Feel that I have made a mistake

Hello All,

Warm Greetings!

I have gone through Jake’s free 7 day course and saw the youtube videos which creates confidence that I can also reverse my myopia.
Based on the centimeter report and my current prescription from the optometrist, I had decided to reduce 1 diopter to have my first differential.

My prescribed reading : Right Eye, Left Eye -
spherical - -2.00 , -3.00
cylindrical - --2.50, -2.00
As per Differential : Right Eye, Left Eye -
spherical - -1.50, -2.50
cylindrical - --1.50, -1.00

Got my differential glasses and was very happy to wear the same with the feeling “I am on the right track”. It has been around 3 months and I thought of checking it.

Went to the lens shop in the evening hours after my work and the test also happened in the dark room with focused light on the chart.
I was surprised to see the result. Measurements state my power has increased by 1 diopter than the earlier prescribed reading. Don’t know what mistake I have made. Did anyone come across this scenario? pls advice.

Welcome to the forum

Your differentials didn’t follow the EM method.
If I oversimplify the EM method: the typical average gap between full prescription and differentials is 1.5D in the sph. This is an oversimplification, a rule of thumb - a lot depends on your eyes and the working distance, too.
Would you mind confirming what your new measurement is by the opto? including cyl - since you had a significant cyl measured in the original prescription… Has that changed while the sph increased?
If the sph increased but the cyl decreased that would count as a win reducing prescription complexity.
And would you mind confirming your own measurements - cm from monitor, acuity on Snellen?

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Do not rely on the results of one lens shop. Learn how you could measure your eyes by yourself consistently. Snellen chart, cm or with help of a device like the ones by EyeQue. I will get EyeQue VisionCheck this week. Can’t wait to test it. Will share my opinion later.

This alone is enough to account for the worse measurement. You would likely get better results in the morning while your eyes are fresh. Eye sight varies a great deal from day to day as well as throughout the day so keep that in mind. One of several reasons we don’t worry over much about the opto measurements here, we learn to rely on our own measurements.
Like Bianca though, I too wonder what prompted your choices in your differentials. You do have a complex correction, but I am not following how you chose the correction you did.

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@BiancaK @Reannon

When I had started I was able to see 20/70 with very less clarity. On April 20th, I got my differentials. I felt some uncomfortable for some days, but later my eyes had adapted to those lenses. I found myself improving through my centimetre measurements ( my centimetre was at 33-36 cm when I had started and then kept increasing gradually till June, i.e, it went till 48 cm. I was able to see clearly without my glasses till 45 - 48 cm ). At the same time I was able to see 20/50, not totally clear, but yes 20/70 was very clear.

It was the month of July when my screen time had increased from 6 hours to 8 - 9 hours, my centimetre measurement went down to 40-43 cm. I thought that, this is the usual variation that comes in cm measurement when eyes are relaxed and under stress. I did not realise the seriousness at that time, my cm measurement never came back to the previous range ( 45-48 cm ). But, I still continued to take measurements and Snellen readings thrice a day. My centimetre went down to 40 cm, my Snellen reading came back to 20/70, 20/50 was totally blur. I was just able to see that there are some letters there, but i was not able to read what was there.

Later, I realised that there is this change in readings and so I had visited the optometrist.
This was the diopter measurement he had given me
Right eye, Left eye
Spherical - -3,00, -3.25
Cylindrical - -3.00, -2.50
I myself couldn’t believe this odd change. (I went to the optometrist after 3 hours of screen time. That might be my greatest mistake).

my differentials?
I reduced 1 diopter from my cylindrical and 0.5 diopter from my spherical.
my screen time
7-8 hours

Do I understand this correctly? With
OD -2.00 -2.50
OS -3.00 -2.00
you saw 20/70 at distance? Or maybe this was uncorrected visual acuity?

Now with the recent refraction (eye measurement in office)
OD -3.00 -3.00
OS -3.25 -2.50
you can read 20/20 at distance (eye chart)?

If I am reading this right it sounds like you need (but have not gotten) stronger normalized for distance vision. You were quite under corrected when you began and have been taking a lot of stress on your eyes through the process. In addition to the strain you are likely also dealing with some blur adaptation. I would recommend you get the normalized very soon.
I am still a bit confused about your differential choice and how you arrived at the decision to make this correction, but if it is working for you, great! If I were you I would prioritize sorting a normalized that gives you stimulus without excessive strain. I prefer to aim for about 20/30 in indoor lighting on a 20 foot chart.

