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Transcript
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!