The document provides information on low vision, including definitions, causes, assessments, and aids. It defines low vision according to the WHO and Indian standards. Common causes that can benefit from low vision aids are discussed. Assessment of low vision patients involves testing visual acuity, visual fields, contrast sensitivity, and other factors. A variety of optical and non-optical low vision aids are described, including magnifiers, telescopes, illumination devices, software, and filters to reduce glare. The goals of low vision management and global prevalence of low vision are also summarized.

1. LOW VISION AIDS
Astha Jain
Shashi Sharma

2. INTRODUCTION

3. DEFINITION (INDIA)
 According to the Person with Disabilities Act 1995, “A person with
low vision means a person with impairment of visual functioning
even after treatment of standard refractive correction but who uses
or is potentially capable of using vision for the planning or execution
of a task with appropriate assistive device.”

4. DEFINITION(WHO)
 WHO (ICD-10) definition
 “A person with low vision is one who suffers visual acuity between
6/18 to 3/60 in the better eye after the best possible correction or a
field of vision between 20 to 30 degrees.”
 Used for reporting and comparison of data
 The WHO working definition of Low Vision (Bangkok definition,
1992)
 “A person with low vision is one 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 of 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 .”
 Defines population in need of low vision services

5. category Corrected WHO working Indian
VA- better eye definition definition
0 6/6 – 6/18 Normal Normal Normal
1 <6/18 – 6/60 Visual Low vision Low vision
impairment
2 <6/60 – 3/60 Severe visual Low vision Blind
impairment
3 <3/60 – 1/60 Blind Low vision Blind
4 <1/60 - PL Blind Low vision Blind
5 No PL Blind Total blindness Total blindness

6. VISUAL DISABILITY CHART
Category no. 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 – nil CF 1 ft - nil 100%
6 6/6 nil 30%

7. FUNCTIONAL EFFECTS OF LOW VISION
 Loss of central vision (eg. macular degeneration, toxoplasma scar etc.)
 Difficulty reading
 Problems writing/ completing paperwork
 Inability to recognize distance objects and faces
 Loss of peripheral vision (eg. Retinitis pigmentosa, glaucoma etc. )
 Difficulty in mobility and navigation
 Difficulty reading if there is constricted central visual field
 Visual acuity may not be affected until very advanced disease
 Cloudy media (eg. Corneal scar, vitreous hemorrhage etc.)
 Blurred vision
 Reduced contrast
 Problems with glare

8. GOALS OF LOW VISION MANAGEMENT
 Increase functionality
 Make the most of the remaining vision
 Provide link to community resources and support services
 Education

9. STRATEGIES
 Be oriented towards activities of daily living
 Use appropriate technology
 Be cost effective
 Utilize appropriate educational and vocational adaption
 Focus on target groups

10. GLOBAL PREVALENCE OF LOW VISION
 True magnitude not known because :
 No uniform definition of low vision
 Incomplete surveys
 Low vision definition does not include standards of near vision,
which is the main area dealt with low vision patients.
 Current Data *
 No. of visually impaired: 180 million
 No. of blind: 45 million
 Those with residual vision: 171 million
 Of these 171 million:
 Those with vision from PL to 3/60 : 36 million
 No. with vision from 3/60to 6/18: 135 million
 No. who can benefit from treatment: 103 million
 True low vision patients: 68 million
*Ramachandra Pararaiasegaram. Low vision care: the need to maximise visual potential. Community Eye Health. 2004; 17: 1-2

12. WHAT ARE LOW VISION AIDS AND HOW DO THEY
WORK ??
 Devices which help the people to use their sight to better advantage
 Can be optical devices like magnifiers or telescopes, or non optical
devices like stands, lamps and large prints.
 Alter the environment perception through
 BBB – bigger brighter and blacker
 CCC – closer color and contrast

13. DISEASES WHERE LOW VISION AIDS ARE HELPFUL
 Retinitis pigmentosa
 Glaucoma
 Macular degeneration
 Corneal scar
 Albinism and aniridia
 Retinal detachment
 Diabetic retinopathy
 Chorioretinitis
 Optic atrophy

14. TYPES OF MAGNIFICATION
 Low vision aids make use of angular magnifications by increasing :
 Relative size
 Relative distance

