L13 Flashcards
(10 cards)
What is the Jackson Cross Cylinder (JCC) technique used for?
The JCC is a subjective refraction technique used to determine both the cylindrical axis and power during astigmatism correction.
What is the structure of a cross-cylinder lens?
It has a positive cylinder on one surface and an equal negative cylinder on the other; the handle denotes the astigmatic interval between the two meridians.
How are the axes marked on a cross-cylinder lens?
The axes are at ±45° to the handle; the plus cylinder axis is generally marked white, and the minus cylinder axis is generally marked red.
When should you use a lower-powered cross-cylinder (e.g., ±0.25D or ±0.50D)?
When the estimated cylinder is small (e.g., if estimated cyl is -1.00DC, use -0.50D or -0.25D cross-cylinder).
What are the two main parts of the cross-cylinder routine?
Find and refine the cylinder axis.
Refine the cylinder power.
Why is it important to have the COLC on the retina during cross-cylinder testing?
Because the cross-cylinder changes the size of the COLC (level of blur) but not its position; accurate results depend on the COLC being on the retina.
What is the recommended sequence after finalizing the cylinder axis and power?
Refine the sphere using the duochrome and letter chart, aiming for the least minus or most plus.
Why must the sphere be adjusted when changing cylinder power?
To maintain the COLC on the retina and ensure optimal vision correction.
What is the main advantage of the cross-cylinder technique over the fan and block method?
It is more sensitive and precise for refining both the axis and power of cylindrical correction.
What should you do if the patient cannot tell the difference between any cross-cylinder positions?
It likely means the patient does not have any significant astigmatism.
