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)
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
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
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
42. Evaluation Of Low Vision
• History
• Visual acuity
• Colour vision
• Visual field analysis
• Glare and Contrast sensitivity
• Look for dominant eye
43.
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
Reading distance is calculated by 100 divided by add
Most patient accept 8,12, 16 or 10 D depending upon the task and degree of impairment. Most patients accept upto 6x magnification
Field of view decreases with magnification
lenses of large aperture and short focal length
Lost cone functions (
Masking device with a line cut out from an opaque, non reflecting black plastic or thick paper.
Larger object subtends a larger visual angle at the eye and is thus easier to resolve
CCTV has control for brightness, contrast and change of polarity
LVIs- autofocal camera,magnification optics,contrast enhancement electronics…. V-max – color camera,liquid crystal display
Bloom portable light
removal of a tooth from the patient or a donor.[2] After removal, a lamina of tissue cut from the tooth is drilled and the hole is fitted with optics. The lamina is grown in the patients' cheek for a period of months and then is implanted upon the eye.
Trachome,Chemival burn, Graft failure, stephen johnson syndrome.
Peripheral field: using Humphery or octopus perimetry,Central field: using Amsler grid
dominant eye by testing contrast sensitivity monocularly and binocularly
Beily lovie logmar distant acuity and reading chart
Left column metric notation . Vision is distance divided by this.
Next column gives the snellens equivalence
Right column log units
