Low vision aids

A presentation on Low vision aids.

1. LOW VISION AIDS
Dr Saurabh Kushwaha
Resident (Ophthalmology)

2. SCOPE
Visual Dysfunctions
WHO Definition -Low Vision
Classification
Goals of management
Indications
Low vision aids
Types of LVA

3. VISUALDYSFUNCTIONS
Visualdisorder
•Deviationfromnormalvisualstructurebydisease,
injuryoranomalyaffectingvision
Visualimpairment
•Reductionofvisualfunctionresultsfromthevisual
disorder
Visualdisability
•Reducedabilitytoperformacertaintask
Visualhandicap
•Non-performanceofthetasksrelatedtoindividualand
socialexpectationbecauseofvisualdisability

4. LOW VISION -WHO DEFINITION
Low Vision (Visual impairment Categories 1 & 2):
•“A person who has impairment of visual functioning
even after treatment and/ or standard refractive
correction, and has a visual acuity of less than 6/18 to
light perception, or a visual field less than 10 degrees
from the point of fixation, but who uses, or is potentially
able to use, vision for the planning and/ or execution of a
task for which vision is essential”
Blindness (Visual impairment Categories 3, 4 & 5)
•“Visual acuity of less than 3/60 or a corresponding
visual field loss of less than 10 degrees in the better eye
with best possible correction.”

5. CLASSIFICATION
Category Corrected
VA-better eye
WHO
definition
0 6/6 -6/18 Normal
1 <6/18 -6/60 Visual
impairment
2 <6/60 -3/60 Severe visual
impairment
3 <3/60 -1/60 Blind
4 <1/60 -PL Blind
5 No PL Blind

6. VISUAL DISABILITYCHART
Category Good eye Worse eye Percent
blindness
1 6/9 -6/18 6/24 -6/36 20%
2 6/18 -6/36 6/60 -Nil 40%
3 6/60 -4/60 3/60 -Nil 75%
4 3/60 -1/60 CF 1 ft -Nil 100%
5 CF 1 ft -NilCF 1 ft -Nil 100%
6 6/6 Nil 30%

7. FUNCTIONAL EFFECTS
Loss of central vision (eg. macular degeneration, toxoplasmascar)
•Difficultyreading
•Problems writing/ completingpaperwork
•Inability to recognize distance objects andfaces
Loss of peripheral vision (eg. Retinitis pigmentosa, glaucoma)
•Difficulty in mobility andnavigation
•Difficulty reading if there is constricted central visualfield
•Visual acuity may not be affected until very advanceddisease
Cloudy media (eg. Corneal scar, vitreous hemorrhage)
•Blurredvision
•Reducedcontrast
•Problems withglare

8. GOALS OF COMPREHENSIVE LOW
VISION EXAMINATION AND VISUAL
REHABILITATION
Identify and evaluate the cause of low vision
Assess ocular health
Emphasize the need of the patient/ beneficiary
Clinical Assessment
Maintain and improve visual function
Optometric rehabilitation & intervention
Counsel and educate
Appropriate visual rehabilitation

9. EVALUATION OF LOWVISION
History
Visualacuity
Refraction
Visual fieldanalysis
Ocular Health Assessment
Supplemental Testing
•Glare
•Colourvision
•Contrastsensitivity
•Electrophysiological tests

10. INDICATIONS
Children:
•Albinism
•ROP
•Congenitalmalformation
YoungAdult:
•Keratoconus
•Ocularinjuries

11. Old age:
•Glaucoma
•ARMD
•Diabeticmaculopathy
•Maculardegeneration
•Retinaldegeneration
•Chorioretinitis
•Opticatrophy
•Myopicdegeneration

