1) The Jackson Cross Cylinder is an optical device used to objectively refine the measurement of astigmatism during refraction examinations. It consists of two equal but opposite cylinders mounted at right angles to each other.
2) The JCC is used to refine the cylindrical axis by placing it parallel to the trial lens cylinder and flipping it to see if there are changes in visual acuity. The trial lens cylinder is rotated based on the direction of clarity.
3) The JCC is also used to refine the cylindrical power by placing it parallel to the trial lens axis and flipping it. If clarity changes, cylinder power is increased based on the side of clarity.
2. “……far more useful and far more
used” than any other lenses in clinical
refraction.
by- Dr Edward Jackson
3. …. OBJECTIVE OF PRESENTATION
•To understand the optics and
procedure of Jackson Cross
Cylinder in clinical refraction.
4. CONTENTS
• Discovery of JCC
• Introduction to JCC
• Optics of JCC
• Detection of Astigmatism by using JCC
• Refinement of cylindrical axis
• Refinement of cylindrical power
• Sources of error
• Summary
• Conclusion
• References
5. DISCOVERY OF JCC
• The original concept of JCC was first described by Stokes in 1849.
• 1855- The stokes lens was used in variation of the present technique
by Dennet
Crisp brought it to the worldwide attention, and it has become
known as JCC technique.
6. The present day
technique of JCC that
was used in clinical
practice was designed
and described by
Dr. Edward Jackson for
the determination of
cylinder power in 1887
and for axis in 1907.
7. INRODUCTION
• The Jackson cross cylinder is a combination of two cylinders of equal strength but with
opposite signs placed with their axis at right angles to each other and mounted in a
handle.
OR
JCC is a spherocylindrical lens having a spherical power component that combined with a
cylinder power component which is twice the power of sphere and of opposite sign.
E.g.- +0.25 DS combined with -0.50 DC. This result in the net power of +0.25 DC in
one axis and -0.25 DC in other axis .
The spherical equivalent of JCC IS 0 . (+0.25 DS/ -0.50 DC @ 90)
8. • The two principle axis of cross cylinder lens exhibit same
power but of opposite sign.
9. MARKINGS OF JCC
• In typical JCC the axis of + cylinder is
lie on the – power meridian while the
axis of – cylinder lie on the + cylinder
meridian.
• The Red sign represent the – meridian
while Green sign represent the +
meridian.
• The axis of JCC which is 45 degree
align to the power meridian.Axis of + cylinder
Axis of - cylinderxis
of
11. ADJUSTMENT OF SPHERE
• Find the spherical power by using the retinoscopy.
• End point of retinoscopy ins the starting point of JCC
refinement.
• Always remember conoid of strum during correction, so that
circle of least confusion fall on retina.
12.
13.
14. PRESENCE OF ASTIGMATISM
Place JCC at 90 and 180 degree and flip in front of
eye to detect whether astigmatism is present or
not.
If patient see any change in visual acuity in
either of position than astigmatism is present.
If no change in visual acuity is detected at
either of position than place jcc at 45 and 135
degree to confirm astigmatism is present or
not.
15. 1- Refinement
of Axis
2- Refinement
of Power
Reason- Correct axis can be found in the presence of wrong
power but full correct power cannot be Found in wrong axis.
16. REFINEMENT OF AXIS
1-
• Place a cylinder lens in a trial frame identify during retinoscopy.
2- • Occlude one eye of patient and ask him to see on the Snellen’s chart.
3-
• Place the JCC in front of eye in such a way that handle of JCC is parallel to the axis of
cylinder lens discovered during retinoscopy.
4-
• Flip the JCC in such a way that both the marking are placed in front of eye.
5-
• Ask the patient is there any change in visual acuity occur by flipping the JCC.
6-
• If the letters on Snellen’s chart are equally clear or equally blurred in either of two position
than the axis that is discovered by retinoscopy is correct.
7-
• If patient recognized any change in visual acuity in either of two position.
17. 8-
• “Minus correcting cylinder should be rotated in the direction of minus cylinder component (
red) of the JCC.
9-
• “Plus correcting cylinder should be rotated in the direction of plus cylinder component ( green
) of the JCC.
10-
• Repeat the procedure until correct axis can be discovered
18. AXIS MOVEMENT IN JCC
• Del Priore and Guyton
gave the guidelines for
the initial change in
the correcting axis
position relative to the
power of correcting
cylinder while
checking the axis.
Source- William j Benjamin,2006 , Borish refraction, Butterworth Hineman Elsevier 20:818
19. REFINEMENT OF POWER
1-
•Place the cylinder lens in trial frame that is discovered by retinoscopy.
2-
• Occlude one eye and ask the patient to look at clear line on Snellen's chart with
other eye.
3-
• Place the cylinder lens that is identified by retinoscopy in trial lens on the axis
that is discovered by JCC.
4-
•Place the JCC parallel to power to axis.
5-
•Flip the JCC in front of patient eye and ask the patient to tell about any change in
visual acuity.
20. 6-
•If patient does not recognized any change in visual acuity in either of
position i.e. the power placed in trial frame is correct.
7-
•If patient recognize any change in visual acuity in either of two position
than add cylinder power on the basis of patient exceptance.
8-
• If patient see clear from minus side of JCC than add minus cylinder power
to the number that is discovered by subjective refraction.
9
•If patient see clear from plus side of JCC than add plus cylinder power to
the number that is discovered by subjective refraction.
