1. 16
Special Senses:
The Eye

2. Learning Outcomes
State the description and primary functions of the eye.
Analyze, build, spell, and pronounce medical words.
Comprehend the drugs highlighted in this chapter.
Describe diagnostic and laboratory tests related to the eye.
Identify and define selected abbreviations.

3. Multimedia Directory Slide 6 Virtual Tour of the Eye Animation
Slide 10 Structures of the Eye Animation
Slide 35 Retina Animation
Slide 36 Rods and Cones Animation
Slide 40 Optic Nerve and Optic Disk Animation 1
Slide 41 Optic Nerve and Optic Disk Animation 2
Slide 50 Cataracts Video
Slide 52 Conjunctivitis Video
Slide 65 Macular Degeneration Video

4. Anatomy and Physiology Overview
Eye
Composed of special anatomical structures that work together to facilitate sight:
Cornea
Pupil
Lens
Vitreous body
Light stimulates sensory receptors (rods and cones) in the retina or innermost layer of the eye.

5. Anatomy and Physiology Overview
Vision is made possible through the coordinated actions of nerves that control:
the movement of the eyeball
the amount of light admitted by the pupil
the focusing of that light on the retina by the lens
the transmission of the resulting sensory impulses to the brain by the optic nerve.

6. Virtual Tour of the Eye Animation
Click on the screenshot to view an animation of the tour of the eye.
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7. Insert table 16-1

8. Insert table 16-1 8

9. Internal structure of the eye.
Figure 16.1
Internal structure of the eye.

10. Structures of the Eye Animation
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The animation may take a moment to begin playing.
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11. External Structures of the Eye
Orbit
A cone-shaped cavity in the front of the skull that contains the eyeball.
Formed by the combination of several bones and is lined with fatty tissue that cushions the eyeball.
This cavity has several foramina (openings) through which blood vessels and nerves pass.
Largest opening is the optic foramen for the optic nerve and ophthalmic artery.

12. External Structures of the Eye
Muscles of the Eye
Six eye muscles control the movement of the eye.
Four are rectus muscles, and two are oblique muscles.
Rectus muscles allow a person to see up, down, right, and left.
Oblique muscles allow the eyes to turn to see upper left and upper right, lower left and lower right.
Insert Fig (ms, p. 6).

13. External Structures of the Eye
Muscles of the Eye
Eye muscles help maintain the shape of the eyeball.

14. (A) Lateral view, left eye.
Figure 16.2
(A) Lateral view, left eye. 14

15. (B) Anterior view, left eye.
Figure 16.2 (continued)
(B) Anterior view, left eye. 15

16. External Structures of the Eye
Eyelids
Protect the eyeball from:
Intense light
Foreign particles
Impact
Keep the eyeball’s surface lubricated and free from dust and debris.

17. External Structures of the Eye
Eyelids
Canthus
Palpebral fissure
Eyelashes
Meibomian Glands

18. External Structures of the Eye
Conjunctiva
A mucous membrane that lines the underside of each eyelid and reflects onto the anterior portion of the eyeball.
This membrane acts as a protective covering for the exposed surface of the eyeball.

19. External Structures of the Eye
Lacrimal Apparatus
Those structures that produce, store, and remove the tears that cleanse and lubricate the eye:
Lacrimal gland
Lacrimal canaliculi (ducts)
Lacrimal sac
Nasolacrimal duct

20. Lacrimal glands and lacrimal canaliculi (ducts).
Figure 16.3
Lacrimal glands and lacrimal canaliculi (ducts).

21. External Structures of the Eye
Lacrimal Gland
Located above the outer corner of the eye.
Secretes tears through approximately 12 ducts onto the surface of the conjunctiva of the upper lid.
This fluid washes across the anterior surface of the eye and is collected by the lacrimal canaliculi (ducts).

22. External Structures of the Eye
Lacrimal Canaliculi
Two ducts at the inner corner of the eye that collect tears and drain into the lacrimal sac.
Lacrimal Sac
The enlargement of the upper portion of the lacrimal duct.
Tears secreted by the lacrimal glands are pulled into this sac and forced into the nasolacrimal duct by the blinking action of the eyelids.

