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Sunday, December 6, 2015

LIGHT ON EYE AND VISION

Eye, Vision , Light
Eye is precious. And Vision is more precious. We must all take utmost care of both eye and vision.The main features of the eye and images of what might be seen in case of three most common eye problems we get afflicted with  are illustrated here. In a recently concluded international conference Lux Pacifica 2015 on Lighting held in Calcutta, a very interesting and revealing paper on the role of Lighting to Eye and Vision was presented by Prof. Warren Julian of Sydney University.It has evoked so much of interest in me that I thought of sharing it with you all to create awareness amongst all my readers. You will find below the excerpts from Prof. Julian's paper.




Main Features of Human Eye

An Idea of What might be seen

VISION THROUGH CATARACT


VISION THROUGH GLAUCOMA

VISION FOR DIABETICS

 Excerpts from Paper presented by Prof Warren Julian of the University of Sydney at Lux Pacifica 2015 held in Calcutta, November 27 to 29,2015 

Considerations in Design for the Visually Impaired

Emeritus Professor Warren Julian
Faculty Architecture, Design and Planning
University of Sydney
The University of Sydney Page 2
The extent of the visual field
60°
95°
Right eye
monocular field
Left eye
monocular field
Total field of
vision is 190°
Binocular
field is 120°
Left eye Right eye
Eyes looking ahead at a distant object


The University of Sydney Page 4
Partial sight / low vision
Partial sight (or low vision) refers to a permanent condition of
diminished visual performance which cannot be rectified by
routine refraction and which is intermediary between normal
vision and blindness.
Typically, even with best spectacle correction, the affected
person cannot read a newspaper at a normal reading distance
(400 mm) but often has no orientation and walking problems.
The clinically most affected visual function is often visual
acuity but can also be visual field and/or contrast sensitivity.
Although there is no generally accepted single definition of
partial sight, an uncorrectable central vision of the better eye
of between 0.3 (20/60) and 0.02 (20/1000) is the visual acuity
criterion most commonly used.
In many countries “legal blindness” is defined as
corresponding to a reduction of visual acuity of the better eye
to less than 0.1 (2/20). Thus, a part of the partially sighted are
legally blind.


The University of Sydney Page 5
Prevalence and incidence
In most developed nations, the prevalence of legal blindness
is in the order of 0.2%.
The incidence is about one-tenth of the prevalence; ie, the
incidence of legal blindness is in the order of 0.02%.
Statistics from the US suggest that, within the legally blind
group, only about 15 to 25% are found to be functionally blind:
ie, at least three-quarters of the legally blind population have
useful vision.
The group that has low vision and is not legally blind is about
3 to 4 times larger than the legally blind population. Thus, in
the US, the prevalence of visual handicap is about 0.8 to 1.0%
of the total population, and its incidence about 0.1%.
Converting for India (conservatively): 13,000,000 with low
vision with 1,300,000 new cases per year.
Around 70% are over 65 years, in developed nations.

The University of Sydney Page 6
Causes
Australia (Dowling, 1980)
cataract 38%
retinal deterioration 22%
glaucoma 21%
vascular conditions 8%
diabetes 7%
other 11%
This is for developed nations where the three major causes of
partial sight are diseases which usually appear late in life.
However, for the world’s population, the causes of blindness
change from the diseases of age to disease related to public
health, malnutrition, parasitic attack and accidents.
The 6 main causes of world blindness are trachoma (bacterial
infection), onchocerciasis (parasitic worm), blinding malnutrition,
cataract, glaucoma and trauma.
Retinitis Pigmentosa
Glaucoma

The University of Sydney Page 8
Near and distance visual acuity
F N P R Z   6/60
E Z H P V       6/44           
D P N F R                                     6/36
R D F U V                        6/30
U R Z V H                             6/24
H N D R U                                 6/19
Z V U D N                                               6/12
V P H D E
E H V D F
U H N Z R
6/6 N U Z F E                                                                  6/6
                        



