Packet 1: low vision rehabilitation Flashcards
most common cause of low vision in the US is
macular degeneration
1 reason for hereditary vision loss is
retinitis pigmentosa
the definition of legal blindness in the US is based off what categories
visual acuity and visual fields
definition of legal blindness in the US is
- 20/200 or less in better seeing eye, best corrected
- less than 20 degrees of visual field in better eye
what does legal blindness definition NOT account for for other types of vision loss
- decreased contrast sensitivity
- visual distortion
- glare disability
- ocular motility deficits
do you have to be legally blind to have low vision?
no
what is low vision but not legally blind definition usually
20/70 or worse in the best eye based on most insurance criteria and medicare
ICD10 code “0”: mild or no visual impairment
equal to or better than 20/70
ICD10 code “1”: moderate visual impairment
- worse than 20/70
- equal or better than 20/200
ICD10 code “2”, severe visual impairment
- worse than 20/200
- equal or better than 20/400
ICD10 code “3”: blindness
- worse than 20/400
- equal or better than 20/1200
ICD10 code “4”: blindness
- worse than 20/1200
- equal to or better than light perception
ICD10 code “5”: blindness
no light perception
what is “any loss or abnormality of psychological, physiological, or anatomical structure or function”
impairment
what is “any restriction or lack of ability to perform an activity in the manner or within the range considered normal for a human being”
disability
does a visual impairment always cause a visual disability?
no
overview of case history in low vision
- chief complaint
- near needs/ abilities
- distance needs/abilities
- activities of daily living issues
- social history
- illumination and glare needs
- mobility needs
- job related needs
what is light projection (vs. light perception)
light projection= direction of light (better than LP only)
3 most common charts used in low vision
- Snellen
- EDTRS/ Bailey Lovie
- Feinbloom
what are some problems with using Snellen charts?
- may not have enough lines
- not enough characters per line (more so for higher acuity loss)
- projector charts may vary in contrast as background illumination changes
why is Bailey Lovie/EDTRS charts considered the Gold Standard?
- 5 letters in each row
- standardized spacing between letters and rows
- progression of letter sizes constant and follows log scale (log MAR)
- every 3 lines down on chart represents a change in acuity of 1/2
what is the highest level of acuity in Bailey Lovie/ETDRS
10/125
if patient has worse than 10/125, what do you do?
use Feinbloom chart or move in to 5 feet
pros/cons of Feinbloom chart
pros: numbers, portable, large type (700ft), generous spacing
cons: limited number of optotypes, psychological advantage (can guess)
what are some special things to include when you record low vision acuity
- type of chart used
- no + or - notation
- test distance where measured (so 10ft usually)
- note illumination conditions during testing
- style and efficiency of how patient read chart
what chart should you use if patient has central scotoma and has poor eccentric viewing skills
feinbloom chart with single optotype may be easiest
what strategy should you use to measure VA on a patient with overall reduced visual field?
start smaller (because larger optotypes may be out os patients field and unable to be fully viewed)
what are 4 ways to notate near visual acuity
- Jaeger
- Reduced Snellen (RS)
- Point size
- M units
what are some cons of Jaeger notation
- style and size vary from chart to chart
- no constant ratio between type sizes (not easily converted to standard notation)
- least useful of all the resting methods
pros/cons of reduced snellen
- same notion as distance snellen
- but reduced snellen assumes testing distance at 40cm so if any other distance, confusion begins
what is point size or N way of measuring near acuity
- used by school teachers, librarians, printers
- refers to the size of the printing press letters are set in
- not an exact system of recording VA (no good)
what is the “N system” way of recording near acuity
“British N”
- variety of point size notation using Times Roman
- ex: N16 at 30cm
the gold standard for near acuity is
Metric (M) notation
how is metric (M) notation work and how is it recorded
- standardized for test distance of 1 meter
- M notation is linear (follows logMAR)
- record test distance in meters over M size
types of near vision charts that can be used
- lighthouse cards (used the most)
- reduced snellen (bad)
- SK read
- MN read
what are some unique things about SK read (Smith-Kettlewell reading test)?
- determines critical print size, magnification requirements, scooters interfering with reading
- can be used as a training tool to promote awareness of scotoma location
what are some unique things about MN read (minnesota low vision reading acuity charts)
-used to assess how reading performance depends on print size (max reading speed, critical print size, reading acuity)
what can you use to plot a person’s contrast sensitivity function?
detailed contrast sensitivity measurements that include both size (spatial frequency) and contrast
your CSF is essential a plotting of the curve that defines the:
lowest contrast sensitivity level you can detect for each spatial (size) frequency tested
what spatial frequencies must have significantly higher contrast to be detected by the human visual system?
higher spatial frequencies (sine-wave gratings with very thin bars)
normal contrast sensitivity function is ___%
2-3%
at 2.5-5% CS function, patient would have difficulty with:
determining facial expressions, recognizing friends, detecting curbs and drop offs
at 10% CS function, patient would have difficulty with:
detecting changes in surfaces, black and white photographs, water on the floor
at 25% CS function, patient would have difficulty with:
safe mobility, night driving
what is considered a functional impact of contrast acuity?
greater than 2 line loss on low contrast acuities
