Eye vision

1. EYE/VISION

2. FUNTIONAL ANATOMY OF THE EYEBALL Globe shaped with diameter of about 24mm. Slightly flattened from above downwards. Made up of two segments; Ant. Part is small, forms 1/6 of eyeball. Post. Part is larger, form 5/6 of eyeball. The radius of the post.part is about 8mm. The post.wall of the post part lined by light sensitive structure - retina.

3. Anti . Pole The center of ant. curvature of the eyeball. Post . Pole The center of post. curvature of the eyeball. Optic axis The line joining the two poles. Visual axis The line joining a point in cornea little medial to ant. pole and the fovea centralis situated to the post.pole. The light rays pass trough the visual axis of eyeball. The optic nerve leaves the eye little medical to the post.pole .

4. ORBITAL CAVITY The eyeball is situated in the bony cavity (except the ant.1/6). Areolar tissue is interposed b/w the bone and the eye. Areolar tissue serves as a cushion to protect the eyeball from external force. The eyeballs are attached to the orbital cavity by the occular muscles.

5. EYELIDS Protects the eyeball. Open and close voluntarily and reflexly. The margins of eyelids have sensitive hairs-cilia. Each cilia has a follicle, surrounded by a nerve plexus. Blinking of eyelids occur when sensory nerves (cilia) are activated. Prevents dust particles from reaching eyeball.

6. EYELIDS 100-150 cilia in the upper lid and about 50-75 in the lower lid. Meibonian glands and some sebaceous glands are also found in the eyelids. These glands open into the follicles of cilia. The infection of these glands leads to the development of common eye sty. The opening b/w the two eyelids is called palpebral fissure.

7. INNERVATION OF EYELIDS Sensory innervation is from the Trigeminal (5 th ) cranial nerve, via the ophthalmic division (upper lid) and maxillary division (lower lid). The orbicularis oculi is innervated by the facial (7 th ) nerve. The levator muscle in the upper lid is supplied by the oculomoter (3 rd ) nerve.

8. BLOOD SUPPLY AND LYMPHATICS The eyelids are supplied by an extensive network of blood vessels which form an anastomosis b/w branches derived from the external carotid artery via the face and from the internal carotid artery via the orbit. Lymphatic fluid drains into the periaricular and sub mandibular nodes. Periaricular lymphadenopathy is a useful sign of infective eyelid swelling (especially viral).

9. CONJUNCTIVA A thin mucous memb. which covers the exposed part of the eye. It covers the ant. surface and also reflected into the inner surface of eyelids. Bulbar portion. The part of conjunctiva covering the eyeball. Palpebral portion. The part covering the eyelids. The opposed portions of conjunctiva slid over each other.

10. CONJUNCTIVA The surface of conjunctiva is lubricated by a thin film of tears secreted by lacrimal glands. At the upper and lower reflections b/w eyeball and eyelid the conjunctive forms two sacs, the superior and inferior fornices.

11. LACRIMAL GLAND Situated in the shelter of bone, forming the upper and outer border of wall of the eye socket. Tears flow from lacrimal gland over the surface of conjunctiva and drains into nose via lacrimal duct, lacrimal sac and nasolacrimal duct. Tear is a hypertonic fluid. Conjunctive is kept moist and is protected from infection due to its continuous washing and lubrication (by tears).

12. LACRIMAL GLAND Tears also contains lysozyme that kills bacteria. Secretion of tears is controlled by the parasympathetic fiber of facial (VII cranial) nerve. At birth, the N/L duct may not be fully developed, causing a watery eye. Acquired obstruction of the N/L duct is a common cause of water eye in adult. It may lead to an acute infection of the sac.

13. WALL OF THE EYEBALL Compose of three layers; Outer layer, which includes cornea and sclera. Middle layer; which includes choroid, ciliary body and iris. Inner layer, the retina.

14. OUTER LAYER OR TUNICA EXTRANA OR TUNICA FIBROSA The outer layer preserves the shape of eyeball. Sclera, is the posterior 5/6 of the outer layer and is opaque. Cornea, is anterior 1/6 of the outer layer and is transparent.

15. SCLERA Formed by the white fibrous tissues and elastic fibers. A vascular (a part from some vessels on its surface). Relatively a cellular. It is perforated posteriorly by the optic nerve, and by sensory and motor nerves and blood vessels to the eye.

16. SCLERA Lamina crib Rosa. The part of the sclera where it is perforated by the above vessels, is thin with perforations . Limbus. The cornea and sclera merge at the corneal edge .

17. CORNEA It is the anterior 1/6 of outer layer. The cornea is transparent because of specialized arrangement of the collagen fibrils within the stroma which must be kept in a state of relative dehydration. The sclera overlaps cornea at its periphery and appears in front as white of the eye. The diameter of the cornea is about 12mm horizontally and 11mm vertically.

18. CORNEA Cornea is formed by five layers; Layer of stratified epithelium. Bowman’s membrane or anterior elastic lamina. Substantia proper. Descemet’s layer or posterior elastic lamina. Layer of endothelial cells.

19. CORNEA Refractory index. 1.376. Sensitive to pain, touch, pressure and cold. Center of cornea is more sensitive to pain because of rich supply of free nerve endings. Cornea is vascular, derives its nourishment mainly from aqueous humor.

