How I learnt active focus... using astigmatism?

So on the 14th of December I figured it out and learnt how to do it, and I hope my technique can help someone else get the hang of it if they’re having trouble. For context my “official” numbers are -4.25sph and -1.25cyl. Measured myself about -3.8sph -0.3cyl. I have a small amount of astigmatism in my eyes and I feel this may have aided the technique but it should work nonetheless.

For measuring the astigmatic axis I pulled up a Siemens star chart, one used to find astigmatism in photographic lenses, and combined it with a protractor around the edge.

Siemens star w protractor

I cover one eye. When I got one axis sharp and the rest in slight defocus I noticed that the blur in the out of focus area wasn’t constant. The interference between the out-of-focus lines created a sort of interference (moire?) that I saw fluctuate radially in and out of the centre.

After a short while of staring at it I noticed I could ever so slightly manipulate how close the blur/interference gets to the centre of the chart. I entertained this idea. The interference of the the out-of-focus lines created a sort of visual feedback to the brain as I tried to manipulate the lens in my eye. The in-focus lines caused by astigmatism presented a reference point to what all the out-of-focus lines ought to be and it became a game.

Eventually I got the blur to retreat closer and closer to the centre, and before long I was seeing all the lines sharp with equal boldness. I wasn’t able to hold it for long at this point, so I practised it a few times to eventually get the technique down.

A couple of days later I was listening to a podcast and looking out of the window at a tree without leaves. I was wearing my differentials of -3sph only, as I hadn’t ordered any normalized yet. At one point I stared at it and tried using the technique I had learnt. To my amazement I watched as the tree very slowly came into focus. Over one dioptre of blur cleared up and even the tiniest branches and the trees in the distance came into sharp focus.

The first time I did this it was quite jarring as it’s so dramatic and I’m technically not supposed to be able to see this clearly with just a -3sph correction. Today I can get it in focus much quicker and hold the focus for a little longer. If I get any double vision or ghosting during AF I can blink and it’s gone, though sometimes it takes a few tries.



yes you will also be able to do this (maybe not to full clarity) without any glasses soon

if my understanding is correct, the double vision should be something you work on - not blink to get rid of it but keep trying to look without blinking - after a while your brain will get that you are trying to clear it up and start fusing the images. This is how I understand the guide to double vision on this forum and I tried it myself and works better after some practice

yes I also initially got much lower cyl value than my official prescription. Don’t want to dishearten you but when the difference is THAT big (1 D) it is highly likely to be measurement error on your part. Took me the best part of a year to get better at measuring cm to blur on the weak axis to get an accurate cyl value . Now I am getting near to what my official prescription is

and don’t forget you are looking at a contact lens prescription when you measure to your eye (compare to that, not to glasses prescription)

1 Like

I did notice that sometimes it fades away after a few seconds. Thanks, will keep that in mind!

I’m not surprised if my cylinder measurement is wrong to be honest. Sometimes the weak axis measures higher cm than the strong axis, which is backwards. That said I picked up a pair of jackson cross cylinders, and -0.5cyl is seems to be a slight over-correction (makes the axis rotate 90°compared to without).

@that_h_guy: Out of curiosity, when you were doing this were you wearing your differentials with cylinder correction or doing something else? I’m trying to see if I can replicate the effect.

I was doing it without any glasses for the most part. My differentials don’t have any cylinder in them, so if I kept distance at the edge of astigmatism while wearing them it’d work too.

1 Like

Okay, that makes more sense. While I have a small amount of astigmatism (-0.50 in one eye and -0.25 in the other) I have retained cylinder in my differentials. I’ll try it without glasses on, or maybe wait until my new trials lens kit shows up and try it with differential correction without cylinder to see how it goes.

Great tip, thank you. May I ask on which point do you focus? On the centre? Or anywhere on the line? Do you change the point you focus on?

I noticed that while staring at it with one eye all lines start kind of dancing and change sharpness but I could not make it to the point you have (blur disappeared).

I kind of looked around the whole image, but mostly in the out-of-focus area.

Yes this is the effect. The trick is to relax but at the same time engage your eye, without facial muscles (at least for me).

1 Like