LOW VISUAL AIDS

1. LOW VISUAL AIDS MAHRUKH KHAN

2. 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. WHAT ARE LOW VISION AIDS AND HOW DO THEY
WORK ??
• A patient with a low vision is a person who because of an
irreversible disorder of the visual eye system cannot perform
customary visual activities without the special vision-
enhancing devices.
• An LVA conventionally refers to an optical device that improves
or enhances residual vision by magnifying the image of the
object at the retinal level.
• In addition, there are some nonoptical aids that may help in
enhancing the visual performance.

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

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

14. 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

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

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

17. 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

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

19. LOW VISION OPTICAL DEVICES
FOR NEAR

20. MAGNIFYING SPECTACLES
Magnifying spectacles are the most commonly
prescribed LVAS and many patients achieve a high
degree of success with their use.
These are especially suited for near and intermediate
distance.
Optical principle. Magnification by a convex lens is
obtained by bringing the object within its focal
distance. An erect, virtual and magnified image is
produced.

21. Types and designs.
• When no distance prescription is required, half eye glasses
are preferable because they reduce the weight, thickness and
size.
• High-add bifocals or high-add trifocals can be used to read
large print at a great distance.
• Both uniocular and binocular spectacles are pre-scribed
depending upon the situation.
• Binocular spectacles prescribed usually vary in power from
+4 D with 6 base-in to +12 D with 14 base-in.
• Monocular spectacles consist of standard aspheric lenses
from +4 D to +20 D in 2 D increments and specially
designed microscopic and double lenses from +24 D (6X) to
60 D (15x).

22. 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

23. 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.

24. HAND MAGNIFIERS
Type and design .
• These are available from +4 to +40 D and even of
more power.
• Most patients accept 8, 12, 16 or 20 D depending
upon the task and degree of impairment.
• Their magnification is variable, since the power
varies with the distance between the object and
focal point of magnifier.
• The hand-held magnifiers should preferably have a
wide field, should be lightweight and should have
self contained illumination.

25. Visolett magnifiers
• are special types of hand-held
magnifiers that almost double the
spectacle magnification or approach
the magnification achieved by reading
without correction, diffusely increase
illumination and provide binocular
vision.
• They have a constant magnification of
approximately 1.8X. These are useful
as LVAS in high myopes.
• Visolett when combined with a
spectacle magnifier almost doubles the
magnification effect.
• This must be used with reading
glasses or at the near point of an
uncorrected myopia because the image

26. 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

27. 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

28. LOW VISION OPTICAL DEVICES
FOR DISTANCE

29. 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

30. 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
the objective is a positive lens
separated by their difference
of their focal length
Both eye piece and objective are
positive lens .
Separated by their sum of focal length
Resultant image is virtual and erect Resultant image is real and inverted.
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

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

32. Types and designs.
• Uniocular as well as binocular telescopes are
available.
• These can be either hand-held or spectacle-
mounted.
• The poorer the vision, the stronger is the the
telescope required. The maximum useful power for
the hand-held telescope is 8X and for the spectacle
type is 4x.
 Monocular telescopes are easy to carry and use.
They have a small but important place in low vision.
 Binocular telescopes give binocular vision.They
allow for a good grip, but are cumbersome to carry.
Moreover, if one eye is worse than the other, then a
binocular telescope offers no improvement in
viewing quality.

33. Indications for use are as follows:
1. Telescopic spectacle systems are used by a
limited number of patients on an intermittent
basis for sedentary distance viewing.
Telescopic systems are used when it is not
possible to obtain the magnification by moving
closer.
2. Hand-held and ring-style telescopes are
suitable for distance spotting, such as street and
bus signs, blackboards and wall menus.

34. 3. For near and intermediate tasks, one can focus the telescope for
near viewing by
(a) adding plus lenses behind the optics of the telescope,
b) adding plus lenses in front of the objective lens
c) increasing the tube length of the telescope.
Such types are called telemicroscopes.
• These are useful for tasks that prohibit close working distances and
require the hands to be free, such as viewing computer monitors,
drafting, artwork and typing.
• These can also be offered to patients as an alternative to reading or
writing when the patient is unable to maintain a close working
distance because of health, postural problems or tremors

35. 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

36. NON OPTICAL DEVICES

37. 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

38. • Natural light is the adequate lighting
for most low vision children; however,
artificial light allows better control of
illumination.
•Incandescent light of 60-75 W is
preferred because it provides a more
continuous spectrum than fluorescent
light
•Fluorescent light emphasizes the
'cooler' blue spectrum, which can
intensify glare.
Everyone, even those without low vision,
should avoid single-tube fluorescent
lamps without a diffuser because they
are intermittent and can cause eyestrain

39. GLARE REDUCING DEVICES and Contrast Enhancement
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)

40. 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

41.  Reading is aided by the use of a typoscope as a line guide and to
isolate the reading material by reducing glare from the surface of
white page.
 Lighting control is of great importance to enhance contrast and
reduce the glare. The type, position and intensity of the light source
should be monitored.
 Absorptive lenses in yellow for low-light environments and amber
for more intense lighting are good prescription options.
 It is also important to support daily activities with aids such as black
felt-tipped pen, bold lines and contrasting colours.

