Standard Definition (WHO 1992)
Impairment of visual functioning in better eye
even after treatment and/or standard refractive
and VA of <6/18 to light perception
a VF loss of <100 from point of fixation
but who uses, or is potentially able to use, vision for
the planning/execution of task
0 6/6 – 6/18 Normal Normal Normal
1 <6/18 –
Low vision Low vision
2 <6/60 –
Low vision Blind
3 <3/60 –
Blind Low vision Blind
4 <1/60 - PL Blind Low vision Blind
5 No PL Blind Total
Anatomical changes in the visual organ caused by the disease of the eye
Functional loss that results from the visual disorder
Refers to vision related changes in the skill and abilities of the patient
Psychosocial and economic consequences of visual loss
Macula in the retina degenerates.
Area effected – macula
VISUALAFFECT LOW VISION AIDS
•Fuzzy & Decreased vision •Good Lighting
•Metamorphopsia •Use of Strong color contrast
•Poor Central Vision •Magnifiers
•Photophobia •Non optical device
•Poor Color Perception •Vision Reabilitation
•Better vision at night
Breakage of retinal blood vessels and leaks.
People with long standing diabetics.
Area affected – Retina.
VISUALAFFECTS LOW VISION AIDS
•Decreased visual acuity •Various illuminators
•Fluctuating Vision •Work under direct light
•Loss of color vision, visual
•Inability to accommodate,
Retinal pigmentary degeneration.
Rods of retina are slowly destroyed.
Area affected – Retina.
VISUAL EFFECTS LOW VISION AIDS
•Decresed visual acuity •Optical aids – telescopes
•Difficulty in night vision •Nightscopes
•Loss of peripheral field vision •Fresnel prism, visual field
•Photophobia •Use of filters
•Poor contrast sensitivity •High contrast letters
•Difficulty to adapt in changing
Aqueous humor does not drain normally &
excessive pressure is built within the eye,
resulting in damage of optic nerve.
Area affected – Optic Nerve.
VISUAL AFFECT LOW VISION AID
•Gradual blurred vision •Magnifiers depending upon
extent of v.f
•Haloes around light •CCTV
•Reduced peripheral vision •CPF lens to reduce glare
Opacification of lens causing less amount of
light to the retina, vision becomes hazy &
Area affected – Crystalline Lens.
VISUALAFFECTS LOW VISION AID
•Blurred vision •Close work use direct light
•Glare, difficulty in bright light •Use sunglass to avoid glare
•Diplopia •Stand magnifiers for near work
•V.F normal. Sometimes Reduction
in side vision
•Filters - amber, red brown filters
•Squinting and amblyopia
Retina is separated from its supporting
structures & receives no nourishment.
Blind area develops in area of detachment
Area Affected – Retina.
VISUALAFFECTS LOW VISION AIDS
•Flashers & Floaters •High illumination
•Visual acuity is decreased •Filters, CPF lens
•Micropsia •Magnification for both near &
•Color vision is impaired •Non optical aids
•Loss of visual field
•Photophobia & glare
Total or partial loss of pigments in the eye.
Characterized by light colored iris, eyebrows.
Area affected – Retina, macula.
VISUALAFFECT LOW VISION AIDS
•Decreased visual acuity •Dim illumination
•DV more effected than NV •Dense sunglasses
•Painful photophobia •Absorptive lenses
•V.F is normal •Telescope for DV
•Color vision is normal •Colored or pinhole type CL
Functional Effects of Low Vision:
Loss of central vision (eg. macular degeneration, toxoplasma scar
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.)
Problems with glare
Detailed history taking
Functional vision assessment
Defining goals of the patient
Trial & selection of LVD
Low vision device training
In the waiting area
On entering the examination room
Mannerisms of the patient
b. Living situation
c. General health
d. Other limitations
e. Family history
f. Previous low vision care
Difficulty in visual tasks
a. Distance visual tasks
b. Near visual tasks
c. Computer usage
d. Light sensitivity
e. Mobility issues
Color vision testing
Visual field assessment
Material required: Variable distance Log MAR
chart [ Bailey Lovie/ETDRS chart] for distance.
Continuous text or word reading chart for near
Setup: Normal room illumination
Start with better eye first
Allow change in head posture, eccentric viewing,
head movements etc.
Check monocular visual acuity followed by
Perform retinoscopy instead of auto refractors
Calculate just noticeable difference
Aim to improve the quality of vision
Purpose: To measure the ability to detect differences
a) Variable contrast fixed symbol size e.g. Pelli
b) Fixed contrast with variable symbol size e.g.
