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Eye and Ear Diseases and Disorders 337
■ Iris—round disk of smooth and radial muscles giving
the eye its color
■ Pupil—round opening in the iris that changes size as
the iris reacts to light and dark
■ Anterior chamber—space between the cornea and
iris/pupil that is filled with clear fluid called aqueous
humor
■ Posterior chamber—space between the iris and lens
that is filled with aqueous humor
■ Lens—clear fibers enclosed in a membrane that
refract and focus light to the retina
■ Posterior cavity—the space in the posterior two-
thirds of the eyeball filled with a thick, gelatinous
material called vitreous humor
■ Posterior sclera—white opaque layer covering the
posterior part of the eyeball
■ Choroid layer—the layer containing blood vessels
between the sclera and retina
■ Retina—the inner layer of the posterior part of
the eye that receives the light rays (visual stimuli)
The mechanism of vision occurs after impulses leave
the retinae and travel through the optic nerves to the brain.
At the optic chiasm, the nerve fibers cross and continue
to the thalamus. These fibers synapse with other neurons
that send the impulses to the right and left visual area of the
occipital lobe of the brain. Because the tracts cross at the
optic chiasm, the stimuli coming from the right visual fields
are translated in the visual area of the left occipital area, and
the stimuli coming from the left visual fields are translated
in the visual area of the right occipital lobe (Figure 16-2).
Consider This...
1
If an individual becomes blind in one eye,
they lose about 20% of their vision but
100% of their depth perception.
Ear
The structures of hearing and equilibrium are divided
into the external ear, the middle ear, and the inner ear
(Figure 16-3). The external ear includes the pinna (auri
cle) and the external auditory canal. The pinna is mostly
cartilaginous tissue with a small amount of adipose tis
sue in the earlobe. The external auditory canal is about
LEFT VISUAL FIELD
RIGHT VISUAL FIELD
Temporal Nasal Nasal Temporal
Left eye Right eye
Optic nerve
Frontal lobe
Optic chiasm
Temporal
lobe
Optic tract
Optic
radiation
Visual cortex
Figure 16-2 The visual pathways of the eye.
1 inch long and contains hair and wax (cerumen, se-ROO-
men) producing glands. The external ear and middle ear
are separated by the tympanic membrane (eardrum).
The middle ear, also called the tympanic cavity, is a
small space containing three bones: the malleus (ham
mer), incus (anvil), and stapes (stirrup). Next to the
stapes is the oval window that leads to the inner ear.
The inner ear is the most sophisticated part of the
ear and is responsible for both hearing and equilibrium
(balance). It consists of a fluid-filled space housing the
vestibule, the semicircular canals, the round window, and
the cochlea. The structures in the vestibule maintain equi
librium during movement of the head. The semicircular
canals assist the body in adjusting to changes in direction,
and the movement of fluid in this area can cause symp
toms of dizziness. The cochlea is the organ of hearing.
The outer ear (pinna) picks up sound waves sent
through the external auditory canal to the tympanic mem
brane. The membrane vibrates in reaction to the sound
waves striking it. These vibrations pass through the three
Chapter 1 6
Figure 16-3 The ear.
tiny middle ear bones, through the oval window, and into
the fluid in the cochlea. Receptor cells respond and trans
fer the sounds into electrical impulses that travel to the
brain through the acoustic nerve. The receiving area of
the brain for auditory impulses is in the temporal lobe.
Common Signs and Symptoms
Common signs and symptoms of eye disease that need
medical attention include:
■ Pain or burning in or around the eye
■ Decreased visual acuity or ability to see
■ Any visual disorder such as seeing flashes of light
■ Eye redness
Common signs and symptoms of ear disease that
need medical attention include:
■ Otalgia (oh-TAL-gee-ah; ot 5 ear, algia 5 pain;
ear pain)
■ Deafness
■ Vertigo (VER-tih-go; dizziness)
■ Tinnitus (tin-EYE-tus; ringing in the ears)
Diagnostic Tests
Diagnostic Tests of the Eye
An ophthalmoscope (aft-THAL-moh-skope; oph-
thalm 5 eye, scope 5 instrument used to look) is the
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Eye and Ear Diseases and Disorders 339
instrument used for a basic examination of the eye.
