Essentials of Pathophysiology
CHAPTER 38
DISORDERS OF SPECIAL SENSORY
FUNCTION: VISION, HEARING, AND
VESTIBULAR FUNCTION
PRE LECTURE QUIZ (TRUE/FALSE)
Conjunctivitis, or inflammation of the
conjunctiva, can be caused only by viral
organisms.
T  The eustachian tube is lined with a mucous
membrane that is continuous with the
nasopharynx, and provides a passageway for
pathogens to enter the middle ear.
T  Ringing of the ears is known as tinnitus.
T  Many drugs are labeled as ototoxic, or damaging
to inner ear structures.
T  Hearing impairment may have a detrimental
effect on language development in children.
F 
PRE LECTURE QUIZ

Cataracts
Glaucoma 
Myopia

Otitis

vertigo

_____________, a group of conditions that feature
an optic neuropathy, is usually associated with an
increase in intraocular pressure.
______________ is a disorder of refraction that
allows an individual to see objects at close
distances without problems, but distant objects are
blurred.
A lens opacity that interferes with the transmission
of light to the retina is known as _______________.
______________ media refers to inflammation of
the middle ear, usually associated with an acute
infection or an accumulation of fluid.
An illusion of motion, often described as a
sensation of spinning or tumbling, is a disorder of
vestibular function known as ________________.
EYE ANATOMY
Discussion

List the structures light must pass through on
its way from the outside to the retina

What part does each structure play in vision?
DISORDERS AFFECTING THE
ANTERIOR CHAMBER

Conjunctivitis

Corneal abrasion

Corneal edema

Keratitis

Glaucoma

Open-angle

Angle-closure
SCENARIO

B. is a 13-year-old girl who is involved in youth
recreation programs at the community center
where you volunteer

She complains of eye irritation

The left eye is reddened and watery, with some
crusting on the eyelashes
Question:

What possible disorders will you consider?
AQUEOUS HUMOR





Aqueous humor is formed by
the ciliary body
It then flows between the iris
and the lens to enter the
anterior chamber
In the anterior chamber, it
delivers food and oxygen to
the lens and cornea
Then it drains into tubules of
the trabecular meshwork
They empty into the canal of
Schlemm
IRIDOCORNEAL ANGLE
The area where the
iris meets the cornea
 It contains the:



Trabecular
meshwork
Canal of Schlemm
ANGLE-CLOSURE GLAUCOMA

The iris is displaced
forward

Usually due to iris
thickening caused by pupil
dilation
The angle is closed so
aqueous humor cannot
flow in to the trabecular
meshwork
 Rapid buildup of aqueous
humor in the anterior
chamber

OPEN-ANGLE GLAUCOMA

The iridocorneal angle remains open

Trabecular meshwork abnormality decreases the
rate of aqueous humor reabsorption

Gradual buildup of aqueous humor
QUESTION
Tell whether the following statement is true or
false.
Angle-closure glaucoma results in gradual
buildup of aqueous humor in the anterior
chamber.
ANSWER
False
Rationale: Open-angle glaucoma results in
gradual buildup of aqueous humor in the
anterior chamber (because the iridocorneal
angle stays open). In angle-closure glaucoma,
the iridocorneal angle is closed, so the
aqueous humor accumulates quickly.
LENS DISORDERS
Disorders of refraction
 Hyperopia
 Myopia
 Astigmatism
 Disorders of
accommodation
 Presbyopia
 Cataracts

RETINAL BLOOD SUPPLY



Retinal artery enters
the eye through the
center of the optic
nerve
Retinal vein leaves the
eye through the same
nerve
The retina has a
second blood supply
from the choroid blood
vessels directly behind
it
NORMAL APPEARANCE OF THE RETINA



Optic nerve enters
at the optic disk
Retinal arteries
and veins can be
seen at the center
of the optic disk
Retinal blood
vessels are
smooth with
relatively straight
paths
QUESTION
What vessel(s) supply blood to the retina?
a. Retinal artery
b. Choroid vessels
c. Optic artery
d. All of the above
e. a and b
ANSWER
a and b
Rationale: The retina receives blood from the
retinal artery (mainly), and secondarily from
the choroid vessels that are posterior/dorsal to
it.
e.
PAPILLEDEMA OR CHOKED DISK



Increased
intracranial
pressure affects the
optic nerve
Optic disk protrudes
into eye, with
blurred margins
Blood vessels in its
center are not
distinct; the
pressure has made
them collapse
RETINOPATHY

Damage to small
retinal blood vessels

Microhemorrhages
“Cotton-wool” exudate

Microaneurysms

RETINOPATHY (CONT.)