23. External Structures of the Eye
Nasolacrimal duct
The passageway draining lacrimal fluid into the nose.
The lacrimal sac is the enlarged upper portion of this duct.

24. Life Span Considerations
The eyes begin to develop as an outgrowth of the forebrain in the 4-week-old embryo and are complete at 24 weeks.
At 28 weeks, eyebrows and eyelashes are present, and the eyelids open.
The newborn can see, and visual acuity is estimated to be around 20/400.

25. Life Span Considerations
Most newborns appear to have crossed eyes because their eye muscles are not fully developed.
At first, the eyes appear to be blue or gray.
Permanent coloring becomes fixed between 6 and 12 months of age.
Tears do not appear until approximately 1 to 3 months because the lacrimal gland ducts are immature.

26. Life Span Considerations
Depth perception begins to develop around 9 months of age.
Visual acuity improves with age, and, by the age of 2 or 3 years, it is around 20/30 or 20/20.
Children are farsighted until about 5 years of age.

27. Internal Structures of the Eye
The eyeball, its various structures, and the nerve fibers connecting it to the brain make up the internal eye.

28. Internal Structures of the Eye
Eyeball
The organ of vision, globe shaped and divided into two cavities:
The ocular cavity
The space in front of the lens.
Further divided by the iris into anterior and posterior chambers.
Anterior chamber is filled with a watery fluid known as the aqueous humor.
A much larger cavity behind the lens is filled with a jellylike material, the vitreous humor, which maintains the eyeball’s spherical shape.

29. Internal Structures of the Eye
Eyeball’s Outer Layer
Composed of:
Sclera, or white of the eye
Cornea, or transparent anterior portion of the eye’s fibrous outer surface.
The curved surface of the cornea is important because it bends light rays and helps to focus them on the surface of the retina.

30. Internal Structures of the Eye
Eyeball’s Middle Layer
Known as the uvea, it lies just below the sclera and consists of the:
Iris
Ciliary body
Choroid

31. Internal Structures of the Eye
Middle Layer: Iris
A colored membrane attached to the ciliary body and suspended between the lens and cornea in the aqueous humor.
Has a circular opening in its center called the pupil.
Has two muscles that contract or dilate to regulate the amount of light admitted by the pupil.

32. Internal Structures of the Eye
Middle Layer: Ciliary body
A thickened portion of the vascular membrane to which the iris is attached.
Smooth muscle forming a part of the ciliary body governs the convexity of the lens.
Secretes aqueous humor that nourishes the cornea, lens, and surrounding tissues.

33. Internal Structures of the Eye
Middle Layer: Choroid
A pigmented vascular membrane that prevents internal reflection of light.
Inner Layer
The retina contains photoreceptive cells (rods and cones) that translate light waves into nerve impulses.

34. Retina as seen through an ophthalmoscope.
Figure 16.4
Retina as seen through an ophthalmoscope.

35. Click on the screenshot to view an animation on the retina of the eye.
Retina Animation
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36. Rods and Cones Animation
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37. Internal Structures of the Eye
Inner Layer
Most of the approximately 6 million cone cells are grouped into a small area called the macula lutea.
In the center of the macula lutea is a small depression, the fovea centralis, which is the central focusing point within the eye and contains only cone cells.

38. Internal Structures of the Eye
Inner Layer
The eye contains approximately 120 million rods that are sensitive to dim light.
The rods contain rhodopsin, a pigment necessary for night vision.
Optic disk: the point at which nerve fibers from the retina converge to form the optic nerve.

39. Internal Structures of the Eye
Inner Layer
Blind spot: the absence of rods and cones in the area of the optic disk creates a blind spot on the retina’s surface; the only part of the retina that is insensitive to light.

40. Optic Nerve and Optic Disk Animation 1
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41. Optic Nerve and Optic Disk Animation 2
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42. Internal Structures of the Eye
Lens
A colorless crystalline body biconvex in shape and enclosed in a transparent capsule.
Suspended by ligaments just behind the iris.
Contraction and relaxation of the ciliary muscle control the tension of the suspensory ligaments to change the shape of the lens.
The function of the lens is to sharpen the focus of light on the retina.