During an ophthalmoscopy (ophthalm 5 eye, oscopy
5 procedure to look), the fundus, or interior aspect of
the eye, is examined. The retina, vessels, and optic disk
of the eye can be visualized easily.
Visual acuity is measured by the use of a Snellen
chart (Figure 16-4). The chart contains lines of letters
in varying sizes with predetermined numbers at the end
of each line. The predetermined numbers indicate the
distance from which an individual with normal vision
can see that particular line of letters. Normal vision is
expressed as 20/20 and is considered normal vision for
an individual viewing a particular line of the chart from
20 feet away.
For testing, the individual is positioned 20 feet
from the chart, or this distance can be simulated with
reflective mirrors. During the testing, one eye is cov
ered, allowing measurement of each eye separately. The
smallest line of letters the individual can read is noted,
and the predetermined numbers at the end of that
line are recorded in a fraction. The first number, 20,
Figure 16-4 The Snellen chart.
expresses the fact that the individual is tested from 20
feet, and the second number expresses the distance
from which an individual with normal vision could
view those same images. For example, 20/220 means
that the tested individual can see at 20 feet what most
people can see at 220 feet.
Diagnostic testing includes tonometry, slit-lamp
examination, and retinal angiography. Tonometry
(toh-NOM-eh-tree; tono 5 tone or pressure, metry
5 measurement) measures the pressure inside the
eye and is therefore useful in determining the pres
ence of glaucoma. A slit-lamp examination uses
a microscope to magnify the surface of the eye by
directing a beam of light, narrowed to a slit, at the
cornea. Instilling fluorescein dye in the eye prior to
the examination can improve visualization of eye dis
orders. A slit-lamp examination is helpful in deter
mining corneal abrasions, keratitis, and cataracts.
Angiography (AN-jee-OG-rah-fee; angio 5 vessel,
graphy 5 procedure to record) is used to discover
vessel disease and problems with blood flow to the
eye. For this test, fluorescein dye is injected into a
vein, usually in the arm, and after the dye fills the
vessels of the eye, X-rays show the vessels. Vascular
disorders such as those caused by diabetic retinopa
thy can be visualized.
Besides angiography imaging tests can include
electroretinography, ultrasonography, pachymetry,
optical coherence tomography, computed tomogra
phy (CT), and magnetic resonance imaging (MRI).
Other tests that can be done include dilated pupillary
exam, refraction, peripheral vision exam, and color
vision exam.
Consider This...
The human eye is the same size from birth
until death, but the ears and nose never
stop growing.
Diagnostic Tests of the Ear
An otoscope (OH-toh-skope; oto 5 ear, scope 5 instru
ment to look) is the instrument used to examine the
ear. During an otoscopy (oto 5 ear, scopy 5 procedure
to look), or otoscopic examination (Figure 16-5), the
340 Chapter 1 6
Pharmacology
Common Drugs for Eye Disorders
■ ■ ■ Bill ^^1 f
Highlight
Category Examples of Medications
Antihistamines
Drugs to relieve seasonal
allergy-related conjunctivitis
Bepotastine besilate 1.5%, epinastine HCL 0.05%,
ketotifen drops, or olopatadine HCL 0.2%
Anti-inflammatories
Drugs used to reduce
inflammation
Dexamethasone, difluprednate, ketorolac
cyclosporine 0.05%, ketorolac tromethamine
solution 0.5% in the eye, or loteprednol drops
Antivirals
Drugs used to treat viral
infections
Ganciclovir, trifluridine, or valganciclovir HCl
Antibacterials
Drugs used to treat bacterial
infections
Chloramphenicol, gatifloxacin, gentamicin,
levofloxacin, or imoxifloxacin
Others
Drugs used to treat macular
degeneration
Aflibercept, ranibizumab, or verteporfin (injection)
Drugs used to treat
glaucoma or ocular
hypertension
Acetazolamide, betaxolol drops, brimonidine drops,
bimatoprost solution, carteolol drops, dorzolamide
drops, or timolol drops
Drugs used to treat low tear
production or dry eyes
Cyclosporine solution, polyvinyl alcohol, or sodium
hyaluronate
Figure 16-5 Otoscopy.
external canal and tympanic membrane can be visu
alized easily. Otitis externa and a ruptured tympanic
membrane can be diagnosed using the otoscope. The
examiner may also ask the individual about symptoms
such as fever, pain, redness or swelling of the outer ear,
headache, bloody drainage, itching, stuffiness, or jaw
pain when chewing.
