Cylinder Axis Refinement

Cylinder Axis Refinement
The next step is to refine the cylinder axis.

Our goal with this step is to get the axis of astigmatism oriented into the position that gives the maximum visual acuity.

The first step in refining the cylinder axis is to isolate a line of letters. Generally, the 20/30 line is used. If the patient cannot see 20/30 at this point, then choose a row that’s one line above his or her best vision.
Swing the JCC in front of the eyes so that the axes of the lens …straddle… the axis of the instrument’s cylinder.

In other words, at this point we don’t want the axes of the lens to be in line with the instrument’s cylinder, like this…..,
…but instead we want it to straddle the axis like this…..

Next, we’re going to flip the JCC lens and, just like in the last step, we’re going to observe which choice our patient likes better. This time, we’re going to pay particular attention to where the white dots are located when Joe makes his choice.

So lets’ do it
We’ll again ask “which is better, one….”.
And now note that the white dots are here…
..and then flip the JCC like this…
“…or two…”
…and now note the white dots are now here.

In this case, Joe likes lens two better,

This is the option where the white dots were, …. clockwise… to the current cylinder axis.

By choosing choice two Joe is telling us that he wants the cylinder axis to be moved towards the white dots. At this point we’re going to move it about 15 degrees in that direction, like this…

From here, we’re going to keep doing what we call “chasing the white dot” and essentially “narrow in” on the patient’s true axis. Every time the patient makes a choice, we’re going to move the cylinder axis towards where he liked the white dots.

If the patient keeps asking us to move the axis in the same direction, in this case clockwise, we’ll keep changing it in 15 degree increments. If he reverses the direction and wants the axis moved counterclockwise we’ll start to adjust it in 5 degree increments. Every time he switches directions we’ll change the axis by smaller amounts until he isn’t able to make a choice anymore.
If he can’t make a choice between the options we’re giving him, we’re where we want to be and this step is over.

One more thing: Sometimes when you’re showing the patient different options with astigmatism, they comment that the letters look stretched or compressed or lean one way or the other. Ask the patient to ignore these details and to focus on which option has the better contrast or simply looks better.


To summarize, the cylinder axis refinement part of refraction involves
… isolating the 20/30 line on the eye chart (or one line bigger than the best vision)
… positioning the JCC’s axes so they’re straddling the astigmatism axis
… flipping the JCC and noting which choice the patient likes better

…and moving the cylinder axis toward where the white dots were when the patient made their choice.