Source
r/optometry•
DevonCM

How should I reduce the strength of my prescription?

So I need to get a weaker pair of glasses for using at shorter distances for long periods of time, like at my PC. But I'm not sure how exactly I need to adjust my prescription to lower the strength while keeping it accurate for my eyes.

I have slight astigmatism, and this is my prescription: OD: -0.75 -1.00 OS: -0.75 -1.25

If I reduce sphere to -0.50 on both but leave the cylinder, will that produce an accurate strength reduction? Or should I also reduce the cylinder values by the same amount?

I'm just getting cheap crap glasses but I want to make sure they at least work well. Thanks!

Posted Dec 2, 2014, 9:45 AM UTC

015
curiousincident•

Unfortunately you can't just go around changing your rx like that.

8
jfier•

What you are asking for needs to be prescribed to you by an optometrist. People over the internet can't do it and you can't do it yourself.

4
DevonCMOP•

Why? I'm not asking for a prescription. I'm asking what adjusting the values will affect, and if the sphere and cylinder are independent of each other.

-2
jfier•

As confusedinthegroove said, the cyl value will generally stay constant. How exactly do you know that reducing the sphere by 0.25 is what you need though? What if you need it reduced by more or what if it's some other problem altogether? It sounds like you're aiming to just order some glasses online and guess what number you should put in. What will you do if they arrive and they don't work as you wanted them to? I'm not in the USA but I've heard that online retailers there will verify with the optom that the prescription you enter is valid as well. You might find some way to get around that but overall you should still discuss the issues you're having with an optometrist.

2
DevonCMOP•

Well, 0 would be no correction. Since my prescription is only -0.75, a .25 change is quite a significant percentage of that. I suppose I could reduce it by .50 instead, but that's a drastic change. I might go for -0.40 if that were possible, but I guess these systems aren't very fine-tuned.

Thanks for the input. Unfortunately I can't just pay a bunch of money I don't have to get some doctor who only has a vague idea of what I want change a number value by a few points for me. Now that I know the values are independent, I can do that perfectly fine on my own.

Until the day comes where I can have nanomachines go in and rebuild everything in my eye for perfect vision, this is the sort of shit I'll have to deal with.

-1
confusedinthegrooveOptometrist FAOI•

Basically, people aren't being very nice in this thread and I really hope the responses, and the downvotes to your questions don't reflect how they treat their own patients.

First thing first, astigmatism is the same for all distances (near and far) for 99.999% of people. The axis(direction) and power remain the same, independent of the sphere (short sighted part).

Secondly, the reasons you're having difficulty using the computer screen could vary. It could be a natural aging process (are you older than 45?). It could be an imbalance or strain in the muscles in your eyes, or you own glasses might be too strong.

You are still best off getting your eyes checked out to find out the reasons you're having difficulty at the computer screen. It's not the best idea just to go tweeking your own prescription. An eye test is also advised every two years to make sure any eye conditions or systemic (full body) conditions don't develop.

There has been mention on this subreddit about how to get a cheap eye exam but I'm not sure where it was mentioned.

2
DevonCMOP•

Thanks for the honest response.

As far as difficulties; I can see my screens well enough close up, but I want to be able to sit slightly further back and still clearly see small text on a high-res display. Sometimes this difference is just leaning back in my chair. The full prescription is perfect for longer distances, but is unsurprisingly overkill for only a few feet. I'm 26, I had tests earlier in the year and everything's good.

0
confusedinthegrooveOptometrist FAOI•

This won't be what you want to hear, but at 26 your eyes should be able to focus through the correct prescription at all distances so the problem is either the prescription is too high (this can change within months) or as I said there is an imbalance or strain in the muscles, or something else. You said everything was ok at the last sight test but unfortunately we can't fully do every test under the Sun at every eye exam. If you were having no symptoms the doctor probably did not do a full muscle check.

Reducing the sphere MAY reduce your symptoms but it's not going to solve the root of the problem.

I know you would rather just tweak the prescription yourself but I still would advise the eye exam. Let me know if you have any more questions.

2
WhatTheJosh•

You're missing a couple of components to your prescription:

  1. You need to know the axis of your cylinder
  2. We'd need to know the strength of your add power
  3. The distance of your monitor in relation to where you keep your head

Also, it's best to just visit your regular optometrist to get an accurate prescription. If your last visit was recent enough, sometimes they'll just write out a prescription to accommodate a PC distance free of charge.

0
DevonCMOP•

Sorry, I didn't think the axis would matter in this case. The full prescription is OD: -0.75, -1.00, x110 OS: -0.75, -1.25, x090

I'm not sure what you mean by "strength of your add power", but this is all that I have listed. The distance I want them for is around 2-7 feet, where my main pair is for outside, driving, movie theaters, etc. The full prescription is just too strong to use at small distances where things aren't as out-of-focus.

I'd go to the doctor but I don't have insurance anymore, and I'm on a very limited budget. I was hoping it would be fairly simple to adjust. Thanks for the reply.

0
ToMetric•

7 feet = 2.13 m

1
WhatTheJosh•

In this case, it's not all that important; although, knowing the axis is important when dealing with astigmatism when generating for eye wear.

The add power is to determine how much magnification is needed to allow you to read up close. You may want to look into presbyopia if you're having difficulties with your kind of prescription.

It sucks, but it may be necessary to actually see an optometrist for a more accurate prescription than what you have currently. No one here will be able to give you a prescription analysis because what you're asking for is a refraction over the internet. I've seen some exams go for as low as $42 without insurance but you'll need to do some research in your area.

-1
curiousincident•

We have no clue how old this person is. Why should they look into presbyopia if we have no clue how old they are?

3
DevonCMOP•

All I want to do is slightly reduce the correction. I just don't know if adjusting the sphere value will throw the cylinder values out of whack and make them useless. If the cylinder values are static/independent of the sphere values, I can easily lower the sphere value to adjust focus/correction while maintaining balance for my eyes.

If they're inherently dependent on each other, I just want to know if they'd need to be adjusted equally. If changing either value completely screws up the other, then it would be a lot more complicated and require a new examination.

Basically, I just want to know if I can weaken them slightly by reducing the values a certain amount without completely changing how they function. I don't need a vastly different type of lens, just a little less strength.

-1
electric_curiosityOptometry Student•

Short answer, you can tweak whatever you like but you can't predict whether it will 'work'. When the optometrist do the the test to reduce the correction, he/she will need to take into account of your AC/A ratio (since you're 26), your lag/lead of accommodation (if you have any) and your final 'eye posture' (phoria, if you want to get technical) with the new reduced correction. If this is a bit technical for you to understand, then you would see why it is not a simple matter of reducing your prescription by a set number and see if it works over the internet.

2