Multiple handicaps
Age-related maculopathy and diabetic retinopathy. These
require high illumination but often less when cataracts develop
because intense illumination causes glare and constriction of
the pupil, further impairing vision.
Both glaucoma and age-related maculopathy are more
prevalent in the elderly and sometimes they occur within the
one eye. Both conditions often cause a need for greater
illumination but glaucoma medication pilocarpine causes
constriction of the pupil demanding more illumination.
Visual impairment associated with impairments in other
systems is particularly frequent in persons more than age 65
in whom sensory and physical disorders as a consequence of
aging become more prevalent.
Many aged partially sighted persons do not even identify poor
sight among their major problems, being overwhelmed by
other disabilities. These include cardiovascular, arthritic and
neurologic (hand tremor, sequellae of cerebrovascular
accidents). Hearing loss is also frequent.


The University of Sydney Page 13
Impact of low vision
Human beings are constantly involved in negotiations
between themselves and their physical and social
environments. Information is received by the senses: that
information is then processed — it is given meaning through
interpretation, organisation and classification.
Orientation and mobility involve becoming aware of the nature
and location of major features in the immediate environment
and being able to safely navigate while travelling purposefully
from one place to another.
Reading and writing are important in modern society and for
most individuals, even for private life (reading personal
correspondence, financial documents, labels, price tags,
telephone directories, etc.).
Participating in society involves interactions with and
observation of other human beings.


The University of Sydney Page 14
Impact of low vision 2
Visually-guided manipulative tasks include the preparation
and eating of food, performing household repairs and
maintenance, repairing and maintaining clothing, and selfgrooming.
Manipulative tasks can be an important part of
recreation, eg, sewing, knitting, carpentry, metalwork,
mechanical assembly, etc.
The appreciation of visual beauty necessarily becomes
restricted when there is visual loss.
Factors in addition to partial sight can affect the behaviour of
partially sighted people, including age, associated non-visual
handicaps, living conditions or occupations, age of onset of
the visual loss, intelligence, mental orientation, education,
motivation and training.
Partially sighted people can develop postural characteristics
which may seem unacceptable to the normally sighted
population. Such mannerisms as screwing up the eyes,
holding the head on one side, not looking at an individual
during conversation, always looking down when walking, etc.


The University of Sydney Page 15
Light lovers and haters
Light lovers are those who obtain better
vision by higher illuminances by two
means: improvement in visual acuity due
to higher E and greater depth of field due to smaller pupil
diameter. There can also be an improvement in contrast
sensitivity.
Higher E is only useful if glare, most particularly disability
glare, is controlled. Glare increases intra-ocular scatter,
reducing contrasts.
Light haters are those sensitive to photopic (normal) light
levels. They often have diseases affecting the receptors,
eg, retinitis pigmentosa and albinism. They often need to
wear dark glasses indoors to reduce luminances. Very
glare sensitive. More light is usually unhelpful

The University of Sydney Page 16

Design for seeing: common sense
We see only by contrast — brightness and/or colour contrast
Can see if critical detail is large enough (at resolution available)
Create contrast by using surface finishes (independent of light direction)
Allow/put light into scene so that extent can be seen unambiguously
Use pattern to reveal objects of importance, safety, etc. Door frame.
Do not use camouflage (eg carpeted stairs), vomit pattern carpets/vinyls.
Make edges obvious (we see by detecting edges)






































4 comments:

Panchalath Suriyothin said...

Thank you very much for the link of yours. I wish I could share a presentation of Prof Warren Julian which is of great relevance to our vision in my faculty very soon.
Phanchalath Suriyothin
Associate Professor
Faculty of Architecture
Chulalongkorn University
Bangkok, Thailand

Warren Julian said...

Thank you for doing that,

Suddhasatwa Chakraborty said...

Thanks a lot for sharing this

Fernando Deco said...

He visitado el blog y está excelente y aporta a la ciencia que tanto nos une

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