20. CORNEA Cornea becomes vascularized in some pathological conditions. The transitional part of the outer layer b/w sclera and cornea is called limbus. Its width is about 1mm.

21. MIDDLE LAYER OR TUNICA MEDIA OR TUNICA VASCULOSA The middle layer surrounds the eyeball completely except for a small opening in front-pupil. This layer comprises three structures; Choroid Ciliary body Iris

22. CHOROID Forms post. 5/6 of middle layer. Separated from sclera by perichoroidal space. Antiaorly the space is limited by the insertion of ciliary muscle into the sclera. Post. The space ends at short distance from the optic nerve. Inner surface of choroid faces to the pigment epithelium of retina. Choroid is composed of a rich capillary plexus, numerous small arteries and veins.

23. CILIARY BODY the choroid is extended anteriorly up to the insertion of ciliary muscle (the level of ora serrata). In front of ora serrata, the middle layer is thickened to form ciliary body. It is in the form of a ring. Its outer surface is separated from the sclera by perichoroidal space. The inner surface of ciliary body faces the vitreous body and lens.

24. CILIARY BODY The ant. surface of the ciliary body faces towards the center of cornea. From the surface, the iris arises. Ciliary body has three parts; O rbiculus ciliaris. Ciliary body proper. Ciliary process.

25. i. ORBICULUS CILIARIS It is continuous with choroid and it forms the posterior 2/3 of ciliary body. It is about 4mm broad.

26. ii. CILIARY BODY PROPER It is made up of two sets of ciliary muscles; Outer longitudinal muscle Inner circular muscle The ciliary muscles are innervated by the parasympathetic fibers of oculomotor nerve (6 th nerve).

27. iii. THE CILIARY PROCESS Finger like projections from the inner surface of the ciliary body. There are about 70 ciliary processes. They projects towards the central axis of the eye to form radial fringes called ciliaris.

28. IRIS It is the colored structure and forms the anterior most part of the middle layer. It is a thin circular diaphram. Pupil is a circular opening in the center of iris. Iris is a muscular structure and has two muscles; Constrictor pupillae, formed by circular muscle fibers. Dilator pupillae, formed by ractial muscle fibers.

29. IRIS Constrictor pupillae: It is also called iris sphinctor muscle or sphinctor pupillae. Contraction of this muscle causes constriction of pupil. Dilator pupillae: It is also called pupillary dilator muscle. Contraction of this muscle causes dilatation pupil. Iris acts like the diaphragm of a camera.

30. IRIS It regulates the amount of light entering the eye by altering the diameter of pupil. Iris separates the space b/w cornea and lens into two chambers, the chambers communicate with each other through pupil. The lateral border of ant. chamber is angular in shape. It is called iris angle or angle of ant. chamber.

31. INNER LAYER OR TUNICA INTERNA OR TUNICA NERVOSA OR RETINA It is the inner nervous layer of eye where inverted image of the object are formed. It develops from primitive brain. Retina extended from margin of optic disk to just behind the ciliary body where it ends abruptly as a dentated border-ora serrata. Retina has the receptors of vision.

32. INNER LAYER OR TUNICA INTERNA OR TUNICA NERVOSA OR RETINA It has the following main layers from within outwards; Layer of optic nerve fibres formed by axons of the ganglion cells which converge to form optic nerve. Layer of ganglion cells have pyriform ganglion cells of various sizes. Inner plexiform layer has synapses formed by dendrites of ganglion cells and axons of bipolar cells.

33. INNER LAYER OR TUNICA INTERNA OR TUNICA NERVOSA OR RETINA IV. Inner nuclear layer is mainly formed by bipolar cells which are small and oval shaped. V. Outer plexiform layer has synapses formed by dendrites of bipolar cells and axons of rods and cones cells. VI. Outer nuclear layer is formed by fibres and nuclei of rods and cones. VII. Rods and cones layer is the photoreceptor layer. Rods are cylindrical, have rhodopsin pigment

34. INNER LAYER OR TUNICA INTERNA OR TUNICA NERVOSA OR RETINA And are associated with dim light-vision (scotopic vision). The cones have pyramidal shape and are associated with bright light vision (photopic vision) and colour vision. Pigment cell layer is composed of single layer of hexagonal epithelial cells, having dark brown pigment (fuchsin). It should be noted that light has to traverse ganglion cells and bipolar cells to reach the photoreceptors rods and cones, where visual impulses are set up, passed onto bipolar cells of inner fibers pass onto cerebral cortex (occipital lobe).

35. MCQ Choose the best answer concerning the retina ? A . Retinal ganglion cell axons comprise the optic nerve. B . Cone photoreceptors fire action potentials under conditions of bright light. C . When light strikes a rod photoreceptor, rhodopsin binds to sodium channels in the outer segment membrane. D . The transmitter released at photoreceptor synapses is cGMP

36. Retinal ganglion cell axons comprise the optic nerve

37. MCQ Which of the following statements about photoreceptors is true? A . Cones detect light better than rods. B . Both Rods and Cones hyperpolarize in response to light. C . Rods are enriched in the fovea. D . Cones are more numerous than rods. E. None of the above statements is true

38. Both Rods and Cones hyperpolarize in response to light

39. THE END