Neovascularization
 New vessels are
more fragile
 New vessels
attach too
tightly to the
vitreous, fusing
it to the retina
RETINAL DETACHMENT

Retina is separated from the choroid blood vessels behind it
 Retinal cells lack oxygen
 Cannot make enough ATP
 Stop functioning
 Painless loss of vision in the part of the retina that is
detached
MACULAR DEGENERATION


Dry
 Degeneration of retinal cells
Wet
 Neovascularization of the choroid
 Blood vessels leak
 Fluid buildup pushes retina away from choroid
QUESTION
Which retinal disorder is caused by ischemia of
the retina?
a. Papilledema
b. Retinopathy
c. Retinal detachment
d. Macular degeneration
ANSWER
Retinal detachment
Rationale: In this disorder, the retina becomes
detached/removed from the blood vessels
behind it (choroid vessels). Because the blood
supply is diminished, less oxygen travels to
retinal cells. Oxygen and glucose are needed to
make ATP (energy); without oxygen, ATP can’t
be produced, and the cells die.
c.
SCENARIO
Mrs. X is 47 years old and has been having
trouble with her eyes; she says that she has
trouble focusing and has had to get reading
glasses
 A few weeks ago she had an episode of
“sparkling” in her left eye, and now there
seems to be a shadow in her vision from that
eye
Question:
 What are the possible explanations for this
client’s visual problems?

SCENARIO (CONT.)
She did not have a detached retina but has returned to
her doctor because the episode recurred and this time
has not gone away
 When the doctor tests her vision, she has identical defects
in the right superior visual field of both eyes
Question:
 What might be going wrong?

DISCUSSION
2
5
6
3
1
4
7
Arrange the structures of
the optic neural
pathways in the correct
order.
 Optic nerve
 Lateral geniculate
nucleus
 Optic radiation
 Optic chiasm
 Eye
 Optic tract
 Visual cortex
DISCUSSION
Eye
Optic nerve
Optic chiasm
Optic tract
Lateral geniculate nucleus
Optic radiation
Visual cortex
DISCUSSION
List the structures a sound wave goes through as it enters
the ear.

Which structures:

Direct the sound wave?

Transmit the sound wave?

Create a nerve impulse in response to the sound
wave?
MIDDLE EAR


Conducts
sound from
eardrum to
inner ear
Eustachian
tube lets air in
and out to
maintain equal
pressure on
both sides of
eardrum
MIDDLE EAR INFECTION

If the Eustachian tube
becomes blocked, fluid
builds up in the middle ear.
This creates a haven for
bacteria and viruses, which
can cause infection.
Doctors can detect fluid in
the middle ear with a
pneumatic otoscope. This
device blows a small
amount of air at the
eardrum, making the
eardrum vibrate. If fluid is
present, the eardrum will
not move as much as it
should.
EAR TUBES, OR TYMPANOSTOMY TUBES

If your child has recurrent ear
infections or fluid that just
won’t go away, hearing loss
and a delay in speech may be
a real concern. One solution is
for your doctor to insert small
tubes through the eardrum.
Ear tubes let fluid drain out of
the middle ear and prevent
fluid from building back up.
This can decrease pressure
and pain, while restoring
hearing. The tubes are usually
left in for 8 to 18 months until
they fall out on their own.
MIDDLE EAR DISORDERS



Problems with pressure in the middle ear
 Patent eustachian tube, eustachian tube
obstruction, acute otitis media
Problems with adhesions between the ossicles
 Adhesive otitis media, otosclerosis
Problems with erosion of the tissues

Cholesteatoma, mastoiditis
CONDUCTIVE HEARING LOSS

Ossicles do not conduct sound from eardrum to inner ear


Sounds that enter through the ear sound faint
Sounds that are conducted through other bones of the
head sound louder

Chewing

Own voice
INNER EAR: COCHLEA AND LABYRINTH
DISORDERS OF THE INNER EAR AND AUDITORY
PATHWAYS


Increased nerve firing

Tinnitus

Focal seizures
Decreased nerve firing

Sensorineural deafness

Presbycusis
QUESTION
Which auditory disorder is characterized by
increased firing of the otic nerve, causing
“ringing” in the ears?
a. Otosclerosis
b. Conductive hearing loss
c. Tinnitus
d. Sensorineural deafness
ANSWER
Tinnitus
Rationale: Increased firing of neurons of the
inner ear results in the classic symptom of
“ringing” in the ears. Sensorineural deafness is
caused by less frequent firing of neurons in the
inner ear; otosclerosis is caused by adhesions
between the ossicles in the middle ear;
conductive hearing loss is the result of the
ossicles’ inability to conduct sound from the
eardrum to the inner ear.
c.
VERTIGO

Motion sickness

Meniere disease

Benign paroxysmal positional vertigo

Central vestibular disorders
Sudden dizziness when positioning head to certain position