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Chapter 37
Disorders of Special Sensory
Function: Vision, Hearing, and
Vestibular Function
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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?
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Disorders Affecting the
Anterior Chamber
• Conjunctivitis
• Corneal abrasion
• Corneal edema
• Keratitis
• Glaucoma
– Open-angle
– Angle-closure
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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?
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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
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Iridocorneal Angle
• The area where the iris
meets the cornea
• It contains the:
– Trabecular meshwork
– Canal of Schlemm
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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
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Open-angle Glaucoma
• The iridocorneal angle remains open
• Trabecular meshwork abnormality decreases
the rate of aqueous humor reabsorption
• Gradual buildup of aqueous humor
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Question
Tell whether the following statement is true or false.
Angle-closure glaucoma results in gradual buildup of
aqueous humor in the anterior chamber.
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Answer
False
Rationale: Open-angle glaucoma results in gradual
buildup of aqueous humor in the anterior chamber
(because the iridocorneal angle stays open). In angleclosure glaucoma, the iridocorneal angle is closed, so the
aqueous humor accumulates quickly.
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Lens Disorders
• Disorders of refraction
– Hyperopia
– Myopia
– Astigmatism
• Disorders of accommodation
– Presbyopia
• Cataracts
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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
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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
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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
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Answer
e. 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.
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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
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Retinopathy
• Damage to small retinal
blood vessels
– Microhemorrhages
– “Cotton-wool” exudate
– Microaneurysms
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Retinopathy (cont.)
• Neovascularization
– New vessels
are more
fragile
– New vessels
attach too
tightly to the
vitreous,
fusing it to the
retina
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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
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Macular Degeneration
• Dry
– Degeneration of retinal cells
• Wet
– Neovascularization of the choroid
– Blood vessels leak
– Fluid buildup pushes retina away from choroid
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Question
Which retinal disorder is caused by ischemia of the retina?
a. Papilledema
b. Retinopathy
c. Retinal detachment
d. Macular degeneration
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Answer
c. 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.
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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?
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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?
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Discussion
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
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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?
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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
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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
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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
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Inner Ear:
Cochlea and
Labyrinth
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Disorders of the Inner Ear and Auditory
Pathways
• Increased nerve firing
– Tinnitus
– Focal seizures
• Decreased nerve firing
– Sensorineural deafness
– Presbycusis
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Question
Which auditory disorder is characterized by increased firing
of the optic nerve, causing “ringing” in the ears?
a. Otosclerosis
b. Conductive hearing loss
c. Tinnitus
d. Sensorineural deafness
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Answer
c. 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.
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Vertigo
• Motion sickness
• Meniere disease
• Benign paroxysmal positional
vertigo
• Central vestibular disorders
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