12. LOW VISION AIDS
Anoptical/non-opticaldevicethatimprovesor
enhancesresidualvisionbymagnifyingtheimageofthe
objectattheretinallevel.
Opticaldeviceslikemagnifiersortelescopes,ornon
opticaldeviceslikestands,lampsandlargeprints.
OpticalLVAsarebasedonthefactthatwithsufficient
magnification,thenormalretinasurroundingthedamaged
centralretinacanbeusedforcentralvision.
Altertheenvironmentperceptionthrough
•BBB-Bigger,BrighterandBlacker
•CCC-Closer,ColorandContrast

13. TYPES OFLVA
Optical LVA:
•Magnifyingspectacles
•Handmagnifiers
•Standmagnifiers
•Telescopes
•Intraocular LVA
Non-opticaldevices:
•Approachmagnification
•Lighting
•Contrastenhancement
•Increasedsizeobject
•Electronicmagnifiers(CCTV,
LVIS,V-max)
•Communicationandwriting
devices

14. TYPES OFMAGNIFICATION
Lowvisionaidsmakeuseofangularmagnificationsby
increasing:
•Relativesize
•Relativedistance
Angular:itistheapparentsizeoftheobjectcompared
withtruesizeoftheobjectseenwithoutthedevice.eg.
Telescopicsystem
Angular magnification M = ω’/ω

15. Relativesize:bymakingtheobjectappearbigger(no
accommodationrequired)eg.CCTV

16. Relative distance: by bringing the object closer (requires
good accommodation) eg. magnifiers

17. LOW VISION OPTICAL DEVICES
FOR NEAR

18. MAGNIFYINGSPECTACLES
Highplusreadingglassestomagnifytheimages
Givenasanaddtothebestdistancerefraction
Readingdistanceiscalculatedby100dividedbyadd
Magnificationis1/4
th
thepowerofthelens.
Usedfornearwork
Amountofaddneededdependsontheaccommodation
andthereadingdistance

19. ReadingaddcanbepredictedusingtheKestenbaum
rulei.etheamountofaddneededtoread1Mprintisthe
inverseofthevisualacuityfraction
Howeverusuallygreateraddisrequiredthanpredicted
asthepatientalsohasreducedcontrastsensitivity
Ifthepatientismonocular,thepoorereyemaybe
occludedifitimprovesthefunctioning
Whenbinocularcorrectionsareneeded:
•Baseinprismsareaddedtocompensatefor
convergenceangle.
•Opticalcentermaybedecentred
Asphericlensesmaybeusedtoreducelenticular
distortion

20. Advantages:
•Handsarefree
•Fieldofviewlargerwhencomparedtotelescope
•Greaterreadingspeed
•Canbegiveninbothmonocularandbinocularforms
•Moreportable
•Cosmeticallyacceptable
Disadvantages:
•Higherthepower,closerthereadingdistance
•Closereadingdistancecausesfatigueand
unacceptableposture
•Patientswitheccentricfixationareunabletofix
throughtheseglasses

21. MAGNIFIERS
Usefulfornearwork
Designedtobeheldclosetothereadingmaterialto
enlargetheimage
Theeyelensdistanceshouldbeminimumtoachieve
largermagnification
Twotypes:
•Handmagnifier
•Standmagnifier

22. HANDMAGNIFIERS
Availablefrom+4.0to+68.0D
Availableinthreedesigns:
•Aspheric–reducesthicknessandperipheraldistortion
•Aplantic–flatandwidedistortionfreefieldandgood
clarity
•Biaspheric–eliminatingaberrationsfrombothsurfaces
Mostpatientsacceptupto6xmagnification

23. Advantages:
•Theeyetolensdistancecanbevaried
•Patientcanmaintainnormalreadingdistance
•Workwellwithpatientswitheccentricviewing
•Somehavelightsourcewhichfurtherenhancesvision
•Easilyavailable,overthecounter
Disadvantages:
•Itoccupiesbothhands
•Patientswithtremors,arthritisetchavedifficulty
holdingthemagnifier
•Maintainingfocusisaproblemespeciallyforelderly
•Fieldofvisionislimited

