1. The Eye

2. Definition
Organ of the sense of sight
Situated in the orbital cavity
Spherical
2.5 cm dia
The space between the eye and the orbital cavity is occupied by fatty tissue; the bony wall and the fat protect the eye from injury.
Strucuturally separate; but certain activities are coordinated and function as a pair.
Two eyes  sense of depth and distance

4. Structure
Three layers in the wall
Outer fibrous layer : sclera and cornea
Middle vascular layer: choroid, ciliary body and iris
The inner nervous tissue layer : retina.
The structures inside the eyeball are the lens, aqueous fluid (humour) and vitreous body

5. Sclera Cornea Sclera = white portion of the eye Outermost layer
Continuous with the cornea anteriorly
Firm fibrous membrane
Gives attachment to the extraocular
Muscles of the eye
Cornea
Continuation of the sclera anteriorly
Transparent
convex
Epithelial membrane
Light rays pass through the cornea to reach the retina
Convexity refracts the light rays (bends)

6. Suspensory ligament is attached to it
Choroid
Lining of the posterior five sixths of the inner surface of the sclera
Rich in blood vessels
Deep chocolate brown in color
Ciliary body
Anterior continuation of the choroid
Consists of smooth muscle fibres (ciliary muscle)
And secretory cells – aqueous fluid into the anterior segment
Suspensory ligament is attached to it
The suspensory ligament is attached to the capsule of the lens at the other end.
Contraction or relaxation of the ciliary muscle changes the thickness of the lens - accommodation
The ciliary body is supplied by parasympathetic branches of the oculomotor nerve.

7. Iris
Visible coloured part of the eye – colour genetically determined
Extends anteriorly from the ciliary body,
Lies behind the cornea
Situated in front of lens
In front of iris – anterior chamber
Behind iris – posterior chamber
The chambers contain aqueous fluid secreted by the ciliray body
Iris is a body composed of pigment cells and two layers of muscle fibres, one circular and one radiating
Centre - hole or aperture – pupil when iris contracts the pupil is constricted and when iris relaxes the iris is dilated – parasympathetic supply - oculomotor

8. Lens Highly elastic Circular biconvex transparent body Behind pupil
Suspended from the ciliary body by the suspensory ligament
Eclosed within a transparent capsule
Thickness controlled by the ciliary muscle
Contraction of the muscle moves the lens forward thereby reducing the pull on the lens and increasing the thickness of the lens

9. Retina
Innermost layer
Stimulated by light rays
Several layers of nerve cell bodies and their fibres
Lying on a pigmented layer of epithelial cells
The layer highly sensitive to light is thelayer is the layer of rods and cones.
macula lutea
fovea centralis – only cone shaped cells
anteriorly there are fewer cones than rods
contain photosensitive pigments convert light rays into nerve impulses.

10. Optic nerve The nerve fibres originate in the retina
All fibres converge to form the optic nerve
Passes through the optic foramen of the sphenoid bone and meets the nerve from the opposite side at the optic chiasma
Optic chiasma
In front of and above the pituitary gland
Nerve fibres of the optic nerve from the nasal side of each retina cross over to the opposite side. The fibres from the temporal side do not cross but continue on the same side

11. Optic tracts These are the pathways of the optic nerves
Posterior to the optic chiasma
Each tract consists of the nasal fibres of the opposite retina and the temporal fibres of the same side retina.
Pass through the cerebrum to synapse with nerve cells of the lateral geniculate bodies of the thalamus. Thence the fibres pass as optic radiations to terminate int the visual area of the cerebral cortex in the occipital lobe of the cerebrum.
Other neurones originating in the lateral geniculate bodies convey impulses from the eyes to the cerebellum where together with impulses from the smicircular canals, and from the skeletal muscles and joints, they contribute to the maintenance of the balance.

12. Rhodopsin (visual purple) - degraded or bleached when exposed to light – regeneration requires vitamin A.
The time taken for the regeneration of rhodopsin is called dark-adaptation
Other pigments present in cones respond to different wavelengths of visible ligt and are responsible for colour vision.
0.5 cm to the nasal side of the macula lutea all the nerve fibres of the retina converge to form the optic nerve which passes through the sphenoid bone  cerebral cortex in the occipital lobe of the cerebrum.
Optic disc or the blind spot – optic nerve leaves the eye. 20

13. Blood supply to the eye
Internal carotid artery through its branches- ophthalmic artery :- ciliary arteries – central retinal artery.
Venous drainage is by anumberof veins, central retinal vein  cavernous sinus.
Central retinal artery and vein are encased in the optic nerve. Entering the eye at the optic disc.

