This document discusses low vision aids for people with vision that cannot be improved through glasses, medicine, or surgery. It defines low vision as visual acuity of 6/60 or less, or a visual field of 20 degrees or less. It describes various types of low vision aids including magnifiers, filters, telescopes, and electronic devices that help improve vision by increasing size, contrast or field of view for activities like reading or distance viewing. It notes challenges of some aids like limited field or depth perception and discusses fitting the correct aid based on a person's visual needs and acuity.

1. Dr. K. Vasantha M.S.,F.R.C.S.
Director RIO Chennai (Rtd)

2.  Low vision aids are needed when the vision
cannot be improved with glasses, medicines
or surgeries
 People who have 6/60 vision or a field of <20
degrees in the better eye and are called
legally blind.
 People who have slightly better vision than
this are the ones best helped by low vision
aids

3.  Defective vision
 Field defects either peripheral or central
 Night blindness
 Slow glare recovery
 Photophobia
 Metamorphopsia
 Oscillopsia

4.  Linear magnifiers – Large print, CCTV
 Relative distance magnifiers – High adds,
hand held magnifiers ( either with handle or
bars which can be moved over the book),
microscopes or convex lenses mounted on a
stand
 High adds are very useful as it can be just
worn as ordinary spectacles

5.  Angular magnifiers – binoculars, telescopes
and video display system
These are used for defective vision

6.  Fixed level of magnification
 Reduced field
 Reduced depth perception
 Close working distance
 Tiresome to use for a long time

7.  Illumination control with filters like sun
glasses – cone dystrophy where the patient
will have severe photophobia
 Illuminated magnifiers
 Contrast enhancement – achieved with CCTV
magnifiers, or yellow filters
 Colored filters – to transform color contrast
to luminance contrast

8.  For automatic gain control,
 To correct abnormal light and dark
adaptation and glare recovery
 To improve contrast sensitivity

9.  Comfortable working distance unlike other
magnifiers
 Can be used for a long time comfortably
 Useful in tubular vision and for central
scotomas (here it will be difficult the patient
to reaffix to a newer object)

10.  Near vision binoculars are used for close
work
 Head mounted binoculars are used increasing
the field of view

11.  Telescopic systems increase the size of the
object projected on to the retina
 It can be used for far, near or intermediate
distances
 For this different telescopes must be used.
Auto focus telescopes are available but
expensive
 Useful when large magnifications are needed
 Working distance for near is comfortable

12.  Field of vision is very limited – so the person
has to keep on readjusting to see a different
object
 Depth perception is low
 Illumination will be low
 Good co ordination is needed
 Can be used only for spotting a distant object
while staying at one position

13.  In this telescope a convex objective lens and
a concave ocular lens are used
 It is small and light but has a limited view
 If the field is constricted then the lenses can
be reversed (convex lens close to the eye) to
increase the field to some extent

14.  Both objective and ocular lenses are convex.
The inverted large image thus produced is
made erect by using prisms.
 This telescope is longer, heavier and costlier
than the Galilean type

15.  Clip on lenses
 If one eye has a much better vision than the
other, monocular telescope can be used in
that eye alone
 Binocular lenses will increase the field and
can be used in nystagmus also

16.  Determine the best corrected vision – this will
be usually around 6/60
 Find out the patients requirements
 Calculate the magnification required
E.G. the magnification required for 6/60 will
be 60 divided by 6 = 10 this is divided by 4
(magnification unit for reading at 25 cm) =
2.5 times i.e. 2.5x

17.  Gaze contingent magnification system – to
improve face recognition for patients with
central scotoma
 Multiplexing prisms in the seeing eye to
expand the field of vision in one eyed
patients
 Finding the preferred retinal location in
bilateral central scotoma to direct the images
with prisms

18.  Camera based collision warning device. This
will help the patient to be more freely
ambulant than the white stick
 Sound of Fittle – this can be 3D printed. The
printed toy will have the name of the object
in Braille. The patient can feel the shape of
that particular object also. It is also like a
jigsaw puzzle.

19.  Portable electronic device
 A digital camera captures the image
 This is displayed on the user’s tongue as
electronic stimulation
 This gives rise to vibrations
 By the patient can perceive, shape, size,
location and motion of objects
 Helps in orientation and mobility

20.  Optometry and Visual Science Volume 95
September 2018
 Principles and practice of ophthalmology by
Albert and Jakobiec