43. Internal Structures of the Eye
Lens
Accommodation keeps the image in the same place on both retinae by combining changes in:
The size of the pupil.
The curvature of the lens.
The convergence of the optic axes.

44. How Sight Occurs
Light rays strike the eye and pass through the cornea, pupil, aqueous humor, lens, and vitreous humor.
Light rays then reach the retina and stimulate rods and cones.
An upside-down image is relayed along nerve impulses to the optic nerve.
The images are transferred to the brain, which turns the images right-side-up.

45. Figure 16.5
Light entering the eye.

46. Image inverted on the retina.
Figure 16.6
Image inverted on the retina.

47. Audio Pronunciations Accommodation Amblyopia Anisocoria Aphakia
Astigmatism a-
= lack of, without
stigmat
= point
-ism
= condition

48. Audio Pronunciations Bifocal Blepharitis Blepharoptosis Cataract
Chalazion
Choroiditis
blephar/o
= eyelid
-ptosis
= prolapse, drooping

49. Cataract of the right eye.
Figure 16.7
Cataract of the right eye.

50. Click on the screenshot to view a video on the topic of cataracts.
Cataracts Video
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51. Audio Pronunciations Conjunctivitis Corneal Corneal transplant
Cryosurgery
Cycloplegia

52. Conjunctivitis Video
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53. Audio Pronunciations Dacryoma Diplopia Electroretinogram Emmetropia
Entropion
Enucleation

54. Figure 16.8
Visual abnormalities. (A) In normal vision, the lens focuses the visual image on the retina. Common problems with the accommodation mechanism involve

55. Figure 16.8
Visual abnormalities. (B) myopia, the inability to lengthen the focal distance enough to focus the image of a distant object on the retina and 55

56. Figure 16.8
Visual abnormalities. (C) hyperopia, the inability to shorten the focal distance adequately for nearby objects. These conditions can be corrected by placing appropriately shaped lenses in front of the eyes. 56

57. Visual abnormalities. (D) Diverging lens is used to correct myopia and
Figure 16.8
Visual abnormalities. (D) Diverging lens is used to correct myopia and 57

58. Figure 16.8
Visual abnormalities. (E) converging lens is used to correct hyperopia. 58

59. Audio Pronunciations Esotropia Exotropia Glaucoma Gonioscope
Hemianopia
Hyperopia
hyper-
= beyond
-opia
= sight, vision

60. Figure 16.9
In glaucoma, the accumulation of aqueous humor in the anterior chamber of the eye causes pressure to build, resulting in eventual loss of vision. (A) and (B) show two forms of glaucoma 60

61. Figure 16.9
In glaucoma, the accumulation of aqueous humor in the anterior chamber of the eye causes pressure to build, resulting in eventual loss of vision. (A) and (B) show two forms of glaucoma 61

62. Figure 16.9
In glaucoma, (C ) shows the narrowing of the optic field that is a typical symptom of untreated glaucoma. 62

63. Audio Pronunciations Intraocular Iridectomy Iridocyclitis Keratitis
Keratoconjunctivitis
Keratoplasty

64. Audio Pronunciations Lacrimal Laser Macular degeneration Microlens
Miotic
Mydriatic
Myopia

65. Macular Degeneration Video
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66. Life Span Considerations
Macular degeneration
An incurable, age-related, progressive eye disease that affects more than 10 million Americans.
Leading cause of blindness for those ages 55 and older.

67. Life Span Considerations
Macular degeneration
For the first time, researchers have linked gene defects to macular degeneration.
Could lead to the ability to identify people at high risk for the disorder and perhaps to ways to treat or prevent vision loss.

68. Life Span Considerations
Stargardt’s disease
Also known as juvenile macular degeneration.
An inherited disease that usually manifests itself between the ages of 7 and 12.
Believed to cause the eye’s central vision to deteriorate because the rod cells just outside the macula erode, which eventually harms the retinal pigment epithelium (RPE).

69. Life Span Considerations
Stargardt’s disease
As the RPE fails, the disease can spread to the macula’s cone cells, causing the characteristic loss of central vision.
Vision loss is usually slow until the 20/40 level and then rapidly progresses to the 20/200 level.
Unfortunately, in some cases, vision can degenerate to 10/200 in a period of months.

