3. Legal Blindness
◦ Best corrected distance visual acuity of CF-1MT or
worse in better eye
◦ Visual field of 10 degrees or less in the better eye
Low Vision
◦ Best corrected visual acuity worse than 20/60 in the
better eye(or) visual field of less then 10⁰ from the point
of fixation.
4. 1)Moderate visual impairment- best corrected VA
less than 6/18 to 6/60.
2)Severe visual impairment- best corrected visual acuity
of less than 6/60 to CF-3MTS (or) visual field diameter
of 20⁰ or less.
3)Profound visual impairment- best corrected visual
acuity of less than CF-3MTS to CF-1MT or visual field
diameter of 10⁰ or less.
5. 4)Near total vision loss- best corrected visual
acuity of CF-1MT or less.
5)Total blindness- no perception of light.
6. Loss of central vision
(visual acuity)
Loss of peripheral vision
(visual field)
Glare and contrast
7. Difficulty reading
Problems writing/
completing paperwork
Inability to recognize
distance objects and faces
8. Need for additional lighting
Problems with glare
Increased adjustment to changes
in illumination
Visual discomfort and fatigue
10. Location of scotoma important!
Generalized loss of visual field
difficult to compensate for
Mobility and independent travel
Reading may require adaptations
11. CENTRAL FIELD DEFICITS:
Macular degenerations, macular hole, diabetic
macular edema and ischemia, myopic
degeneration, toxoplasmosis , histoplasmosis,
phototoxicity, drug toxicity, focal or grid laser for
CSME, iatrogenic central and paracentral
scotoma.
12. PERIPHERAL FIELD DEFICIT:
Retinal dystrophies, RP , RD , PDR,
Glaucoma,Ischemic optic
neuropathy,Stroke,Trauma,Tumour,Panretinal
laser photocoagulation.
13. History/ intake
Visual acuity
Visual field testing
Pupils
Extraocular muscle testing
Refraction
Color vision and Contrast Testing
Ocular Health
17. Ishihara
Color Vision Testing Made Easy
D-15
Pelli-Robson
Vistech Contrast System
Mr. Happy
18.
19.
20. Enlarges image on retina to stimulate more retinal
cells
Can be achieved in many ways
◦ Relative Distance
◦ Relative Size
◦ Optical / Angular
◦ Electronic
23. Hand held telescopes
Mounted telescopes
Electronic systems
24. Spectacles
◦ Prismatic ½ eyes
◦ Full-field microscopes
Magnifiers
◦ Hand held or Stand held
◦ Illuminated or non-illuminated
Telemicroscopes
Electronic Devices
25. Magnifying devices work by increasing the angle
subtended by the object at the eye thus producing
an enlarged retinal image(angular magnification).
MP= RETINAL IMAGE WITH USE OF
INSTRUMENT/RETINAL IMAGE WITH OUT USE
OF INSTRUMENT.
26. Convex lenses are used as hand held magnifiers
or stand magnifiers.Here the object is located
between the first principal focus and lens gives
virtual,erect,magnified image for the eye.
As the object moves nearer to first principal
focus,the virtual image becomes larger and is
situated futher from the eye.
27. Field of vision depends upon size or aperture
of the lens and on eye lens distance.
Greater the eye lens distance smaller the field
of vision.
Conex cylindrical lenses which has no
refractive power or only a low converging
power in its long axis and high converging
power in cross section provides vertical
magnification of powers.
28. Galilean telescopes composed of convex
objective and concave eye piece, seperated by
difference of their focal length.
It produces a errect, magnified image.
It mainly acts by increasing angle subtended by
the object at the eye.
29. Astronomical(keplers) telescopes consists of two
convex lenses seperated by sum of their focal
lengths.
This system produces a magnified,inverted image.
Prisms or mirrors are used to invert the image.
30. Types & designs-
1)Binocular spectales
2) Monocular spectacles-standard aspheric lenses
from +4D to +20D in 2D increments
-specially designed microscopic and double lenses
from +24D to 60D.
3)Half eye glasses are preferable because they reduce
the weight,thickness & size for near vision.
31.
32.
33. 4)High add bifocals or high add trifocals can be
used to read large prints at great distance.
