Transcript Magnification and Field of View in Low Vision Aids

Bi0ptic Telescopes
The patient, the decisions, and the training
Ian L Bailey, OD, DSc, FAAO
School of Optometry
University of California, Berkeley. CA 94720-2020
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Optometry
[email protected]
Basic Vision Functions and Driving
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Optometry
Visual acuity
reading signs, seeing detail
Contrast sensitivity
seeing larger objects, borders, textures
Visual fields
seeing things to the side
Color vision
ability to see traffic signals, warning lights
Glare
veiling haze from headlights or bright light
Adaptation (light/dark) adjusting to changes in light level
Light sensitivity
ability to see in dim conditions
Should visually impaired people be allowed to drive?
The Dilemma
Public Safety
Risk of accidents,
Interference with
traffic flow
Individual's
Independence
Travel for work, or
social participation
For denial to be justified
Evidence of individual incompetence
Evidence (associations) of highly elevated risk
Strong prima facie argument for highly elevated risk
Caution when considering statistical evidence
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Associations describe trends - they are not rules
Higher crash rates for a given group is insufficient,
by itself, to disqualify all members of that group
Should visually impaired people be allowed to drive?
Licensing Authorities (DMV’s) have the responsibility
to test driving abilities, to allow or deny licensure,
and to impose any restrictions
They may consider
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Special driving tests
Past driving experience
Anticipated driving needs
Causative disorder
Other health issues (sensory, motor, cognitive)
They may impose
Closer monitoring of driving record
More frequent vision and driving tests
Restrictions on routes, time of day, etc.
Restricted vehicle categories, speed
Optometry
They may require
BiOptic telescopes
What is the use of BiOptic Telescopes?
BiOptic telescopes are
Head mounted telescopes Typically magnification (for driving) = 2x to 4x
Arranged to allow easy interchange from viewing with and without the telescope
BiOptic telescopes magnify
Enable distant details to been seen to be seen more easily.
Advantages for driving
Signs, signals and other features with more small details
can be seen at a longer distance than they otherwise could be
Disadvantages
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Ring scotoma can reduce field of view
Brightness may be reduced
Head and/or eye movements are required to interchange
Vision impairment and Nystagmus
Congential Nystagmus
Albinism
Reduced visual acuity
Normal contrast sensitivity
Normal visual fields
Astigmatism, High refractive error (+)
Some sensitivity to light
Achromatopsia
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Reduced visual acuity
Normal contrast sensitivity
Normal visual fields
Astigmatism
Reduced visual acuity
Reduced contrast sensitivity (somewhat)
Normal visual fields
Poor color discrimination
Photophobia
Astigmatism, High myopia in some (Blue cone)
Is seeing fine detail important to driving?
Yes!
Reading signs
(freeway signs, street signs, warnings, parking, house numbers, building signs)
Traffic signs size and location usually designed on assumptions that
drivers will have a visual acuity of 20/40 (6/ 12 or 0.5)
But!
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Reading signs, or attending to fine details
required for short-term and infrequent driving tasks
Especially in familiar areas, and other situations where need to read signs is minimal
BiOptic telescopes allow fine details
to be seen from a longer distance
A driver who obtains 20/40 or better through telescope,
should be able to read roadway signs, etc., from the intended distance
BiOptic telescopes only engaged intermittently
for short periods when attending to signs
(or other fine detail)
BUT
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Potential danger when looking through telescope
because part of visual field is occluded (RING SCOTOMA)
Illustration of RING SCOTOMA with 3x telescope
OBJECT SPACE
Ring s cotom a is blue are a block ed by the 3x e nlar ge m e nt of ye llow are a
For a 3x
telescope
Occluded area
is 8x larger than
the area being
magnified
A B C D EF G H I J K L M N O P Q R S TU V W XY Z A B C D EF G H I J K L M N O
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a bcd e f g h i j k l m n o pqrs t u vwx y z a bcd e f g h i j k lm n o pqrs t u vwx y z
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a bcd e f g h i j k l m n o pqrs t u vwx y z a bcd e f g h i j k lm n o pqrs t u vwx y z
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IMAGE SPACE
3x e nlar ge d ye llow ar e a occlude s a s ubs tantial are a
