Week 1 - Visual Efficiency

Question 1

What is ergonomics?

Answer 1

Scientific discipline concerned with human interactions with others or systems in carrying out purposeful activity
- Improves human wellbeing and compatibility
- First developed after ww2

Question 2

Why do optoms need to be aware of ergonomics?

Answer 2

• Consider environmental and occupational needs of patients
• Screen patients for ocular abnormalities

Question 3

Posture hints with monitor:-

Answer 3

• 15-30° below eyesight
• No light shining in eyes/screen
• Forearms + thighs 90° from spine

Question 4

3 focus points for Visual ergonomics:-

Answer 4

• Visual performance
- Illumination
- Glare
•Visual comfort
- Light intensity
- colour rendering
• Visual environment
- Shadiness
- Direction of light
- Light colour

Question 5

Difference between night day + cells in retina:-

Answer 5

• Difference between night/day is 10^11 fold change in intensity
• Cones: 6-7million (red 64%, green 32%, blue 2%; small receptive fields
• Rods: 120million rods; not sensitive to colour; large receptive fields

Question 6

Cellular Receptive field facts:-

Answer 6

• Receptive neuron field is a region where presence of stimulus alters firing of neurone
• “On centre”
- Inhibiting surround, excitatory centre
• “Off centre”
- Inhibiting centre, excitatory surround

Question 7

Pupil and light adaptation:-

Answer 7

• Pupil diameter determines amount of light illuminates retina
• Age reduces pupil diameter (senile miosis)
- Reduces overall level of light, reducing ability to cope with different levels of light

Question 8

What age factors influence on light adaptation?

Answer 8

• Transmission through lens decreases due to ocular media opacification
• Retinal changes; AMD
• Elderly have problems adapting to night
- Differences in adaptation between young/old differ by factor of 100-1000

Question 9

define light adaptation, who is it important for and what it can be affected by:-

Answer 9

• Light adaptation: quick adaptation of the eye to the background illumination in order to be able to distinguish objects in this background.
- Changes in contrast
- Can either be dark>light or light>dark
• Important for sailors, military, drivers
- Dark adaptation affected by; Retinitis pigments and Vit A Deficiency

Question 10

Time taken for a visual response:-

Answer 10

• Space scotoma
- Partial alteration in visual field with degradation of visual acuity that is surrounded by normal acuity. Blind spot is example.
• 0.1 second for brain to see image and project a visual sensation, therefore pilots traveling 150ft in 0.1s will have a space scotoma of 0.1s/150ft

Question 11

What is flicker:-

Answer 11

• Critical flicker fusion frequency is highest temporal frequency that can be resolved (Hertz)
• Ferry-porter law:- CFF is proportional to log of luminance of flickering stimulus

Question 12

Flicker examples:-

Answer 12

• Driving with flicker through sunlight through array of trees
• Elderly people who have smaller pupils: less prone to flicker
• Rotation of machinery at more than CFF can blur rotating blades into invisibility
- Stroboscopic effects between lights sources and machinery may occur
- Neutral density filters could reduce the apparent flicker

Question 13

Position in visual field/visual field size:-

Answer 13

• Must scan visual field to place fovea on object
• Normal human VA: 60 deg nasally, 100 deg temporarily, 60 deg above, 75 deg below
• UK minimal requirement is 50 deg either side vertically, and 20deg above and below
• The macula: Central 13 deg of visual field
• The fovea: Central 3 deg of visual field

Question 14

Viewing distance is affected by:-

Answer 14

• Depends on accommodation and convergence
• Accommodation amplitude falls with age
• Accommodation response is slow

Question 15

Viewing distance definition:-

Answer 15

• Weston devised a system for specifying distances, based on demands of accommodation and convergence
- Teloramic (d>2) (D<0.5)
- Mesoramic (2>d>0.25) (0.5<D<4)
- Ancoramic (d<0.25) (D>4)

Question 16

Visual Classification of task detail:-

Answer 16

Classification:-
• Large : >12’ : 6/72
• Medium : 4’-2’ : 6/12 to 6/24
•Small: 2’-1’: 6/6 to 6/12
•Very small: 1’ : >6/6 (magnification)

Question 17

Contrast:-

Answer 17

Contrast = Lmax - Lmin/ Lmax
• Object contrast is reduced in foggy weather, snowy conditions and rain or at night

Question 18

Clarity:-

Answer 18

• Clarity related to image sharpness
• Poor lighting impairs the perception of small details
• Poor weather can affect clarity of drivers

Question 19

Task surround:-

Answer 19

• Larger light area surrounding a task gives better visual efficiency than a small surround

Question 20

Colour of task:-

Answer 20

• Colour vision is important for recognition of traffic lights or road signs
• Accurate matching of colour in paints, fabrics, vegetables requires excellent colour discrimination

Question 21

Motion vision is measured as:-

Answer 21

• Dynamic Visual Acuity:- DVA: Ability to perceive lateral motion and motion in depth
• Dynamic VA is lower than static visual acuity

Question 22

Stereopsis Task Requirements examples:- (2 total)

Answer 22

• Monocular vision - problems:
pouring coffee
• Binocular vision:
positioning large objects with a crane.

Question 23

Visual field requirements for driving tips:-

Answer 23

• Good peripheral vision is essential for driving.
• A restriction of the visual field can never be fully overcome.

Improved by:-
• Head and eye movements and adding extra mirrors to the car can help.

Reduced by:
•Artificial reductions eg: thick spectacle frames and car design.
• Pathological: Glaucoma, retinitis pigmentosa, cataracts may cause problems.