24. STANDMAGNIFIERS
Themagnifiersarestandmounted
Thepatientneedstoplacethestandmagnifieronthe
readingmaterialandmoveacrossthepagetoread
Hasafixedfocus
Advantages:
•Theyareachoiceforpatientswithtremors,arthritis
andconstrictedvisualfields
Disadvantages:
•Fieldofvisionisreduced
•Tooclosereadingpostureisuncomfortableforthe
patient
•Blocksgoodlightingunlessselfilluminated

25. CLOSED CIRCUIT TELEVISION
SYSTEM
Closedcircuittelevisionsystem(CCTV)consistsofa
monitor,acameraandaplatformtoplacethereadingtext
Ithascontrolforbrightness,contrastandchangeof
polarity
Magnificationvariesfrom3Xto60X

26. LOW VISION OPTICAL DEVICES
FOR DISTANCE

27. TELESCOPES
Workontheprincipleofangularmagnification
Telescopeswithmagnificationpowerfrom2xto10xare
prescribed
Theycanbeprescribedfornear,intermediateand
distanttasks
Fieldofviewdecreaseswithmagnification
Types:
•Handheldmonocular
•Clipondesign
•Biopticdesign:mountedonapairofeyeglasses

28. Principal
•Telescopesconsistoftwolenses(inpracticetwo
opticalsystems)mountedsuchthatthefocalpointof
theobjectivecoincideswiththefocalpointoftheocular.
•Objectivelensisaconverginglens
Galilean telescope Kepleriantelescope
The eye piece is a negative
lens and the objective is a
positive lens
Both eye piece and objective
are positive lens
Resultant image is virtual and
erect
Resultantimageisrealand
inverted. Prisms are
incorporatedtoerecttheimage
Loss of light reduces
brightness of the image
Loss of light is more in this
system
Field quality is poor Field quality is relatively good

29. Magnificationofatelescopeisgivenbytheformula
M=f
o/f
e
Telescopescanbeusedtofocusnearobjectsby
•Changingthedistancebetweenobjectiveand
ocularlens
•Increasingthepoweroftheobjectivelens

30. Advantages:
•Onlypossibledevicetoenhancedistantvision
Disadvantage:
•Restrictionofthefieldofview
•Appearanceandapprehension
•Expensiveandcostly
•Depthperceptionisdistorted

31. NON OPTICALDEVICES

32. ILLUMINATION
Positioning
•Light source should be to the side of bettereye
•Moving light closer will yield higherillumination
Higher levels of illumination is needed in patientswith
•Lost cone functions (maculardegeneration)
•Glaucoma
•Diabeticretinopathy
•Retinitis pigmentosa,Chorioretinitis
Reducedillumination
•Albinism
•Aniridia

33. READINGSTAND
Easy comfortable posture to thepatient

34. WRITINGGUIDE
Black cards with rectangular cut outs horizontally along the
card
The patient can feel the empty cut out spaces andwrite

35. SIGNATUREGUIDE

36. TYPOSCOPE / READINGGUIDE
Maskingdevicewithalinecutoutfromanopaque,non
reflectingblackplasticorthickpaper.
Reducesglareandcontrolscontrast.

37. NOTEX
Itisarectangularpieceofcardboardwithstepsontop
rightcornerwhichhelpsinidentifyingthecurrencyof
thenote
1
st
cutindicatesRs.500,2
nd
cutindicatesRs.100,3
rd
cutindicatesRs50andsoon.

38. RELATIVE SIZEDEVICES
Larger object subtends a larger visual angle at the eye
and is thus easier to resolve
•Large print material
•Large type playing cards, computer keyboards
•Enlarged clocks, telephones, calendars

39. COMPUTER SOFTWARE
Jaws screen readingsoftware
Connect out loud internet and emailsoftware
Magic 8.0 screen magnification software andspeech

40. GLARE REDUCING DEVICES
Glare is described as unwanted light
It is disabling in patients with cataracts, corneal opacities,
albinism, retinitis pigmentosa
Devices to prevent glare:
•Sunglasses
•Caps
•Umbrella
•Polaroid glasses
•NoIRfilters
•Corning photochromicfilters (CPF glasses)

