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.
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CAUSES & FUNCTIONAL IMPLICATIONS OF VISUAL IMPAIRMENT The eyes and associated structures must be normal in structure & function. The neurological pathways.
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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
• 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 Dry Wet
• Macula ARMD 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.
• 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