Transcript CAUSES & FUNCTIONAL IMPLICATIONS OF VISUAL IMPAIRMENT

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
CLINICAL LOW VISION
• Purpose of an evaluation
• Referral for an evaluation
Sequence of a Typical Evaluation
• Members of the Low Vision Team
Sequence of a Typical Evaluation
• Case history
• Preliminary observation
• Distance visual acuity testing
– measurement charts
• fixation refers to the ability of the individual to
hold his attention to the object being viewed
– distance acuity notations
– assessment of young children
•
•
i. observation
ii. tests of visual functions
– special considerations
Functional Vision Testing
• Behavioral
•
OKN (optokinetic nystagmus) cortical
• PLT (preferential looking test)- Teller acuity
• Chromatic Luminance- contrast sensitivity
• Tracking a toy or light- see textbook for
sizes and distances
Electrophysiological
• VER- Visual Evoked Potential (visual
pathways)
• ERG- Electroretinogram (cone & rod
retinal function)
• EOG- Electrooculogram (measures charge
& potentials of eyes)
Subjective
•
•
•
•
•
•
•
•
•
•
Acuity
LEA Charts
Snellen
Tumbling E
CSF- Contrast Sensitivity Function
Flicker Fusion- macular function
Color- Ishihara
Visual Fields
Confrontation
Ganzfeld globe
Visual Efficiency Testing
• ISave (APH)
• Program to Improve Visual Efficiency
(Barraga)
Near Visual Acuity Testing
•
•
•
1. measurement charts
2. near-acuity notations
3. special considerations
Refraction
• determination of refraction
•
retinoscopy- streak of light reflex
•
instruments for refraction
•
trial frame & lens set
Color Vision Testing
•
•
Ishihara color plates
Farnsworth D15
Contrast Sensitivity Testing
Interpretation of the Eye Report
•
•
•
•
•
•
•
•
•
•
•
•
CUMULATIVE RECORD OF VISUAL FUNCTIONING
Name:
Sex:
DOB:
Parent/Guardian:
Address:
Home Telephone:
Work Telephone:
Schools attended:
Location:
Dates:
______________________________________________________
Visual Information
Eye condition
Ophthalmologic findings
Eye Surgery
Eye Medications
Eye Report
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Visual Acuity
OD
OS
OU
OD OS OU
(without correction) (with correction)
Distance vision
Near vision
OD
OS
Sphere
Cylinder Axis
Visual fields
(tested w/with correction)
(reported central & peripheral
w/blind spot)
Color vision
Refractive error
OD
bifocal
OS
Bifocal
Eye Report
• Strabismus
•
•
Binocularity
•
•
Stereopsis
• Is eye condition stable?
Eye Report
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Visual Aids
Glasses prescribed:
To be worn when?
To be worn where?
Low Vision Aids prescribed:
Classroom aids:
Print point size
Lighting
Reading aids (lamps, stands, globes)
Magnification devices
Telescopic devices
Visors
Shields
Tables
Pencils, Pens, Markers *
Paper
Electronic Aids
Computer glare filter
Zoom Text
Software
CCTV
Date:
Eye Report
• I. Conditions for Optimal Visual Functioning
•
A. Prefers to control natural light by:
•
Wearing tinted glasses
•
Adjusting window shades
•
Wearing visors
•
Seeking existing shade areas
•
Creating shade areas
•
Moving to source of light
•
Turning to source of light
•
Turning from source of light
Eye Report
• B. Prefers to control artificial light by:
•
Direction of source (specify)
•
Degree of intensity (specify)
•
Prefers combined diffused and directed light
Prefers incandescent light
•
Prefers fluorescent light
•
Prefers halogen light
•
Prefers a glare-free work surface (specify)
•
Prefers absorbent work surface
•
Prefers limited work surface
Eye Report
• C. Improves own visual functioning by
(specify optical aids &
• circumstances)
Eye Report
• D. Audiovisual viewing
•
Prefers print point:
•
Prefers black & white (specify distance)
•
Prefers color (specify distance)
•
Type of illumination
•
Dimly illuminated screen
•
Prefers high or low contrast (specify)
•
Prefers viewing distance of reading materials:
•
Prefers viewing distance from computer:
• The following audiovisual materil cannot be seen from
the student's desk:
Eye Report
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Visual Functioning Under Optimal Conditions:
A. Outdoors
Can easily adapt to sudden changes in illumination
Can visual identify an individual (specify distance)
Can distinguish between lawn & sidewalk
Can distinguish lines on pavement such as for crosswalks & safety zones
Can visually avoid stationary obstructions before physical contact
Can detect variations of walking levels
steps
curbs
Can detect ball in air (specify size)
Can recognize features of a persons & objects (specify distance)
Can usually see traffic lights at night
Can usually see traffic lights during the day
Can use visual landmarks to establish line of direction
Can select own visual landmarks
While walking
From a moving vehicle
Can see if a curb is absent low lying has rounded corners
Can see house numbers from street or sidewalk
Can see direction of moving escalators
Can see unoccupied seat in auditorium bus
Adaptation time from indoors to outdoors
from outdoors to indoors
ramps
Eye Report
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
. Indoors
Can locate source of natural light
Can locate source of artificial light
Reaches for objects within arm's length without search
Moves toward objects over 5 feet away
Can see hands on wall clock
Can differentiate between small & large hands on clock
Can identify without touch eating utensils placed at random on desk or table
Can imitate pose or gesture of teacher at _____distance
Uses APH graph paper: 4" 1" 1/8"
Uses APH lines paper with pencil marker pen
Uses APH outline maps
Reads chalkboard at ____ distance
Reads dry-erase at ___ distance
Can use pictures in large-type books
color
black & white
Specify smallest print size
Can read numerals on paper money
Identifies coins by sight or touch
Primary color identification
Report of Clinical Findings
• Other Considerations
•
Individuals with multiple disabilities
•
Emotional aspects of the evaluation
•
Funding issues
Visual Functioning
• Visual Ability
Finding
– Visual acuity
– Visual fields
– Contrast sensitivity
– Light sensitivity
– Color vision
– Oculomotor control
– accomodation
Implications