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Eye
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Light rays enter through the cornea, pass through the lens to the receptor cells of the retina
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Rods: black and white
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Cones: color
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Visual stimuli are conducted by the optic nerve to the occipital lobe
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Interpretation and processing
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Posterior cavity
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Between lens and retina
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Vitreous humor
Formed during embryonic development
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Anterior cavity
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Between cornea and lens
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Anterior and posterior chambers
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Aqueous humor
Glaucoma
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Result of increased IOP caused by excessive accumulation of aqueous humor
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Acute or chronic
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Signs and symptoms:
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Halos around lights at night
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Loss of peripheral vison
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Pain if IOP in greatly increased
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Acute: narrow angle
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Area between cornea and iris is decreased
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May be triggered by pupil dilation
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Block outflow of aqueous humor
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Chronic: open angle
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Thickening or tubular network
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Ischemia and damage to retinal cells
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Damage to optic nerve
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Can lead to blindness
Cataracts
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Progressive opacity or clouding of the lens
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Interferes with light transmission
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Etiology:
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Age related
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Excessive sun
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Congenital
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Trauma
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Blurred vison over visual field
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Becomes darker with time, hard to drive at night
Detached retina
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Acute emergency
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Retina tears away from underlying choroid
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Retinal ischemia can lead to irreversible loss of receptors
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No pain
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Visual field contains areas of blackness (scotomas)
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Tear allows vitreous humor to flow behind retina
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Increasing portion of the retina is lifted away from the choroid
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Retinal cells cease to function
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Surgical intervention
Macular Degeneration
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Age related macular degeneration (AMD)
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Common cause of visual loss in older adults
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Combination of genetic factors and environmental exposure
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Dry or atrophic
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More common – deposits form in retinal cells
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Wet or exudative
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Neovasculariza-tion
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Central vision becomes blurred, then lost
Ears
Pathway of sound -^
Sound waves enter the external ear canals
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Vibrations of the tympanic membrane causes the ossicles to vibrate
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Motion of stapes against oval window initiates movement of the fluid in the cochlea
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Stimulation of hair cells in organ of corti
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Initiation of nerve impulses
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Impulses conducted to the auditory area in the temporal lobe of cerebral cortex for interpretation of sound
Semicircular canals -^
Three structures at right angles with each other
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Crista ampullaris of each semicircular canal
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Contain receptor hair cells
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Stimulated by motion of the endolymph in response to head movements
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Stimuli conducted by vestibular branch of the auditory nerve to cerebellum and medulla
Hearing Loss (2)
Conduction deafness -^ Sound is blocked in the external ear or middle ear
-^ Accumulation of wax, foreign object, scar tissue -^ Otosclerosis od the ossicles Sensorineural impairment -^ Damage to the organ od corti or auditory nerve -^ Infection -^ Head trauma -^ Neurological disorders -^ Ototoxic drugs -^ Loud or prolonged sounds
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Presbycusis or congenital defects
Otitis Media (ear infection)
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Inflammation or infection of the middle ear
-^ Exudate builds up in cavity -^ Causes pressure on tympanic membrane -^ Auditory tube may be obstructed by inflammation
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May cause rupture of tympanic membrane
-^ Prolonged infection is likely to produce scar tissue and adhesion
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Can lead to permanent conductive hearing loss or speech problems
-^ Chronic infection may lead to mastoditis
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Infection involving mastoid cells or temporal bone
Otitis Externa
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Swimmers ear
-^ Usually bacterial – pseudomonas aeruginosa -^ Or fungal -^ Infection of the external auditory canal and pinna -^ Often associated with swimming, irritation when cleaning ear, headphones -^ Pain is usually increased with movement of pinna
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Purulent discharge and hearing deficit
Meniere’s syndrome
- chronic disorder - inner ear labyrinth disorder causing severe vertigo and nausea -^ Intermittent, with remission -^ Excessive endolymph production -^ Last minutes or hours
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Barometric pressure change could be sign of attack
-^ Balance test, electronystagmography, MRI
