Special Senses: The Eye

Medical TerminologyMedical TerminologyA Word-Building Approach

Medical Terminology: A Word-Building Approach, Seventh EditionJane Rice

CHAPTER

Seventh Edition

Special Senses:The Eye

Learning OutcomesLearning 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.

Multimedia DirectoryMultimedia Directory

Virtual Tour of the Eye Animation

Structures of the Eye Animation

Retina Animation

Rods and Cones Animation

Optic Nerve and Optic Disk Animation 1

Optic Nerve and Optic Disk Animation 2

Cataracts Video

Conjunctivitis Video

Macular Degeneration Video

Anatomy and Physiology Anatomy and Physiology OverviewOverview

• 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.

Anatomy and Physiology Anatomy and Physiology OverviewOverview

• 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.

Virtual Tour of the Eye AnimationVirtual Tour of the Eye Animation

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Insert table 16-1

Figure 16.1Internal structure of the eye.

Structures of the Eye AnimationStructures of the Eye Animation

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External Structures of the EyeExternal 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.

• 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.

• Muscles of the Eye– Eye muscles help maintain the shape of the

eyeball.

Figure 16.2(A) Lateral view, left eye.

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

• Eyelids– Protect the eyeball from:

Intense light Foreign particles Impact

– Keep the eyeball’s surface lubricated and free from dust and debris.

• Eyelids– Canthus– Palpebral fissure– Eyelashes– Meibomian Glands

• 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.

• 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

Figure 16.3Lacrimal glands and lacrimal canaliculi (ducts).

• 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).

• 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.

• Nasolacrimal duct– The passageway draining lacrimal fluid into

the nose.– The lacrimal sac is the enlarged upper portion

of this duct.

Life Span ConsiderationsLife 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.

• 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.

• 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.

Internal Structures of the EyeInternal Structures of the Eye

• The eyeball, its various structures, and the nerve fibers connecting it to the brain make up the internal 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.

• 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.

• Eyeball’s Middle Layer– Known as the uvea, it lies just below the

sclera and consists of the: Iris Ciliary body Choroid

• 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.

• 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.

• 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.

Figure 16.4Retina as seen through an ophthalmoscope.

Retina AnimationRetina Animation

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Rods and Cones AnimationRods and Cones Animation

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• 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.

• 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.

• 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.

Optic Nerve and Optic Disk Optic Nerve and Optic Disk Animation 1Animation 1

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Optic Nerve and Optic Disk Optic Nerve and Optic Disk Animation 2Animation 2

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• 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.

• 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.

How Sight OccursHow 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.

Figure 16.5Light entering the eye.

Figure 16.6Image inverted on the retina.

• Accommodation

• Amblyopia

• Anisocoria

• Aphakia

• Astigmatism

stigmat

Audio PronunciationsAudio Pronunciations

= lack of, without

= point

= condition

• Bifocal

• Blepharitis

• Blepharoptosis

• Cataract

• Chalazion

• Choroiditis

blephar/o

-ptosis

= eyelid

= prolapse, drooping

Figure 16.7Cataract of the right eye.

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• Conjunctivitis

• Corneal

• Corneal transplant

• Cryosurgery

• Cycloplegia

Conjunctivitis VideoConjunctivitis Video

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• Dacryoma

• Diplopia

• Electroretinogram

• Emmetropia

• Entropion

• Enucleation

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

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

Figure 16.8Visual 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.

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

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

• Esotropia

• Exotropia

• Glaucoma

• Gonioscope

• Hemianopia

• Hyperopia

hyper-

= beyond

= sight, vision

Figure 16.9In 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

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

• Intraocular

• Iridectomy

• Iridocyclitis

• Keratitis

• Keratoconjunctivitis

• Keratoplasty

• Lacrimal

• Laser

• Macular degeneration

• Microlens

• Miotic

• Mydriatic

• Myopia

Macular Degeneration VideoMacular Degeneration Video

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• 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.

• 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.

• 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).

• 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.

• Stargardt’s disease– Peripheral vision generally remains. – Presently, there is no cure or effective

treatment.

• Nyctalopia

• Nystagmus

• Ocular

• Ocular fundus

• Ophthalmologist

• Ophthalmology

• Ophthalmoscope

• Optic

• Optician

• Optometrist

• Optomyometer

• Orthoptics

-meter

= muscle

= instrument to measure

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

• Phacoemulsification

• Phacolysis

• Phacosclerosis

• Photocoagulation

• Photophobia

• Presbyopia

• Pupillary

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

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

• Radial keratotomy

• Retinal detachment

• Retinitis

• Retinitis pigmentosa

• Retinoblastoma

• Retinopathy

• Retrolental fibroplasia

Figure 16.12Retinal detachment.

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

• Scleritis

• Strabismus

• Sty(e)

• Tonography

• Tonometer

• Trichiasis

• Trifocal

Figure 16.14Schiötz tonometer for measuring intraocular pressure.

• Uveal

• Uveitis

• Xenophthalmia

• Xerophthalmia

Drug HighlightsDrug Highlights

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

• Drugs used to treat glaucoma– Prostaglandin analogues– Adrenergic drugs– Alpha antagonist

• Drugs used to treat glaucoma– Beta blockers– Carbonic anhydrase inhibitors– Cholinergic (miotic)

• Drugs used to treat glaucoma– Cholinesterase– Combination of beta blocker and carbonic

anhydrase inhibitor

• Mydriatics: Agents used to dilate the pupil.– Anticholinergics– Sympathomimetics

• 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

Diagnostic and Lab TestsDiagnostic 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.

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

• Gonioscopy– Examination of the anterior chamber of the

eye via a gonioscope.

• Keratometry– Process of measuring the cornea via a

keratometer.

• 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.

• Ophthalmoscopy– Examination of the interior of the eyes via an

ophthalmoscope.

• Tonometry– Measurement of the intraocular pressure of

the eye via a tonometer.

• 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.

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

Abbreviations

Combining Form Match Up QuizCombining Form Match Up Quiz

1. ambly/o a. angle

2. anis/o b. unequal

3. goni/o c. straight

4. orth/o d. old

5. presby/o e. dull

Special Senses: The Eye

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