The basic test for hearing is called audiometry
(AW-dee-OM-eh-tree; audio 5 sound, metry 5 mea
sure). During the test, sound is delivered in varying lev
els, or decibels, through a headset to each ear separately.
The greater the amount of sound needed for the indi
vidual to hear or recognize it, the greater the amount of
deafness or hearing loss.
Common Diseases of the Eye
The most common problem of the eyes is a decrease in
visual acuity, the ability to see clearly. The most com
mon cause of poor visual acuity is refractive errors.
Other common problems include those related to
inflammation or infection, which usually affects the
outer eye because of its contact with the environment.
Other eye disorders are clouding of the lens (cataract),
increased inner eye pressure (glaucoma), altered eye
movement (nystagmus, strabismus), degenerative dis
orders (such as macular degeneration), secondary dis
ease (diabetic retinopathy), and hereditary disorders
(color blindness).
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Eye and Ear Diseases and Disorders 341
Pharmacology
Common Drugs for Ear Disorders
Highlight
Category Examples of Medications
Antibiotics
Drugs used to treat ear Azithromycin, amoxicillin, cefpodoxime,
infections ciprofloxacin, clarithromycin, ofloxacin
Analgesics
Drugs used to treat pain in the Acetaminophen, naproxen, or codeine
ear
Antihistamines
Drugs used to reduce or stop Desloratadine or diphenhydramine
allergy symptoms with otitis
interna, insect bites, or allergic
rashes of the ear
Others
Drugs used to help remove Antipyrine-benzocaine otic, carbamide
excessive ear wax peroxide
Consider This...
The pupil of the eye gets approximately
45% larger when an individual looks at
something or someone he or she finds
pleasing.
Refractive Errors
■ Description. Refractive errors are those caused by the
eye’s inability to focus images correctly on the retina.
Approximately one-third of the population is affected
by refractive errors.
■ Etiology. The cause of refractive errors is unknown,
although some run in families, suggesting an inheri
tance pattern. Although these disorders affect individ
uals of all ages, incidence increases with age. There are
four common types of refractive errors:
■ Myopia (my-OH-pee-ah) is commonly called
nearsightedness or short-sightedness. Individuals
with myopia can see nearby objects but have diffi
culty seeing distant objects. Light entering the eye
of a myopic individual falls short of the retina due
to the eyeball being abnormally long from front to
back (Figure 16-6). Myopia can be treated with
prescriptive lenses, radial keratotomy (RK), auto
mated lamellar keratoplasty (ALK), laser-assisted
in-situ keratomileusis (LASIK), and implantable
contact lenses (ICL) surgery (as described in the
section titled, “Treatment”).
■ Hyperopia (HIGH-per-OH-pee-ah) is commonly
called farsightedness. Individuals with hyperopia can
see objects that are far away but have difficulty seeing
close objects. Light entering the eye of a hyperop
tic individual falls too far past the retina due to the
eyeball being abnormally short from front to back
(see Figure 16-6). Hyperopia can be treated with pre
scriptive lenses, conductive keratoplasty (CK), ALK,
laser epithelial keratomileusis (H-LASEK), and ther
mal keratoplasty.
■ Presbyopia (PRES-bee-OH-pee-ah; presby 5 old age)
is hyperopia that is age-related. It is not due to the
shape of the eyeball but, rather, is related to the inabil
ity of the aging lens to focus light rays properly. When
the eye focuses on a distant object, the muscles of the
eye pull the lens into a flatter shape. As the eye focuses
on nearby objects, the muscles relax, allowing the lens
to return to a more spherical shape. In presbyopia,
the lens does not return to the normal shape, causing
light rays to fall beyond the retina (see Figure 16-6).
Presbyopia usually affects individuals age 40 or older
and can be corrected with reading glasses, bifocals,
CK, and monovision LASIK.