70. Life Span Considerations
Stargardt’s disease
Peripheral vision generally remains.
Presently, there is no cure or effective treatment.

71. Audio Pronunciations Nyctalopia Nystagmus Ocular Ocular fundus
Ophthalmologist
Ophthalmology

72. Audio Pronunciations Ophthalmoscope Optic Optician Optometrist
Optomyometer
Orthoptics
opt/o
= eye
my/o
= muscle
-meter
= instrument to measure

73. Use of an ophthalmoscope to examine the interior of the eye.
Figure 16.10
Use of an ophthalmoscope to examine the interior of the eye.

74. Audio Pronunciations Phacoemulsification Phacolysis Phacosclerosis
Photocoagulation
Photophobia
Presbyopia
Pupillary

75. Figure 16.11
Phacoemulsification is used to remove the cataract, then an artificial lens is implanted. 75

76. Figure (continued)
Phacoemulsification is used to remove the cataract, then an artificial lens is implanted. 76

77. Figure (continued)
Phacoemulsification is used to remove the cataract, then an artificial lens is implanted. 77

78. Audio Pronunciations Radial keratotomy Retinal detachment Retinitis
Retinitis pigmentosa
Retinoblastoma
Retinopathy
Retrolental fibroplasia

79. Figure 16.12
Retinal detachment.

80. Figure 16.13
Appearance of the ocular fundus in diabetic retinopathy. (Courtesy of the National Eye Institute, National Institutes of Health)

81. Audio Pronunciations Scleritis Strabismus Sty(e) Tonography Tonometer
Trichiasis
Trifocal

82. Schiötz tonometer for measuring intraocular pressure.
Figure 16.14
Schiötz tonometer for measuring intraocular pressure.

83. Audio Pronunciations
Uveal
Uveitis
Xenophthalmia
Xerophthalmia

84. Drug Highlights
Drugs used to treat glaucoma: Either increase the outflow of aqueous humor, decrease its production, or produce both of these actions.

85. Drug Highlights Drugs used to treat glaucoma Prostaglandin analogues
Adrenergic drugs
Alpha antagonist

86. Drug Highlights Drugs used to treat glaucoma Beta blockers
Carbonic anhydrase inhibitors
Cholinergic (miotic)

87. Drug Highlights Drugs used to treat glaucoma Cholinesterase
Combination of beta blocker and carbonic anhydrase inhibitor

88. Drug Highlights Mydriatics: Agents used to dilate the pupil.
Anticholinergics
Sympathomimetics

89. Drug Highlights Antibiotics
Used to treat infectious diseases, especially those caused by bacteria. Can be in the form of an ointment, cream, or solution.
Antifungal Agents
Antiviral Agents

90. Diagnostic and Lab Tests
Color vision tests
Use of polychromatic (multicolored) charts or an anomaloscope (a device for detecting color blindness) to assess an individual’s ability to recognize differences in color.
Exophthalmometry
Process of measuring the forward protrusion of the eye via an exophthalmometer.

91. Figure 16.15
Color vision chart. A person who is color blind will not see the number 27 in the circle.

92. Diagnostic and Lab Tests
Gonioscopy
Examination of the anterior chamber of the eye via a gonioscope.
Keratometry
Process of measuring the cornea via a keratometer.

93. Diagnostic and Lab Tests
Ocular ultrasonography
Use of high-frequency sound waves (via a small probe placed on the eye) to measure for intraocular lenses and to detect orbital and periorbital lesions.

94. Diagnostic and Lab Tests
Ophthalmoscopy
Examination of the interior of the eyes via an ophthalmoscope.
Tonometry
Measurement of the intraocular pressure of the eye via a tonometer.

95. Diagnostic and Lab Tests
Visual acuity
Acuteness or sharpness of vision.
A Snellen eye chart can be used to test it; the patient reads letters of various sizes from a distance of 20 feet. Normal vision is 20/20.

96. Test of distance vision using the Snellen eye chart.
Figure 16.16
Test of distance vision using the Snellen eye chart.

97. Abbreviations 97

98. Combining Form Match Up Quiz
ambly/o a. angle
anis/o b. unequal
goni/o c. straight
orth/o d. old
presby/o e. dull