Using JCC for cyl axis & cyl power (9)

what are the 2 starting points for JCC routine

1. ret as starting point

2. BMS determined subjectively or no ret result at all or no cyl found during ret or removal of cyl found during ret does not make letters less clear

1. ret as starting point

• ive cylinder was found during ret and when we chck, px says its worse when we remove the cyl found from ret

• so leaving in the cyl form ret 

here JCC is used to modify a cylinder found using ret 

2. BMS dtermined or no ret/no cyl found/ removal of cyl found doesnt make letters less clear

so we are starting JCC with no cyl in place 

here JCC used to establish if a cylinder is needed and if so, what the power and axis should be 

JCC used for both cyl power and axis determination

to check for cyl axis, hold handle of the JCC along the axis in the trial frame 

eg in position 1 axis is 170

look at the red markings 

position 1: 170 in trial frame. if prefers this, white markings need rotating clockwise for a preferred position

position 2: if px prefers this, rotating anitclockwise

JCC for determinng the cyl power

to check cyl power, hold axis markings for the JCC along the axis of the cyl in the trial frame

red markings are along axis of cylinder 

when twirled, white markings are along the axis of the cylinder 

if px prefers position 1 that means they wants more minus cylinder

if px prefers position 2 means they want less cylinder

JCC routine: eg1: ret result R:  -3.00 /-0.75 × 170 , VA with ret result is 6/7.5 (VAR 95)

one way to check on ret result is to measure VA with ret result and then re measure VA when ret cyl has been removed 

eg, when we take out the ret cyl, VA drops to 88

so we put the -0.75 × 170 back in 

offer a +0.50DS then -0.50DS as per BMS/BVS

now CLC is on the retinal so its time for JCC; hence switch on the rings 

1st, check the cylinder axis 

eg1 same: refining the cylinder axis

1. direct the px attention to the rings

2. if the rings are too small, the discrimination wont be possible for the px

3. if rings are too big then they wont notice the difference

4. Place JCC in front of the px eye. Align the handle with the axis markings of the trial frame cylinder and ask the question if its better 1, or 2 ( when flipping the JCC)

5. px responds , note position of the JCC which gives rounder and clearer rings

6. rotate trial cylinder towards towards minus axis of JCC when in rounder or clearer position

when would we choose a +- 0.25 crossed cyl

if VA improves slightly

if VA with ret is poorer than 85 use the higher powered JCC +-0.50 crossed cyl or higher

cyl axis refinement with JCC: eg1 same 

handle held along the axis of cylinder eg 170 

if position 1 was preffered, rotate the handle clockwise towards the red markings 

is position 2 was preffered then rotate anticlockwise 

in eg. px say circles are rounder and sharper with the JCC in position1: so rotate towards 125 ( as the red markings are 45 away from 170)

eg1 continued

as position 1 was preffered, trial frame cylinder axis is rotated towards minus axis of JCC when in prefered position

rotated around 20 degrees to now at around 150

so handle of JCC moves to 150, red markings at 105

ask again, which is better, 1 or 2

px says circles better in position 2

means that needs to move axis anticlockwise xloser to original axis

move to 160; rotated cylinder towards neg axis by 10 degrees

eg 1 continued

so now axis moved to 160

have handle at 160 and ask again if position 1 or position 2 when flipped is better

position 1 was preffered

so rotate the cyl axis towards the negative axis of JCC by 5 degrees

now 155

eg 1 continue 

trial frame cylinder now at 155 

ask same question 

px has no preference for position 1 or 2 cylinder axis end point for now 

so refined: -0.75 × 155 

had 2 reversals so we can accept that the correct -ve cyl axis for this eye is 155 

if power of the cyl changes, then need to go back and check if axis needs refining or not

axis determination steps

1. rotate trial framw cyl towards negative axis of JCC in the rounder and clearer position

2. for the next presentation of JCC, if the cylinder needs to be rotated in the same direction, rotate it by the same amount

3. if rotation in the opposite direction is needed, this is reversal

4. when theres reversal, rotate cyl by hald the previous amount

5. rotation of trial fame cyl is braketed; this means starting with larger rotation angles and reducing the angle of rotation when the direction of rotation changes

