Visual, Auditory, and Vestibular System Flashcards
What is visual acuity a function of?
Central vision involving the macula
What is color vision a function of?
Macula
Improved acuity when looking through a pinhole suggests the problem with visual acuity is ___. If it does not improve, what should be suspected?
Ocular; lesion of the optic nerve or macula
The normal blind spot abnormally enlarges in size in the presence of what pathology?
Papilledema
What are scotomas?
Pathological, abnormal blind spots elsewhere in the visual field of one eye, where vision is lost or decreased
Causes of scotomas?
Retinal lesions (infections or inflammation, macular degeneration, retinal detachment) or optic nerve lesions (demyelination or ischemia)
Patients with constricted or contracted visual fields may have underlying ___ or a ___ disease.
Glaucoma; retinal degenerative
Tunnel vision is usually due to what type of problem?
Psychiatric
Describe how vision is transmitted from the outside world to the cortex.
Visual image in the R side of the patient’s world is detected by the L halves of each retina
Transmitted by optic nerve fibers which, beyond the optic chiasm, are continued as a pathway through the L optic tract, then the L optic radiations, ending in the L occipital visual cortex
Presentation of post-chiasmal lesions on the left?
R-sided visual impairments
A visual image in the uppermost part of the patient’s world is detected by the ___ portions of the retinae, and these fibers continue past the optic chiasm as the ___ of the temporal lobe.
Inferior; inferior optic radiations
Presentation of a temporal lobe lesion involving the inferior optic radiations?
Contralateral deficit in the patient’s superior visual world
Presentation of a L optic nerve lesion (excluding ocular/retinal causes)?
Blindness of the L eye
Presentation of an inner optic chiasm lesion?
Bitemporal heteronymous hemianopsia
Presentation of a L outer optic chiasm lesion?
R sided nasal heteronymous hemianopsia
Presentation of a L inferior optic radiation lesion (temporal lobe, Meyer’s loop)?
R superior homonymous quadrantanopsia
Presentation of a L superior optic radiation lesion (parietal lobe)?
R inferior homonymous quadrantanopsia
Presentation of a L occipital lobe lesion?
R homonymous hemianopsia with macular sparing
Congruence of visual field deficits increases when the lesion is more ___.
Posterior (occipital lobe, superior and inferior optic radiations)
In summary, optic ___ lesions produce scotomas or monocular blindness. Optic ___ lesions produce heteronymous visual field defects. Lesions of the ___ or ___ or ___ cortex produce homonymous visual field defects.
Nerve; chiasm; tract; radiations; occipital
Causes of acute unilateral optic nerve lesions in younger and older adults?
Younger - demyelination (MS, etc.)
Older - ischemia
Presentation of optic neuritis?
Sudden blindness of part (scotoma) or all of one eye, which may feel achy or tender with eye movement; pupils constrict poorly or not at all with light shined into the involved eye, but constrict normally with light shined into the normal eye
Optic disc appears swollen with indistinct, blurry margins
Weeks to months after acute optic neuritis, vision has recovered completely or partially. What residual deficits may remain?
Residual scotoma with or without impaired visual acuity or color vision; possible relative afferent pupillary defect
Presentation of optic atrophy (due to loss of ganglion cell axons)?
Optic disc appears more white or pale with sharply defined edges
Fundoscopic findings of papilledema?
Swollen and indistinct optic discs
Flame hemorrhages may be seen around the optic discs
Blood vessels passing through the optic disc may appear from the plane of focus as the rise up over the “mound” of the elevated, swollen disc
Vision is not affected initially, but may be impaired or lost if the increased ICP continues
Describe the progression of a pituitary tumor arising from the sella turcica.
Initially, the decussating inferior nasal retinal fibers would be affected, creating a visual deficit in the superior temporal quadrants; total lesion will produce a bitemporal heteronymous hemianopsia
What can cause lesions in the optic radiations?
