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Chapter 54
Disorders of Visual Function
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Causes of Alterations in Vision
• Disorders of the eyelids and optic globe (conjunctiva,
cornea, and uvea)
• Intraocular pressure (glaucoma)
• Lens (cataract)
• Vitreous humor and retinas
• Dual pathways and visual cortex
• Extraocular muscles and eye movement
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Weakness of the Eyelid
• Ptosis
– Weakness of the levator muscle
– Unopposed action of the orbicularis oculi
• Weakness of orbicularis oculi causes an open eyelid
• Entropion
– Turning in of the lid margin
• Ectropion
– Eversion of the lower lid margin
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Inflammation of the Eyelid
• Blepharitis
– Seborrheic form
• Usually associated with seborrhea (i.e., dandruff)
of the scalp or brows
– Staphylococcal blepharitis
• May be caused by Staphylococcus epidermitis or S.
aureus
• The lesions are often ulcerative.
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Inflammation of the Eyelid (cont.)
• Hordeolum
– Infection of the sebaceous glands of the eyelid; can
be internal or external
– Stye
• Chalazion
– May follow an internal hordeolum
– Chronic inflammatory granuloma of a meibomian
gland
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Dry Eyes
• Tear film protects and hydrates the surface of the eye.
• Deterioration/disruption of film
– Aging
– Loss of reflex lacrimal gland secretion
– Contact lenses
– Sjögren syndrome
• Treatment
– Artificial tears, plug lacrimal puncta, ointments
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Disorders of the Conjunctiva
• Conjunctivitis
– Infectious conjunctivitis
• Bacterial conjunctivitis
• Viral conjunctivitis
• Chlamydial conjunctivitis
• Ophthalmia neonatorum
– Allergic conjunctivitis
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Redness vs. Severe Conditions
• Conjunctivitis vs. serious eye disorders, such as corneal
lesions and acute glaucoma
• Moderate to severe discomfort associated with corneal
lesions or the severe and deep pain associated with acute
glaucoma
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Question
• Which of the following disorders is not an inflammatory
disease?
a. Blepharitis
b. Hordeolum
c. Chalazion
d. Ptosis
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Answer
a. Blepharitis
b. Hordeolum
c. Chalazion
d. Ptosis: Ptosis is weakness of the levator muscle or
unopposed action of the orbicularis oculi.
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Disorders of the Cornea
• Corneal trauma
– Corneal edema
• Keratitis
– Bacterial keratitis
– Herpes simplex keratitis
– Acanthamoeba keratitis
• Abnormal corneal deposits
– Arcus senilis
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Uveal Tract
• Middle vascular layer
• Incomplete ball with gaps at the pupil and the optic
nerve
• Light-absorptive function
• Three distinct regions
– Iris
– Choroid
– Ciliary body
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Pupillary Reflex
• Controls the size of the pupil
• Controlled by the autonomic nervous system
– The parasympathetic nervous system controls pupillary
constriction.
– The sympathetic nervous system controls pupillary dilation.
• Alterations
– Damage to CN III
– Opiate usage
– Miotic drugs
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Control of Intraocular Pressure
• The aqueous humor
– Serves to maintain the intraocular pressure
– Provides for the nutritive needs of the lens posterior
cornea
– Mediates the exchange of respiratory gases
– Contains a low concentration of protein and high
concentrations of ascorbic acid, glucose, and amino
acids
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Glaucoma
• Definition
– An optic neuropathy characterized by optic disk
cupping and visual field loss
• Causes
– An increase in intraocular pressure that results from
abnormalities in the balance between aqueous
production and outflow
– Most common cause is an interference with aqueous
outflow from the anterior chamber, rather than
overproduction of aqueous humor
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Classifications of Glaucoma
• Angle-closure (narrow-angle) vs. open-angle (wideangle)
– Depends on location, circulation, and resorption
• Congenital vs. acquired condition
• Primary vs. secondary disorder
– Primary: no evidence of preexisting ocular or systemic
disease
– Secondary: results from inflammatory processes affecting
the eye, tumors, or blood cells of trauma-produced
hemorrhage
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Symptoms of Congenital or Infantile
Glaucoma
• Excessive lacrimation and photophobia
• Affected infants tend to be fussy, have poor eating habits,
and rub their eyes frequently.
• Diffuse edema of the cornea usually gives the eye a
grayish white appearance.
• Enlargement of the entire globe (buphthalmos)
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Question
• Which of the following is known to affect the pupillary
reflex?
a. Opiate usage
b. Damage to CN II
c. Infection of the uveal tract
d. Increase in intraocular pressure
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Answer
a. Opiate usage: Opiates will result in dilated pupils that are
unresponsive to light.
b. Damage to CN II
c. Infection of the uveal tract
d. increase in intraocular pressure
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Structure of the Lens
• The lens is an avascular, transparent, biconvex body, the
posterior side of which is more convex than the anterior
side.
• A thin, highly elastic lens capsule is attached to the
surrounding ciliary body by delicate suspensory radial
ligaments called zonules, which hold the lens in place.
• When changing lens shape, the tough elastic sclera acts
as a bow, and the zonule and the lens capsule act as the
bowstring.
