Jackson Crossed-Cylinder

Indra P. Sharma

Optometrist

“....far more useful and far more used” than any other lenses in clinical refraction.-Dr. Edward Jackson

JCC(Sharma IP)

Objective

To understand the optics and proper use of Jackson Crossed-Cylinder in clinical practise.

JCC(Sharma IP)

Contents1. Introduction to JCC2. Historical Perspective3. Optics – How is it made?4. The choice of JCC5. Detection of astigmatism6. Refinement of axis7. Refinement of power8. Sources of Error9. Points to ponder-Summary10. Conclusion11. Reference

JCC(Sharma IP)

Introduction to JCCJackson Crossed-Cylinder is a

combination of two cylinders of equal strength but of opposite signs placed with their axis at 90 degrees to each other and mounted in a handle.

Jackson Crossed-Cylinder (JCC) technique is also called the flip-cross technique.

JCC(Sharma IP)

Historical Perspective1849-The original concept of crossed cylinders was described by Stokes.

1855-The Stokes lens was used in a variation of the present technique by Dennet

Crisp brought it to worldwide attention, and it has become known as the JCC technique.

JCC(Sharma IP)

Contd.....

The present technique -designed and described by Dr. Edward Jackson for the determination of cylinder power in 1887 and for axis in 1907.

JCC(Sharma IP)

Optics- How is it made?A typical JCC lens is a spherocylindrical lens

havinga spherical power component combined with a

cylinderpower component of twice the power of the sphere,

andof opposite sign.Eg: +0.50 DS combined with -1.00 DC. This

results in a net power of +0.50 DC in one axis and -0.50 DC in the other axis(+-50 DC).

+0.50/-1.00 @90 JCC(Sharma IP)

Axis for + cyl

(+0.25@90)

Power: +0.25DC

+ =

+0.25DS/-0.50DCx180

Axis for – cyl

(-0.25@180)

Power: -0.25DC

Contd...

JCC(Sharma IP)

Contd...Crossed cylinders of +0.25 DS combined with

-0.50 DC (+-25 DC) or +0.37 DS combined with -0.75 DC (to.37 DC), etc.,are available.

Thus, the two principal axes of a crossed-cylinder

lens exhibit equal cylinder power of opposite signs.

JCC(Sharma IP)

Marking of Principle meridianThe principal

meridians are marked in the periphery of JCC lens

In the UK, it is the opposite.

JCC(Sharma IP)

White dots = axis of the plus

cylinder

Red dots = axis of the minus

cylinder

Handle of JCCA handle is attached between the two marked axes,

which enables the lens to be "twirled" before the eye by

rotation of the handle.

In this manner, the positions of the minus and plus axes are interchanged rapidly and alternately.

The common term used for the rotating the handle is known as flipping.

Hence, the JCC is often termed as flip-cross cylinder.

JCC(Sharma IP)

Contd.... 0.5 D Jackson cross-cylinder

in primary orientation. The handle is down to the right and at 45º to the horizontal. The label +.50 is in the usual orientation for reading; -.50 reads upward. The markings are in red (as here) and white (shown black here).

JCC(Sharma IP)

JCC(Sharma IP)

In almost all modern phoropters, the rotation of the JCC lens is automated

Choice of JCCVision 6/9 or better: use 0.25DC x-cyl

If results unreliable, then change up to 0.50 x-cyl. and see if more reliable

Vision 6/12 or worse: use 0.50DC x-cylIf results reliable and vision improves, change down to 0.25

Use a larger target until the vision improves!

Vision 6/24 or worse: try 0.75DC x-cylIf results unreliable, use alternative method of astigmatic correction (Astigmtic Fan, keratometry etc)

JCC(Sharma IP)

BE

Today’s

topic

JCC(Sharma IP)

Procedure

JCC(Sharma IP)

Starting point for JCCAfter retinoscopy.....adjust sphere.

End point of spherical adjustment is the starting point of JCC refinement.

Circle of least confusion must be on retina (ILM), so check sphere first.

Remember Strums Conoid

JCC(Sharma IP)

Eg: Simple myopic astigmatism

Interval of Sturm

Circle of Least Confusion

Blur is due to combination of…

CLC in front of the retina

Focal lines being separated

“It’s very blurred”

With best spherical correctionCircle of Least Confusion

Has moved, is now on the retina

Interval of SturmLength unchanged

Reason the vision is still blurred

“That’s better but it still isn’t clear”

JCC(Sharma IP)

1.Discovery of Astigmatism

JCC(Sharma IP)

If astigmatism is present

But WHY

- because the correct axis can be found in the presence of an incorrect power but the full cylindrical power will not be found in the presence of an incorrect axis.

JCC(Sharma IP)

2. Refinement of Axis

JCC(Sharma IP)

Procedure

JCC(Sharma IP)

Contd......

JCC(Sharma IP)

ExampleYou have performed retinoscopy on a patient

Retinoscopy value -1.00DS/-1.00DCx180, 6/9

You have checked the sphere power

Now lets refine axis of the cyl.