342 Chapter 1 6
Normal eye
Light rays focus on the retina
(A)
Myopia (nearsightedness)
Light rays focus in front
of the retina
(B)
Hyperopia (farsightedness)
Light rays focus beyond
the retina
■ Astigmatism (ah-STIG-mah-tizm) is an irregular
ity in the surface of the cornea, causing light rays
to spread over the retina rather than focus properly
on part of the retina (see Figure 16-6). This refrac
tive error can lead to blurred or fuzzy vision, often
described as seeing halos around objects. Astigma
tism can be treated with prescriptive lenses or LASIK.
■ Symptoms. Common symptoms of refractive errors
include squinting, blurred vision, headaches, and rub
bing of eyes.
■ Diagnosis. Tests for visual acuity include an ophthal
moscopic examination to look inside the eye and the
individual reading a Snellen chart.
■ Treatment. Refractive errors are commonly corrected
with prescriptive eyeglasses or contact lenses. Surgical
treatments include:
■ Radial keratotomy (RK) (KER-ah-TOT-oh-me;
kerato 5 cornea, otomy 5 incision) is a procedure
to correct myopia. Incisions are made in a radial
fashion in the cornea to flatten the cornea, short
ening the length of the eyeball and correcting the
refractive error (Figure 16-7). RK is still performed
(C)
Presbyopia
Light rays focus
behind the retina
Astigmatism
Light rays focus on multiple
areas of the retina
(E)
Figure 16-6 Normal eye vision, myopia, hyperopia,
presbyopia, and astigmatism.
Figure 16-7 Radial keratotomy. (A) Cross-section of the
eye prior to surgery. (B) Small incisions are made in the
cornea from the middle outward. (C) This causes the cor
nea to become flatter, thereby improving vision.
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Eye and Ear Diseases and Disorders 343
Healthy Highlight
UV Light Exposure ealthy exposure to sunlight can be a positive activity but eyes should always be pro
tected from harmful rays. Spending time outdoors can help prevent nearsighted-ness
an ouiyes in children. Natural light exposure also improves sleep. However, UV rays can cause cat
aracts, corneal burn, or macular degeneration. The three types of UV rays are UVA,
UVB, and UVC. UVA and UVB rays are the types that are causing eye damage. UVC
rays are blocked by the ozone layer. Choose UV-blocking sunglasses that block out
99-100% of UVA and UVB rays. Large lenses or wraparound sunglasses provide more
protection than small-lens glasses. The amount of tinting on the lenses does not affect
the protection, so choosing a darker pair of lenses might not mean it is any better
than a lighter tinted pair. Always check the tag that states the percent of protection
when purchasing a pair of sunglasses. Other tips to protect your eyes include wearing
a broad-brimmed hat, avoid looking directly at the sun, do not use tanning beds, and
remember that clouds do not block UV light.
Source: Turbert (2020)
and even recommended for certain eye cases, but it
is quickly being replaced by laser procedures.
■ Automated lamellar keratoplasty (ALK) is a sur
gery using a device called a microkeratome to sepa
rate and remove a thin disc of cornea. The thickness
of the disc removed determines the change in the
refractive error.
■ Laser-assisted in-situ keratomileusis (LASIK) is
the newest form of RK and is rapidly becoming the
procedure of choice. This process uses a precisely
controlled, intense beam of ultraviolet laser light to
vaporize selected cells and flatten the curvature of the
cornea. With this procedure, the tissue around and
underneath the tissue that is removed is not affected.
■ Photorefractive keratotomy (PRK) is very similar
to LASIK. In this process the very top epithelial layer
of the cornea is moved aside before the excimer laser
sculpts the cornea.
■ Implantable contact lenses (ICL) permanently
implant contact lenses into the eye. An advantage
of ICL over surgeries that flatten the cornea is that
overcorrection or undercorrection can be reme
died by replacing the contact lens with the correct
prescription.
■ Conductive keratoplasty (CK) surgery uses mild
heat from radio waves to shrink connective tis
sue (collagen) around the edge of the cornea. This
circular pattern acts like a belt that tightens around
the cornea, causing it to bulge or steepen the center
of the cornea, thus lengthening the too-short eyeball.
■ Laser epithelial keratomileusis (H-LASEK) surgery
loosens the surface area of the cornea and pushes it to
the side; a laser reshapes the inner layer of the cornea,
and then the outer surface is replaced.
■ Thermal keratoplasty (TK) uses heat to change the
shape of the cornea by shrinking collagen fibers.