Tumors or ischemic infarcts
What causes cortical blindness?
Severe visual loss from bilateral occipital lobe lesions; usually a stroke syndrome from thrombosis of the distal basilar artery or emboli down its PCA branches
Note - pupillary light reflex intact, optic discs normal
Two types of hearing impairment?
Conductive deafness
Nerve (sensorineural) deafness
Cause of conductive deafness?
Impaired air conduction of sound stimuli, such as water or wax plugging up the external ear canal, or fusion or disruption of the bony ossicles
“Before” the hair cell receptors
Cause of nerve (sensorineural) deafness?
Damage or impairment of the hair cell receptors or auditory nerve, as from drug toxicity or persistent exposure to loud noise
Low-tone hearing loss is typical of ___ deafness, while high-tone hearing loss occurs with ___ deafness.
Conductive; nerve (sensorineural)
Severe or complete unilateral nerve deafness is usually due to what lesion?
CN VIII (as the more proximal, ascending auditory pathways are bilaterally represented)
Bone conduction is the means by which vibrating sounds, such as one’s own voice, are transmitted through the skull to sound receptors. Air conduction allows the detection of airborne sounds by the tympanic membrane and ossicles, which amplify the stimuli before sounds are transmitted to the cochlea. Which is more efficient normally and why?
Air conduction, because of the amplification system
What is the Weber test and what is it examining?
Holding the vibrating tuning fork at the top of the skull or middle of the forehead
If nerve deafness has occurred in one ear, both air and bone conduction are impaired. The vibrating tuning fork is heard better in the normal ear.
If conductive deafness has occurred in one ear, the vibrating tuning fork is heard better in the affected ear, since bone conduction is enhanced.
What is the Rinne test and what is it examining?
Hold the vibrating tuning fork at the mastoid bone, allowing the vibration to be heard by bone conduction. When no longer heard here, the vibrating fork is then held outside the ipsilateral ear, where it should still be normally heard, since air conduction is better than bone conduction. If partial nerve deafness is present, air conduction is still better than bone conduction. If there is conductive deafness, air conduction is no longer more efficient, so the fork is not heard once bone conduction stops.
Dysfunction of the vestibular system typically produces what symptom?
Vertigo or motion-induced dizziness
What is the Dix-Hallpike maneuver and what does it test?
Patient lies supine with head titled about 45 degrees below the edge of the table, turned to one side; selectively tests the posterior semicircular canal with the tilted lowered ear. If the position creates rotatory nystagmus, that canal is overly sensitive and likely the cause of positional vertigo
Sudden severe unilateral deafness may be due to trauma particularly with ___ bone fractures, or from ischemia in what territory?
Petrous; AICA
Presentation of acute labyrinthitis?
Viral infection or inflammation of the labyrinth of the inner ear leads to severe vertigo with N/V, hearing impairment, and unsteady gait
Nystagmus, unilaterally decreased hearing, and gait ataxia on exam
Rx acute labyrinthitis?
Symptoms resolve within days to weeks, temporarily helped with benzo,s antihistamine, or antiemtitics
Presentation of Meniere’s disease?
Recurrent episodes of vertigo, deafness, and tinnitus
Cause of Meniere’s?
Membranous labyrinth swells and ruptures, allowing potassium-rich endolymph to leak into the surrounding perilymph, disrupting the ionic gradient required for normal hair cell function
Rx Meniere’s?
Same as acute labyrinthitis; however, repeat episodes may lead to permanent deafness. Dietary salt restriction and diuretic medications may help reduce production of endolymph and decrease the risk of deafness
Presentation of benign positional vertigo?
Elderly; transient but annoying vertigo when standing or turning heads
Cause of benign positional vertigo?
Degeneration of otoliths and and displaced calcium crystals can lodge around the cilia of semicircular canal hair cells, making them oversensitive to minor movements
Rx BPV?
Head-turning exercises to disperse debris