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Structure of the Lens (cont.)
• The suspensory ligaments and lens capsule are normally
under tension, causing a flattened shape for distant
vision.
• Contraction of the muscle fibers of the ciliary body
produces a more spherical or convex shape for near
vision.
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Disorders of Refraction
• Hyperopia or farsightedness
– The anterior-posterior dimension of the eyeball is too
short; the image is focused posterior to (behind) the
retina
• Myopia or nearsightedness
– The anterior-posterior dimension of the eyeball is too
long; the focus point for an infinitely distant target is
anterior to the retina
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Age-Related Changes of the Eye
• Presbyopia
– Refers to changes in vision that occur because of
aging
• Cataract
– Lens opacity that interferes with the transmission of
light to the retina
– The most common cause of age-related visual loss in
the world
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Cataract
• Lens opacity that interferes with the transmission of light to
the retina
• Cause of cataracts are multifactorial.
– Effects of aging, genetic influences, environmental and
metabolic influences, drugs, and injury
– Diabetes
– Long-term exposure to sunlight
– Heavy smoking
– Developmental defect
– Secondary to trauma or diseases
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Cataract Treatment
• No effective medical treatment for cataract
• Surgery is the only treatment for correcting cataractrelated vision loss.
– Intraocular lens implantation
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Retina
• Receive visual images
• Partially analyzes them
• Transmits this modified
information to the brain
• Three layers of neurons
– Posterior layer of
photoreceptors
– Middle layer of bipolar
cells
– Inner layer of
ganglion cells that
communicate with the
photoreceptors
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Types of Photoreceptors Present in the
Retina
• Rods, capable of black–white discrimination
• Cones, capable of color discrimination
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Disorders of the Retina
• Ischemia of the retina
• Papilledema
• Central retinal artery occlusion
• Central retinal vein occlusion
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Retinitis Pigmentosa
• Slow degenerative changes in the retinal photoreceptors
• Autosomal and sex-linked forms
– 36 RP genes
• Night blindness
• Bilateral symmetric loss of mid-peripheral fields
• Visual field defects gradually increase both centrally and
peripherally.
• Cone photoreceptor cells are also affected, and day vision and
central visual acuity are compromised.
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Papilledema
• Entrance and exit of the central artery and vein of the
retina through the tough scleral tissue at the optic papilla
– May be compromised by any condition causing
persistent increased intracranial pressure
– Cerebral tumors, subdural hematomas,
hydrocephalus, and malignant hypertension
• Results in the destruction of the optic nerve axons
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Diabetic Retinopathy
• Nonproliferative: confined to the retina
– Engorgement of the retinal veins, thickening of the
capillary endothelial basement membrane, and
development of capillary microaneurysms
– Macular edema
• Proliferative: characterized by formation of new, fragile
blood vessels
– Bleed easily
– Retinal detachment
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Retinal Detachment
• Separation of the neurosensory retina from the pigment
epithelium
– Exudative
• Accumulation of fluid in the subretinal space
– Traction
• Scar tissue
– Rhegmatogenous
• Vitreous begins to liquefy and collapse
• Most common type of retinal detachment
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Macular Degeneration
• Degenerative changes in the central portion of the retina
(the macula) that result primarily in loss of central vision
• Age-related macular degeneration
– Dry form
• Atrophic, nonexudative
– Wet form
• Exudative
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Disorders of Neural Pathways and Cortical
Centers
• Visual field defects
– Retinal defects
• Disorders of the optic pathways
• Disorders of the visual cortex
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Disorders of the Optic Pathways
• Interruption of the visual pathway due to vascular lesions,
trauma, and tumors
– Anopia: blindness in one eye
– Hemianopia: half of the visual field for one eye is
lost
– Quadrantanopia: quarter the visual field is lost for
one eye is lost
– Heteronymous hemianopia: loss of different halffields in the two eyes
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Disorders of Visual Cortex
• Cortical blindness
– Bilateral loss of the entire primary visual cortex
• Visual agnosia
– Extensive damage to the visual association cortex
that surrounds an intact primary visual cortex,
resulting in a loss of the learned meaningfulness of
visual images
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Extraocular Eye Muscles and Their
Innervation
• Innervated by three cranial nerves
– The abducens nerve (CN VI) innervates the lateral
rectus.
– The trochlear nerve (CN IV) innervates the
superior oblique.
– The oculomotor nerve (CN III) innervates the
remaining four muscles.
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Eye Movement
• Smooth pursuit movements
• Saccadic movements
• Optic tremor
• Vergence movements
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Disorders of Eye Movement
• Amblyopia
– A condition of diminished vision in which no
detectable organic lesion of the eye is present
• Strabismus
– Any abnormality of eye coordination or alignment
that results in loss of binocular vision
• Paralytic strabismus
• Nonparalytic strabismus
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Question
• Which of the following conditions is the clinical name for
“farsightedness”?
a. Hyperopia
b. Myopia
c. Presbyopia
d. Strabismus
e. Ptosis
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Answer
a. Hyperopia: The image is focused posterior to (behind)
the retina and is thus farsighted.
b. Myopia
c. Presbyopia
d. Strabismus
e. Ptosis
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