The eye (sense of sight organ)

THIS POWER POINT PRESENTATION IS TO GIVE READERS AN OVERVIEW ON THE ANATOMY AND PHYSIOLOGY OF THE EYE: STRUCTURES, FUNCTIONS OF EACH PART OF THE EYE, AS WELL AS THE PHYSIOLOGY ON HOW THE IMAGE IS CAPTURED IN THE EYE AND TRANSLATED BY THE BRAIN IN ORDER TO HAVE THE MEANINGFUL VIEW OF THE IMAGE.

1. THE EYE
BY
MR. MWELWA JORDAN

2. GENERAL OBJECTIVE
At the end of the lecture, students should be able to acquire
knowledge and have the understanding on the anatomy and physiology
of the eye.

3. SPECIFIC OBJECTIVES
At the end of the lecture, students should be able to:
• Describe the structures of the eye.
• State the interior structures/parts of the eye.
• State the blood supply of the eye.
• Describe the nerve supply of the eye.
• State the accessory organs and protection of the eye.
• State the extraocular muscles of the eye.
• Explain the physiology of the sight.

4. INTRODUCTION
The eye is a specialized sense organ that helps us to understand our
environment. It is a sensory unit composed of three parts: receptor,
sensory pathway, and a brain center.
It is spherical shaped and is about 2.5 cm in diameter. It is situated in
the orbital cavity.

5. STRUCTURES OF THE EYE

6. STRUCTURES OF THE EYE CONT’
ANATOMICAL FEATURES:
1. Sclera: The sclera, or white of the eye forms the outer most layer of
tissue of the posterior lateral of the eye ball and it continues anteriorly
with the transparent cornea. It consists of a firm fibrous membrane
that maintains the shape of the eye and gives attachment to the
extraocular or extrinsic muscles of the eye.

7. STRUCTURES OF THE EYE CONT’
2. Cornea: Light rays pass through the cornea to reach the retina. The
cornea is convex anteriorly. Involved in refracting or bending light rays
to focus them on the retina.
3. Choroid: The choroid lines the posterior five-sixths of the inner
surface of the sclera. It is very rich in blood vessels and is deep
chocolate brown in color.

8. STRUCTURES OF THE EYE CONT’
4. Ciliary body
• Consisting of ciliary muscle (smooth muscle fibers) and secretory
epithelial cells.
• Contraction and relaxation of the ciliary muscle changes the thickness
of the lens which bends, or refracts light rays entering the eye to focus
them on the retina.
• The epithelial cells secrete aqueous fluid into the anterior segment of
the eye, i.e. the space between the lens and the cornea (anterior and
posterior chambers).

9. STRUCTURES OF THE EYE CONT’
• The ciliary body is supplied by parasympathetic branches of the
oculomotor nerve (3rd cranial nerve).
• Stimulation causes contraction of the smooth muscle and
accommodation of the eye.

10. STRUCTURES OF THE EYE CONT’
5. Iris:
• visible colored part of the eye.
• It is a circular body composed of pigment cells and two layers of
smooth muscle fibers, one circular and the other radiating. In the
center there is an aperture called the pupil.
• The iris is supplied by parasympathetic and sympathetic nerves.
• Parasympathetic stimulation constricts the pupil and sympathetic
stimulation dilates it.

11. STRUCTURES OF THE EYE CONT’

12. STRUCTURES OF THE EYE CONT’
Retina:
• Innermost layer, extremely delicate structure and is especially
adapted for stimulation by light rays.
• It is composed of several layers of nerve cell bodies and their axons,
lying on a pigmented layer of epithelial cells which attach it to the
choroid.
• The layer highly sensitive to light is the layer of sensory receptor cells:
rods and cones.
• Near the center of the posterior part is the macula luteal, or yellow
spot.

13. STRUCTURES OF THE EYE CONT’
• In the center of the area there is a little depression called the fovea
centralis, consisting of only cone-shaped cells.
• Towards the anterior part of the retina there are fewer cone-than
rod-shaped cells.
• The rods and cones contain photosensitive pigments that convert
light rays into nerve impulses.
• The small area of retina where the optic nerve leaves the eye is the
optic disc or blind spot. It has no light-sensitive cells.

14. STRUCTURES OF THE EYE CONT’

15. STRUCTURES OF THE EYE CONT’
Interior of the eye:
• The anterior segment of the eye, i.e. the space between the cornea
and the lens, is incompletely divided into anterior and posterior
chambers by the iris.
• Both chambers contain a clear aqueous fluid(humor) secreted into
the posterior chamber by ciliary glands.

16. STRUCTURES OF THE EYE CONT’
• It circulates in front of the lens, through the pupil into the anterior
chamber and returns to the venous circulation through the scleral
venous sinus (canal of Schlemm) in the angle between the iris and
cornea.
• There is continuous production and drainage but the intraocular
pressure remains fairly constant between 1.3 and 2.6 KPa(10 to 20
mmHg).

