This document discusses low vision aids and their use for people with low vision. It defines low vision as visual acuity between 6/18 and 3/60 in the better eye after correction, or a field of vision between 20 to 30 degrees. Common causes of low vision include macular degeneration, glaucoma, and diabetic retinopathy. Optical low vision aids like magnifying spectacles, hand magnifiers, and telescopes use magnification to improve vision. Non-optical aids include increased lighting, contrast enhancement, and electronic magnifiers. Proper evaluation and prescribing of low vision aids depends on the patient's needs, vision status, and motivation. The goal is to prescribe simple, portable devices to help low vision

1. LOW VISION AIDS
By
Capt Ayinun Nahar
Dept of Ophthalmology
Armed Forces Medical Institute

2. Definition
“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 .”
(WHO/PBL/93.27)

3. 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.”
(WHO : ICD-10 definition)

4. Visual dysfunctions
 Disorder
 Impairment
 Disability
 Handicaped

5. Visual dysfunctions
• Visual disorder
Deviation from normal visual structure by disease, injury
or anomaly affecting vision
• Visual impairment
Reduction of visual function results from the visual
disorder

6. Visual dysfunctions
• Visual disability
Reduced ability to perform a certain task
• Visual handicap
Non-performance of the tasks related to individual and
social expectation because of visual disability

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

8. Low vision Aids
An optical/non-optical device that improves or
enhances residual vision by magnifying the image of
the object at the retinal level.

9. Basic principle of LVA
Optical LVAs are based on the fact that with
sufficient magnification, the normal retina
surrounding the damaged central retina can be used
for central vision.

10. Types of magnification
Low vision aids make use of angular magnifications by :
– Relative size
– Relative distance

11. Angular : It is the apparent size of the object compared
with true size of the object seen without the device.
Angular magnification M = ω’/ ω

12. Relative size: By making the object appear bigger (no
accommodation required) eg. CCTV

13. Relative distance: By bringing the object closer
(requires good accommodation)

14. Indication
Children :
• Albinism
• ROP
• Congenital malformation
• Optic neuropathy
Yound Adult :
• Keratoconus
• Ocular injuries
• Late menifestation of congenital
malformation

15. Indication
Old age :
• Glaucoma
• ARMD
• Diabetic maculopathy
• Macular degeneration
• Retinal degeneration
• Chorioretinitis
• Optic atrophy
• Myopic degeneration

16. Types of LVA
• Optical devices
• Non-optical devices

17. Optical LVA :
• Magnifying spectacles
• Hand magnifiers
• Stand magnifiers
• Telescopes
• Intraocular low vision aids
• Other optical devices

18. Non-optical devices :
• Approach magnification
• Lighting
• Contrast enhancement
• Increased size object
• Electronic magnifiers ( CCTV, LVIS, V-max)
• Writing and communication devices
• Orientation and mobility LVAs

19. Magnifying Spectacles

20. Magnifying Spectacles
Optical Principle
• Magnification by a convex lens is obtained by bringing
the object within it’s focal length
• An erect,virtual and magnified image is produced

21. Magnifying Spectacles
• High plus lens is used to magnify the images
• Magnification is 1/4th the power of the lens.
• Suited for near and intermediate distance
• Monoocular or binocular

22. Magnifying Spectacles
Advantages :
• Hands are free
• Field of view larger when compared to telescope
• Simultaneous near and intermediate vision
• Can be given in both monocular and binocular forms
• More portable
• Cosmetically acceptable

23. Magnifying Spectacles
Disadvantages:
• Spherical aberration
• 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
• Illumination problem

24. Hand magnifiers
• Indicated for spot or short-time tasks in patient with field
of vision reduced to 10’ or more.
• Available from + 4.0 to + 40 D.
• Available in three designs:
– Aspheric
– Aplantic
– Biaspheric

25. • Advantages :
– Working distance is more
– Accommodation is not required
– Easy to manipulate for viewing eccentrically
– Some have light source which further enhances vision
• Disadvantages:
– It occupies both hands
– Not useful in absence of manual dexterity
– Field of vision is limited
– Need to be held at the correct distance

26. Stand Magnifier
• Forms a virtual image a short distance behind the lens
• The patient needs to place the stand magnifier on the
reading material and move across the page to read
• Has a fixed focus

27. • Advantages :
– Technically simple
– They are a choice for patients with tremors, arthritis
and constricted visual fields.
• Disadvantage :
– Small field of vision
– Too close reading posture is uncomfortable for the
patient
– Difficult to use if the surface is not flat

28. Telescopes
• Used to magnify distant objects
• Work on the principle of angular magnification
• Telescopes with magnification power from 2x to 10x are
prescribed

29. Optical 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

30. Types :
1. Galilean telescope
2. The astronomical (Keplar’s) telescope

31. • Advantages :
– Best possible LVA to enhance distant vision
• Disadvantage:
– Restriction of the field of view
– Depth perception is distorted
– Loss of light transmission
– Expensive and costly

32. Other Optical Devices
• Absorptive lenses
- Tinted lenses
- Photochromatic lenses
- Filters
- Polarization
- Corning CPF filters
• Visual field enhancement devices
- Fresnel prism
- Hemianopic mirrors

33. Approach Magnification
Partially sighted patients should be encouraged to move as
close as possible to the object

34. Illumination
Positioning
• To the side of better eye
• Moving light closer
Higher levels of illumination is required :
• macular degeneration
• Glaucoma
• Diabetic retinopathy
• Retinitis pigmentosa
• Chorioretinitis
Reduced illumination required :
• Albinism
• Aniridia

35. Contrast Enhancement
• Using a typoscope
• Contrast modification of visual environment

36. Relative size devices
• Large print material
• Enlarged clocks, telephones,
• Calendars, computer keyboards
• Large type playing cards

37. Electronic magnifiers
• Close-circuit television
• Low vision imaging system
• V-max

38. Writing and communication devices
• Writing guides
• Signature guides
• Check guides
• Notex
• Tactile or raised line papers

39. Sensory Substitute Assistive Device
• Auditory substitutions
-Talking books
• Tactile substitutions
- Braille
- Paperless braille output
- Tactile Braille output

40. Mobility assisting devices
Patients with low vision suffer a major problem of
mobility
• Long canes
• Strong portable lights

41. Newer technology
• Intraocular LVAs
• Keratoodontoprosthesis
• Bionic eye

42. Evaluation Of Low Vision
• History
• Visual acuity
• Colour vision
• Visual field analysis
• Glare and Contrast sensitivity
• Look for dominant eye

44. Prescribing LVAs
• Aim
• Simple, lightweight, portable and flexible
• Patient’s visual and mental status, needs, and motivation
• Working distance and field of vision decrese with an increased
magnification
• All the devices should be tried
• Both eyes should be corrected
• Careful consideration of children, old age and single eyed
person

48. Conclusion

49. THANK YOU