VITREOUS HUMOUR T he VITREOUS HUMOUR is a gel-like material that fills the space between the back of the lens and the front of the optic nerve head. This material is also transparent and does not contain blood vessels.

26. AQUEOUS HUMOUR This is a transparent water-like fluid that fills the front part of the eye between the back of the cornea and the front of the iris (anterior chamber) and between the back of the iris and the front of the lens (posterior chamber). This fluid is produced by the non pigmented ciliary epithelium of the ciliary body into the posterior chamber. It then drains through the pupil to the anterior chamber. From the anterior chamber it gets to the anterior chamber angle and then passes through the trabecular meshwork to the canal of Schlemm. From the canal the aqueous then pass through the aqueous veins to the episcleral vessels into the circulation.

27. AQUEOUS HUMOUR cont. The functions of the aqueous include Maintenance of the pressure inside the eye (intraocular pressure) Transportation of oxygen and nutrients to the lens and cornea Transportation of metabolic waste from the lens and cornea

28. BLOOD SUPPLY TO THE EYEBALL The eyeball gets it bloods supply from the ophthalmic artery and it is drained by the ophthalmic vein . This artery gives blood to all the extraocular muscles and the conjunctiva. Some branches known as short ciliary arteries enter the eye around the optic nerve to form the choroids plexuses and some long ciliary arteries enter the eye and go to the front part to supply the ciliary body and the iris. The choroid supplies the outer retina while a branch of the ophthalmic artery called central retina artery enters the optic nerve and goes to supply the inner retina. The choroid is drained by the VORTEX veins, which are 4 in number. These vortex veins together with other veins form the superior and inferior ophthalmic veins that drains to the cavernous sinus.

29. NERVE SUPPLY TO THE EYEBALL Sensation of pain from the eye particularly the cornea is transmitted via the ophthalmic branch of the 5 th cranial nerve (trigeminal nerve). The control of accommodation and construction of the iris sphincter is by the parasympathetic part of the autonomic nervous system via the ciliary ganglion. The dilation of the pupil is by sympathetic part of the autonomic nervous system via the superior cervical ganglion. The visual sensation is transmitted via the optic nerve.

30. SUMMARY OF THE NERVE SUPPLY TO THE EYE PARTS NERVES SUPPLY Corneal sensation and pain ophthalmic branch of CN IV Pupillary dilatation sympathetic system Pupillary construction and accommodation parasympathetic system Visual sensation optic nerve (CN II)

31. VISION Vision is made possible only when all the elements and structures described above are functioning optimally. As the light enters the eye, the cornea refracts it (i.e. bends it) towards the lens. The lens now bends it further to focus it on the retina. As the focused light falls on the retina, the special pigment sensitive to light on the plates of the rods and cones pickup this light and react chemically to produce electrical impulses. These impulses are transmitted through the bipolar cells of the retina to the ganglion cells. The amount of the electrical transmission is regulated or modified by special amacrine and horizontal cells. The ganglion cells now transmit this message to the brain through their axons which form the optic nerve. Note that the photosensitive chemical pigment in the retina is retinol gotten from Vitamin A

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