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Disorders of the Eye and Ear

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					         Chapter 24

Disorders of the Eye and Ear
Eye – Review

                  Protected by bony orbit of skull
                    –   Bony protection of the eye
                  Eyelids and eyelashes
                    –   Deflect foreign material from eyes
                    –   Protect against excessive sunlight
                        and drying
                  Conjunctiva
                    –   Mucous lining of eyelids
                    –   Covers sclera
                  Tears
                    –   Produced by lacrimal glands
                    –   Contain lysozyme – antibacterial
                        enzyme
Eye – Review (Cont’d)

                    Six extraocular skeletal
                     muscles for movement
                     of the eyeball
                    Muscles controlled by
                     cranial nerves III, IV,
                     and VI (Oculomotor,
                     Trochlear, and
                     Abducens)
Eyeball

             Outer layer is the SCLERA
                     The “White” of the eye
               – The anterior portion is the
                  CORNEA
                     Transparent portion that
                       sticks out of the eye.
                     Most common injury are
                       scratches to it.
                     Light rays pass and are
                       refracted
                     Does not contain blood
                       vessels
                     Nourished by fluids around
                       it and Oxygen diffusing
                       from atmosphere
Eyeball (Cont’d)

                      Middle layer is the CHOROID
                        –   Choroid is a dark vascular layer interior to
                            the sclera
                        –   Absorbs scattered light
                        –   In anterior segment of the eyeball
                                 LENS-a transparent lens, which
                                   along with the cornea, refract light
                                   rays so they hit the retina properly
                                 Its cells have no organelles
                                 Receives nourishment from
                                   aqueous solution.
                                 IRIS- is pigmented muscle which
                                   dilates and contracts based on light
                                   exposure or autonomic nervous
                                   system responses.
                                 PUPIL-an opening of the iris
                                 The size of its opening is based on
                                   the movement of the iris.
Eyeball (Cont’d)


                      Inner layer is the RETINA.
                         – Contains no pain receptors
                         – Located in the posterior 2/3 of eye
                         – It contains billions of Photoreceptor cells
                               1. RODS – used for dim light and
                                night vision (black and white)
                               2. CONES – used for color vision
                         – They convert light into electrical energy
                           and then transmit that to the brain for
                           processing.

                        –   FOVEA CENTRALIS
                              Area of retina with the most cones,
                                thus the area with most acute
                                vision.
Fluids in the Eye

   Posterior cavity
     – Space between lens and
        retina
     – Contains VITREOUS
        HUMOR
           Jelly-like fluid
   Anterior cavity
     – Between cornea and lens
     – Filled with AQUEOUS
        HUMOR
           Amount formed should
             be equal to the amount
             reabsorbed –
             maintenance of normal
             intraocular pressure
             (IOP)
The Visual Pathway

                    Light rays pass through cornea.
                       –    Refraction of rays
                    Through aqueous humor and pupil
                    To the retina (rods and cones) where
                     light is turned into electrical impulses.
                    Retina turns into optic nerve (II) in the
                     back of the eye.
                    Optic chiasm
                       –    Fibers cross
                       –    Left occipital lobes receive images
                            from right visual fields; right
                            occipital lobes from left visual fields
                    Perception occurs in visual sensory and
                     association areas of the occipital lobes of
                     the cortex.
Structural Defects of the Eye




   Myopia
     –  Nearsightedness
     –  Far away items are blurry
     –  Image focused in front of the lens
   Hyperopia
     –  Farsightedness
     –  Close items are blurry
     –  Eyeball is too short.
     –  Image focused behind the retina
Structural Defects of the Eye (Cont’d)



   Astigmatism
     –   Irregular curvature in the cornea or
         lens
   Strabismus (squint or cross-eye)
     –   Results from deviation of one eye
         typically due to one of the eye
         muscles not working properly.
     –   Patch or surgery are treatments.
Infections and Trauma

   Stye
    –   Infection involving a hair
        follicle on the eyelid
    –   Usually by staphylococci
        bacteria
    –   Swollen, red mass forms
        on eyelid
Conjunctivitis

   Infection of the conjunctiva-the outer layer of the sclera.
   Called “Pink eye” – Staphylococcus aureus
      –  Frequently occurs in children
      –  Sclera and eyelid appear red; purulent discharge
      –  Spread by fingers or contaminated towels
             Occurs with contact lens use; contaminated makeup, contaminated medication
      –  Antibiotic treatment to prevent damage to cornea
Keratitis

