THE SPECIAL SENSES (EYE & EAR)

1. THE SPECIAL SENSES(EYE & EAR)

2. Overview of the Eye • Eye acts much like a camera • Lens of eye adjusts to bring object into clear focus • Pupil of eye constricts to allow less light to enter in bright setting or dilates to allow more light to enter in darker setting • Through bending of light rays, image reaches retina • Sensitive nerve cell layer of the eye • Image is transmitted to brain for interpretation

3. Structures of the Eye(Front View) • Sclera • White portion of the eye • Tough connective tissue • Maintains the shape of the eyeball • Serves as protective covering for the eye • Iris • Colored portion of the eye • Pupil • Opening in the center of the eye • Controls the amount of light entering the eye

4. Structures of the Eye(Front View) (continued) • Conjunctiva • Thin mucous membrane layer that lines anterior part of eye and inner part of eyelids • Colorless, but appears white because it covers sclera • Lacrimal gland • Located at upper outer edge of each eye • Produces tears • Lacrimal duct • Located at inner edge of eye • Tears drain from eye through this duct

5. Structures of the Eye(Front View) (continued) Front View of the Eye

6. Structures of the Eye(Front View) (continued) • Eyelids • Continuous with the skin and cover the eyeball • Keep surface of eyeball lubricated and protected from dust and debris through blinking motion • Eyelashes • Located along the edges of the eyelids • Help protect eyeball by preventing foreign materials and/or insects from coming in contact with surface of eyeball

7. Structures of the Eye(Cross Section) • Sclera • “White of the eye” • Thinnest over the anterior surface of the eye • Thickest at the back of the eye, near opening for optic nerve • Cornea • Continuous with anterior portion of sclera • Transparent, nonvascular layer covering the colored part of the eye

8. Structures of the Eye(Cross Section) (continued) • Conjunctiva • Mucous membrane that lines inner surfaces of the eyelids and outer surfaces of the eye • Choroid • Vascular middle layer of the eye • Just beneath the sclera • Contains extensive capillaries that provide blood supply and nutrients to the eye • Contains the iris, ciliary body, and suspensory ligaments

9. Structures of the Eye(Cross Section) (continued) • Iris • Colored portion of the eye • Can be seen through the transparent corneal layer • Pupil • Located in center of iris • Controls amount of light entering eye • Lens • Colorless biconvex structure that aids in focusing the images clearly on the retina

10. Structures of the Eye(Cross Section) (continued) • Ciliary Body • Located on each side of the lens • Contains muscles that are responsible for adjusting the lens to view near objects • Suspensory Ligaments • Radiate from the ciliary body and attach to the lens • Hold the lens in place • Assist in adjusting the shape of the lens for proper focusing of the eye

11. Structures of the Eye(Cross Section) (continued) • Retina • Sensitive nerve cell layer • Changes the energy of the light rays into nerve impulses • Transmits nerve impulses via optic nerve to brain for interpretation of the image seen by the eye • Nerve cells of retina • Rods are responsible for vision in dim light and for peripheral vision • Cones responsible for visualizing colors, central vision, and vision in bright light

12. Structures of the Eye(Cross Section) (continued) • Retina (continued) • Macula Lutea • Oval, yellowish spot near the center of the retina • Fovea Centralis • Small depression located within the macula lutea • Sharpest image is obtained when image focuses directly on fovea centralis = central vision

13. Structures of the Eye(Cross Section) (continued) • Optic Nerve • Receives impulses from retina and transmits them to the brain • Images are then interpreted as vision • Optic Disc • Contains no rods or cones • Known as the “blind spot” of the eye • Center of optic disc serves as point of entry for artery that supplies retina

14. Structures of the Eye(Cross Section) (continued) Lateral Cross Section of the Eye

15. Structures of the Eye(Cross Section) (continued) • Anterior Cavity of the Eye • Anterior Chamber • Located in front of the lens • Filled with clear, watery fluid called aqueous humor • Posterior Chamber • Located behind the lens • Also filled with aqueous humor – flows back and forth between both chambers