17. STRUCTURES OF THE EYE CONT’
• An increase in this pressure causes glaucoma. Aqueous fluid supplies
nutrients and removes waste from the transparent structures in the
front of the eye that have no blood supply, i.e. the cornea, lens and
lens capsule.

18. STRUCTURES OF THE EYE CONT’
SENSORY RECEPTORS & OTHER EYE PARTS
•Rods–cylindrical photoreceptors found in greatest concentration on
the edges of the retina; most common type of receptor; allow us to
see in low light and provide for peripheral vision.
•Cones–Conical photoreceptors found in greatest concentration
near the center of the retina; there are three varieties of cones, each
most sensitive to a particular wavelength (color) of light –blue, green,
& red; allow for visual acuity (sharp vision) and color vision

19. STRUCTURES OF THE EYE CONT’
•Fovea centralis–a depression, or pit, in the center of the retina that
contains only cones; provides for the most acute vision & color
sensitivity.
•Optic disk (blind spot) –area where optic nerve attaches to the
retina; does not contain any photoreceptors.
•Lens –flexible, biconvex, crystal-like structure that brings rays of
light into focus and produces an image on the retina.
•Suspensory ligament –holds the lens in place; attached to the
ciliary body, which controls the amount of tension exerted on the
Lens.

20. STRUCTURES OF THE EYE CONT’
FLUIDS IN THE EYE
•Aqueous humor –watery fluid that provides nutrition and helps
maintain the shape of the cornea; found in the smaller, anterior
chamber of the eye.
Vitreous humor –thick, gel-like substance that fills the largest chamber
of the eye and helps to hold its spherical shape.

21. BLOOD SUPPLY
Carotid artery
Ophthalmic artery
Ciliary artery & Central retinal artery
Eye

22. OPTIC NERVE SUPPLY
•The fibers of the optic nerve originate in the retina of the eye. All the
fibers converge to form the optic nerve about 0.5cm to the nasal side
of the macula lutea. The nerve pierces the choroid and sclera to pass
backwards and medially through the orbital cavity. It then passes
through the optic foramen of the sphenoid bone, backwards and
medially to meet the nerve from the other eye at the optic chiasma.

23. ACCESSORY ORGANS & EYE PROTECTION
• Orbital cavities (bony sockets) –house & protect the eye.
• Adipose tissue –cushions the eye

24. LACRIMAL APPARATUS
Lacrimal glands –produce tears that lubricate & have a germicidal effect.
Lacrimal ducts
Superior or inferior lacrimal canal
Lacrimal sac
Nasolacrimal duct
Nasal cavity

25. ACCESSORY ORGANS & EYE PROTECTION CONT’
• Eyebrows–protect against foreign articles, perspiration, & direct rays
of light.
• Eyelids–folds of skin that cover the surface of the eye; close by reflex
action when an object approaches.
• Eyelashes–secrete oils that prevent lids from sticking together.

26. ACCESSORY ORGANS & EYE PROTECTION CONT’
EXTRAOCULAR MUSCLES
•Rectus Muscles
-superior rectus
-inferior rectus
-medial rectus
-lateral rectus
•Oblique Muscles
-Superior oblique
-Inferior oblique

28. PHYSIOLOGY OF SIGHT
•Light falling on object is reflected. Reflected rays fall on the eye.
• These rays are refracted through the cornea and the aqueous humor
(watery fluid) onto the lens.
• The lens causes further refraction and the rays converge to a focus on
the retina.
• The image on the retina stimulates either the rods or the cones
depending on the intensity of the light.

29. CONT’
• Image formed can be:
–Upside down (inverted)
–Back to front (reversed)
–Smaller in size than the object being observed (diminished).
• Impulses produced by light falling on the rods and cones are
transmitted via the optic nerve to the rear of the cerebrum.
• The brain interprets these impulses.

30. SUMMARY
•The eye is the sense organ specialized in sight. It has the cornea, iris,
pupil, sclera, choroid, retina, optic nerve, vitreous body and aqueous
humor.
•The sensory receptors for light which are the rods and cones. These
are found on the retina.
•The blood supply is through the carotid artery, ophthalmic artery,
ciliary artery, then the eye.
•The nerve supply is through the optic nerve.

31. SUMMARY CONT’
•Tears are produced and drained through the lacrimal apparatus.
•The extraocular muscles aid in movement of the eye.
•The light rays are refracted through the cornea, aqueous humor and
lens to the retina. The retina stimulates either the rods or cones
depending ion the intensity of light, impulses are sent to the brain for
interpretation.

32. REFERENCES
•David S, Jackie B and Ricki L. (2003), Hole’s Essentials of Human
Anatomy and Physiology, International edition, McGraw-Hill Higher
Education, New York, USA.
•Roger Watson (2005), Anatomy and Physiology for Nurses, 20th
edition, Elsevier, Oxford, UK.
•Waugh A & Grant A (2001), ROSS AND WILSON Anatomy and
physiology in health and illness, 9th Ed, Church-Hill Livingstone,
Toronto.

33. THANK
YOU