6. continue until positions 1 and 2 are the same to the px

by how much do we initially rotate the cyl axis

depends on cyl power

rules on changing the axis of the TF cyl

move the cyl axis un a systemic fashion and half the change when u change direction

for every axis change, you must consider cyl power and previous responses

make note of px responses during JCC axis determination eg ret cyl was -0.25 with axis at 180 then → 30 degrees → 60 degrees _45 degrees → 50 degrees with px saying at 50 its the same

must have observed at least 1 axis reversal before you know axis is end point

eg if px says 90 →80→ 70→.. px responds same, must change axis to 60 to check for reversal

if cyl axis comes back to 70 when px says same then we know its the right axis

EG1: same refindnig the CYL POWER 

now need to align the JCC axis markings with axis markings of the trial cylinder 

flip JCC and note which position the JCC gives clearer and rounder rings 

how do we know whether to + or - cyl power

if the patient prefers negative meridian along the trial frame axis- increase the -ve cyl power

if the patient prefers positive meridian along the trial frame cylinder- decrease the -ve cyl power

eg 1 continue: JCC markings along the cyl axis in trial frame

red markings correspond to the axis of the minus cyinder

knowing if they want more minus or less minus cylinder

px prefers position 1: which is the negative meridian along axis of trial cylinder axis

so increase trial frame cylinder by -0.25DC= -1.00 DC

keep it at the same axis (155)

eg 1 continued : cyl power refinement

now with the -1.00 in place, place JCC axis markings along the axis markings of trial frame cylinder 

ask if better in 1 or 2 when flipped 

px says no preference for poition 1 or 2 

cylinder power end point - dont need a reversal when establishing a cyl power 

= -1.00 × 155

rechecking the cyl axis after cyl power has been determined

as the cylinder power has been changed, go back and re check the cylinder axis

with small changes in power, expected that there isnt a change in cyl axis and if it does, its usall by a very small amount , if changed by ± 0.25 no need to check

larger change ( ± 0.50 or more may change the axis so need to check the axis again with the JCC

final axis check

re align the JCC hadle with the trial frame cylinder axis markings (155)

px says no preference so end point for cylinder axis

JCC routine: cyl power and axis endpoint

R: -3.00/-1.00 × 155 

check the VA with this sph/cyl combination 

final check on the sphere: offer +0.25 then -0.25 

stop when +0.25 makes VA worse and -0.25 doesnt improve VA 

finally try +1.00DS test

expect around 4 line reduction since a +1.00DS lens added to a corrected eye will generate -1.00DS myopia 

3-5 line reduction is okay : this confirms that you have not over minused or under plussed

worried if VA reduction is 2 lines or less with the +1.00DS 

record result  if +1.00DS result as expected.. sph/cy axis and VA

if px can stil read with +1.00, take out try +2.00, and if sill +3.00 etc to see how many dioptres out you are from real correction

eg2; no cylinder was found during ret

or cyl from ret made acuity worse

or no ret result exists

BMS: +2.00DS giving VA of 6/7.5 ( VAR 95)

starting with the BMS sphere in the trial frame

can estimate that the eye has around 1.00 astig since the VA with BS reduced by around 2 lines

use +-0.25 crossed cylinder

px observes smallerr ring targets

flips jcc with axis at 90 /180 then at 45 and 135

working out axis

if position 1 was preffered, with the red markings at 90, the px -ve cyl axis is nearer to 90 than 180

if position 2 was preffered, then the px -ve cyl axis is nearer to 180 than to 90

if px prefers position 1 with the red markings along 45 then the px -ve cyl axis is nearer to 45 than 135 

if position 2 is preffered then the px -ve cyl axis is nearer to 135 than to 45 

eg 2 : continued

• if the rings are clearer with minus axis of JCC at 180 and 45:

insert -0.25DC with axis 20 or 25 which is halfway between 180 and 45

• if rings are clearer with minus axis of JCC at 45 and 90 : insert -0.25DC with axis at 65/70 which is halfway between 45 and 90

• if rings are much clearer with the minus cyl axis of JCC at 180 compared to 90 and a little clearer when minus cyl axis of JCC is at 135 compared to 45: insert a -0.25DC x 170

choice of JCC lens power

if the visual acuity /12 or better, use the lower powered JCC

if worse, use the higher powered JCC

if we start JCC with only a sphere in place, what initial power of cyl lne shsould we choose 

start by introducing a -0.25DC or -0.50 DC 

but if the VA with BMS reduces by 4 lines, might expect there to be around -2.00DC of astigmatism, so introducing -1.00 initially 

so usually initial cyl power will be -0.25 and increase in -0.25 increments 

but if the VA is poor with the BMS we may consider using higher cyl power steps