■ Monovision surgery adjusts or fits one eye to see at a
distance, leaving the other eye unadjusted for seeing
close up, such as is needed for reading. (Normally,
the eyes work equally to look at an object, a process
called binocular vision.) The monovision idea is easy
to achieve also with contact lenses in that one lens
can be left out, allowing one eye to be corrected while
the other is not.
LASIK surgeons are capable of producing mono
vision in presbyopic patients by purposefully adjust
ing one eye to see nearsighted. This technique does
not work in all cases because some individuals cannot
become accustomed to monovision. Monovision can
affect depth perception and should be avoided by indi
viduals such as airplane pilots, professional drivers, and
some athletes.
■ Prevention. There are no preventive measures for
refractive errors.
344 Chapter 1 6
Consider This...
Individuals with poor eyesight are often
found to have a higher IQ.
Inflammation and Infection
Inflammation of the eye and related structures is com
monly caused by infectious microorganisms. Internal
infections, or infection affecting the inside of the eye, are
rare and are usually related to trauma; more common
are inflammations or infections of the surface of the eye
and its related structures. Eye infections are commonly
caused by viruses and bacteria and can be secondary
to allergies, trauma, and upper respiratory infections.
Microorganisms can reach the eye from the individual’s
hands and contaminated washcloths and towels. Good
handwashing and cleanliness are preventive measures.
Conjunctivitis
■ Description. Conjunctivitis is an inflammation of the
conjunctiva, the pink membrane lining the inner eyelids
(Figure 16-8).
■ Etiology. Conjunctivitis can be caused by excessive
exposure to wind, sun, heat, and cold. The eyelids
become red and swollen.
■ Symptoms. Affected individuals might complain
of excessive tearing, itching, burning, and pain. An
acute, contagious bacterial infection of the conjunctiva
Figure 16-8 Conjunctivitis.
is called pinkeye, which can become epidemic among
school-aged children.
■ Diagnosis. Diagnosis is usually simple because of
obvious symptoms and is confirmed by a medical his
tory and physical examination of the eye. If infection is
a consideration, a swab of eye drainage can be obtained
for a bacterial culture and sensitivity test.
■ Treatment. Treatment includes warm compresses,
anti-inflammatory medications, and analgesics to
relieve pain. If a culture identifies a microorganism,
antibiotic ointment or drops might be needed.
■ Prevention. Good hygiene measures, including fre
quent handwashing, using protective eye wear, avoid
ing allergens such as dust and pollen, and using a clean
tissue to remove drainage in the eye, can prevent most
cases.
Blepharitis
■ Description. Blepharitis is inflammation of the edge
of the eyelid, including the eyelash follicles and glands
(Figure 16-9).
■ Etiology. Blepharitis can be caused by bacterial infec
tion and allergic reaction to smoke, dust, or chemicals.
Seborrhea, a disorder of the sebaceous gland, or oil
secreting gland, also can cause blepharitis.
■ Symptoms. Affected individuals might complain of
itching and burning and a feeling of something in the
eye. The eyelids appear red, swollen, and crusted.
■ Diagnosis. A routine examination of the eye with a
slit-lamp microscope is usually all that is needed for
diagnosis.
■ Treatment. Treatment is directed toward removal of
the cause and can include antibiotics, allergy medica
tion, or treatment for seborrhea.
Figure 16-9 Blepharitis.
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Eye and Ear Diseases and Disorders 345
Healthy Highlight
What Is a
Blepharospasm?
B
lepharospasm is a blinking or twitching of the eyelid that the individual cannot
control. Some sources describe it as an involuntary blinking, or a tight closing or
spasm of the eyelid. This could happen in a variety of conditions such as eyelid irrita
tion, stray eyelashes, dry eyes, inflammation of the eyelid, or allergies. Lifestyle stresses,
caffeine, alcohol intoxication, and lack of sleep might also trigger the spasm. It is
caused by an abnormal function of the basal ganglion which is the part of the brain that
controls muscles. It could be a warning that the individual has a more serious under
lying problem. It can be treated by the injection of botulinum toxin or surgery called a
myectomy. Some alternative therapies include biofeedback, acupuncture, hypnosis, psy
chotherapy, and nutritional therapy. It is recommended that the individual see an eye
doctor if the twitching lasts more than a few weeks, if the eye closes completely when
twitching, or if other parts of the face begin to twitch.