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A B C D EF G H I J K L M N O P Q R S TU V W XY Z A B C D EF G H I J K L M N O
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a bcd e f g h i j k l m n o pqrs t u vwx y z a bcd e f g h i j k lm n o pqrs t u vwx y z
A B C D EF G H I J K L M N O P Q R S TU V W XY Z A B C D EF G H I J K L M N O
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a bcd e f g h i j k l m n o pqrs t u vwx y z a bcd e f g h i j k lm n o pqrs t u vwx y z
A B C D EF G H I J K L M N O P Q R S TU V W XY Z A B C D EF G H I J K L M N O
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a bcd e f g h i j k l m n o pqrs t u vwx y z a bcd e f g h i j k lm n o pqrs t u vwx y z
A B C D EF G H I J K L M N O P Q R S TU V W XY Z A B C D EF G H I J K L M N O
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a bcd e f g h i j k l m n o pqrs t u vwx y z a bcd e f g h i j k lm n o pqrs t u vwx y z
A B C D EF G H I J K L M N O P Q R S TU V W XY Z A B C D EF G H I J K L M N O
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yzabc d
TUVWX
19 20 21 22
yzabc d
Projecting a telescope ring scotoma
20m = 65 ft
1.8 sec @ 40 km/hr
(25 mph)
0.7 sec @ 100 km/hr
(63 mph)
Ke ple rian
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Gali le an
REAL
WORLD
Object
s pace
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SUB JECT
SEES
I mage
s pace
3x
3x
Ring scotoma could be hazardous
When viewing through telescope. There must be
a substantial para-central field loss from the ring scotoma,
IF -- the second eye is occluded
OR -- if the second eye is functionally blind
OR -- if there is a binocular telescope system
BUT
When viewing through telescope, there is no field loss
Provided -- second eye does not have a telescope
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remains open
can readily detect large peripheral objects
does not have profound suppression
Some visual criteria for selecting patients
for BiOptic Telescopes for driving
Best corrected Visual Acuity - 20/160 to 20/50 range (6/48 to 6/15)
Telescope V A (M= 4x or less)
- 20/40 to 20/32 range
(6/12 to 6/9.5)
Should not have more than a 3x (0.5 log units) reduction in CS
Should not have significant field defects
Telescope before one eye only (better reading eye)
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Second eye should have VA of 20/400 or better (6/120)
Second eye should not have profound suppression
Before prescribing
Optometric consideration of visual abilities
Hard numbers on Visual acuity
Contrast sensitivity
Visual fields
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Evaluate as needed
Color vision
Glare
Adaptation (light/dark)
Light sensitivity
Consider
Motor and mental agility
Reaction time
Vision in clutter
Divided attention
10 M
8.0
6.3
5.0
4.0
3.2
2.5
2.0
1.6
1.25
1.0
0.8
0.63
0.5
0.4
0.32
0.25
0.2
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Some variations on usual more common tests
Visual Acuity
Word Reading
10 words each size
Grade 3 word lists
Sentences
60 characters
MNRead
Reading efficiency for words and sentences
pretty only loves side along
visits cold months smiled part
ride about begins work today
ready called draw tired jump
Put your first name on this paper
if you will help tomorrow
Many people came to help us
clean the place after the party
Some variations on usual more common tests
Visual Fields
Effect of illumination
Variable luminance backgrounds
EITHER
Plot fields
OR
Ask about letters visible on chart
at different luminances
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RP, ARM etc
fields change with luminance
Some variations on usual more common tests
Contrast Sensitivity
Number search
6 1
Response Efficiency Tests
Flashing squares
4 2
3
5
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Output display
Response time
vs Log CS
Response (secs)
3
2
Less than 2 mins per test
2 measures at 24 contrasts
1
0
0.0
0.2
0.4
0.6
0.8
1.0
log CS
1.2
1.4
1.6
1.8
Some variations on usual more common tests
Useful Field of View (UFOV)
Test patient’s ability to respond to peripheral stimuli
Delayed reaction times for peripheral visual stimuli
Failure to see brief, peripheral visual stimuli
(i.e., reduced measured visual field)
When there is
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Divided visual attention
Visual clutter
Multi-tasking
Before prescribing
Ensure good skill using telescopes
Hand held telescope -
magnification equal to, or stronger,
than planned bioptic
Achieve 20/40 with telescope
Efficient spot viewing - both indoors and outdoors
stationary observer - stationary object of regard
stationary observer - moving object of regard
moving observer - stationary object of regard
moving observer - moving object of regard
