Visual Acuity

• What is the definition of visual acuity (VA)?

  The ability of the individual to discriminate detail
• What does visual acuity measure?

  How well someone can see
• What are the components of visual acuity?

  • Central vision: ability to discriminate fine high-contrast detail
  • Peripheral vision: field of vision
• How is visual acuity tested in literate adults and children?

  Using capital letters
• What is the relationship between visual angle and visual acuity?

  Visual acuity is related to the visual angle subtended at the nodal point of the eye
• What is the threshold for minimum visible angle?

  Threshold of 1 second (") – diameter of a cone (0.004mm)
• What does minimum detectable (distinguishable) acuity measure?

  The ability to identify features or internal arrangement in a visible target
• What is hyperacuity?

  The ability to perceive alignment and orientation of linear stimuli
• What are the two types of charts used for minimum recognizable acuity?

  Snellen and LogMAR charts
• What is the significance of the Snellen fraction 6/6?

  It indicates normal visual acuity
• How is the Snellen fraction calculated?

  VA = d / D, where d is the test distance and D is the distance at which each component of a letter subtends 1 minute of arc
• What is the method for testing VA using the Snellen chart?

  Patient seated at 6m, occlude one eye, and ask to read letters
• What are some problems associated with the Snellen test?

  Some letters are easier to read, spacing varies, and there is no crowding on top letters
• What does LogMAR stand for?

  Logarithm of the Minimal Angle of Resolution
• What is the advantage of using LogMAR charts?

  Values can be averaged and analyzed statistically
• What is the method for scoring LogMAR tests?

  • Able to see 3 letters on a line – check next line
  • Back fill incorrect with correct from next line
  • Each line scored 0.1 logMAR
  • Each letter scored 0.02 logMAR
• What is the purpose of the Glasgow acuity test?

  To test crowded acuity in preschool children
• What is the principle behind forced choice preferential looking (FCPL)?

  Infants prefer to look at patterned rather than a blank surface
• What is the significance of spatial frequency in FCPL testing?

  The narrower the strip, the higher the spatial frequency and visual acuity
• What is the testing distance for FCPL?

  38cm
• What is the advantage of using Lea gratings paddles?

  They are fast to perform and portable
• What is the method for testing with Lea gratings paddles?

  Use one blank paddle and three double-sided with gratings
• What is the conversion needed for cycles per cm (cpcm) in Lea gratings paddles?

  Cycles per cm need to be converted to cycles per degree (cpd)
• What are the testing distances and corresponding cycles per cm for Lea gratings paddles?

  • 29cm: 0.12 cpd
  • 57cm: 0.25 cpd
  • 86cm: 0.40 cpd
  • 114cm: 0.50 cpd
• What is the range of visual acuity (VA) in cycles per degree (c/deg) mentioned in the study material?

  0.18 - 38 c/deg
• What does one spatial cycle consist of in visual testing?

  One black and one white stripe
• What is the testing distance for the 'Staircase' method in visual acuity testing?

  38 cm
• What is the duration for which the FCPL is suitable for testing?

  8 weeks to 6-12 months
• What is an advantage of using Lea gratings paddles?

  Fast to perform
• What is the suitability of Lea gratings paddles for testing?

  Suitable for children under 1 year and adults with disabilities
• How can the difficulty of the Lea gratings paddles test be altered?

  By changing the testing distance
• What is the VA range for Cardiff acuity cards?

  6/60 – 6/6 fixing at 1m
• What is the method for using Cardiff acuity cards?

  Occlude one eye and present cards at eye level
• What problems might arise when testing the vision of a 1.5-year-old toddler?

  Limited vocabulary and concentration
• What is the purpose of Kay pictures in vision testing?

  To assess visual acuity using familiar pictures
• What is the testing distance for Kay Picture Single logMAR?

  3m
• What is the VA range for Kay Picture crowded logMAR?

  1. 00 - -0.100 logMAR
• What is the method for using Lea symbols in visual acuity testing?

  Occlude one eye and count the number of symbols seen
• What is the method for using Landolt C / Tumbling E charts?

  Indicate where the gap is in the E or C
• What is the testing distance for the Sheridan Gardiner test?

  6m