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I get it. We have exchanged 1.00 of cyl for an additional -0.50 of sphere and then dropped 1.00 from sphere. Supposedly cyl can be lowered by not more than 1.00. Norms can be reduced by 1-1.5 D. It might not be the ideal, but I found the diffs decision-making confusing myself.

I dropped sphere but did not reduce cyl at all for diffs and that was a mistake.


@Reannon @shaerah
My reading is the following:

When the opto prescription was
Right Eye, Left Eye -
spherical - -2.00 , -3.00
cylindrical - --2.50, -2.00

At that time the uncorrected vision was 20/70 with significant blur / little clarity on Snellen and the cm measurement was 33-36cm at that time.

This showed improvement in June.
To reading 20/50 uncorrected on Snellen - with significant blur / little clarity. But by that time the 20/70 was clear.
Parallel to that the cm increased to 45-48cm

Then came July
increased screen time and worsening habits and the new opto measurement at the end of a tiring day as:
Right eye, Left eye
Spherical - -3,00, -3.25
Cylindrical - -3.00, -2.50

What I suspect is that you may be mixing up terminology.

Differentials: glasses worn in front of a screen (at 45 to 90cms typically).
Normalised: used for distance at home or when walking, etc
Full correction: used for night driving, driving or situation when sharp vision is crucial

If you had good acuity (did you have good acuity?) at screens at 48cms it means you wouldn’t need differentials. However, based on your initial prescription with the high cyl that doesn’t sound very likely.
So the basic questions is: were you OK with good acuity, no eyestrain, at good distance with screen when uncorrected. If yes, then you don’t need differentials.
If not, and if you wore glasses with high cyl before on a daily basis, then your eyes are probably quite used to the cyl being in the correction. In that case, your reduction from the cyl may be too much. And the reduction from the sph - just by the general EM rule of thumb - is not enough.
So it is possible that the glasses you chose were too strong in front of the screen, but with not enough cyl to prevent you from straining your eyes. If you combine that with increased hours in front of the screen that can very well result in eyesight worsening.
I’m afraid you’ll have to get back to the drawing board to plan your correction from scratches again.


Mathematically you are correct of course.

However, if someone has had cyl in the prescription long and those glasses were worn daily over years, even the 1D cyl is a huge stretch to drop. The max 1D drop is more suggested for those people whose total cyl is less than 1D and the cyl in the prescription is relatively recent (i.e. the eyes have not got used to the distorted correction), but here the initial cyl was -2.5 and -2…
If purely converted by the formula as 1D cyl = 0.5D cyl, the original April correction was -3.25 and -4 in sph only.
The rule of thumb for differentials is closer to -1.5D when compared to the starting opto full prescription. For a -1D sph reduction only for close up, I’d say the distance from the monitor should be 90+ cms. I don’t get the impression that is the case here…


I definitely agree. These nuances are not easy to see when starting out.

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Well I am thinking maybe @Bianca might be getting more out of the post than I am… I didn’t get 20/70 as the uncorrected vision based on the shared correction (I inferred that was the acuity with the original correction prior to receiving diffs and being remeasured) but without further clarity from user I am kind of lost altogether here…
Based on this:

I am understanding that the user is indicating that they are quite under corrected in their distance correction, though it is possible upon revisiting I am thinking maybe they meant in the diffs? And if my impressions are correct here I feel as though user might be wearing diffs most of the time? Or else Bianca is reading it correctly in which case I would assume user is quite over corrected…
@ocean-write what is your home measured acuity in your full correction from prior to the new measurements? Maybe you could clear up the above questions?

Fair enough, though user hasn’t indicated if the diffs correction is working well or not, only that they felt good about being “on the right track”. As Bianca indicated though unless the user is at a larger than typical distance from the screen these diffs are likely still on the strong side and therefore still causing hyperopic defocus, added to the increased screen time in July I can understand why the new opto measurement indicate worse vision, though since it is a short term change it should be easy enough to reclaim that ground.

For sure! Some backpedaling is almost always required.


@Reannon @BiancaK , shaerah

Yes I do wear my differentials for most of the time. Also it did cause some strain.

Yes I had some discomfort wearing differentials. Under a relaxed condition, I was able to read 45-48 cm away from the screen without any glasses.

That should have been my mistake.

A fresh start will help me correct my mistakes. New normalised and differentials.(so far i used only my complete correction and differentials and had no ‘new’ normalised.) I will drop the mathematical approach to calculate my differential dioptre.

Thank you for advising.


Yes back to square one sounds like a good move.

This indicates that your diffs were much too strong.

Might help some more yet… Hope your next go works out better.