Transcript Functional Fields of Bioptic: implications for driving

T HE S CHEPENS
E YE RESEARCH INSTITUTE
An Affiliate of Harvard Medical School
Functional Fields
of BiOptic Telescopes:
Implications for Driving
Eli Peli, M.Sc., O.D.
Professor of Ophthalmology
Acknowledgements
• Russell Woods
• Ivonne Fetchenheuer
Supported in part by NIH grant #EY12890
• Keplerian Vs. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation
Bioptic Telescope:Categories
Galilean
•
•
•
•
•
Small, light weight
Narrower field
Exit pupil inside Tx
Head movement
Micro Tx
DVI 3.0X
– Eye movement
BITA 6.0X
Bioptic Telescope:Categories
Keplerian
• Larger, heavier
– Image erecting
system
• Wider field of view
• Exit pupil behind Tx
• Head movement
DVI 4.0X
– Eye movement
(BTL)
Ocuthech VES 4.0X
Telescopes Tested
Keplerian
• 4.0X EFT DVI
• 3.0X Ocutech Mini
• 4.0X Ocutech VES
• 3.0X BTL
Galilean
• BITA
– 2.5X, 3.0X and 6.0X
• 3.0X DVI
Field-of-View of a Telescope
obj
Based on
pinhole pupil
ocu


obj’
e
L
FVM
d
FoV  2  min  (obj' ),  (ocu)
FoV = Retinal Field-of-View
Object Field-of-View = FoV/M
Field-of-View of a Galilean
obj
ocu
Illustrated for
M = 3.0


obj’
e
L
d
1 R (obj ' )
1 R (obj )
 (obj ' )  tan (
)  tan (
)
d e
dM  L
e
D(obj ' ) 
L
M
D(obj )
M
Expanding the field of a Galilean
obj
ocu

obj’
e
L
d
By moving the telescope closer to the eye
Dangerous?
Field-of-View of a Keplerian
obj
ocu

e
L
d
obj’
Reminder: based on pinhole pupil
What happened when we open the pupil?
Half Luminance FoV
obj
ocu