42. ELECTRONIC MAGNIFIERS
Electronic magnifiers available for use in low vision
include:
• Closed-circuit television,
• Large print computers,
• Low vision imaging system (LVIS; formerly
called as low vision enhancement system)
and
• V-max.

43. WRITING AND COMMUNICATIONDEVICES
Writing and communication devices include
• handwriting guides
• signature guides
• check guides
• bold line papers
• tactile or raised line paper
• felt tip pens or markers (black)
• inbuilt light pens.
Fibre-tipped pens with black ink provide best contrast while
writing.
The writing aids are quite useful for signature and cheque writing

44. READING STAND
Easy comfortable posture to the patient

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

46. SIGNATURE GUIDE

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

48. ORIENTATION AND MOBILITY LVAS
Orientation and mobility LVAS can be divided into primary and secondary aids.
I. Primary Aids
Primary aids include sighted guide, canes of various lengths and dog guides.
i. Canes include:
• Long canes: For those with severe vision loss when people have problems detecting
obstacles.
• Identification canes: Thin, light-weight cane positioned diagonally across the front of
the body. For those who can detect obstacles but need help for depth perception.
• Support cane: For those who need extra support to lean upon and stability when
walking.

49. ii. Guide dogs: Help to travel around safely and independently and are
most commonly Labradors and golden retrievers.
II. Secondary Aids: Electronic
These are used with the primary aids to provide additional information
like overhead obstacles and location of doorways.
i. Electronic orientation devices: Most popular is the Miniguide which
sends out ultrasonic beams and provides vibratory/auditory
feedback to the user when met with obstacle.
ii. GPS devices: Global positioning systems (GPS) verbally guide the
user along specified routes to destinations.

50. SENSORY SUBSTITUTE ASSISTIVE AND ADAPTIVE
DEVICES
 Auditory substitutions are talking books, reader
services and audio-descriptive devices.
 Tactile substitutions include Braille, paperless
Braille outputs and non-Braille tactile output.

51. NEW TECHNOLOGY LOW
VISUALAIDS

52. NEWER TECHNOLOGY LOW VISION AIDS
Advances in consumer electronics are also im-Proving quality of life for people with
low vision. These new advances are not a cure for all those with low vision but for
many people they offer options for portable, lower cost LVAS.
i. E-readers (kindle, i-pad):
• Portable and more affordable alternatives to CCTV.
• Allow users to adjust the font size and contrast settings of the display. Text-to-
speech functionally present and can read aloud to the user.
• Disadvantage: Cannot offer same level of magnification as CCTV.

53. ii.Smart phones and tablets: Both Apple- andAndroid-based smart phones
and tablets offer a Range of applications and built-in functions to help
people with low vision:
 Magnify: iRead, iLoupe and Magnify use the device’s camera and light
source to magnify and illuminate text; portable and less expensive
alternative to CCTV.
 Sight book: Digitally communicates vision changes to ophthalmologists
(wirelessly) by measuring visual function with a set of near vision tests.
 Map Quest: (Apple and Android phones) Provides voice-guided
directions and tells the driver when to turn.
 Voice interface: Siri, voice recognition system on i-phone , allows user
to check weather,Email or calendar without navigating series of icons.
Android-based phones also have voice recognition capability allowing
user to dictate texts/emails without typing.

54. Help when there is no cure

55. Thank you

56. Thank you
Thank you
Thank you

60. 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.

61. GALLELIAN TELESCOPE

62. KREPLERIAN TELESCOPE

64. 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

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

66. 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

67. 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

68. EYE DISORDERS AND LOW
VISION

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

70. ANIRIDIA
Tinted glasses and cap

71. ALBINISM
Typoscope
Dark glasses

72. CORNEAL DAMAGE
Multiple pin hole glasses Hand magnifier

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

74. a
β
Objective
Eye piece
F
GALILEAN TELESCOPE

75. βα
Objective
Eye piece
F
KEPLERIAN TELESCOPE

76. KEPLERIAN TELESCCOPE

77. TELESCOPE FOR NEAR