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Real world location and viewing of targets in visual clutter
first locate the target object, and then engage telescope
Before prescribing
Advising the patient
Advise patients about their visual disabilities and functional relevance
Bioptic telescope does not ensure ability to pass driving test
Bioptic telescopes do not restore vision to normal
Even with bioptic telescopes, they remain at a visual disadvantage
Need to drive with extra caution
Should have companion drive when possible
Need practice in viewing with bioptic telescope system
Need supervised training using bioptic telescope for driving
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If no driving experience, likely to need more instruction than usual from
a professional driving instructor
Optometry
The DMV makes the final decisions
Prescribing BiOptic Telescopes
• Select telescope Magnification
Design
(Designs for Vision, Ocutech)
Galilean,
smaller, light weight, small field
Keplerian,
longer, heavier, larger field
Focus
fixed, adjustable, auto
Exit Pupil
• Select frame
smaller or larger than pupil
Suitable for telescope mounting
Sturdy and comfortable
Adjustable to vary height, lateral position and angle
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• Determine lens powers for telescope and carrier lens
• Select characteristics of carrier lens
(SV, bifocal, tint)
Prescribing
Positioning & Angling BiOptic Telescopes
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Training: Using a BiOptic Telescope
Rehabilitation Staff
Five to fifteen lessons of 30 minutes.
Home practice after each lesson
Begin practice indoors with flash cards,
Practice outdoors while walking (include traffic signs)
Practice while a passenger in a car
residential, business and freeways
(locate signs, signals, landmarks and then engage telescope)
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WHEN patient is proficient with telescope while a passenger
THEN we issue DMV report form, patient applies for permit
AND patient begins training with professional driving instructor
Training
Test Cards for bioptic telescope evaluations
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Dealing with the
Department of Motor Vehicles
• Appointment with a “Driver Safety Referee”
• Present vision report that includes information
VA with and without telescope
Fields, contrast sensitivity
Causative eye disease or disorder, stability and prognosis
May be considered a learner’s permit
THEN the patient takes the written test
THEN driving permit may be issued
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LATER, patient takes drive test
Department of Motor Vehicles
Driving test
Driving test appointment with a “Driver Safety Referee”
Driving test
Longer course than usual
Exposure to more visually-demanding driving tasks
Night time drive test may be requested
if patient wants to remove “no night driving” restriction
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Department of Motor Vehicles
Issue of a Driving License
Unrestricted or Restricted License??
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Special considerations Driving skill tests
Causal disease
Driving experience
Visual abilities
Driving record
Extent of vision loss
Driving need
Prognosis, stability
Anticipated driving
Variability of vision
Sensory motor disabilities Other visual disabilities
Special constraints
Monitor
Accidents
Violations
Increase frequency
Renewal
Vision reports
Driving tests
Restrict
Time of day
Visibility conditions
Routes
Purpose
Distance from home
Vehicle category
Require
BiOptic Telescope
Special mirrors
Some Conclusions
Visual acuity tasks
much less important
than visual field and contrast sensitivity tasks
BiOptic Telescopes
enable seeing of finer detail,
when needed
Visually impaired drivers
should be given opportunity
to demonstrate ability to drive safely
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Optometry
It can be reasonable to specify definite limits
OPINIONS :New California limit -better than 20/200 (6/60) -is acceptable
No driving with hemianopia is reasonable
Thank you!
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O p t o m et r y
Optometry
[email protected]
For Europe
POLICIES TO DEMAND
 BiOptic telescope is a corrective lens system
 Telescope must allow visual acuity of 6/12 (20/40 or 0.5)
 Telescope must be before one eye only
 BiOptics are to be used with two eyes open
so, relevant visual field test is with both eyes open
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COMPROMISES TO ACCEPT O R CONCEDE
 Vision report every 5 years (at least)
 Maximum mag = 4x, or without TS, VA > 6/48 (20/160 or 0.125)
 Driving should be conditional on wearing telescope
 Initial license should be for daytime use only
 Night driving cannot be considered until 3 years experience