Non optical devices and viewing strategies Flashcards
what is a non optical device
Any device other than a magnifier that enables VI individuals to function more easily
what is the most important non optical aid and how many % 0f LV patients only require this
- lighting
- 10-20% of low vision patients need only a GOOD REFRACTION and ADVICE ON LIGHTING’’
i.e. if a patient uses the right amount of lighting that may not need an LVA and may only need to use their glasses
what is the definition of Luminous Flux and what is it measured in
Amount of light emitted by a light source
Measured in Lumens
what is the definition of Luminous Efficacy
Ratio of the light output (lumens) to the energy input (watts)
what is the definition of Illuminance and what is it measured in
The quantity of light per unit area hitting the working surface or task.
Measured in Lumens per square metre (Lux)
what is the definition of the inverse square law
and what happens as the distance of the light source to the object doubles
Illuminance of an object is inversely proportional to the square of the distance of the light source from that object
As distance doubles area illuminated increases fourfold, but illuminance decreases by a factor of four
i.e. if the light is brought closer, the illuminance decreases in area, but the light hitting the surface increases/is more intense
what is the definition of luminance and what is it measured in
explain when this is used and what implications it can have
The intensity of light (brightness) emitted or reflected in a particular direction by an area which is either self luminous, or is reflecting incident light
Measured in Candelas per square metre
important when we look at computer screens as its reflecting light or in the clinic when are measuring va’s.
we may be using a computer screen or a custom made chart, so the luminance of the chart is very important because if its very low, the patient will struggle to read off the chart, given inaccurate va’s so the luminance of the chart should be at least 150 candelas per metre squared
what is colour appearance characterised by and what it is measured in
- characterised by colour temperature
- 7,500 kelvin colour temperature appears bluish (cold)
- 2,700 kelvin colour temperature appears yellow (warm)
what does colour rendering describe and what colour index value reveals a colour well
describes the affects of a light source on the colour appearance of objects as compared with their appearance under a natural light source
the colour rendering index is between 80 and 100 reveals a colour well
describe what general lighting is and what task lighting is
General lighting:
can be in a room e.g. a sitting/bedroom
lighting may be attached to a roof or walls or free standing
Task lighting:
near a telephone to help with dialling, lights in a cupboard, under the stairs
light will be strategically placed in different places
list the 5 different types of lamps
- Tungsten or GLS
- Fluorescent
- Compact fluorescent
- Halogen
- LED
how is light produced by a tungsten or GLS lamp and what is a advantages (2) and disadvantages (3) of this lamp
- light is produced by heating a tungsten filament
advantage:
- cheap and full light output when switched on
- can also dim/brighten the light using a dimmer switch
disadvantage:
- produces too much heat
- doesn’t last very long
- expensive to run and is energy inefficient
what is the advantages (4) and a disadvantage (1) of a fluorescent lamp
advantage:
- 5x more efficient than a tungsten bulb
- is cheaper to run
- does not get very hot
- lasts a long time, 8x more than tungsten
disadvantage:
- not easy to dim/brighten
what is a advantage and a disadvantage of a compact fluorescent lamp
advantage:
- can bend fluorescent tubes into different shapes = more compact
disadvantage:
- takes time for light to become brighter when switched on, no good for VI patient e.g. when using a staircase
what is the advantages (4) and disadvantages (2) of a halogen lamp
advantage:
- more efficient than tungsten
- comes on instantly when switched on
- reasonable price
- can attach a dimmer switch on them
disadvantage:
- less efficient than a fluorescent lamp
- produces lots of heat so uncomfortable when close
what is the advantage and disadvantage to LED lamps
advantage:
- cheap to run and lasts long
disadvantage:
- expensive to buy (but then lasts longer)
how does visual performance improve
how much light does a 60 year old retina receive compared to a 20 year old
- Performance increases with improvements in task illuminance
- 60-year-old retina receives one-third the amount of light that reaches the 20-year old retina (Weale,1961)
even if not visually impaired, need more light to see
list 5 things that can be done to optimise lighting for VI patients
- Increase general ambient level of illuminance
- Providing enhanced illumination for detailed tasks in a localised area (task lighting)
- Localised lighting not only while reading but also for other tasks such as over telephone, under wall mounted kitchen cabinets etc
- Carry torch when ambient lighting is poor
- Lighting for outdoor mobility
list 3 things that can be done to optimise light by Increasing general ambient level of illuminance
- Draw curtains well back, clean curtains regularly and avoid use of net curtains
- Paint house walls with light colours
- Use fluorescent fittings
list 3 things that can be used to optimise light by increasing lighting for outdoor mobility and which type of eye condition will this be beneficial for
- Mobility lights
- Wide-Angle Mobility Light (WAML)
- Night Vision Scopes
beneficial for retinitis pigmentosa
what is a disadvantage of Wide-Angle Mobility Light (WAML)
need to carry a battery pack to use them, which is heavy and impractical
how do Night Vision Scopes work
they work from IR radiation to help see in the dark
explain how ideal localised lighting should be used
- Place lamp in front of face, with shade arranged so that there is no light shining directly into the eyes
- Lamp should have flexible arm with heavy base
so can adjust the distance between the light source and e.g. the book - Light should NOT be at eye level, but should be placed BELOW eye level to avoid glare
- Do not recommend tungsten or halogen bulbs for this, it is better to use fluorescent bulbs
when does photophobia occur
when theres something wrong with the eyes e.g. uveitis and can’t look at bright light
which 2 classifications of glare is there and list the 3 types of glare and what causes them
which types of patients suffer from glare
- physiological/pathological
- Discomfort Glare: bright sunny day, VA is still the same
- Disability Glare: causes reduction in VA due to it being very bright, this tends to happen in VI people
- Reflection Glare
what can you use to quantify glare clinically and objectively
explain how to use this
- brightness acuity tester
Method:
- get px to read snellen chart
- then give them the brightness acuity tester
- the instrument produces different glare sources
- if the patient stars of to read 6/6 and then you give the BAT and dial a particular glare source
- then see what the px reads on the snellen chart
- if glare has no effect on px, then va will be the same
- if glare gives them a problem, then va will be reduced
- it is a good test for a cataract px
- can implicate surgery
list 7 things that can be done/used to decrease or eliminate glare
- Changes in the environment
E.g. Move child away from Blackboard
Use matt instead of gloss - Visors and shields
- Glasses with multiple pinholes
- Artificial Iris Contact Lenses (e.g. for albinism)
- Typoscopes (cut off glare from a page)
- Tints for discomfort glare
- Tints for disability glare