CAUSES & FUNCTIONAL
IMPLICATIONS OF VISUAL
IMPAIRMENT
•The eyes and associated structures must be
normal in structure & function.
•The neurological pathways from the retina &
optic nerve to the visual cortex must be in tact.
•The brain must be capable of interpreting the
information received.
What does 20/20 mean?
• Numerator is distance patient is from chart
• (usually 20 feet)
• Denominator is how far away a person
with normal (emmetropic) vision can see
that letter on the chart.
• Your distance 20/40 how far away a
normal eye could
be
VISUAL IMPAIRMENT
• 20/200 central acuity
• Less than 20 degrees of visual field
Conditions That Result In Low
Visual Acuity
• Ocular muscle disorders- eyes that are not
in proper alignment
Strabismus & Amblyopia
• Defects of the eye muscle system
• Can result in loss of vision in one eye due
to lack of use
• phoria- tendency of eye to deviate,
particularly when fatigued or fusion broken
• tropia- marked deviation of an eye
.
• Esotropia- turning in of one or both eyes
• Exotropia- turning out of one or both eyes
• Hypertropia- turning up of one or both
eyes
• Hypotropia- turning down of one or both
eyes
Nystagmus
• Null point- point of least nystagmus & best
vision
• Pendular nystagmus- up-and-down
movements of equal speed, amplitude &
duration
• Jerk nystagmus- slower movement in one
direction
Typoscope
Disorders Relating to the Shape of
the Eye
• Refractive Disorders
• Myopia- nearsightedness
• Hyperopia- farsightedness
• Anisometropia- more than 1 diopter
difference in refractive error between both
eyes
• Aniseikonia- difference in shape or image
received by both eyes
• Microphthalmia- abnormally small eye
• Macrophthalmia- abnormally large eye
• Anophthalmia- underdeveloped or
nondevelopment of eyes
Lid Anomalies
• Entropion- lid turns in
• Ectropion- lid turns out
• Ptosis- droopy eyelids
Corneal Disorders & Diseases
Astigmatism
• A. Keratoconus- cornea cone-shaped
– 1 .extreme type of corneal curvature
• B. Keratitis- inflamed or ulcerated cornea
•
1. ocular herpes
•
2. STDs- clamidia, syphilis, gonococcal
C. Corneal dystrophies
•
1. genetic
• D. Corneal scarring
Disorders Relating to Absent or
Dysfunctional Irises
• Aniridia
– Aniridia.org
Dysfunctional iris- does not constrict or
dilate
Coloboma or iris or choroid- keyholeshaped iris
Iritis- inflammation of iris
Lens-Related Conditions
• Presbyopia
less flexible lens due to aging
Cataracts- opacity of the lens
• Pseudophakia- intraocular lens (IOL)
• Aphakia- no lens
• Dislocated lens
Types of Cataracts
•
•
•
•
Juvenile
Sutural
Posterior subcapsular (PSC)
Senile
Diseases of Anterior Segment
• Glaucoma– Open angle
– Closed angle
– Congenital glaucoma
– Peters anomaly
Signs & Symptoms of Glaucoma
• Signs
– High intraocular pressure (IOP)
– Cupped disc
– Increased angle of anterior segnment
• Symptoms
– Pain if pressures very high
– Progressive loss of visual field
Disorders Relating to Vitreous
Opacities
• vitrectomy- removed of portion of vitreous
due to opacity
Retinal Disorders
• 2 visual systems of eye
– Central, color vision (photopic)
– Peripheral, nigh, movement vision (scotopic)
Color Deficiencies
• Achromatopsia- lack of color vision
– Often accompanied by photophobia (light
sensitivity) & nystagmus
– Genetic abnormality of color receptors
Albinism
NOAH.org
• Lack of pigment
– pink eyes
– nystagmus, photophobia, strabismus, low acuity
• Ocular albinism
– blue eyes
– nystagmus, photophobia, strabismus, low acuity
Retinal edema
• swelling of the retina
Diabetic retinopathy
• proliferative diabetic retinopathy- vitreous
pulls away from retina, vessels
hemorrhage
• nonproliferative diabetic retinopathymicroaneurisms
• normal retina
lasered retina
• proliferative diabetic retinopathy
Retinopathy of Prematurity
• fibrovascular proliferation into the vitreous
• refractive errors, amblyopia, strabismus,
nystagmus, glaucoma, cataracts, corneal
changes, retinal-vitreous abnormalities
• Treatment: laser therapy on avascular
retina to anchor; scleral buckling
ROPARD.org
• Stage 3 & 4 ROP
Conditions Resulting Central Visual
Loss
• Macular degeneration
– Best's vitelliform degeneration- macular lesions, sometimes
minor visual loss
– Stargardt-Behr disease- rapidly progressive, RPE degeneration
• Age-Related Macular Degeneration (ARMD)
•
-wet
•
-dry
• Cone dystrophies- ERG detects loss of cone function
•
-Central scotoma- "blind spot“ leading to
eccentric viewing
• Normal
• Macula
Dry
ARMD
Wet
ARMD
Central Field Loss
• ARMD, Cone dystrophy, Bests, Stargardts
Peripheral field impairments
• hemianopsias- compressive lesions on
optic nerves
• retinal detachments
• retinitis pigmentosa- field loss, night
blindness, cataracts
• glaucoma
• chorioretinitis
Hemianopsia
Retinal detachments
•
•
•
•
•
•
High myopia
Cataract surgery
Trauma
Retinopathy of prematurity
Posterior vitreous detachment
Lattice degeneration
Retinitis Pigmentosa
• retinitis pigmentosa- night blindness, field
loss, cataracts
• begins in the first decade of life, gradually
progressive
• Usher syndrome when associated with
sensorineural deafness
• genetic
RP
Glaucoma
Retinal Eye Diseases
•
•
•
•
Chorioretinitis
Rubella
Toxoplasmosis
Cytomegalovirus
• normal retina
cytomegalovirus
Chorioretinitis
• Inflammation of the uveal tract, choroid
and/or retinal
• Results in scotomas (blind spots)
Combined Central & Visual Field
Impairments
• Coloboma- embryonic defects resulting in
incomplete formation of the lids, iris, retina
and/or choroid
• Optic nerve disorders & diseases
• Optic atrophy- disorder of the optic nerve
interrupting transmission of visual stimuli
• Optic nerve hypoplasia & septo-optic
dysplasia- optic nerve fails to develop
• Strokes
Coloboma
• CHARGE syndrome
– Coloboma & cranial nerves
– Heart problems
– Atresia of the choanae
– Retardation of growth & development
– Genitourinary abnormalities
– Ear & hearing abnormalities
Cortical Visual Impairment
• Disturbance of visual pathways and/or
occipital cortex
• Inconsistent vision due to processing
issues
• Causes can be asphyxia, ischemia, head
injury, brain defects, infection or
hydrocephalis
Leber’s Optic Neuropathy
• This is a rare inherited condition which involves the optic nerves with
either complete or partial loss of central vision.
