Functional Fields of BiOptic Telescopes: Implications for Driving

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Functional Fieldsof BiOptic TelescopesImplicati
ons for Driving
Eli Peli, M.Sc., O.D. Professor of Ophthalmology
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Acknowledgements

• Russell Woods
• Ivonne Fetchenheuer

Supported in part by NIH grant EY12890
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• Keplerian Vs. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation

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Bioptic TelescopeCategories
Galilean
DVI 3.0X

• Small, light weight
• Narrower field
• Exit pupil inside Tx
• Head movement
• Micro Tx
• Eye movement

BITA 6.0X
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Bioptic TelescopeCategories
Keplerian

• Larger, heavier
• Image erecting system
• Wider field of view
• Exit pupil behind Tx
• Head movement
• Eye movement (BTL)

DVI 4.0X
Ocuthech VES 4.0X
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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

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Field-of-View of a Telescope
Based on pinhole pupil
FVM
FoV Retinal Field-of-View Object Field-of-View
FoV/M
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Field-of-View of a Galilean
Illustrated for M 3.0?
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Expanding the field of a Galilean
By moving the telescope closer to the eye
Dangerous?
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Field-of-View of a Keplerian
Reminder based on pinhole pupil What happened
when we open the pupil?
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Half Luminance FoV
Additional Field is imaged through less than ½
the pupil
Full Luminance FoV
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How does the Field-of-View of the Telescope
Interact with the Visual Field of the User?
Functional Fields
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Monocular Visual Field Extent
40 mm (137 minarc) 5 mm (17 minarc) 1 mm (3.4
minarc) at 1m
Binocular visual field 90 deg
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Binocular visual field extent
Right eye
Left eye
Binocular
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Scotoma(ta) in the Visual Fields

• Scotoma
• Absolute
• Relative

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• Keplerian Vs. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation

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Vignetting

• Galilean

• Fading away at edge
• Reduced light transmission
• Isopters are shifted
• Poorer optical quality

DVI 3.0X
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Vignetting

• Keplerian

• Inherently wider Field
• Can be limited to reduce vignetting
• Isopters collapse

4.0X EFT DVI
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• Keplerian Vs. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation

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Ring Scotoma
Jose Ousley, 1984
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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)

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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

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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

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What Causes the Ring Scotoma?
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Magnification Causes Ring Scotoma
No structure effect needed
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Ring Scotoma
3.0? DVI

• Can be measured with perimeter
• Note, shift of physiological scotoma and
  asymmetric ring scotoma

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When you really dont like BiOptic!
6?3.0 18
Measuredscotoma 28 ?
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Jose Ousley, 1984
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Jose Ousley, 1984
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Jose Ousley, 1984
Why is it asymmetric?
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• Keplerian Vs. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation

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Image shift in telescope

• Caused by axial misalignment
• Consequences?
• Possible benefit
• Control image position

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Ring Scotoma with Tx
3.0X DVI Bioptic
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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 neededto clear the view
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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
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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
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Fitting the telescope

• Real

Ocutech
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Consequences of Image Shift?

• Shift of physiological scotoma
• Shift of magnified image
• Possibility to control the position of Ring
  Scotoma

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• Keplerian Vs. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation

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BITA telescope SimulVision
Spatial Multiplexing
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BITA SimulVision

• Shifted magnification scotoma
• Shifted physiological scotoma
• Caused by lens tilt

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Magnification Scotoma Shifted Down

• Behind-the-lens Tx

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In-the-Lens Telescope
Better Cosmesis Unimpeded Eye Contact
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In-the-Lens Telescope Shifting of Scotoma
Front View
Side View
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• Keplerian Vs. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation

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Monocular Bioptic Telescope
Bi-ocular Multiplexing
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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 BTS- fitted eye fixates. (Lippmann, et al,
  1988)

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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)

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Binocular field with Monocular Tx
Normally Sighted
4.0? DVI, OD
Real World?
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Ocutech Horizontal TelescopeManual or Auto
focus
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Binocular Visual Fields

• Most Conventional HLP-VES

BITA BTL no binocular scotomata
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• Keplerian Vs,. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation

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Impact of central field loss

• Subject RP (JMD, right 20/175, left 20/225)

Monocular, OD
Binocular
OD OS Monocular Fields
With Monocular Telescope
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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)

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Impact of central field loss

• Subject PJ (JMD, right 20/250, left 20/400)

Monocular, OD
Binocular
With Monocular Telescope
OD/OS
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Impact of central field loss
Subject RG (Cone- Rod Dystrophy, right 20/200,
left 20/200)
Monocular, OD
Binocular
OD/OS
With Monocular Telescope
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• Keplerian Vs,. Galilean
• Vignetting
• Ring scotoma
• Image shift
• Simulvision
• Binocular fields
• Central field loss
• Adaptation

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Initial Responseof Visually Impaired Users

• Naïve Users
• PJ intermittently suppressed fellow eye
• RG intermittently suppressed fellow eye
• CN suppressed magnified image
• BE no suppression

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Initial Responseof Visually Impaired Users

• Experienced bioptic users
• RP no suppression
• BR suppressed fellow eye in magnified field
• Simple visual environment
• Real world?

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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

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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 eyes view in driving
• Blocking fellow eyes view may help in initial
  training

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Thank You!