best vision sphere jackson cross Flashcards
(8 cards)
What is the purpose of using the Jackson Cross Cylinder (JCC) in optometry?
The Jackson Cross Cylinder (JCC) is used to refine the axis and cylinder power in the correction of astigmatism during subjective refraction.
How does the JCC lens work in subjective refraction?
The JCC lens presents two perpendicular cylindrical lenses of equal power but opposite signs, alternating between them, to help the patient identify the sharpest image and refine both axis and cylinder power.
What is the typical structure of a JCC lens?
A JCC lens is a spherocylindrical lens with a spherical component and a cylindrical power that is twice the value of the spherical component but of opposite sign (e.g., +0.50 sphere and -1.00 DC).
: What is the first step in performing Jackson Cross Cylinder (JCC)?
The first step is to establish the Best Vision Sphere (BVS) by refining the sphere to give the best visual acuity and bring the circle of least confusion onto the retina.
After determining the Best Vision Sphere (BVS), what is the next step in JCC?
After establishing the BVS, the next step is to estimate the axis and cylinder power of the astigmatism, then introduce the JCC lens to refine both the axis and cylinder power.
How do you determine the axis of the cylinder using JCC?
The JCC lens is placed in the trial frame, and the patient is asked to compare clarity as the JCC lens is rotated 90 degrees. The correct axis is when the clarity is the same in both orientations.
How do you determine the cylinder power using JCC?
The JCC lens is rotated until the patient reports the sharpest image. The cylinder power is refined by increasing or decreasing the cylinder based on which axis provides the sharpest image.
What happens when the sharpest image is observed with the minus axis during JCC testing? What does it mean when the sharpest image is seen with the plus axis during JCC testing?
If the sharpest image is seen with the minus axis, the cylinder power needs to be increased to correct the astigmatism.
If the sharpest image is seen with the plus axis, the cylinder power needs to be decreased to correct the astigmatism.
