Optical low vision devices for near.. It includes both electronic and non electronic optical devices.. CREDITS ; Aarju Singh

1. Low Vision Devices For
Near
Presenter
Aarju Singh
3rd year B.sc optometry

2. Def of Low Vision
According to WHO :- a person with low vision is one
who
 Has a impairment of visual functioning even after treatment
and /or standard refractive correction
 Has a visual acuity less than 6/18 to light perception
 Or visual field less than 10 degree from the point of fixation
 But who uses , or is potentially able to use, vision for
planning and/or execution of a task.

3. LOW VISION AIDS
The assistance given to the LV
patient to maximize the
functional level of vision by
optical or non- optical means is
called LV aids .
The optical device can be used
for distance and near .

4. Near Optical Devices :- are used for
close-up, detail viewing, such as reading,
writing, and sewing.
It includes :-
 Spectacles Magnifier
 Magnifiers :- Hand and Stand magnifier
 Magnifying reading Glasses
 Clip - on loupes
 Telemicroscopic Glasses
 Electrical devices :- CCTV, HMD

5. Spectacle magnifiers
 High plus reading glasses to magnify the images
 Given as an add to the best distance refraction
 Used for Near work

6. Contd…
 Amount of add needed depends on the accommodation and
reading distance
 Reading add can be predicted using the kestenbaum rule i.e
the amount of add needed to read 1M print is the inverse of
VA fraction
 However usually greater add is required than predicted as
the patient also has reduced contrast sensitivity

7. Contd…
 If the patient is monocular ,the poorer eye may be occulded
if it improves the functioning
 When binocular correction are needed :-
base in prism are added to compensate for
convergence angle.
Optical center may be decentered.
 Aspheric lenses may be used to reduce lenticular distortion

8. 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 accepatble

9. Disadvantages
 Higher the power ,closer the reading
distance
 Closer reading distances causes fatigue
and unacceptable posture
 Patient with eccentric fixation are unable
to fix through these glasses

10. Magnifiers
 Useful for near work
 By keeping at near and distance ,we can
achieve different magnification
Two types :- Hand magnifier
Stand magnifier

11. Hand magnifiers
 It consist of a convex lens surrounded by
a plastic or metal carrier attached to a
handle .
 For maximum magnification with hand
magnifier place the object at the focal
point.
 The distance from a hand magnifier to
the printed page must be kept constant .

12. Contd…
 To find this distance start the lens on
the page and slowly pull it away from
the print until optimal focus is reached.
 It should be used with distance glasses
 If the material is brought closer to your
eyes , bring the reading material closer
as well.
 Available from +4.0 to 68.0 D (1x-17x)

13.  Available designs
- Aspheric – reduces thickness and peripheral distortion
- Aplantic – flat and wide distortion free field and good clarity.
- Bispheric – eliminating aberrations from both surfaces.
 Most patients accept upto 6x magnification
Contd…

14. Advantages
 The eye to lens distance can be varied.
 Patient can maintain normal reading distance
 Work well with patient with eccentric viewing
 Some have light source which further enhances
vision
 Easily available ,over the counter

15. Disadvantage
 One hand tied up
 Difficult to held steady in proper position
at all times
 Limited FOV ,depends on eye to lens
distance
 Patient with tremors ,arthritis etc have
difficulty holding the magnifier

16. Stand Magnifier
 Magnifiers are stand mounted
 Patient needs to place the
stand magnifier on the reading
material and move across the
page to read
 Has a fixed focus

17. Types
 Variable focusable stand magnifier :- Have
lenses that can be adjusted closer to or
farther away from the material .
 Fixed focus stand magnifier :- lens at fixed
distance from the base.

18. Advantages
 Do not have to hold
 Can slide across page
 Constant lens to page distance
 Inexpensive and easily available
Disadvantages
 FOV is reduced or limited
 To close reading posture is uncomfortable for the pt
 Block good lighting unless self illuminated
 Heavy , fatigue problem

19. Magnifiers Reading glasses
 Allow an individual to read for longer periods of time
 Also called as “microscope”
Advantages
 Wide field of view
 Portable
 Hands are free
Disadvantages
 Holding things very close

20. Clip-on loupes
 Clip-on loupe attaches to glasses and allow
the person to be hands free while viewing
text , computer screen etc.
Advantage
 Hands are free
 Convenient and easy to use flip
 Inexpensive
Disadvantage
 For larger loupe , they may heavy
 distracting

22. Telemicroscopic Glasses
 Eyeglass mounted telescopes
can be made to focus at any
WD.
Advantages
 More comfortable working
distances
 Hands are free
 Have excellent optics

23. Disadvantages
 Smaller FOV
 Reading difficulty especially if a book is
heavy ,reading longer period of time
 Image may be some what dark
 Feel heavy on your nose
 Expensive

24. Electrical devices
CCTV
 An electronic magnification
system for reading and writing
 Consist of 3 major components
camera
monitor
movable reading platform

25. Contd..
 It provide excellent contrast and magnification ,color .
 Magnification upto 60x .
Advantages
 Provides distortion free ,brighter ,magnified image
with enhanced contrast on a larger screen .
Disadvantages
 Expensive , heavy and difficult move around .
 Difficulty in operation for patient .

26. Head –mounted Display
 It is display device ,worn
on the head or as a part of
a helmet ,that has a small
display optic in front of
one (monocular HMD) or
each eye(binocular HMD).