Week 2 - Dentist Visual Task Analysis Flashcards
Objectives of VTA:- (7 reasons)
Determines visual requirements for tasks:-
• Produces visual specification for tasks
• reducing visual load + increasing efficiency
• Avoids accidents with compromised vision
•Avoids expensive training of potential workers with inadequate visual capabilities
• Helps in design training procedures
• Also helps with prescriptions for optimal aids
• VTA considers non-visual factors, such as fatigue, seating, temperature, ventilation.
Factors determine Visual Efficiency:- (14)
- Adaptation effects (light / dark / glare)
- Time taken to respond
- Flicker (strobe effect)
- Position in visual field
- Viewing distance a) accommodation b) convergence
- Visual subtense of task detail (size / acuity)
- Motion of task
- Contrast of task detail
- Colour of task
- Clarity of task detail
- Stereopsis requirements
- Visual field requirements
- Hazards
- Training requirements
- Adaptation effects : light /dark adaptation:-
• Dark adaptation Not significant
- All work carried out in brightly lit consultation office
• Light adaptation is important factor, subjects with poor light adaptation operate inefficiently
- Glare can reduce efficiency
- Adaptation effects: What is Glare?
• Glare is light in the wrong place:
- The discomfort or impairment of vision experienced when parts of the visual field are excessively bright in relation to the general surroundings.
Two main types of glare?
• Disability glare. This prevents the detection of important details and causes serious loss of visual efficiency. Occurs when there is an area of high luminance close to the line of sight.
• Discomfort glare. This is the commonest type of glare: annoyance, but no serious loss of visual efficiency. It is often only apparent after prolonged exposure.
Glare - Classification by origin:- (5)
• Direct glare - when the origin is bright source (45 deg)
• Reflected glare - Light is reflected from specular or mirror like surfaces
• Adaptive glare: Range of luminance in visual field too great to be acceptable
•Successive glare: Occurs when subject moves from relative darkness to brightness or vice versa; the visual system takes time to adapt
• Veiling glare: Reflections are superimposed on object of regard
- Time taken to Respond (space scotoma)
• Dentist close to patient
• In static environment
• Space scotoma doesn’t exist
- Flicker
• Tools rotate at stroboscopic speeds
• Dentist must be aware of positions of their drill bit
- Position in visual field / visual field size
• Good oculomotor control is required
• Work requires exclusive foveal vision
• Working extensively in mouth: but other parts of visual field needed to locate equipment
- Viewing distance a) accommodation
• Near vision predominantly
• Distance vision may be needed when use of mirror:-
- 30cm from upper teeth
- 40cm from side of mouth
May need specific presbyopia correction for necessary range of vision
- Viewing distance b) convergence
• Due to close working distance on top teeth: good convergence amplitude required
• Dentists examine X-rays, just below eye level
- May be clipped onto operating lamp
• Due to large time spent near vision: large bifocal/trifocal segment may be required
- Visual subtense of task detail (size / acuity)
• Needs good acuity to see fine details of teeth
• Good visuomotor control to use small instruments in small space
- Motion of task
Little or no motion involved in task that the dentist is performing
- Contrast of task detail
• The contrast of the task detail may be low, especially when looking for subtle changes in tooth or gum colour.
- Therefore high luminance is required
• Operating lamp provides this illumination whilst being designed to minimise direct glare
- Colour of task
• Colour matching for dentists are important: selecting correct material colour to match filling/crown of px teeth
• Illumination of operating lamp should have high colour rendering index
• Ultra-violet light used for fillings: if viewed directly may cause distortions in colour perceptions for future patients
