Author Topic: -5 both eyes, what do I do when reading a book ?  (Read 1290 times)

Offline rtdfgdfgdfgdfg

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-5 both eyes, what do I do when reading a book ?
« on: October 08, 2014, 04:39:35 PM »
After reading this site

I am confused.

Should I use a plus lens to read a book ?

However, when I do this, I am closer to the book,

than when I read without glasses at the "blur point".

My question is, will reading with a plus lens, even if I am closer to the print, improve my eyesight ?

so for example, my active focus point is 15 cm from a book without glasses.
with a plus lens, it is 10 cm.
Will using the plus lens improve my eyesight ?
I have to get closer to the book to see it. How could this help me ? It doesn't sound it would.
Or does it ?

Click image to understand


« Last Edit: October 08, 2014, 05:42:58 PM by rtdfgdfgdfgdfg »

Offline Hillyman

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Re: -5 both eyes, what do I do when reading a book ?
« Reply #1 on: February 27, 2015, 09:04:54 PM »
The plus lens system is meant to be used on the distance prescription, i.e., with your glasses on (as if you were emmetropic, or had natural 20/20 vision). The idea is that with the plus, you would be able to focus at close things but have less close-point strain. With less close-point strain, the eye can adapt and become less myopic. (Myopia is the eyes' exquisite adaption to reduce close-point strain, by making the "infinity" point closer and so making the distance blurry. Of course, putting minus lenses that restores the infinity to a distance point--so you see distant things clearly again; that's why people go to the optometrist--actually puts the eye into a vicious circle of becoming even more myopic to continue to try to relieve the new and continuing near-point strain.)

So if you have a plus 1 diopter lens with your regular prescription and you are holding the book at 40 cm or so, your eyes are actually at the accommodation that it would usually have for looking at something 65 cm or so. Likewise, if you held the book at 30 cm, your eyes are at the accommodation for 40cm.

Using a plus 1 lens on your -5 prescription is the same as saying that you are using a -4 prescription. Your distance vision would be blurred, but your eyes would have less strain when you are reading.  What you want to get is a plus lens that in combination with your glasses will given you a reading distance that would allow your eyes to see the book clearly but with no or very little near-focus strain (your distance vision will be totally blurry when you look up from the book). I would guess that this would a prescription equivalent to your current prescription with a +2 adjustment, or about -3.00.

As a postscript (added a day after the above): if you read without your glasses, that's equivalent to using a +5 lens for an emmetropic person. You can practice the active focus (Dr. Frauenfeld's term) or print pushing (I have seen this term in this forum, I believe) by holding the print just a little bit beyond the blur horizon. The blur horizon is that point at which you start losing the acuity.  Doing so encourages the eye to "reach out" to see farther.
« Last Edit: February 28, 2015, 07:27:52 AM by Hillyman »