15.  Angular : it is the apparent size of the object compared with true
size of the object seen without the device.eg. Telescopic system
Angular magnification M = ω’/ ω

16.  Relative size: by making the object appear bigger (no
accommodation required) eg. CCTV

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

18. VISUAL ASSESSMENT

19. HISTORY
 Ocular history:
 To know cause of low vision
 To know the progression of disease
 Systemic diseases that may pose difficulty in using certain devices
eg. arthritis, tremors
 Task analysis

20. VISUAL ACUITY
 Distance visual acuity:
Lighthouse distance visual acuity test chart is preferred over the standard
snellen’s chart as it has :
 Equal line difficulty
 geometric progression of optotype size from line to line
 5 letters on each line
 More lines at lower level of visual acuity
 Test distance of 2 meters can be used to cover visual acuity upto 20/400

22.  Near visual acuity:
 Text samples are better than single letter acuity charts
 Metric notations are used
 1M symbol subtends an angle of 5 minutes of arc at 1 meter and is
roughly equal to the size of the newsprint
 Visual acuity is recorded as distance of reading material (in meters) over
the letter size (in M units)
 Snellens equivalent can be calculated from the metric notations

24. OTHERS
 Contrast sensitivity
 Visual field analysis:
 Peripheral field: using Humphery or octopus perimetry
 Central field: using Amsler grid
 Glare :
 History
 Measuring visual acuity both with and without illumination in the chart
 Colour vision
 Look for dominant eye:
 by testing contrast sensitivity monocularly and binocularly

25. LOW VISION AIDS
OPTICAL
DISTANCE
 Hand held telescopes
 Mounted telescopes
NEAR
 Spectacles
• Prismatic ½ eyes
• Bifocals
 Magnifiers
• Hand held vs. stand
• Illuminated vs. non-illuminated
 Electronic Devices

26. NON-OPTICAL
 Glare reduction devices
 Contrast enhancement devices
 Computer software
 Accessory devices
 Talking watches, clocks, etc
 Writing guides
 Tactile markers

27. LOW VISION OPTICAL DEVICES
FOR NEAR

28. MAGNIFYING SPECTACLES
 High plus reading glasses to
magnify the images
 Given as an add to the best distance refraction
 Reading distance is calculated by 100 divided by add
 Magnification is 1/4th the power of the lens.
 Used for near work
 Amount of add needed depends on the accommodation and the reading
distance

29.  Reading add can be predicted using the Kestenbaum rule i.e the amount
of add needed to read 1M print is the inverse of the visual acuity fraction
 However usually greater add is required than predicted as the patient also
has reduced contrast sensitivity
 If the patient is monocular, the poorer eye may be occluded if it
improves the functioning
 When binocular corrections are needed :
 Base in prisms are added to compensate for convergence angle.
 Optical center may be decentred
 Aspheric lenses may be used to reduce lenticular distortion

30.  Advantages :
 Hands are free
 Field of view larger when compared to telescope
 Greater reading speed
 Can be given in both monocular and binocular forms
 More portable
 Cosmetically acceptable
 Disadvantages:
 Higher the power, closer the reading distance
 Close reading distance causes fatigue and unacceptable posture
 Patients with eccentric fixation are unable to fix through these glasses

31. MAGNIFIERS
 Useful for near work
 Designed to be held close to the reading material to enlarge the image
 The eye lens distance should be minimum to achieve larger magnification
 Two types:
 Hand magnifier
 Stand magnifiers.

32. HAND MAGNIFIERS
 Available from + 4.0 to + 68.0 D.
 Available in three designs:
 Aspheric – reduces thickness and peripheral distortion
 Aplantic – flat and wide distortion free field and good clarity
 Biaspheric – eliminating aberrations from both surfaces
 Most patients accept upto 6x magnification

33.  Advantages
 The eye to lens distance can be varied
 Patient can maintain normal reading distance
 Work well with patients with eccentric viewing
 Some have light source which further enhances vision
 Easily available, over the counter
 Disadvantages:
 It occupies both hands
 Patients with tremors, arthritis etc have difficulty holding the magnifier
 Maintaining focus is a problem especially for elderly
 Field of vision is limited

