The College of Optometrists

I dont tend to always use duochrome, when do other people mainly use it and why is it better to keep it equal or just on the green before cross cyl?

i use duochrome as a check on all young & competent pxs to ensure that i haven't overminused/overplussed. a -/+0.25 should usually switch clarity to the opp colour (you can use 1D blur test as well for this)

u can either get best vision sph on the test chart, or equalise duochrome (when reliable) before cross cyl. principle is to have the circle of least confusion on or just behind the retina. just on the green (add -0.25) for younger pxs to allow accommodation to put circle of least confusion on retina.

remember to adjust your sph by half of the opposite sign cyl as you increase the cyl power. again this is to maintain the circle on retina.

Now I am opposite - idon't use the duo chrom unless I am stuck. For me, it is far too subjective and depends on clear media and large pupils to be sensitive. Some times it can be over sensitive.

For children I always finish with a plus one blur as a final check (if that still gives 6/6- - I consider cyclo)

My routine will balance - but I always push them hard for very tiny letters - it is hard to hold your accom steady to read really tiny letters and this helps me understand the end point.

"why is it better to keep it equal or just on the green before cross cyl?"

So when you do cross-cyl the blur of the target changes size, but not shape.

"when do other people mainly use it?"

I find it very good for balencing the two eyes in myopes without media opacities. However, equal on Duo should not in my opinion be considered a technique for pushing the plus. Specifically, when binocular balencing I ensure BE same on Duo: equal, sl red, or sl green - it does not matter, as long as the eyes are the same. Then I fog BE with plus spheres and gradually reduce binocularly until maximum VA achieved. This is their refraction. Determining their prescription is more of an art.

I bow to the master :-) palfo

I was let to believe that the duochrome should be balance or just on green before cross cyl is to allow the Px to have some accommodation to move the circle of least confusion thus allowing them to decided which lens gives a clearer image?

I agree with palfi, I hardly use the duochrome as I find it is too subjective and does not relate to visual tasks in the real world.

To binocular balance, I simply use the last 2 or 3 letters on the line of best acutiy and just push the plus with the other eye fogged appropriately. Offtern it is useful to recheck the fisrt eye after it has fogged for sometime.