34. Cosmetically acceptable
Comfortable and easy to use
Both hands are free
Field of vision is large
Simultaneous vision for near & distance vision is
possible
Less expensive
35. Spherical aberations are created with high plus
lenes unless aspherical lenses are used.
Short focal length of high plus lenses makes the
patient hold print close to the eye thereby
illumination decreases.
36. Mainly used for near vision problem
Does not require accomidation to see the
image
Indications-
-for spot or short time tasks in patients with
field of vision reduced to 10⁰ or more.
-as auxiliary lens for finer jobs.
37.
38. Available from +4 to+40D
Their magnification is variable,since the power
varies with distance between the object and focal
point of magnifier.
These has wide field of vision,light weight, self
contained illumination.
39. Working distance is more
Accomidation is not required for reading
Easy to view eccentrically
40. Hand is not free.
Inconvenient and tiring
Reduced field of vision when compared to
spectacles.
Not useful in the absence of manual dexterity.
Need to be held at correct distance to obtain
maximum power.
41. Types & design-
-available in two forms
1)Prefocused
2)Focusable
-range in power from +4 to +60D.
-self illuminated devices available which
prevent glare.
-requires some accomidative effort.
42.
43.
44. Technically simple as they are prefocused and
rest on a rigid mount.
Choice for patients with hand tremors.
45. Small field of vision
Difficult to use if surface is not flat.
46. TYPES & DESIGNS:
Monocular telescopes- easy to carry and use
Binocular telescopes- offers a good grip,
cumbersome to carry. If one eye is worse than
other, these offers no improvement in viewing
quality.
47.
48.
49.
50.
51.
52. Telescopes can be either hand held or spectacle
mounted.
The poorer the vision, stronger is the power of the
telescope required.
The maximum power useful for hand held type is
8X and for spectacle type is 4X.
53. Telescopic spectacle systems are used for
intermitent basis for sedentary distance viewing.
Telescopic systems are used when it is not
possible to obtain magnification by moving closer.
Hand held and ring style telescopes are used for
distance spotting.
54. For near and intermediate tasks, one can focus
the telescope for near viewing by
a)adding plus lenses behind the optics of
telescope
b)adding plus lenses infront of objective lenses
c)increasing the tube length of telescope.
55. Reduction in the field of vision
Ring scotomas
Parallax and a decrease in the depth of focus
Not useful for ordinary distance viewing as
illumination decreases.
These are consider contravesial for driving
because of constricted fields.
56. Closed circuit television
Large print computers
Low vision enhancement system
57.
58. In this camera picks up the reading
material,magnifies it and displays it on the TV
screen.
CCTV magnifiers provide excellent contrast and
magnification(linear magnification electronically
upto 60x).
59. It provides a distortion free, brighter, magnified
image with enhanced contrast on a larger screen.
White letters on a black field helps in improvement
of image clarity
60. Expensive
Heavy
Difficult to move around
May be difficult for some patients to operate it.
61. Computer can provide enlarged print on the
screen through standardized or dedicated
software.
Software is also available to provide speech for
the computer.
62.
63. Recent advances in low vision rehabilitation
It comprises surgical implantation of
intraoccular telescopic aids.
Intraoccular low vision aids consists of special
lense that provides a 3x magnification in the
fundus of patients eye.
Resultant retinal image is perceived through
peripheral retina.
64.
65.
66. Absorptive lenses- used to reduce the glare and
dark adaptation time.
Especially used in patients with albinism.
Types- Tinted lenses
-Photochromatic lenses
-Polarization
-Filters
67.
68.
69.
70. Field expanders
used in patients with defects in peripheral
visual fields
Types- Fresnel prisms
-Gottlieb field expanders
-Reverse telescopes
-Hemianopic mirrors
71.
72.
73.
74.
75.
76. Approach magnification
Lighting
Contrast enhancement
Increasing the size of the object to be viewed
Personal items
Auditory aids
77.
78.
79. Electronic devices
Writing and communication devices
Medical assistive devices
Mobility assistive devices
Tactile substitute include Braille,paperlessBraille
outputs and non-Braille tactile outputs.
80.
81. Orientation and mobility training
Independent living skills training
Support groups
Braille instruction
Computer training
Genetic counseling