Lecture 1 - Intro Flashcards
What is Low Vision?
Low vision can be defined as any chronic visual condition, not correctable by glasses, contact
lenses or medical intervention that impairs everyday function.
Low vision is one of three categories of sight, the other two being normal vision and blindness.
“Blindness” may be defined as the lack of any useful pattern vision.
Low Vision Aid (LVA) assessments aims to help the patient to:
- make the best use of remaining vision
- maintain independence
Types of Low Vision Aids include:
Optical LVAs:
* Magnifiers
* Telescopes
Non-optical LVAs (for example):
* Electronic Vision Enhancement Systems (EVES)
* Apps & software
* Lighting
* Tints
* Large print
* Talking books
* Environmental design features
* Sensory substitution
o Braille, Echolocation
o White canes
* Guide dogs
LVA assessments are carried out by:
Optical:
* Optometrists and dispensing opticians within the Hospital Eye Service (HES)
* In private practices for HES and Health Boards (local schemes)
* Private LVA assessments
Non-optical:
* Social Services
* Charities
Definition of blindness and visual impairment
Most countries set standards based on:
* Reduction in visual acuity
* Constriction of the visual fields
What are vision standards and what dont they consider?
Standards are necessary to evaluate the patient’s eligibility for benefits and welfare rights, to get a measure of health and social services required in a region and for epidemiological studies.
Vision standards usually do not consider:
Dark adaptation, colour vision, dynamic acuity and many others, although these are certainly deficits which might affect patients. In addition, people with the same reduced acuity levels or field loss may have very different coping abilities.
What is the description, and Max+Min VA for categories 0, 1, 2 and 3 (with Max+Min VF)
0 Normal 6/6, 6/18
1 Low vision-visual impairment<6/18 6/60
2 Low vision-severe visual impairment 6/60 3/60
3 Blind <3/60 1/60
≤10º around Central fixation
>5º around Central fixation
What is the description, and Max+Min VA for categories 4 and 5 (with Max+Min VF)
4 Blind <1/60 Light perception
≤5º around Central fixation
5 Blind No light perception
(NPL)
UK Definitions of blind
Blind: ” …so blind as to be unable to do any work for which sight is essential…”
Partial Sight: There is no legal definition of sight impairment. A person can be certified if they
are ‘…substantially and permanently handicapped by defective vision caused by congenital defect or illness or injury’.
Royal College of Opthalmologists: Group 1:
People who are below 3/60 Snellen
* Certify as blind: most people who have VA below 3/60 Snellen
* Do not certify as blind: people who have a VA of 1/18 Snellen unless they also have a
considerable restriction of the visual field
* In many cases it is better to test the person’s vision at one meter. 1/18 Snellen indicates a
slightly better acuity than 3/60 Snellen. But it may be better to specify 1/18 Snellen,
because the standard test types provide a line of letters which a person with full acuity
should read at 18m.
Royal College of Ophthalmologists: Group 2:
People who are 3/60 but below 6/60 Snellen
* Certify as blind: people who have a very constricted field of vision
* Do not certify as blind: people who have a visual field defect for a long time and who do not
have a very contracted field of vision. For example, people who have congenital nystagmus,
albinisim, myopia and other conditions like these
Royal College of Opthalmologists: Group 3:
People who are 6/60 Snellen or above
* Certify as blind: people in this group who have a contracted field of vision especially if the
contraction is in the lower part of the field
* Do not certify as blind: people who are suffering from homonymous or bitemporal
hemianopia who still have central VA 6/18 Snellen or better
What other points need to be considered when registering someone as blind?
How recently the person’s eyesight has failed? A person whose eyesight has failed recently may find it more difficult to adapt than a person with the same visual acuity whose eyesight failed a long time ago.
How old the person was when their eyesight failed? An older person whose eyesight has failed recently may find it more difficult to adapt than a younger person with the same defect.
Royal College of Opthalmologists: Partially Blind
- 3/60 to 6/60 with full field
- Up to 6/24 Snellen with moderate contraction of the field, opacities in media or aphakia
- 6/18 Snellen or even better if there is a gross field defect, e.g hemianopia or if there is a marked contraction of the visual field, for example, retinitis pigmentosa or
glaucoma
Definition of functionally blind and functionally sighted
Functionally Blind:
Can not see to read or write even with the help of LVA’s and can not move in unfamiliar surroundings without dog, cane or sighted guide
Functionally Sighted:
Visually Impaired but can read with LVA’s or visually identify objects and can move in unfamiliar surroundings without needing dog, cane or sighted guide
