Contrast Sensitivity

Question 1

What is illuminance?

Answer 1

The amount of light landing on a surface

Question 2

What is luminance?

Answer 2

The amount of light coming from a surface (emitted or reflected)

Question 3

What is the contrast threshold for photopic conditions?

Answer 3

2% difference

Question 4

What is the contrast threshold for scotopic conditions?

Answer 4

14% difference

Question 5

What is the high-frequency cut-off of the CSF?

Answer 5

60 c/deg

Question 6

What is the low-frequency roll-off of the CSF?

Answer 6

0.3 c/deg

Question 7

What’s the peak frequency of the CSF?

Answer 7

3-6 c/deg

Question 8

Why does the high-frequency cut-off occur?

Answer 8

Optics of the eye limit the detail that can be resolved

Question 9

Why does the low-frequency roll-off occur?

Answer 9

Lateral inhibition (objects so large that they inhibit receptive fields of surrounding retinal cells)

Question 10

What factors affect CSF?

Answer 10

Age
Optics of the eye
Retinal illuminance
Retinal eccentricity
Receptive fields
Pupil diameter
Spatial frequency channels

Question 11

What is a spatial frequency channel?

Answer 11

Different areas of sensitivity to spatial frequency which together make up the CSF when combined

Question 12

What does a Fourier analysis do?

Answer 12

Separates the CSF into SF channels

Question 13

What charts can be used to measure contrast sensitivity?

Answer 13

Pelli-Robson
Low contrast Bailey-Lovie
Vistech

Question 14

What pathologies can affect the CSF?

Answer 14

Cataract
Diabetic retinopathy
Retinitis pigmentosa
AMD
Glaucoma
Optic neuritis/atrophy
Uncorrected refractive error
Keratoconus
Iritis
CLs
Recovery from refractive surgery
Amblyopia

Question 15

What can low contrast sensitivity affect?

Answer 15

Facial recognition
Reading
Mobility
Viewing low contrast objects

Question 16

How can the issues caused by low contrast sensitivity be helped?

Answer 16

Improved lighting
CCTV system with contrast enhancement
Higher contrast on objects (e.g. when reading)

Question 17

How does age affect contrast sensitivity?

Answer 17

For babies: very low, so more sensitive to lower spatial frequencies (can’t detect detail). 2-3 c/deg. Has a much flatter curve. Improves with age.
Peak of CSF at age 20.
Older people: lose high spatial frequencies (can’t detect detail and contrast sensitivity reduced)