34. STAND MAGNIFIERS
 The magnifiers are stand mounted
 The patient needs to place the stand magnifier on the reading material
and move across the page to read
 Has a fixed focus
 Advantages :
 They are a choice for patients with tremors, arthritis and constricted
visual fields.
 Disadvantage:
 Field of vision is reduced
 Too close reading posture is uncomfortable for the patient
 Blocks good lighting unless self illuminated

35. CLOSED CIRCUIT TELEVISION SYSTEM
 Closed circuit television system (CCTV) consists of a monitor, a
camera and a platform to place the reading text
 It has control for brightness, contrast and change of polarity
 Magnification varies from 3X to 60X

36. LOW VISION OPTICAL DEVICES
FOR DISTANCE

37. TELESCOPES
 Work on the principle of angular magnification
 Telescopes with magnification power from 2x to 10x are prescribed
 They can be prescribed for near, intermediate and distant tasks
 Field of view decreases with magnification
 Types:
 Hand held monocular
 Clip on design
 Bioptic design: mounted on a pair of eyeglasses

38.  Principal
 Telescopes consist of two lenses (in practice two optical systems) mounted such
that the focal point of the objective coincides with the focal point of the ocular.
 Objective lens is a converging lens
Galilean telescope Keplerian telescope
The eye piece is a negative lens and Both eye piece and objective are
the objective is a positive lens positive lens
Resultant image is virtual and erect Resultant image is real and inverted.
Prisms are incorporated to erect the
image
Loss of light reduces brightness of Loss of light is more in this system
the image
Field quality is poor Field quality is relatively good

39.  Magnification of a telescope is given by the formula M = fo/fe
 Telescopes can be used to focus near objects by
 changing the distance between objective and ocular lens
 Increasing the power of the objective lens

40. GALILEAN TELESCOPE
Objective
Eye piece
a
β fo
fe

41. KEPLERIAN TELESCOPE
Objective Eyepiece
fo fe
α β

42. TELESCOPE FOR NEAR

43.  Advantages:
 Only possible device to enhance distant vision
 Disadvantage:
 Restriction of the field of view
 Appearance and apprehension
 Expensive and costly
 Depth perception is distorted

44. NON OPTICAL DEVICES

45. ILLUMINATION
 Positioning
 Light source should be to the side of better eye
 Moving light closer will yield higher illumination
 Higher levels of illumination is needed in patients with
 Lost cone functions (macular degeneration)
 Glaucoma
 Diabetic retinopathy
 Retinitis pigmentosa, Chorioretinitis
 Reduced illumination
 Albinism
 Aniridia

46. READING STAND
 Easy comfortable posture to the patient

47. WRITING GUIDE
 Black cards with rectangular cut outs horizontally along the card
 The patient can feel the empty cut out spaces and write

48. SIGNATURE GUIDE

49. TYPOSCOPE / READING GUIDE
 Masking device with a line cut out from an opaque, non reflecting
black plastic or thick paper.
 Reduces glare and controls contrast.

50. NOTEX
 It is a rectangular piece of cardboard with steps on top right corner
which helps in identifying the currency of the note
 1st cut indicates Rs. 500, 2nd cut indicates Rs.100, 3rd cut indicates
Rs 50 and so on.

51. RELATIVE SIZE DEVICES
 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

52. COMPUTER SOFTWARE
 Jaws screen reading software
 Connect out loud internet and email software
 Magic 8.0 screen magnification software and speech

53. 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
 NoIR filters
 Corning photochromic filters
(CPF glasses)

54. CPF GLASEES
o Attenuate 100% of UVB wavelengths.
o Block 99% of UVA wavelengths.
o The blue light portion of the visible spectrum is most likely to scatter
in the eye, causing discomfort and hazy illusion.
o Attenuate 98% of high-energy blue light, with exception of CPF
450, which is 96% of high-energy blue light.
o The number of the CPF glasses correspond to wavelength in
nanometers above which light is transmitted

55. CPF® 550 (red) Lens colour varies from retinitis pigmentosa
orange-red when lightened albinism
to brown when darkened.
CPF® 527 (orange) Orange-amber lens darkens retinitis pigmentosa
to brown in sunlight, giving diabetic retinopathy
individuals better visual
function and reduced glare
CPF® 450 (yellow) enhances contrast and helps optic atrophy
control glare indoors albinism
pseudophakia
CPF® 511 (yellow Medium-range filter macular degeneration
orange) provides moderate blue light glaucoma
filtering aphakia
pseudophakia
optic atrophy
developing cataracts

56. NOIR FILTERS
 Absorbs the short wavelengths of the visible spectrum that can
scatter within the ocular media,
 Also absorbs ultraviolet light (to 4000 nm) and infrared light
 Manages overall visible light transmission (VLT) to allow the proper
amount of light energy to reach the eyes.