   Severe pain and photophobia
     –  Develops when cornea is infected or irritated
     –  Herpes simplex can be cause.
           Transfer from herpes lesion around mouth
           Transfer by fingers, dental office, spray of contaminated saliva
     –  Keratitis – increased risk of ulceration eroding the cornea
     –  Scar tissue formation interferes with vision.
     –  Other causes may be trauma to cornea and damage from chemicals, splashes, fumes
Glaucoma

   Result of increased Intra-ocular pressure
    caused by excessive accumulation of
    aqueous humor in the front of the eye.
   Most common and preventable loss of
    vision in developed countries
   May be acute or chronic
   Signs and symptoms
      –  Halos around lights at night
      –  Loss of peripheral vision
      –  Pain may occur if IOP is greatly
         increased as in acute form.
      –  Treatment-
              Eye drops which reduce the amount
               of aqueous humor produced or
               surgery (shunt put in to drain fluid to
               vitreous humor).
Cataracts

               Progressive opacity or clouding of the
                lens
               Size, site, and density of clouding vary
                among individuals.
                  –  May be different in individual’s two
                     eyes
               Changes may be
                  –  Age related or caused by metabolic
                     abnormalities
                  –  Excessive exposure to sunlight
                  –  Congenital
                  –  Traumatic
                  –  Radiation
Cataracts (Cont’d)

   Blurred vision over visual field
      –  Becomes darker with time
      –  Night driving especially difficult
   Rate of impairment varies.
   One eye’s cataract may develop faster
    than the other’s.
   May interfere with person’s ability to
    function or work
   Outpatient surgery involves lens
    replacement.
Detached Retina

                     Acute emergency
                      –   Retina tears away from
                          the underlying choroid.
                      –   Retinal ischemia can
                          lead to irreversible loss
                          of receptors.
                      –   No pain or discomfort
                      –   Visual field contains
                          areas of blackness
                          (scotomas) as if a curtain
                          has fallen over eye.
Detached Retina (Cont’d)

                    Tear allows vitreous
                     humor to flow behind
                     retina.
                     –   Increasing portion of the
                         retinal is lifted away form
                         the choroid.
                     –   Retinal cells cease to
                         function.
                    Surgical intervention
                     –   Reattachment of retina
Parts of the Ear

                      The Ear, housed in the Temporal Bone, has 3
                       Sections
                      A. External ear
                         –   Includes the Pinna, the external flap of
                             cartilage
                         –   and External Auditory Meatus (ear canal)
                      B. Middle ear
                         –   Includes the Tympanic membrane (ear
                             drum)
                         –   Bony ossicles (3 tiny bones)
                                 Malleus
                                 Incus
                                 Stapes
                         –   Eustachian Tube which connects to the
                             nasopharynx.
                      Inner ear
                         –   Cochlea (snail-looking organ) that
                             features the Organs of Corti
                         –   Semicircular canals
                                 Balance and equilibrium
The Pinna

               Also known as the
                “Auricle”
               It collects sound by
                acting as a funnel to
                send it to the ear canal.
               Major parts
                –   Helix- outer ridge
                –   Lobule- lower part
Eardrum

   Known as the tympanic
    membrane
   Border between the
    outer ear and the
    middle ear.
   Amplified sound hits the
    drum which stimulates
    the malleus bone
    (which is on the other
    side of the drum)
Ear Canal

   Also known as External
    Auditory Meatus (EAM)
   Ear canal is lined with wax
    called Cerumen. It:
    –   Protects the lining of the ear canal
    –   Provides lubrication
    –   Excess cerumen may lead to
        impaired hearing and increase ear
        infections.
   The EAM ends at ear drum.
        The Ossicles “tiny bones”

   3 small bones
    –   When sound hits the eardrum, it
        vibrates which causes the
        malleus to move.
    –   The 1) Malleus then hits the 2)
        Incus
    –   The Incus hits the 3) Stapes
    –   The Stapes hits the Oval
        Window of the Cochlea.
            The Oval Window is the border
             between the middle and inner
             ears.
           Inner Ear (Known as the “labyrinth”)
   The Inner Ear (aka the labyrinth) is divided into 2
    pain parts
   1. Semicircular canals