Additional Field is imaged through less than ½ the pupil
Full Luminance FoV
Functional Fields
How does
the Field-of-View of the Telescope
Interact with the
Visual Field of the User?
Monocular Visual Field Extent
40 mm (137 minarc)
5 mm (17 minarc)
1 mm (3.4 minarc)
at 1m
Binocular
visual field
+90 deg
Binocular visual field extent
Right eye
Left eye
Binocular
Scotoma(ta) in the Visual Fields
Scotoma
• Absolute
• Relative
• Keplerian Vs. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation
Vignetting
Galilean
• Fading away at edge
– Reduced light transmission
• Isopters are shifted
– Poorer optical quality
DVI 3.0X
Vignetting
Keplerian
• Inherently wider
Field
• Can be limited to
reduce vignetting
• Isopters collapse
4.0X EFT DVI
• Keplerian Vs. Galilean
• Vignetting
•Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation
Ring Scotoma
90
10
180
7
12
12
Jose & Ousley, 1984
270
11.5
0
What Causes the Ring Scotoma?
• “..exists because the lenses subtend a
greater angle at the eye than the angular size
of the of the optical field of view through
the telescope.
– The angular width of the ring scotoma is equal
to half the angular size of the objective lens at
the eye minus half the angular size of the
optical field of view.” (true if ocular at the eye)
– Feinbloom, 1977.
• “The physical housing of the telescope”
– Taylor (1990), citing Fonda (1986)
What Causes the Ring Scotoma?
• “The rim of the telescopic portion (of the
bioptic spectacle) creates a ring-shaped...”
– Corn, 1990
• “There is a ring scotoma caused by the edge
of the telescope extending…”
– Lippmann, et al, 1988
• The ring around the bioptic telescope
creates a scotoma or a blind spot that will
affect peripheral (side) vision.”
– Gottlieb et al, 1996
What Causes the Ring Scotoma?
• “Although both magnified and unmagnified
fields can be viewed simultaneously, the
telescope housing creates a considerable
ring scotoma around the magnified zone.”
– Christine Dickinson, 1998
• “A ring scotoma is a blind area in the visual
field produced by the housing of the
telescope.”
– Your Guide to Prescribing and Fitting
Spectacle-Mounted Telescopes. The Lighthouse
Driving Kit, Lighthouse International, 2003
What Causes the Ring Scotoma?
45 degree field
Magnification Causes Ring Scotoma
No structure effect needed
Ring Scotoma
• Can be measured with
perimeter
• Note, shift of
physiological scotoma
and asymmetric ring
scotoma
3.0 DVI
When you really don’t like BiOptic!
6°3.0 = 18°
Measured
scotoma
28° ?
90
10
180
7
12
12
Jose & Ousley, 1984
270
11.5
0
Superior & Inferior Fields
with 3x EFTs
• Car Hood 80 cm High
Jose & Ousley, 1984
• Driver 120 cm High
• Eye To Hood Distance 210 cm
• Eye To Hood Angle 10.8
• With 4.8 Tilt Down
200
150
100
50
4.2 M
11.6 M
Visual Field & Scotoma with 3x EFTs on
6.1 Meter Road Assuming 12
91
76
Jose & Ousley, 1984
61
57.7 M
46
38.4 M
30
19.2 M
15
0
9.6 M
15
19.2 M
11.5 M
30
28.8 M
23 M
46
34.5 M
61
Why is it asymmetric?
76
30
61
91
122
152
183
213
244
274
305
• Keplerian Vs. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation
Image shift in telescope
• Caused by axial misalignment
• Consequences?
–Possible benefit
• Control image position
Ring Scotoma with Tx
3.0X DVI Bioptic
Fitting the telescope
Ideal alignment:
eye to center of leveled telescope
Tilt head up ~10º to be leveled
Telescope blocks
the view of leveled eye
Further head tilt is needed
to clear the view
Measured Head Tilt
• Needed to move from
viewing through the
telescope to viewing
through the carrier
lens
• All much larger than
10 degrees
• Some uncomfortably
large
Telescope
Tilt in
degrees
Spiral EFT
4.0X
25.5
Bioptic
3.0X
20
VES-MINI
3.0X
14.5
Micro Spiral
6.0X
17
Fitting the telescope
Another Aproach
Start with a 10º mounted telescope.
Head leveled. Move telescope up to
clear the view under telescope
A 10º head tilt levels the telescope.
Eye is not centered on telescope
Results in image shift
Fitting the telescope
Real
Ocutech
Recent Illustration
Consequences of Image Shift?
•Shift of
physiological scotoma
•Shift of
magnified image
•Possibility to control the
position of Ring Scotoma
• Keplerian Vs. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation
BITA telescope SimulVision
Spatial Multiplexing
BITA SimulVision
• Shifted magnification
scotoma
• Shifted physiological
scotoma
• Caused by lens tilt
Magnification Scotoma Shifted Down
•Behind-the-lens Tx
In-the-Lens Telescope
Better Cosmesis
Unimpeded Eye Contact
In-the-Lens Telescope
Shifting of Scotoma
t
t
Front View
Side View
• Keplerian Vs. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation
Monocular Bioptic Telescope
Bi-ocular Multiplexing
Binocular Fields with Monocular Tx
• “Drivers with a bioptic telescope before only
one eye have no significant loss of
functional visual field.” (Feinbloom, 1977)
• “Simple confrontation experiment,
however, verify that objects obscured by
BTS ring scotoma can be perceived within
the field of the naked eye while the BTSfitted eye fixates.” (Lippmann, et al, 1988)
Binocular Fields with Monocular Tx
• “When tested on a Goldman Perimeter
with both eyes open a scotoma of any
kind can not be plotted.”
(Jose & Ousley, 1984)
Binocular field with Monocular Tx
Normally Sighted
4.0 DVI, OD
Real World?
Ocutech Horizontal Telescope
Manual
or Auto focus
Binocular Visual Fields
Most Conventional
HLP-VES
BITA & BTL no binocular scotomata
• Keplerian Vs,. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation
Impact of central field loss
Subject RP (JMD, right: 20/175, left: 20/225)
OD & OS
Monocular Fields
Monocular, OD
Binocular
With Monocular Telescope
Binocular fields with monocular Tx
• “When tested on a Goldman Perimeter
with both eyes open a scotoma of any
kind can not be plotted.”
(Jose & Ousley, 1984)
Impact of central field loss
Subject PJ (JMD, right: 20/250, left: 20/400)
Monocular, OD
OD/OS
Binocular
With Monocular Telescope
Impact of central field loss
Subject RG (Cone- Rod Dystrophy, right 20/200, left 20/200)
Monocular, OD
OD/OS
Binocular
With Monocular Telescope
• Keplerian Vs,. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation
Initial Response
of Visually Impaired Users
Naïve Users
• PJ: intermittently suppressed fellow eye
• RG: intermittently suppressed fellow eye
• CN: suppressed magnified image
• BE: no suppression
Initial Response
of Visually Impaired Users
Experienced bioptic users
• RP: no suppression
• BR: suppressed fellow eye in magnified field
Simple visual environment
Real world?
Conclusions
• People without CFL can have
scotomata in binocular visual field
• CFL usually causes scotomata in
binocular visual field
• People with CFL may suppressed one
eye when viewing through monocular
telescope
• Scotomata can be shifted/controlled
Recommendations
• Visual field measurements can help
assess bioptic wearers potential for
effective use in mobility (driving)
and monitor the state of suppression
• Studies are needed to determine the
usefulness of the other eye‘s view in
driving
• Blocking fellow eye‘s view may help
in initial training
Thank You!