Orthoptics I - Contrast Sensitivity

What is contrast sensitivity?

measure of how much contrast a person needs to see a target

What is the contrast threshold?

the level of contrast at which a light and dark pattern is first discriminated

What kind of gratings are used to measure CS?

sine-wave/sinusoidal: gradual changes from light to dark

What fraction of adult CS levels are present at birth?

1/30th

Describe CS development

rapid development in the first 6 months, with adult levels for low spatial frequencies present at 3 months
- development extends to 8 y/o

What are the two variables for measuring CS?

spatial frequency and contrast threshold

What does CS tests aim to measure?

contrast threshold over a range of spatial frequencies

Who has a higher contrast threshold for mid - high spatial frequencies?

children and the elderly

How can CS be implicated in ambylopia treatment?

CS will improve before VA

How is varying spatial frequency sensitivity represented on the retina?

different visual channels
- fovea: high acuity and high spatial frequencies
- periphery: low frequency channels

Describe the conditions a CS test is performed in

patient must be sat at the correct distance from the chart
result taken as the least contrast with positive identification
performed binocularly and monocularly
room must be well-lit
head must be straight
glasses on
do not test after any lights have been shone into the eyes

Describe the Pelli-Robson chart

16 letters in groups of 3, each letter per group has the same contrast
1m away from target
2/3 letters must be identified to move onto the next group

Describe VISTECH

two types: one for 1/3m and one for 3m
40 small circles with sinusoidal gratings at either-15degs, 0degs or +15degs
5 rows, 9 coloums
CS decreases from left to right
record result as least contrast discriminated for each spatial frequency

Describe the Bailey-Lovie chart

6m
logMAR
letters decrease in size at a consistent contrast
high and low contrast charts used in conjunction - start with high and go to low - is there a difference
normally, two lines LESS would be read on the low contrast chart, if more = loss in CS

Describe Cambridge low contrast grating chart

rapid and simple
6m
12 plates, stripes of varying contrast
plates sequentially changed until px fails to respond
4 series completed: score of each is noted and added and final total value converted using provided chart

Describe the Regan chart

3 letters with contrasts of 97%, 7% and 4%
3m
8 letters per line
continue until px fails to respond
letter size reduces but contrast remains the same

Describe the FACT chart

10ft
sinusoidal gratings with varying frequencies
5 spatial frequencies - columns, increasing from top to bottom
9 levels of contrast - rows, decreasing left to right
determine last grating seen for each row by identifying orientation of the grating
- plotted onto a CS chart

Describe the Arden plate

booklet with several sinusoidal grating patterns
vertical orientation
contrast varies from top to bottom (top = lowest)

Describe the Hiding Heidi

based on preferential looking
6 contrast levels: 100%, 25%, 10%, 5%, 2.5%, 1.25%
position at eye level, covering face with blank card
move blank card and contrasted face at the same time
observe eye movements - do they follow the face

Describe Lea grating paddles

preferential looking
57cm
frequency of black stripes (cycles per centimetre, cpcm)
- levels: 0.25, 0.5, 1, 2, 4 and 8
quick and mobile

Describe CSV-1000E

4 rows of sinusoidal gratings
2.5m
test the following frequencies: 3, 7, 12 and 18 cpd

Describe CSV-1000RS

used for screening refractive surgery patients
tested in logMAR alongside sinusoidal gratings
allows for vision and CS to be determined together

Describe CSV-1000S

cataract patient
tests: standard VA, spatial frequency gratings, real world simulation

Describe CSV-1000 CVA

assessing contrast sensitivity and low contrast acuity
3 contrast levels

Describe CSV-1000 Lan C

same as CSV-1000S but VA is expressed with landolt C
used for those with a language barrier

Describe CSV-1000-1.5 CPD

FDA trial
8ft
tests one spatial frequency at 1.5 cpd

How do we interpret CS test results?

logCS
higher the measurement, better the CS

Name some factors affecting CS

drugs (even ibuprofen)
toxic chemicals
pituitary adenomas
optic neuropathy
diabetic retinopathy
glaucoma
refractive surgery/errors
contact lenses
cataract
age

What are the clinical implications of low CS?

ambylopia
suspected optic nerve dysfunction
do they have difficulty with object distinguishment
cerebral lesions
demyelination
optic neuritis

What are some symptoms of low CS?

issues with night driving
needing extra light to read
tired eyes when reading/watching TV
not being able to see fine details
missing facial gestures

What spatial frequencies are impacted in strabismic or anisometropic ambylopia?

either all or high