JCC(Sharma IP)

Position 1

Resultant axis

-1.00

JCC(Sharma IP)

“ Clear now”

Resultant axis

Position 1

JCC(Sharma IP)

Refining axisPatient response

“Lens position 1 was clearer”

So, we rotate the cylinder lens towards the position of the red markingsIn this case, position 1

Initially, move by steps of about 15 deg, then use smaller steps as we get closer

JCC(Sharma IP)

Patient responseWe rotated the axis of the trial lens AND the handle

of the x-cyl by 20 deg“Both lenses are equally blurred”

This means that the cyl axis of the trial frame now matches the patient’s cyl axisThe true axis is 160 deg

In real life, you would continue until the patient sends us in the other direction (reversal)There is usually a range where the images appear equal,

and we need to find the limitsChoose the axis mid-way between the two reversals

JCC(Sharma IP)

“ They are same”May be on axis, therefore move cyl axis by about 20deg and

check to see if it returnsMay be within range of uncertainty (next slide)0.25DC JCC may give insufficient difference

Try 0.50DC0.50DC JCC may give too much distortion

Move down to 0.25DC If none of the above help, use alternative technique.

JCC(Sharma IP)

Range of uncertainty In real life, most patients will report that both lenses are

equally blurred over a range of axes

This is more common with low cyl powerYou need to identify the range

Find where the patient tells you to rotate in the opposite direction at each end

Select the axis in the middle of the range

JCC(Sharma IP)

How much axis to move?Del Priore and Guyton

gave the guidelines suggested in Table 20-2 for the initial change in correcting axis position relative to power of the correcting cylinder while checking the axis.

JCC(Sharma IP)

Source:William J Benjamin,2006, Borish’s Clinical Refraction, Butterworth Heineman Elsevier. 20: 818

2. Refinement of Power

JCC(Sharma IP)

Optical principle of power refinementWhen determining the power, JCC will either increase or decrease residual cyl, either expanding or collapsing the astigmatic interval and circle of least confusion

Thereby making the target less or more clear

JCC(Sharma IP)

Option 1Circle of Least Confusion

Increases in size

Does not change position!

Interval of SturmLonger

“That looks awful”

JCC(Sharma IP)

Option 2Circle of Least Confusion

Decreases in size

Does not change position!

Interval of Sturm

Shorter

“That is much better”

JCC(Sharma IP)

Procedure

JCC(Sharma IP)

3. JCC is placed with its axis parallel to the axis of the cylinder in the trial frame.

Contd...

JCC(Sharma IP)

ExampleUsing ± 0.50 JCCRetioscopy : -1.00DS/-0.75 DC X 120

If the patient prefers the lensWhen red marks are aligned with trial cyl axis (120

deg), add -0.50 DCWhen white marks are aligned with trial cyl axis

(120), reduce -0.50DCEqually clear: you have the right power

JCC(Sharma IP)

Contd.....

JCC(Sharma IP)

For each -0.50DC change, you need to add +0.25DS, to keep the circle of least confusion on the retina Add -0.25DS for each +0.50DC change

So in the example : -1.00DS/-0.75 DC X 120

If the patient prefers red marks

Final power is:

-0.75DS/ -1.25 DC X 120

Refining power

JCC(Sharma IP)

Add – 0.50

Deduct – 0.50

Sources of Error

JCC(Sharma IP)

Common errors1.Not keeping the circle of least confusion on the

retinaStarting with the wrong sphere powerForgetting to change sphere power if cyl is

changed by 0.50DC or more

2.Assuming the axis is correct if the patient says “they look the same” without checkingCould be no astigmatism at allCould be 90deg off

3.Incorrect presentation time – esp too quick4.Poor alignment of JCC and trial frame axis

JCC(Sharma IP)

Points to ponder- SummaryJCC is always a sphero-cylindrical lens such that one meridian

is plus power and the other meridian is of equal minus power.

The red dots identify the axis of the minus power and the white dot is of plus power.

While refining axis: JCC handle is parallel to trail lens cylinder axis

While refining power: JCC lens axis is parallel to trail lens cylinder axis.

When patient says “ both sides are same” exclude all posibilities.

JCC(Sharma IP)

ConclusionThe most accepted procedure used by the

overwhelming majority of examiners is the JCC technique.

Freeman and Purdum and Goar considered the JCC to be the most delicate test for astigmatism.

The use of JCC is very important in clinical parctise of refraction and an it serves as an important instrument for optometrist.

JCC(Sharma IP)

Reference1. William J Benjamin,2006, Borish’s Clinical Refraction, Butterworth

Heineman Elsevier. 20: 816-8292. Wunsch SE. 1971. The cross cylinder. Int Ophthalmol Clin 11:131-153.3.Brookman KE. 1993. The Jackson cross-cylinder: Historical perspective.

JAm Optom Assoc 64:329-331.4. Crisp WHo 1943. Photographing cross cylinder tests. Am J Opht 26:758-

760.5. Duke Elder, 1998. Practise of Clinical Refraction, Butterworth Heineman

Elsevier. 4: 181-1836. Khurana AK 2013. Optics and refraction, 6: 133-1347. Perlstein SII. 1982. Mounted cross-cylinder: A new mounted Jackson cross-

cylinder. Ann Opht/Ullmol 14:992.8..Del Priore LV, Guyton DL. 1986. The Jackson cross cylinder, a reappraisal.

Ophthalmology 93: 1461-1465.9. Sims CN, Durham DG. 1986. The Jackson cross-cylinder disproved. 'hans

Am Ophthailltol Soc 84:355-386.

JCC(Sharma IP)

Orthoptics as a career (ZG)

Blog: optomindra@blogspot.com