16. Structures of the Eye(Cross Section) (continued) • Posterior Cavity of the Eye • Posterior to the lens • Filled with vitreous humor • Clear, jellylike substance that gives shape to the eyeball • Not constantly reproduced • Blindness can result if vitreous humor escapes from eye

17. Process of Vision • Process Begins as Light Rays Enter Eye • Transmitted through cornea, aqueous humor, pupil, lens, and vitreous humor to retina • Sensitive nerve cells of retina transmit image through optic nerve to brain • Brain interprets image as vision

18. Process of Vision (continued) • Refraction • Process of bending of light rays as they pass through the various structures of the eye to produce a clear image on the retina • Errors of Refraction • Occur when eyeball is abnormally shaped • Occur when lens has lost ability to accommodate to near vision • Vision will be blurred • Can be adjusted with corrective lenses

19. Diseases of the Eye

20. Astigmatism • Pronounced • (ah-STIG-mah-tizm) • Defined • A refractive error causing the light rays entering the eye to be focused irregularly on the retina due to an abnormally shaped cornea • Correction: contact lenses or eyeglasses, which neutralize the defect

21. Blepharitis • Pronounced • (blef-ah-RYE-tis) • Defined • Inflammation of the eyelid margins stemming from seborrheic, allergic, or bacterial origin

22. Blindness • Pronounced • (BLINDNESS) • Defined • The absence of vision or the need for assistive devices and/or assistance from others to accomplish daily activities due to the inability to see

23. Monochromatism(Color Blindness) • Pronounced • (mon-oh-KROH-mah-tizm) • Defined • An inability to sharply perceive visual colors • Daltonism – unable to distinguish greens from reds • Achromatic Vision – cannot distinguish any color; perceives only white, gray, and black

24. Cataract • Pronounced • (KAT-ah-rakt) • Defined • Lens in the eye becomes progressively cloudy losing its normal transparency • Thus altering the perception of images due to the interference of light transmission to the retina

25. Conjunctivitis, Acute • Pronounced • (kon-junk-tih-VYE-tis acute) • Defined • Inflammation of the mucous membrane lining the eyelids and covering the front part of the eyeball • Also called “Pinkeye”

26. Glaucoma • Pronounced • (glau-KOH-mah) • Defined • Ocular disorders identified as a group due to the increase in intraocular pressure

27. Glaucoma (continued) • Chronic Open-Angle Glaucoma • Primary disorder • Breakdown in drainage system of the circulation of aqueous humor • Gradual elevation of internal pressure leads to decreased blood supply to optic nerve and retina • Peripheral vision is gradually lost when untreated

28. Glaucoma (continued) • Acute Closed-Angle Glaucoma • Mouth of drainage system is narrow and closes completely – allowing no flow of aqueous humor • Rapid occurrence characterized by severe pain, blurred vision, photophobia, redness, and seeing “halos” around light • If untreated, person can lose his or her sight within several days

29. Hyperopia • Pronounced • (high-per-OH-pee-ah) • Defined • A refractive error in which the lens of the eye cannot focus on an image accurately, resulting in impaired close vision that is blurred due to the light rays being focused behind the retina because the eyeball is shorter than normal • Also called farsightedness

30. Hyperopia (continued) Hyperopia (Farsightedness)

31. Myopia • Pronounced • (my-OH-pee-ah) • Defined • A refractive error in which the lens of the eye cannot focus on an image accurately, resulting in impaired distant vision that is blurred due to the light rays being focused in front of the retina because they eyeball is longer than normal • Also known as nearsightedness

32. Myopia (continued) Myopia (nearsightedness)

33. Presbyopia • Pronounced • (prez-bee-OH-pee-ah) • Defined • A refractive error occurring after the age of 40, when the lens of the eye(s) cannot focus on an image accurately due to its decreasing loss of elasticity resulting in a firmer and more opaque lens • Also called farsightedness due to better clarity of distant objects

