Contrast sensitivity is a measure of the ability to detect slight differences in luminance or color. It is tested using sine wave or square wave gratings that vary in spatial frequency and contrast level. Contrast sensitivity is a better predictor of visual function than visual acuity alone, as it can detect losses from conditions like cataracts, glaucoma, and AMD even before acuity is affected. Contrast sensitivity is measured using charts like Pelli-Robson, FACT, and Arden plates that test sensitivity across spatial frequencies. Many ocular and systemic factors can influence contrast sensitivity, including refractive error, age, cataracts, diabetes, glaucoma, and macular diseases. Contrast sensitivity testing provides additional information about visual

1. CONTRAST SENSITIVITY
Presenter- Dr. Sharmistha Mukherjee
PGT CNMC&H

2. Introduction
• Contrast:- is the degree of blackness of target
to whiteness of background.
• Contrast threshold:-is the smallest amount of
contrast required to be able to see the target.
• Contrast sensitivity:- is the reciprocal of the
contrast threshold.

3. What is Contrast Sensitivity?
• The ability to perceive slight changes in
luminance between regions which are not
separated by definite borders and is just as
important as the ability to perceive sharp
outlines of relatively small objects.

4. Snellen’s visual acuity versus
contrast sensitivity
• Person may have good VA in Snellen’s chart
due to very high contrast
• But vision drops in the situation of low
contrast in day to day work
• Hence contrast sensitivity is the better
predictor of vision

5. Gratings
• Equidistant & parallel lines or bars
• One adjacent pair of light and dark
bars makes up one cycle
• The thickness of the grating is
described by their spatial
frequency which expresses the
number of pairs of dark and light
bars subtending an angle of one
degree at the eye
• Units of SF is cycles per degree
(cpd)
ONE CYCLE

6. Sine wave gratings
• These gratings are lacking in
sharp borders
• Sinusoidal gratings are used
because they are not subject
to defocus aberration,
diffraction, light scatter

7. Square wave gratings
• Square-wave gratings
have characteristics
like a square such as
sharp edges
Red curve- Square wave
Blue curve- Sine wave

8. Contrast Sensitivity curve
CONTRAST
SPATIAL FREQUENCYLOW HIGH
LOW
HIGH
Human vision- intermediate spatial frequency range
Cat - low spatial frequencies
Falcon - high spatial frequencies

9. Contrast Sensitivity Function(CSF)
• The manner in which CS
changes as function of
spatial frequency of the
target is called CSF
• CSF has a peak value of
approximately 1 to 8
cycles/ degree.
• Distinction of high
frequencies not possible
because of limited number
of photoreceptors

10. Calculation of contrast sensitivity
1. MICHELSON FORMULA:(Lmax - Lmin)/(Lmax + Lmin)
Lmax = Luminance on the lighter surface
Lmin = Luminance on the darker surface
2. WEBERS FORMULA: ( Lb – Lt) /Lb
Lb-Luminance of the background
Lt- Luminance of the target
Weber contrast used in calculating the contrast of letters

11. Types of contrast sensitivity:
1. Spatial contrast sensitivity
2. Temporal contrast sensitivity

12. Spatial contrast sensitivity
• Detection of striped pattern at
various levels of contrast and spatial
frequency
• Sine wave gratings of parallel light
and dark bands
• Asked to tell minimum contrast at
which bars can be seen at each
frequency
• Width of the bar is defined as
spatial frequency
• High spatial frequency- narrow bars
• Low spatial frequency- wide bars

13. Temporal contrast sensitivity
• Temporal contrast sensitivity is measured with
gratings that reverse contrast at various rates over
time.
• Here contrast sensitivity function is generated for
the time related processing in the visual system by
presenting a uniform target field modulated
sinusoidal in time.
Both the system provides more complete and systemic
data on the status of visual performance.

14. Neural mechanism of contrast
sensitivity
• Campbell and Green gave the concepts that the
retina is not uniform.
• Fovea is specialized for high acuity and is
responsible for high spatial frequencies.
• In the retinal periphery, only low frequency
channels are represented.
• For coarse grating ,central and peripheral retina
have equal CS, but larger the retina is stimulated
greater is the CS. Thus CS is reduced in peripheral
retinal diseases & use of low frequency grating
provide rapid check of peripheral retinal function.

15. Contribution of M and P pathways
Ganglion cells divided into
– P- Cells :- small , slow conducting axons that input
into parvocellular layers of LGB
– M-Cells :- large , fast conducting axons that input
into magnocellular layers of LGB
• The M-cell information is biased to lower
spatial and mid-temporal frequencies. P-cell
information is biased to mid-higher spatial
and lower temporal frequencies.