57.  Includes a full range of lenses (spanning 90% to 1% VLT)
 2% dark amber: 100% UV, infrared and blue light protection, helpful on very
bright days
 13% standard grey: good for postoperative cataract, glaucoma, diabetics and
those who had corneal transplants
 20% medium plum: good in low light situations and can be worn indoors
 58% light grey: reduce indoor glare especially under fluorescent light
 65% yellow: retinitis pigmentosa and macular dgeneration

58. COLOR AND CONTRAST ENHANCEMENT
 Maximize contrast by using a light color against black or dark color
 Choose colors in the room or working area which have high contrast

59. PINHOLE GLASSES
 Multiple holes of approximately 1mm size are made in the glasses
 The distance between the holes should be atleast 3-3.5 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

60. MOBILITY ASSISTING DEVICES
 Patients with low vision suffer a major problem of mobility
 Long canes
 Strong portable lights

61. FIELD EXPANDING DEVICES
 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

62. FUTURE

63. BIONIC EYE
 Designed for patients who are blind due to diseases like retinitis
pigmentosa or 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

64. Camera captures an image
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 stimultaed electrodes generate electrical signals that travel to the visual cortex

65.  Requires training by the subject to actually see an object
 Subjects have to learn to interpret the array of white and dark dots as
object
 It is still in clinical trial stage

66. Help when there is no cure

67. Thank you

68. Thank you
Thank you
Thank you

72.  Various forms are available
1. Powers usually available are +4.0, +5.0, +6.0, +10.0 , +12.0, +16.0,
20.0 and +24.0
2. Binocular corrections are needed –Base in prisms are added to
compensate for convergence angle.
 Optical quality of the lens should be an aspheric design to eliminate
peripheral aberration and provide reasonable field.
 The reading glass should be prescribed as an addition over the distance
correction.

73. GALLELIAN TELESCOPE

74. KREPLERIAN TELESCOPE

76. OPTICS OF LOW VISION AIDS
 Principle : Magnification = D/4
on the assumption that the patient can sustain just enough
accommodation to hold the matter at 25 cm.
 Modified formula : M = D + A-h AD/2.5 where
A is the amplitude of accomodation
h is the eye lens distance in meters.
 To increase magnification:
 Eyes should be kept close to the lens (reduce h)
 Object should be as close to the patient’s eye as his accomodation
allows

77. Left: simulated with cataracts. Middle: CPF 511 lenses. Right:
normal eyes.

78. IMPACT OF OCULAR DISEASE ON THE PATIENT
 Visual disorder
Anatomical changes in the visual organ caused by the disease of the eye
 Visual impairment
Functional loss that results from the visual disorder
 Visual disability
Refers to vision related changes in the skill and abilities of the patient
 Visual handicap
Psychosocial and economic consequences of visual loss

79.  Legal Blindness
 Best corrected distance visual acuity not exceeding 6/60 in the
better eye
 Visual field of 20 degrees or less at widest point in the better eye
 Low Vision
 Best corrected visual acuity between 6/60 to 6/18
 Significant field loss
 Impaired function
 All these definitions however do not consider
 Near vision
 Scotoma, hemianopia
 Visual performance like contrast

80. EYE DISORDERS AND LOW
VISION

81. RETINOPATHY OF PREMATURITY
Retinopathy of prematurity requires bright light and
near additions required for near work

82. ANIRIDIA
Tinted glasses and cap

83. ALBINISM
Typoscope
Dark glasses

84. CORNEAL DAMAGE
Multiple pin hole glasses Hand magnifier

85. DIABETIC RETINOPATHY
Diabetic Retinopathy with near glasses, hand magnifiers and
a reading lamp

86. GALILEAN TELESCOPE
Objective
Eye piece
a
β F

87. KEPLERIAN TELESCOPE
Objective
Eye piece
α β
F

88. KEPLERIAN TELESCCOPE

89. TELESCOPE FOR NEAR