Vision Screening Flashcards
What factors influence visual performance?
Visual capability of each participant
Task visibility
Psychological and general physiological factors
What are the intrinsic factors that contribute to someone’s visual capability?
Detection
Recognition
Colour discrimination
Depth perception
What is detection influenced by?
VF
Head/eye movements
Light threshold
Light adaptation
Flicker sensitivity
Contrast sensitivity
What is recognition influenced by?
Static VA
Time to view
Luminance
Contrast
Size/distance of target
What are the types of colour discrimination?
Comparative
Aesthetic
Connotative
Denotative
What is comparative colour discrimination?
Being able to tell the difference between colours and compare them
What is aesthetic colour discrimination?
Being able to tell which colours look good together
What is connotative colour discrimination?
Ability to derive meaning from colour
What is denotative colour discrimination?
Ability to assign meaning to colour (e.g. use to speed up a task)
What are the extrinsic factors of a task?
Size
Contrast
Colour
Time viewed
Illumination
Movement
How can a task’s visibility be improved?
Increase stimulus size
Use an optical aid
Optimise light levels
Eliminate glare and reflections
Use colour symbolisation
What is Grundy’s visibility indicator?
A tool to demonstrate the effect of task lighting
Can compare between consulting room and home - if there is a difference, task lighting should be improved
What is a nomogram?
Scale which allows determination of equivalent VA if object size and distance are known
What should be considered when using a nomogram?
Gives absolute acuity - only suitable for spot tasks
If prolonged task, consider acuity reserve
What do the national screening committee do?
Identify those at increased risk of disease/conditions.
Offer info, tests, and treatment to people who have a positive screening result.
Advise ministers and NHS about screening.
Support implementing new screening programmes.
Review existing screening programmes based on new research outcomes.
When can screening be justified?
Condition is common and disabling.
Condition has a recognised latent or pre-symptomatic phase.
Screening test is reliable, valid, repeatable, easy, sensitive, specific and low-cost.
Treatment is available on the NHS and there is an agreed policy on who to treat.
What are some examples of NHS screening programmes?
Pregnancy and newborn screening
Cervical screening
Breast screening
Bowel cancer screening
What is sensitivity of a screener?
The proportion of people with the condition who are correctly identified.
(those who fail the test AND have the condition)
What is a false negative?
Someone who has the condition but passes the test
What is the specificity of a test?
Proportion of people who are identified as having the condition when they don’t
(those who fail the test but DON’T have the condition)
AKA false positive
What is the aim of visual screening?
To identify people w/o sxs but have defective vision.
To detect those whose visual ability is below the required standard for the task/occupation.
Who should undergo visual screening?
Babies and children
At risk groups (e.g. diabetics, FH glaucoma)
Working adults (occupational)
When is neonatal vision screening carried out?
Within 72 hours of birth and 6-8 weeks
What is neonatal vision screening checking for?
Retinoblastoma
Congenital cataract