     –   Organ responsible for maintaining balance
     –   Canals full of fluid called endolymph and little
         “hair cells”
     –   Movement in the head causes the fluid to “hit”
         the hair cells which sends impulses through
         the Vestibule nerve of Cranial Nerve 8
         (Vestibulocochlear) to the cerebellum for
         processing.
   2. Cochlea
     –   Snail-like organ that is responsible for hearing
     –   Cochlea is full of endolymph and specialized
         hair cells called the Organ of Corti, the
         parenchyma cells responsible for hearing.
     –   They turn sound waves into nerve impulses
         and they in turn are sent through the Cochlear
         nerve of Cranial Nerve 8 nerve to the temporal
         lobe for processing.
Pathway of Sound

                  Sound waves enter the external ear
                   canals.
                  Vibration of the tympanic membrane
                   causes the ossicles to vibrate.
                  Motion of stapes against oval window of
                   cochlea initiates movement of the
                   endolymph fluid.
                     –   Stimulation of hair cells in organ of
                         Corti
                     –   Initiation of nerve impulses
                  Impulses conducted to the auditory area
                   in the temporal lobe of cerebral cortex for
                   interpretation of sound
Hearing Loss

                  Two types
                    –  1. Blockage
                           Sound is blocked in the
                            external ear or middle ear
                           Accumulation of wax, foreign
                            object, scar tissue
                           Otosclerosis (hardening) of the
                            ossicles
                    –  2. Sensorineural impairment
                           Damage to the organ of Corti
                            or auditory nerve
                           Infection
                           Head trauma
                           Neurologic disorders
                           Ototoxic drugs
                           Sudden very loud sounds or
                            prolonged exposure to loud
                            noise
Hearing Loss (Cont’d)

                    Newborns are screened for hearing
                     deficits.
                      –    Audiologists and otolaryngologists
                           for consultation
                    Hearing aids
                      –    Used if appropriate for individual
                           hearing deficit
                    Cochlear implants
                      –    Used successfully in some cases of
                           sensorineural loss
Ear Infections (Cont’d)

                     May be asymptomatic
                      in chronic stages
                     Most often – severe
                      pain or earache
                     Tympanic membrane
                      red and bulging
                     Mild hearing loss or
                      feeling of fullness
                     Fever, nausea might be
                      present
Ear Infections – Otitis Media

                     Inflammation or infection of the middle
                      ear
                        –  Exudate builds up in cavity.
                        –  Causes pressure on tympanic
                           membrane
                        –  Auditory tube may be obstructed by
                           inflammation.
                               May cause rupture of the
                                tympanic membrane
                        –  Prolonged infection is likely to
                           produce scar tissue and adhesion.
                               Can lead to permanent
                                conductive hearing loss or
                                speech problems
Otitis Media (cont)

                     May spread along nasopharynx and
                      respiratory structures
                     Pneumococci, beta-hemolytic
                      streptococci, staphylococci
                     Viral infections also common
                        –   Frequently complicated by
                            secondary bacterial infections

                     Treatment
                        –  Ibuprofen or acetaminophen to
                           reduce discomfort in first 48 hours
                        –  Use of antibacterials if bacterial
                           infection
                        –  Decongestant may be useful in
                           draining auditory tube.
                     Surgery may be done to insert temporary
                      tubes in tympanic membrane to allow for
                      drainage.
Otitis Externa

   Also referred to as “swimmer’s” ear
   Infection of the external auditory canal
    and pinna
   Usually bacterial but may be fungal
   Often associated with swimming
      –  Irritation when cleaning ear
      –  Frequent use of earphones or
         earplugs
   Pain usually increased with movement of
    pinna
   Purulent discharge and hearing deficit
Chronic Disorders of the Ear

                    Otosclerosis
                      –  Imbalance in bone formation and
                         resorption
                      –  Development of excess bone in
                         middle ear cavity
                             Stapes becomes fixed to oval
                              window.
                      –  Blockage of conduction sounds to
                         cochlea
                      –  May be due to genetic or
                         environmental factors
                      –  Surgical removal of stapes and
                         replacement prosthesis to restore
                         hearing
Chronic Disorders of the Ear (Cont’d)

                       Meniere’s syndrome
                         –  Inner ear labyrinth disorder causing
                            severe vertigo and nausea
                         –  Intermittent with remissions and
                            exacerbations
                         –  Excessive endolymph produced
                         –  Attack may last minutes or hours
                               Change in barometric pressure
                                  may precipitate an attack
                         –  Balance test,
                            electronystagmography,
                            electrocholeography, MRI
                         –  Treatment with drugs
                               Home exercise programs to
                                  reduce sensitivity to motion

				
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