• The optic nerve is the "information cable" joining the eye, the
"camera", to the brain. If damage occurs to the retina or the optic
nerve then some of the "wires" in the optic nerve will die.
•
A healthy nerve looks pink and one that has been damaged pale
and is called "atrophic". In LHON the nerve can look abnormally pink
and slightly swollen
• Normally males lose their eyesight between the ages of 15 and 45.
Often vision is lost in one eye a few months before the other.
• There is loss of central vision and diminished colour vision. Children
will have difficulty with reading and fine detail tasks especially with
low contrast and small detail work.
Optic Neuritis
• Inflammation of the optic nerve.
• Eye can be painful on movement.
• Contrast vision generally permanently
decreased.
• Highly correlated with multiple sclerosis
• Retrobulbar- behind the eye
Optic Atrophy
•
•
•
•
Pale optic nerve
Visual loss
Congenital or adventitious
Loss of fibers that transmit visual impulses
Optic Nerve Hypoplasia
• Congenital underdevelopment of optic
nerve
• Appears small and pale
• Nystagmus is common
Conditions Caused by External and
Other Factors
• Monocularity- use of one eye
• Trauma
–
–
–
–
puncture wounds
sympathetic ophthalmia
blunt trauma
burns
• Electromagnetic radiation
• Disorder caused by tumors of the eye
– retinoblastoma
– melanoma versus nevus
• Conjunctivitis- allergic, vernal, chemical, fungal,
bacterial, viral
Genetically Determined Conditions
• autosomal recesive
• autosomal dominant
• sex-linked
Perceptual Difficulties
• Dyslexia & learning disabilities
• Scintillating scotomata/migraine
• Charles Bonnet syndrome
Cortical Vision Loss
• damage of one or both occipital lobes of
visual cortex
Progressive Visual Impairment
•
•
•
•
•
regular eye care & self-monitoring
diabetes
posterior vitreous detachment
glaucoma
cataract
OPTICS & LOW VISION
DEVICES
Basic Optics
• The Composition of Light
• The Measurement of Light
• Refraction- the bending of visible light rays
– index of refraction- speed of light passing
through various media
• Refraction & the ocular system
The Optics of Lenses
• Structure of a lens
Snell's law- the line that will travel upon
exiting glass
focal point or image point- where light rays
come together & converge on a point
Types of lenses
• spherical lenses
– convex or plus lenses bulge outward
– planoconvex- bulges on one side
– chromatic aberration- light disperses as are colors in
a prism
– biconcave- bulges inward on both planes
– planoconcave- bulges inward on one side
– cylindrical lenses
– plano lenses- lens cut flat on both sides
– combination of lenses
– prism lenses- moves light rays into functional field
Lenses for Refractive Errors
• Myopia (nearsightedness) = biconcave
(minus)
• Hyperopia (farsighted) = biconvex (plus)
• Astigmatism (irregular cornea) = cylindrical
+ axis (location on cornea)
• Strabismus = prisms (base in or out)
Measurement of Lenses
• focal distance- fd
• power is measured in diopters D
Types of Magnification
•
•
•
•
Relative distance magnification
Relative size magnification
Angular magnification
Projection magnification
Near Vision Optical Devices
• Microscopes
• Magnifiers
handheld magnifiers
bar magnifiers
Near Vision Optical Devices
• Stand magnifiers
• Illuminated magnifers
Distance Vision Optical Devices
• Telescopes
• Hand-held monocular telescopes
• Clip-on monocular telescopes
• Spectacle-mounted telescopes
•
full-field telescope systems
•
bioptic telescopes
• Contact lens telescopes
• Behind-the-lens telescopes
Non-Optical Systems
•
•
•
•
•
•
•
Illumination
1. types of light
2. position of light
3. adaptation of light to dark
4. glare
Illumination control
Nonoptical magnification
Electronic Systems
•
•
•
•
Common electronic systems
Closed circuit TVs (CCTVs)
Computer systems
Other magnification systems
Field-Expansion Systems
• Bioptics
• Fresnel prisms