16. Merigan and colleagues represent how the spatial and temporal
contrast sensitivity function is affected by lesions to parvo- and
magno-cellular regions of the LGN of the monkey.

17. Measurement Of Contrast Sensitivity
• Best possible optical correction
• Luminance must be kept constant
– Low luminance- low frequency falloff disappear
– High luminance- little change in shape of normal CSF
• There are three variables in measurement of contrast
sensitivity:
1. Average amount of light reflected depends on
illumination of paper and darkness of ink.
2. Degree of blackness in relation to white background
that is contrast.
3. The distance between the grating periods or cycles
per degree of visual angle.

18. • The various methods available to measure CS
include-
Pelli-Robson contrast sensitivity chart
Vision contrast test system (VCTS) by Visitech
Cambridge low contrast gratings
Arden gratings
FACT charts
Vector vision charts (CSV 1000)
Regan charts

19. Pelli-Robson contrast sensitivity charts

20. Visitech Contrast Sensitivity Test
• Sine wave
gratings
• Three
orientations:
vertical 90
degrees, 15
degrees
clockwise or
anticlockwise
• VCTS-6500 for
distance testing
and VCTS- 6000
for near testing
• 3m for distance,
40cm for near

21. Functional Acuity Contrast Testing(F.A.C.T)
• 2nd Generation Visitech chart
• Uses smaller step size

22. Cambridge Low Contrast Grating
• Performed at a distance of 6m
• Set of 10 plates & 1 page in each pair
contains gratings other is blank
• Shown in order of descending
contrast, stop when first error made
• Then a new series is begun starting 4
plates prior to where the patient
failed to respond.
• Four such series are completed and
the score of each series is noted
(numbered as per the number of
plate read) and added.
• The final total value is converted into
CS from conversion table.

23. The Arden Plate Test
• Introduced in 1978
• Studied at 57 cm
• Consists of a booklet containing 7 plates(1
screening, 6 diagnostic) with spatial frequency
increasing from 0.2 cpd to 6.4 cpd (each being
double the previous one)
• The contrast changes from top to bottom
• Score 1-20 for each plate

24. Factors Affecting Contrast Sensitivity
1. Refractive errors
2. Age
3. Cataract
4. Contact lenses
5. Refractive surgery
6. Glaucoma
7. Diabetic retinopathy
8. Optic neuropathies
9. Pituitary adenoma
10. Drugs
11. Toxic chemicals
12. Amblyopia
13. Corneal pathology (edema,
distortion)

25. Refractive errors
• Decline in contrast sensitivity first at higher
spatial frequencies for mild refractive
disorders
• As the degree of refractive disorder increases,
contrast sensitivity declines at middle to lower
spatial frequencies

26. Age
• There occurs a definite decrease in contrast
sensitivity with increasing age.
• The pathogenesis of this decline in vision is
likely involves changes in the spherical
aberration of the crystalline lens

27. Pupil size
• Miotic pupil- diffraction reduces CS
• Mydriatic pupil- optical aberration reduces CS

28. Cataract
• Early cataracts cause contrast sensitivity losses
similar to refractive disorders at higher spatial
frequencies
• The addition of glare source will exacerbate
the results
• Contrast sensitivity scores may offer
additional information over standard VA tests
in patients with early age-related cataracts

29. Glaucoma
• Reduce contrast sensitivity for all grating sizes,
mostly at the middle spatial frequencies
• Early progression of Glaucoma can be
measured with CS testing

30. Diabetic retinopathy
• Before developing DR, diabetic patient may
show lowering of CS
• PRP in PDR & macular laser in DME reduce CS
hence it is important to undergo CS testing
before photocoagulation

31. Age Related Macular Degeneration
• Patients with treatable macular diseases
should have CS testing as preoperative
evaluation to assess the effectiveness of
treatment
• CS testing indicates how far AMD has
progressed, so used as follow up test also

32. Amblyopia
•The reciprocal of the
contrast threshold is plotted
against the stimulus spatial
frequency
•The higher the spatial
frequency, the greater the
loss of sensitivity of the
amblyopic (red symbols)
compared with the fellow
fixing eye (blue symbols)

33. IOLs
CONTRAST
SENSITIVITY
MULTIFOCAL MONOFOCAL
CONTRAST SENSITIVITY AT
DISTANCE(1 ,3,6,12 AND 18
MONTHS)
CONTRAST SENSITIVITY AT
NEAR
L Cataract refractive surgery.2003apr;29(4):703-11

34. Contrast sensitivity and LASIK