CHAPTER 38

DISORDERS OF SPECIAL SENSORY FUNCTION: VISION, HEARING, AND VESTIBULAR FUNCTION

Essentials of Pathophysiology

PRE LECTURE QUIZ (TRUE/FALSE)

Conjunctivitis, or inflammation of the conjunctiva, can be caused only by viral organisms.

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.

Ringing of the ears is known as tinnitus. Many drugs are labeled as ototoxic, or

damaging to inner ear structures. Hearing impairment may have a detrimental

effect on language development in children.

F

T

T

T

T

PRE LECTURE QUIZ _____________, 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 ________________.

Cataracts

Glaucoma

Myopia

Otitis

vertigo

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

FalseRationale: 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 arteryb. Choroid vesselsc. Optic arteryd. All of the abovee. a and b

ANSWER

e. a and bRationale: The retina receives blood

from the retinal artery (mainly), and secondarily from the choroid vessels that are posterior/dorsal to it.

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. Papilledemab. Retinopathyc. Retinal detachmentd. Macular degeneration

ANSWER

c. Retinal detachmentRationale: 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.

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

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

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. Otosclerosisb. Conductive hearing lossc. Tinnitusd. Sensorineural deafness

ANSWER

c. TinnitusRationale: 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.

VERTIGO

Motion sickness

Meniere disease

Benign paroxysmal positional vertigo

Central vestibular disordersSudden dizziness when positioning head to certain position