Generally checked binocularly in patients with low
If contrast sensitivity is impaired, then advice and
recommend the ways to enhance contrast in the living
Usually done with Farnsworth munsell d-15
Performed in ambient illumination
With appropriate correction
Can emphasis on using vibrant Colors in the
environment if required.
• Assess peripheral VF
• Checked in all 4 quadrants
• Quick and basic.
Low vision device:
It is a device that enables the patient to
improve his/her residual visual performance & helps to
attain functional vision for the particular task of
Categories of LVD:
b] Non optical
d] Assistive devices
BASIC PRINCIPLE : MAGNIFICATION.
Enlarges image on retina to stimulate more
Can be achieved in many ways
Optical / Angular
Relative Size Magnification:
Any activity of daily living in which the object
being viewed can be made larger (E.g. Large print
Relative Distance Magnification:
Any activity of daily living in which the distance
between the object and the viewer can be reduced
(E.g. moving closer to television)
Use of an optical system between the eye and the
object to make the object appear larger (E.g. Use of
a telescope to see a distant object)
Enable copying from the black board
Identifying street signs
Seeing traffic signals
Seeing bus numbers
Watching movies in theatre
Enjoying sporting events
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
Hand held monocular
Clip on design
Bioptic design: mounted on a pair of eyeglasses
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
Both eye piece and objective are
Resultant image is virtual and erect Resultant image is real and inverted.
Prisms are incorporated to erect the
Loss of light reduces brightness of
Loss of light is more in this system
Field quality is poor Field quality is relatively good
Magnification of a telescope is given by the formula M =
Telescopes can be used to focus near objects by
changing the distance between objective and ocular lens
Increasing the power of the objective lens
Prismatic ½ eyes
Hand held vs. stand
Illuminated vs. non-illuminated
5/20/2014APPROACH & ASSESMENT OF LVC-CME 62
Spectacle magnifier is a
spectacle mounted convex lens
This uses the principle of relative
Useful for prolonged reading
Short working distance
Useful for prolonged
Large field of view Inconvenient for spot reading
Binocularity is possible
with lower magnification
Limited range of magnification
Useful for other near
tasks such as writing
Not effective in constricted fields
5/20/2014APPROACH & ASSESMENT OF LVC-CME 64
A stand magnifier is a convex lens
mounted at a fixed distance from
Both angular magnification and
relative distance magnification are
Device of choice for tremors,
arthritis, constricted fields
Predictable focus Poor posture unless reading
stand is used
Device of choice for
Reduced illumination in case
of non illuminated sand
Portable Requires flat surface to keep
Variable eye to lens
Reduced field of view
5/20/2014APPROACH & ASSESMENT OF LVC-CME 67
A hand-held magnifier is a convex
lens that holds by means of handle
at various distances from reading
Suitable in patients with eccentric
May be self illuminated
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
Magnification varies from 3X to 60X
5/20/2014APPROACH & ASSESMENT OF LVC-CME 72
Relative size and larger assistive device
Glare, Contrast and lighting control device
Posture and comfort maintenance device
Hand writing and written communication device
Orientation and mobility techniques and devices
Sensory substitution device
Medical management and life skill device
Bold line note books and papers
Black ink bold tip pens
Soft lead pencil – 2B,4B,6B
Black cards with rectangular cut outs horizontally along the card
The patient can feel the empty cut out spaces and write
It is a rectangular piece of cardboard with steps on top
right corner which helps in identifying the currency of the
1st cut indicates Rs. 500, 2nd cut indicates Rs.100, 3rd cut
indicates Rs 50 and so on.
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
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
Closed circuit television
Monitor CCTV Portable CCTV Mouse model
5/20/2014APPROACH & ASSESMENT OF LVC-CME 83
5/20/2014APPROACH & ASSESMENT OF LVC-CME 84
BUDDY PLAYER QUICK LOOK ZOOM CLASSMATE READER
Mostly used chart for assessing near
acuity of a low vision patient.
It was developed at Minnesota laboratory
for low vision research.
1. Black letters on white background.
2. White letters on black background.
1. Reading Acuity
2. Critical Print Size
3. Maximum Speed
Measurement Of Reading Acuity
Measuring Reading Speed
It’s a continuous-text reading acuity
Each sentence contain 60 characters
printed in three lines.
It contains 19 different print sizes.
Its print style is similar to that found in
many newspapers and books.
The text is printed with high contrast.
Reading speed = 60*(10-errors)/(time
If more than 10 errors were made
then reading speed can be assumed
to be zero.
“Visually disabled are not fallen souls”
“Positive attitude towards them will make them
socially amicable, psychologically adjustable and
The unlimited opportunities and experiences
extended to them will make them physically fit
mentally alert and totally independent in the