The Special Senses (Eye and Ear)

1. The Special Senses(Eye and Ear) CHAPTER 14

2. Overview of the Eye • Eye acts much like a camera • Lens of eye adjusts to bring object into 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 eye • Image is transmitted to brain for interpretation

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

4. Structures of the Eye(Front View) • 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)

6. Structures of the Eye(Front View) • Eyelids • Continuous with skin and cover the eyeball • Keep surface of eyeball lubricated and protected from dust and debris through blinking motion • Eyelashes • Located along edges of 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 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 colored part of the eye

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

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

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

11. Structures of the Eye(Cross Section) • Retina • Sensitive nerve cell layer • Changes energy of light rays into nerve impulses • Transmits nerve impulses via optic nerve to brain for interpretation of image seen by 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) • Retina • Macula Lutea • Oval, yellowish spot near center of retina • Fovea Centralis • Small depression located within macula lutea • Sharpest image is obtained when image focuses directly on fovea centralis = central vision

13. Structures of the Eye(Cross Section) • 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) Lateral Cross Section of the Eye

15. Structures of the Eye(Cross Section) • Anterior cavity of the eye • Anterior chamber • Located in front of lens • Filled with clear, watery fluid called aqueous humor • Posterior chamber • Located behind lens • Also filled with aqueous humor • Flows back and forth between both chambers

16. Structures of the Eye(Cross Section) • Posterior cavity of eye • Posterior to 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 • 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. PATHOLOGICAL CONDITIONS The Eye

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

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

22. Blepharoptosis(Ptosis) • Pronounced • (blef-ah-roh-TOH-sis) • Defined • Occurs when eyelid partially or entirely covers the eye as a result of a weakened muscle

23. Blepharoptosis Blepharoptosis

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

25. Monochromatism (Color Blindness) • Pronounced • (mon-oh-KROH-mah-tizm) • Defined • 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

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

27. Chalazion • Pronounced • (kah-LAY-zee-on) • Defined • Cyst or nodule on eyelid resulting from an obstruction of a meibomian gland, which is responsible for lubricating margin of the eyelid

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

29. Corneal Abrasion • Pronounced • (COR-nee-al ah-BRAY-zhun) • Defined • Disruption of the cornea’s surface epithelium commonly caused by an eyelash, a small foreign body, contact lenses, or a scratch from a fingernail

30. Diabetic Retinopathy • Pronounced • (dye-ah-BET-ik reh-tin-OP-ah-thee) • Defined • Condition that occurs as a consequence of an 8 to 10-year duration of diabetes mellitus in which the capillaries of retina experience scarring

31. Diabetic Retinopathy • Causes of retinal capillary scarring • Abnormal dilation and constriction of vessels • Hemorrhages • Microaneurysms • Abnormal formation of new vessels causing leakage of blood into the vitreous humor • Leakage causes permanent decline in sharpness of vision

32. Ectropion • Pronounced • (ek-TROH-pee-on) • Defined • “Turning out” or eversion of the eyelash margins from the eyeball leading to exposure of the eyelid and eyeball surface and lining • Occurs especially in the lower eyelid

33. Entropion • Pronounced • (en-TROH-pee-on) • Defined • “Turning in” of the eyelash margins resulting in the sensation similar to that of a foreign body in the eye (redness, tearing, burning, and itching) • Occurs especially in the lower margins

34. Exophthalmia • Pronounced • (eks-off-THAL-mee-ah) • Defined • Abnormal protrusion of the eyeball(s) usually with the sclera noticeable over the iris • Typically due to an expanded volume of orbital contents

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

36. Glaucoma • 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

37. Glaucoma • 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

38. Hemianopia • Pronounced • (hem-ee-an-NOP-ee-ah) • Defined • Loss of vision or blindness in one-half of the visual field

39. Hordeolum (Stye) • Pronounced • (hor-DEE-oh-lum) • Defined • Bacterial infection of an eyelash follicle or sebaceous gland • Originating with redness, swelling, and mild tenderness in margin of eyelash

40. Hyperopia • Pronounced • (high-per-OH-pee-ah) • Defined • Refractive error in which the lens of the eye cannot focus on an image accurately • Results in blurred vision due to light rays focused behind the retina because eyeball is shorter than normal • Also called farsightedness

41. Hyperopia Hyperopia (Farsightedness)

42. Hyphema (Hyphemia) • Pronounced • (high-FEE-mah) • Defined • Bleed into anterior chamber of eye • Resulting as a postoperative complication or from a blunt eye injury

43. Keratitis • Pronounced • (kair-ah-TYE-tis) • Defined • Corneal inflammation caused by a microorganism, trauma to eye, a break in sensory innervation of cornea, hypersensitivity reaction, or a tearing defect • May be due to dry eyes or ineffective eyelid closure

44. Myopia • Pronounced • (my-OH-pee-ah) • Defined • Refractive error in which the lens of the eye cannot focus on an image accurately • Resulting in blurred distant vision due to light rays focused in front of retina because eyeball is longer than normal • Also known as nearsightedness

45. Myopia Myopia (nearsightedness)

46. Nyctalopia(Night Blindness) • Pronounced • (nik-tah-LOH-pee-ah) • Defined • Inadequate vision at night or in faint lighting following reduction in synthesis of rhodopsin • Compound in rods of retina that enables the eye to adjust to low-density light

47. Nystagmus • Pronounced • (niss-TAG-mus) • Defined • Vertical, horizontal, rotary, or mixed rhythmic involuntary movements of the eye(s) • Caused by use of alcohol or certain drugs, lesions on the brain or inner ear, congenital abnormalities, nerve injury at birth, or abnormal retinal development

48. Ophthalmia Neonatorum • Pronounced • (off-THAL-mee-ah nee-oh-nay-TOR-um) • Defined • Purulent (contains pus) inflammation of conjunctiva and/or cornea in newborn • Cause of the keratitis and conjunctivitis results from newborn’s exposure to viral, bacterial, chemical, or chlamydial agents

49. Presbyopia • Pronounced • (prez-bee-OH-pee-ah) • Defined • Refractive error occurring after age of 40 • Lens of the eye(s) cannot focus on an image accurately due to loss of elasticity • Also called farsightedness due to better clarity of distant objects

50. Pterygium • Pronounced • (ter-IJ-ee-um) • Defined • Irregular growth developing as a fold in the conjunctiva • Usually on nasal side of the cornea • Disrupts vision if it extends over pupil • Can be caused by allergies and excessive ultraviolet light exposure