Hey, [s2Get user_field=”first_name” /].  It’s time we chat a bit about astigmatism.

I have been promising you more on the subject of astigmatism for a while now. There is good reason that we do not discuss it in much detail before this point, and the program locks these sessions to avoid any jumping of the proverbial gun.

Astigmatism correction, in many cases, is excessive, and harmful.

We have discussed some of the background in the past. As your eyeball elongates, it stops being perfectly round. Keep in mind that it just takes a single millimeter of axial change to equal -3D in loss of vision acuity. These are minute changes in optimal shape, having drastic impact on your eyesight.

As your eyeball elongates, your vision begins do deteriorate differently, on every axis.

That is the short of it. For an in-depth discussion of the optics and biology, look to the blog for related subjects. For this program installment though, we will start to look at what this means to your case, specifically.

Before we continue – please keep in mind that this is ‘common case’ scenario.  Use the forum with questions specific to your case, and I’ll try to offer more specific suggestions for you.

There are always cases that will deviate from what we are about to discuss. It is likely though, that you fit this profile, if:

You have a normalized prescription of -2.25D or lower (we will discuss higher myope cases in an upcoming session).

At most, your astigmatism correction should be -0.50D. Accounting for overprescription, the dark room at the optic shop, let’s consider up to -0.75D. Anything higher than that, definitely drop me a note. It is quite likely that the prescription is simply erroneous or exaggerated – but I’d rather not make assertions in this general of a format, for your case.

Let’s look at this common low myope example:

  • You have been partaking in the whole program and all sessions so far.
  • You have had at least one normalized prescription change (for two distance prescription changes total).
  • You have reduced your prescription by at least -0.75D in the program.
  • You are at -2.25D or lower, normalized (and you can see at minimum 20/30 with it).
  • You have an astigmatism correction of -0.75D or less.

This is a very common case. You may have started at a -3.50D (or close to), you are on your second normalized prescription, you are good about using only differential or no glasses for close-up work. Here is the (likely) reality for you:

You don’t need any astigmatism correction.

And if you are at -1.50D or lower, even if you only had your first normalized prescription (for at least 60 days), you don’t need astigmatism correction, either.

There are two problems, with this statement:

1. Not needing it, doesn’t necessarily equal being able to just drop it.

None of us needs nicotine or alcohol, either. Still, a sudden withholding might have some adverse health consequences. Likewise, dropping a -0.75D of focal plane correction may be too much, all at once.

2. You can’t (or shouldn’t) change your normalized prescription for more than one axis, at a time.

If your next normalized prescription should be a quarter diopter lower, but you want to work on astigmatism now, we can’t do both at once.

Of course all of these insights creates questions:

  • Should you go for astigmatism correction change, for your next normalized prescription?
  • Are your eyes ready for this change, now?
  • How much could you drop from your astigmatism correction, at any one time?
  • What if you are above -2.25D?

We will address all of these questions in the upcoming session about astigmatism correction. Today’s news is simply, that if you meet above criteria, you actually don’t need it. Just as the rest of your prescription history is one of gradual, incremental overprescription, astigmatism correction is significantly overused.

If you have higher myopia, we can’t be so black and white about these statements. A high myopia case of -6.00D could have significant enough axial elongation that some degree of astigmatism correction is warranted – though not the high numbers I often witness.

We will cover high myopia cases, as well. A bit more forum input may be appropriate there, to provide you with specific suggestions.

A few other links worth checking out:

Everything astigmatism related, in the blog.

A quick astigmatism test.

Let’s dig into this more soon, and if you’re low myopia and fit the above scenario, getting away from astigmatism correction, in particular for your differential, is going to be a great next step!



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