41. CPFGLASEES
Attenuate100%ofUVBwavelengths.
Block99%ofUVAwavelengths.
Thebluelightportionofthevisiblespectrumismost
likelytoscatterintheeye,causingdiscomfortandhazy
illusion.
Attenuate98%ofhigh-energybluelight,withexception
ofCPF450,whichattenuates96%ofhigh-energyblue
light.
ThenumberoftheCPFglassescorrespondto
wavelengthinnanometersabovewhichlightis
transmitted

42. CPF® 550
(red)
Lens colour varies from
orange-red when lightened
to brown when darkened.
Retinitis pigmentosa
Albinism
CPF® 527
(orange)
Orange-amber lens darkens
to brown in sunlight, giving
individuals better visual
function and reduced glare
Retinitis pigmentosa
Diabetic retinopathy
CPF® 450
(yellow)
Enhances contrast and
helps control glare indoors
Optic atrophy
Albinism
Pseudophakia
CPF® 511
(yellow
orange)
Provides moderate blue
light filtering medium-range
Filter
Glaucoma
Aphakia
Pseudophakia
Optic atrophy
Developing cataracts

43. NoIRFILTERS
Absorbstheshortwavelengthsofthevisiblespectrum
thatcanscatterwithintheocularmedia,
Alsoabsorbsultravioletlight(upto4000nm)and
infraredlight
Managesoverallvisiblelighttransmission(VLT)toallow
theproperamountoflightenergytoreachtheeyes.

44. Includesafullrangeoflenses(spanning90%to1%
VLT)
•2%darkamber:100%UV,infraredandbluelight
protection,helpfulonverybrightdays
•13%standardgrey:goodforpostoperativecataract,
glaucoma,diabeticsandthosewhohadcorneal
transplants
•20%mediumplum:goodinlowlightsituationsand
canbewornindoors
•58%lightgrey:reduceindoorglareespeciallyunder
fluorescentlight
•65%yellow:retinitispigmentosaandmacular
dgeneration

45. COLOR AND CONTRAST
ENHANCEMENT
Maximize contrast by using a light color against black
or darkcolor
Choose colors in the room or working area which have
highcontrast

46. PINHOLEGLASSES
Multiple holes of approximately 1mm size are made in
the glasses
The distance between the holes should be atleast3-3.5
mm or approximately the size of the pupil
Used in patients with corneal opacities or conditions
with irregular reflexes
Not used in patients with central field defects as it
reduces illumination and visual acuity

47. MOBILITY ASSISTINGDEVICES
Patients with low vision suffer a major problem ofmobility
•Longcanes
•Strong portablelights

48. FIELD EXPANDINGDEVICES
As the magnification increases, the field of view
decreases
Three methods of increasing the field:
•Compress the existing image to include more of
available area
•Provide prisms that relocates the image from a non
seeing to a seeing area
•Use a mirror to reflect an image from a non seeing
area
Reverse telescopes: they are usually not accepted due
to minification
Fresnel lenses with power of 10-15D with base in the
direction of field loss

49. FUTURE

50. BIONICEYE
Designed for patients who are blind due to diseases like
retinitis pigmentosaor AMD
Can also be tried for those with severe vision loss
Relies on patient having a healthy optic nerve and a
developed visual cortex
Cannot be used for people who were born blind
The prosthesis consists of :
•A digital camera built into a pair of glasses
•A video processing microchip built into a hand held unit
•A radio transmitter on the glasses
•A receiver implanted above the ear
•A retinal implant with electrodes on a chip behind the
retina

51. Camera captures animage
Send image to microchip
Convert image to electrical impulse of light and dark pixels
Send image to radiotansmitter
Transmits pulses wirelessly to the receiver
Sends impulses to the retinal implant by a hair thin implanted wire
The stimulated electrodes generate electrical signals that travel to
the visual cortex

52. THANK YOU