34. Strabismus • Pronounced • (strah-BIZ-mus) • Defined • Failure of the eyes to gaze in the same direction due to weakness in the muscles controlling the position of the eye • Most common type is nonparalytic strasbismus, an inherited defect in which the eye position of the two eyes has no relationship

35. Strabismus (continued) • Convergent Strabismus • Also known as “Crosseye” • Also known as “Esotropia” • Affected eye turns inward • Usually develops in infancy or early childhood

36. Strabismus (continued) • Divergent Strabismus • Also known as “Walleye” • Also known as “Exotropia” • Affected eye turns outward

37. Strabismus (continued) Strabismus:(A) Convergent;(B) Divergent

38. Overview of the Ear • Two important functions of the ear • It enables us to hear • It functions as the sensory organ of balance or equilibrium • Location of one ear on each side of head produces binaural hearing • Hearing from both sides

39. Structures of the Ear • External Ear • Visible portion of the ear not contained within the head • Auricle or pinna • Cartilaginous flap that has a fleshy, lower portion called the ear lobe • External auditory canal • Tube leading from the auricle to the middle ear • Lined with tiny hairs called cilia which aid in transmitting sound waves inward • Tympanic membrane (eardrum) • Separates external ear from middle ear

40. Structures of the Ear (continued) • Middle Ear • Contains three tiny bones known as the auditory ossicles • Malleus • Resembles the shape of a hammer • Connected to tympanic membrane and transmits sound vibrations to second auditory ossicle • Incus • Resembles the shape of an anvil • Transmits sound vibrations from malleus to third auditory ossicle

41. Structures of the Ear (continued) • Middle Ear (continued) • Stapes • Shaped like a tiny stirrup • Transmits sound vibrations from incus to the inner ear • Eustachian tube • Connects the middle ear to the pharynx • Also called the auditory tube • Oval window • Separates the middle ear from the inner ear • Base of the stapes fits into the oval window

42. Structures of the Ear (continued) • Inner Ear • Vestibule • Central portion of the inner ear • Located next to stapes and between cochlea and semicircular canals • Contains the utricle and saccule-membranous pouches or sacs that aid in maintaining balance • Cochlea • Snail-shaped bony structure • Contains endolymph and perilymph • Auditory fluids that aid in transmission of sound vibrations

43. Structures of the Ear (continued) • Inner Ear (continued) • Organ of Corti • True organ of hearing • Contained within the cochlea • Here, sound vibrations are converted into nerve impulses that are transmitted to the brain for interpretation as hearing • Semicircular canals • Located behind the vestibule • Three bony, fluid-filled loops that help to maintain one’s balance

44. Structures of the Ear (continued) Structures of the Ear

45. The Process of Hearing Pathway of Sound Vibrations

46. Diseases of the Ear

47. Mėniėre’s Disease • Pronounced • (may-nee-ARYZ dih-ZEEZ) • Defined • Chronic inner ear disease in which there is an over accumulation of fluid in the labyrinth, characterized by recurring episodes of vertigo, hearing loss, feeling of pressure or fullness in the affected ear, and tinnitus

48. Otitis Externa (Swimmer’s Ear) • Pronounced • (oh-TYE-tis eks-TER-nah) • Defined • Inflammation of the outer or external ear canal • Result of growth of bacteria or fungi in the external ear • Major symptom is pain, especially when the ear is tugged on, along with a red swollen ear canal

49. Otitis Media, Acute • Pronounced • (oh-TYE-tis MEE-dee-ah) • Defined • A middle ear infection, which predominately affects infants, toddlers, and preschoolers

50. Suppurative Otitis Media • Pronounced • (SOO-per-ah-tiv oh-TYE-tis MEE-dee-ah) • Defined • A purulent collection of fluid in the middle ear causing the person to experience pain (possibly severe), an elevation in temperature, dizziness, decreased hearing, vertigo, and tinnitus • Also called acute otitis media