I found 2 videos that are really practical in explaining how to use the test lens kit to measure astigmatism. Basically they are walking you through the measurement step by step with much better details than other videos.
With Stenopic Slit
Step by step explanation on how to use the stenopic slit with the fogging lens
This one is a bit difficult to listen to, but super practical and I absolutely important points on how to check if the cyl was selected correctly and if needed at all
0:26 What is JCC and how is it made? Plus available powers
3:00 Meridians and marking on the JCC
4:06 Verification of cylindrical axis with steps
6:20 With examples
8:29 Was the cylindrical axis correctly selected?
Important point: No improvement of clarity in both position = the power of cylindrical lens in trial frame is correct. I believe this is what a lot of high street optos miss with short time per client. They just trust the machines’ measurement on the axis.
9:29 Verification of cylindrical power with step by step also shows the end point of power verification
11:00 Determination of presence of astigmatism i.e. do you need a cylinder correction at all?
Watching it at 1.5 speed makes it easier to listen to
I don’t wear corrections anymore, I don’t have a test lens kit, I only have 2x JCCs (cost me about 15 euros). One with 0.25D and one with 0.5D and I just check my transient astigmatism. It’s wandering around depending on the habit inducing the vision deterioration.
I developed this idea that when I have many bad days in a row with lots of screen time and very little good habits then my eyes don’t get equally ruined. The first sign is some astigmatism. A part of the eye giving up on accommodation. If the bad habits are kept up long enough this could turn into a full SPH drop… (Full SPH because I do stop the root cause, just don’t always have the time immediately to compensate with good vision time to reverse. Otherwise I’d induce cyl progression)
Hope these videos will be helpful for others, too