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)