Without Retinoscopy Result

• 1a) Determining Axis: no estimated cylinder in trial frame

  • Hold JCC so -ve axis is at 180 deg and twirl (-ve moves onto 90 deg). Make a mental note of whether 90 or 180 is preferred and the same for 45 and 135.
  •  If there is no preference on both occasions then there is no astigmatism
  •  If there is only preference for one axis shown(90, 180, 45, 135) then the cylinder axis will beclose to this orientation
  •  If there is a preference on both occasions the axis of the cylinder required is likely to be between these two preferences - AXIS = [A1 + A2] / 2
• 1b) Refining Axis: estimated cyl in trial frame

  • Put estimated cylinder at the estimated axis into trial frame and adjust the sphere power (by +0.25 DS for every -0.50DC)
  • Hold handle parallel to trial cylinder and twirl offering two positions. (SAME COLOUR)

  * No difference between two lenses = Axis is is correct

  *Preference = move trial cylinder axis towards minus axis on JCC in the position preferred

  • Continue to adjust trial cylinder axis until patient reports no difference between 1 and 2.
  • Bracketing = halve degs range in axes if patient prefers opposing sides (until it gets to 2.5 deg)
• What you'll need beforehand:

  • Measure distance PD and fit the trial frame
  • Measure vision and do pinhole if VA<6/9
  • Do best sphere using Snellen Chart
  • Ensure patient sees the duo chrome circles clearer on green (add minus sphere if necessary)
  • Ask patient: which lens makes the circles clearer, rounder and blacker ?


  *if no preference = leave it as it is

  *always start with -0.25 DC cross cylinder even if VA at 6/5

  *whenever there is a preference for an AXIS - keep JCC in that position and rotate it towards the -ve power on the JCC only
• 2) Refining power: estimated cylinder already in trial frame

  • Hold the cross cylinder so +ve axis markings parallel to trial cylinder axis (both colours)
  • Twirl the cross cylinder offering +ve and -ve positions

  *No difference = correct power

  *Preference = -ve add more cyl , +ve take away cyl

  • Continue to adjust the power of the trial cylinder until the patient sees no difference or ‘reversal’ occurs

  *Reversal = leave patient on least -ve cyl

  ! for every -0.50DC added you must add +0.25 DS and for every -0.50DC removed you must add -0.25 DS
• 3) Checking Tests:

  • Measure VA of new results using Snellen
  • +1.00 Blur - should blur to 6/18
  • Duochrome - leave it on equal (red = older , green = younger )