Jackson Cross Cylinder

• What is the primary purpose of the Jackson X-cyl technique?

  Astigmatism determination without fog
• What does the Jackson X-cyl technique rely on during the procedure?

  COLC being placed on the retina
• What is the abbreviation for the cross cylinder used in the Jackson X-cyl technique?

  1. cyl
• What does the Jackson X-cyl technique utilize for astigmatism determination?

  Comparison of separate images and bracketing techniques
• What is the design of the X-cyl lens?

  • Positive cylinder on one surface
  • Negative cylinder of numerically equal power on the other surface
  • Axes of the cylinders at right angles

  
• What is the spherical equivalent of the X-cyl lens?

  Plano -0.25 +0.25
• What are the common powers of the X-cyl lens?

  0.25, 0.37, 0.50, 0.75
• When is the 0.25 X-cyl most commonly used?

  If visual acuity is better than 6/12 with BVS
• How is the X-cyl lens mounted when used with a trial frame?

  Mounted in a handle at 45° to the axes
• How is the X-cyl lens marked?

  With the position of the axes, preferably with plus or minus signs
• What color is usually used to denote the negative sign on the X-cyl lens?

  Red
• What color is usually used to denote the positive sign on the X-cyl lens?

  White
• What should be checked regarding the markings on the X-cyl lens in the U.K.?

  They may be opposite, so it's best to check markings
• What are the components of the phoroptor X-cyl setup?

  • Trial lens cylinder
  • Cross cylinder
  • Adjustment for trial lens cylinder
• How is the X-cyl used during the examination?

  The lens is 'twirled' or 'flipped' for patient comparison
• What will happen if the patient is emmetropic during the X-cyl examination?

  Both views will appear the same
• What occurs if the patient is ametropic during the X-cyl examination?

  One view will be preferred
• What does axis determination rely on in the Jackson X-cyl technique?

  The effect of obliquely crossed cylinders
• What does power determination rely on in the Jackson X-cyl technique?

  Changes in the interval of Sturm
• What is the significance of the mean power of the lens being zero in the X-cyl technique?

  The position of COLC is not affected by the cross cylinder

  
• What does the patient view during the axis location determination?

  A circular target equivalent to 6/12
• How is the X-cyl introduced for axis location determination?

  With axes along 90° and 180°
• What happens when the lens is flipped or twirled during axis location determination?

  The axes are interchanged
• What does the patient need to indicate during the axis location determination?

  Whether the circle appeared sharper with the lens in the first or second position
• What should be noted regarding the preferred position of the X-cyl minus axis?

  It indicates the orientation of the patient's astigmatism
• What does it mean if the preferred position of the X-cyl minus axis is at 180°?

  The minus axis of the astigmatism lies nearer horizontal than vertical
• How is the X-cyl introduced for further axis location determination?

  With axes along 45° and 135°
• What should be noted when the lens is twirled during this determination?

  Which view is better
• What does the preferred position of the X-cyl minus axis indicate?

  It indicates the orientation of the patient's astigmatism
• What should be done after determining the patient's minus cylinder axis?

  Introduce a working cylinder at the estimated axis
• How is the power of the trial lens cylinder determined?

  It depends on visual acuity with BVS

  
• What should be used if the visual acuity is better than 6/9?

  • 0.50 DC trial lens cylinder
• What should be done if the visual acuity is worse than 6/9?

  Work out from retinoscopy, tables, or rule of thumb
• What must be added during the Jackson X-cyl procedure for every -0.50 DC added?

  A +0.25 DS lens
• How should the X-cyl be introduced during axis refinement?

  Handle aligned with the estimated axis
• What happens when the X-cyl is flipped during axis refinement?

  The patient is asked which view is better
• What does the combination of the trial lens cylinder and the oblique placed X-cyl create?

  A resultant cylinder
• What should be noted regarding the preferred position of the X-cyl minus axis during axis refinement?

  It indicates the direction for rotating the trial lens cylinder
• What should be done if the trial lens cylinder needs to be rotated in the opposite direction?

  Reduce the amount of rotation and bracket
• What indicates that the trial lens cylinder is at the precise axis of required correction?

  Both views will be the same