Contrast Sensitivity

• What is contrast in visual perception?

  Contrast is a measure of the amount of lightness or darkness an object has in comparison to its background.
• How does a black tie against a white dress shirt illustrate high contrast?

  It shows a significant difference in lightness between the tie and the shirt.
• What is the contrast threshold?

  The contrast threshold is the smallest difference in lightness and darkness that can be distinguished.
• How is contrast sensitivity related to contrast threshold?

  Contrast sensitivity is the inverse of the contrast threshold.
• In what units is contrast sensitivity often expressed?

  Contrast sensitivity is often expressed in log units.
• What are the broad ways to measure visual function?

  • Visual acuity measurement
  • Contrast sensitivity
  • Colour vision measurement
  • Visual field measurement
• Why is contrast measurement useful in assessing visual function?

  It is a useful adjunct to measuring visual acuity.
• What does spatial vision refer to?

  Spatial vision refers to the ability to perceive and interpret visual information based on spatial frequency.
• How can any visual image be represented?

  Any visual image can be represented as the linear sum of a number of sine wave components.
• Who first presented patients with vertically orientated gratings of a certain spatial frequency?

  Campbell and Green first did this in the 1960s.
• What does contrast sensitivity provide information about?

  It provides information beyond visual acuity.
• Why might some patients have normal visual acuity but reduced contrast sensitivity?

  Because visual acuity measures recognizing small high contrast objects, while many real-world objects are not high contrast.
• How is contrast sensitivity related to daily life function?

  It is related to function in daily life as it affects the ability to see in various lighting conditions.
• In which conditions is contrast sensitivity often assessed?

  It is often used in assessing patients with cataract.
• What visual pathway disorders can contrast sensitivity screening help identify?

  It can help screen for optic neuritis, multiple sclerosis, and Parkinson's disease.
• How does spherical refractive error affect contrast sensitivity?

  Spherical refractive error causes greater loss at high spatial frequencies.
• What conditions generally cause greater loss at medium to low spatial frequencies?

  AMD, macular edema, and cataract generally cause greater loss at medium to low spatial frequencies.
• What is a notch defect in contrast sensitivity?

  A notch defect may occur from astigmatic refractive error and monocular diplopia from bifocal contact lenses.
• Why is assessing contrast sensitivity important in the clinic?

  It helps evaluate visual function, which is not always predicted from other vision measures.
• What does CS testing help to screen for?

  It helps screen for early ocular disorders when there is suspicion of a problem.
• What factors can affect the shape of the contrast sensitivity function (CSF)?

  Factors include luminance, temporal characteristics, target size, grating motion, and grating shape.

  
• Why is measuring the whole CSF time-consuming?

  It is useful in research but not practical in the clinic.
• What clinical tests are available to measure contrast sensitivity?

  • Pelli Robson
  • Melbourne Edge Test
  • Australian Vision Chart
• What does the Pelli Robson test measure?

  It measures peak contrast sensitivity using triplets of letters.
• How is the Pelli Robson test administered?

  The chart is held at 1 meter from the patient, and letters are read until no longer visible.
• What is the normal result for Pelli Robson for those 50 years and younger?

  1. 80 log units.
• What is the normal result for Pelli Robson for those older than 50 years?

  1. 65 log units.
• How does the contrast value change in the Pelli Robson test?

  Contrast increases by 0.15 for each 3-letter block.
• What does the Melbourne Edge Test measure?

  It measures the contrast of a single edge using circular stimuli.

  
• How is the Melbourne Edge Test administered?

  Patients determine the orientation of the edge using a forced choice method.
• What is the normal range for the Melbourne Edge Test for those under 65 years?

  19 - 22 dB.
• What is considered abnormal in the Melbourne Edge Test?

  Less than 15 dB indicates significant contrast sensitivity loss.
• What does a change of more than 2 dB between tests indicate?

  It indicates a need to ensure conditions are the same for accurate comparison.
• What does severe impairment indicate in the Melbourne Edge Test?

  Less than 10 dB indicates difficulty with visual performance in everyday activities.
• What does the Australian Vision Chart measure?

  • It is a low contrast letter acuity chart.
  • It presents two letter charts: one at high contrast (~90%) and one at low contrast (10%).
  • It records the number of lines difference between high and low contrast.

  
• What is the normal range for the Australian Vision Chart for those under 65 years?

  0.21 logMAR (2 lines) difference between high and low contrast.
• What is considered abnormal in the Australian Vision Chart?

  More than 3 lines difference indicates significant contrast sensitivity loss.
• What advice is given to those with reduced contrast sensitivity?

  They are advised to use bigger, bolder, and brighter objects to improve visibility.
• What does the contrast sensitivity function tell us about visual function?

  • It provides more information than high contrast visual acuity.
  • It helps assess visual function in various conditions.