Source: NIH: National Eye Institute (2020)
■ Prevention. Good eyelid hygiene and a regular
cleaning routine usually control blepharitis. Eyelid
hygiene includes frequent hand and face washing,
warm water soaks on the eyelids, and eyelid and eye
lash cleansing with warm water and baby shampoo.
Good eyelid hygiene is very important upon awak
ening due to the secretions that accumulate on the
eyelids during sleep.
Keratitis
■ Description. Keratitis is inflammation of the cornea,
usually unilateral, affecting only one eye.
■ Etiology. A frequent cause of keratitis is infection
by herpes simplex virus secondary to an upper respi
ratory infection involving cold sores (herpes sim
plex). Allergies and contact lenses can also lead to
this condition.
■ Symptoms. Symptoms include pain, photophobia
(photo 5 light, phobia 5 fear), and excessive tearing.
■ Diagnosis. A slit-lamp examination of the surface of
the cornea will confirm the diagnosis.
■ Treatment. Treatment can include antibiotic oint
ment or drops to treat or prevent infection, analgesics
for pain, and an eye patch to treat photophobia.
■ Prevention. Preventing trauma and avoiding unnec
essary touching and rubbing of the eye help prevent
keratitis.
Stye (Hordeolum)
■ Description. A stye, or hordeolum (hor-DEE-oh-
lum), is an inflammatory infection of a sebaceous
(oil-secreting) gland of the eyelid (Figure 16-10) at the
base of a hair follicle or eyelash.
■ Etiology. Most styes are caused by Staphylococcus
bacteria and are often seen in blepharitis. They are also
found more frequently in individuals who have diabetes
and seborrhea.
■ Symptoms. A tender, painful, red bump, often resem
bling a pimple, is located at the base of an eyelash or
inside the eyelid. Often there is swelling or edema along
Figure 16-10 Stye (hordeolum).
Courtesy of Mark L. Kuss
the entire lid. Purulent drainage can come from the eye
lash line or on the conjunctival surface of the eye.
■ Diagnosis. Diagnosis is made on the basis of exam
ination of the eye and presence of symptoms.
■ Treatment. Warm compresses may relieve pain, help
localize the infection, and promote drainage. Since
Chamomile tea has a natural antibiotic effect, some cli
nicians recommend using a warm Chamomile tea bag
for the compress. Styes usually form a soft spot, open,
and drain and heal within a week without further treat
ment. In some cases, styes may need to be incised to
promote drainage and healing. In chronic conditions,
topical (placed on the skin) antibiotic or systemic (taken
by mouth or injection) antibiotics may be needed.
■ Prevention. Good eyelid and eye hygiene are preven
tive measures.
Cataract
■ Description. A cataract is a clouding of the lens of the
eye (Figure 16-11).
■ Etiology. Cataracts develop from a change in metab
olism and nutrition within the lens, most commonly
from aging. Approximately 60% of all individuals 70
years of age or older will have clouding of a lens. Cat
aracts also can be caused by trauma, birth defects, and
other diseases such as diabetes mellitus. Cataracts usu
ally develop very slowly in one or both eyes.
■ Symptoms. The main symptom is a decrease in visual
acuity or a complaint about not being able to see clearly.
Other symptoms include blurred vision, glare, and a
decrease in color perception. In advanced cases, the
Figure 16-11 Cataract.
Iris
Figure 16-12 Cataract extraction with placement of
intraocular lens.
cataract can be seen through the pupil, giving the pupil
a white, cloudy appearance.
■ Diagnosis. Diagnosis is confirmed by slit-lamp
examination.
■ Treatment. Cataracts are commonly treated with
surgery, which involves removing the cloudy lens and
replacing it with a clear artificial lens (Figure 16-12).
This surgery, commonly called cataract extraction with
placement of intraocular lens, is routinely performed as
outpatient surgery. Postoperative prognosis is usually
good.
■ Prevention. There are no known preventive measures
but those who smoke, have diabetes, or have exposure to
UV light are more likely to develop cataracts.
Glaucoma
■ Description. Glaucoma is a common condition char
acterized by excessive pressure inside the eye from the
fluid inside the eye, known as aqueous humor, which is
produced constantly by blood. It circulates through the
eye and is reabsorbed into the bloodstream.
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