14. Interior of the eye ball
Anterior segment
Posterior segment
Aqueous fluid (humour)
Secreted into the posterior chamber by ciliary glands
It passes in front of the lens through the pupil into the anterior chamber and returns to thevenous circulation through the canal Schlemn (scleral venous sinul) in he angle between the iris and cornea. – continuous production and drainage –

15. Intraocular pressure remains 1. 3 to 2
Intraocular pressure remains 1.3 to 2.6 kPa (10 to 20 mm Hg) increase  glaucoma.
Aqueous – nutrients- to transparent structures cornea lens, lens capsule
Behind the lens and filling the cavity - vitreous body (humour)
Soft coloureless, transparent, jelly-like substance
Water salts mucoproteins
Intraocular pressure maintained by the humours.

16. Extraocular muscles of the eye
Six extrinsic muscles
Attached to the eye ball at one end and to the walls of the orbital cavity at the other end.
4 straight muscles and 2 oblique muscles :
Medial rectus – rotates inwards
Lateral rectus – rotates outwards
Superior rectus – rotates upwards
Inferior rectus - rotates downwards
Superior oblique – downwards and outwards
Inferior oblique – upwards and outwards
Voluntary muscles – needed for convergence and accommodation

17. Nerve supply to the muscles of the eye
extrinsic muscles
Superior rectus
Inferior rectus
Medial rectus
Inferior oblique
Intrinsic muscles
Iris
Ciliary muscle
All of the above six muscles are supplied by oculomotor nerve
Superior oblique – trochlear nerve
Lateral rectus – abducent nerve

18. Eye brows
Arched
Supra orbital
Protect the eye from sweat, dust, and other foreign bodies
Eye lids (palpebrae)
Movable folds of tissue
Upper and lower
Free edges have hair – eye lashes
Layers of the eyelids are:
Skin
Areolar tissue
Two muscles – the orbicularis oculi and levator palpebrae superioris
Tarsal plate – thin sheet of dense conective tissue
A lining of conjuctiva

19. Conjuntiva
Transparent membrane lining the eyelids and the front of the eyeball
On the eyelids the conjunctiva has highly vascular epithelium
Corneal conjunctiva consists of less vascular stratified epithelium.
Lower portion – lower conjunctival sac
The medial and lateral angles of the eye where the upper and lower lids come together are called respectively the medial canthus and the lateral canthus

20. Eyelid margins
Along the edges sebaceous glands
Ducts open into the hair follicles and on to the eyelid margins between hairs.
Meibomian glands (tarsal glands) are modified sebaceous glands embedded in the tarsal plates – ducts open into the inside of the free margins of the eyelids – oily secretion – spread to delay evaporation of the tears

21. Lacrimal apparatus
For each eye this consists of
1 lacrimal gland and its ducts
2 lacrimal canaliculi
1 lacrimal sac
Nasolacrimal duct

22. The lacrimal glands
In recesses in the frontal bones on the lateral aspect of each eye just behind the supraorbital margin
Have secretory epithelial cells
Tears are secreted – water mineral salts, antibodies and lysozyme, a bactericidal enzyme
Several small ducts – pass over the front of the eye under the lids towards the medial canthus where it drains into two lacrimal canaliculi the opening of each is called the puncum
The two canaliculi lie on lie one above the other separated by a small red body, the caruncle.
The tears then drain into the lacrimal sac the upper end of the nasolacrimal duct
Nasolacrimal duct opens into the nasal cavity opening at the level of the inferior concha.

23. Eye model nerves

24. Eye model blood supply

25. Eye model cross-section

26. Eye model inside skull

29. slide 4

30. Back to slide 4
five

34. The human eye works like a living camera
The human eye works like a living camera. Like a camera, the eye processes light and takes mental snapshots of images, which are then developed in the brain. In order to create vision, all parts of the eye must work together as a team. The cornea, the clear, film-like part of the eye, is the leader. When light enters the dark pupil of the eye, the cornea bends it. The refracted light travels to the lens behind the pupil. The lens changes its shape to adjust the focus on both distant and near objects. This process is known as accommodation.

35. The lens projects light from the outside world as an inverted image into the retina, which then acts like film in a camera and captures the image. The image is sent to the brain in the form of electric impulses to be developed.

39. Near sighted

46. The optic nerve and the central retinal blood vessels enter the back of the eye at the disc (also called the blind spot). 
The back 2/3 of the eye is called the retina and gives us our wide field of view vision. It contains millions of rod and cone cells which convert light energy into electrical signals sent to the brain via the optic nerve. 
The macula (6x7 mm) is the tiny spot on the retina where finer detail focus occurs.  The fovea (1.5 mm) is just behind the macula where the highest concentration of cone photoreceptors are concentrated.  Light rays are focused by the lens onto the fovea for straight ahead vision and fine detail. 
The sclera is the tough outer wall of the eye and the choroid is the thin spongy layer between it and the retina filled with blood vessels.

47. 13

48. Ten
Eight
Back to 14

81. The End