Sitting far away from computer

Hello Fellow EM’ers,

I use a wireless keyboard and mouse for computer work and typically sit about 70-80 cm away from my monitor. For my differentials, I’ve been using plus lenses (+0.75) over my contact lenses (-9.50R/-9.50L).

If I were to remove the plus lenses and sat further back (say 90-100 cm away from monitor), i.e., until I reach the edge of blur, is this essentially achieving the same objective as wearing differentials, which is to avoid being overprescribed for close-up (to reduce eye strain).

In other words, is “contacts with plus lenses at 70-80 cm (edge of blur)” = “contacts only at 90-100 cm (edge of blue)”? Note: Under both scenarios, I would be sitting ergonomically.

I’d love to hear your thoughts.


Wearing distance correction for near work = wearing distance correction for near work.

I don’t know about the math. It doesn’t add up.

100 / 90 cm = 1 D
100 / 0.75 = 133 cm

You have to figure out what distance is the edge of blur for you. You can test it by sitting at 90 cm from monitor with contact lenses in. Are you just at the edge of blur? A little closer is clear and a little back is blurred?

Perhaps ciliary spasm is contributing here.


Hi shaerah,

Yes, you’re right, my math doesn’t add up. I didn’t really measure exactly my edge of blur. Because of that, I probably should have asked my question more generally, which is:

Can my “differentials” be achieved by not wearing plus lenses and sitting back further (just at edge of blur)?

I was just wondering/curious if, by doing this, my EM journey will not be as successful. Most of what I’ve read on the EM blog/wiki/forum talks only about wearing plus lenses over contacts for differentials.

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If you are at the edge of blur and then that should be fine – except how can that be if you are wearing distance correction? If your distance is under-corrected by enough then technically I suppose you would be wearing differential contacts.


I think as long as you’re able to keep the screen back far enough you should be achieving the goal of keeping your eyes from accommodating constantly for near and entering cilliary spasm. That having been said, the usual rationale for plus lenses over contacts is that the contacts provide the proper correction for distance vision (or almost the full correction for distance vision) and the plus lenses make it so the monitor is at the end of your range of blur.

If the contacts are only enabling you to see clearly 90-100 cm in front of you, it would be hard to drive or walk anywhere wearing only the contacts. Do you wear a separate pair of minus glasses over the contacts when you get up from your desk?

As for the math, with contacts that leave you under-corrected by 0.25, your distance to blur in meters should be 1/0.25=4 meters. With plus lenses of 0.75 on over the contacts, the distance to blur should be 1/(0.25+0.75)= 1m = 100cm.

If in fact the edge of blur is 90cm with your contacts, then your contacts are leaving you with an under-correction for distance of 1/.9= 1.11D which is a big under-correction. So with those contacts you’d want to wear minus glasses of about -1D over your contacts for outdoor or driving time.

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If your contacts are your norms and give you acuity well under 20/20 on the Snellen and you sit very far from the screen you might be able to create a tiny blur.
However, if your contacts as norms give you clarity at distance, it is very unlikely that you can sit far enough from the monitor to create blur and still be able to work at the same time…
So the most important question is if you can create “clearable” blur at monitor distance with your contacts.

If you asked this question because you work in front of a screen and you can’t stand the glasses for the 8+ working hours, there is always the option to wear contacts that are differentials in strength. If you work from home you can choose a strength that you can wear all around the house, but those will definitely be glasses that will require you to sit around a metre from the monitor when working.
And then when you go outdoors, you can pop a pair of extra -0.5D or -0.75D over them. Assuming the distance vision time is a lot shorter than the working hours, so it will be 1 to 3 hours vs. wearing reading glasses for 8+ hours in front of the monitor.
People who are able to wear contacts all day long every day seem to prefer this way.

Or you can wear differential contacts at home and change them to stronger contacts before leaving home.


People try many things to avoid diffs. but diffs are the first big step in the right direction for vision improvement. If you go through your journey trying to find hacks, you are most likely going to waste a lot of time repeating mistakes others have already made. That is not to say you can’t work out what works for you, but the foundational things are foundational for a reason.
Also point of reference I actually do use my computer at between 100 and 110cms and still use diffs .5 to .75 below my normz (depending on where I am in reduction cycle). So unless you are using your tv as a monitor from like 15 feet away I would stick to diffs. Bianca made solid suggestions above.
Best Wishes


I actually re-remeasured today and with my -9.50D contacts on, my distance to blur is more like 110-120 cm, although at that distance from the computer, it’s a bit difficult to really see exactly where the edge of blur is. I’m measuring this by looking at a Word document with 12-pt font. Depending on the time of day, I can see 20/30 to 20/40 with my contacts. For driving, I wear -0.50D over my contacts.

Yes, this was why I was asking the question. I basically wanted to know what my options were, so that I can change it up every now and then throughout the day. For example, I’d wear my contacts (norms) and plus lenses for a few hours, and then take off the glasses and sit further back. I’ll probably take this approach for now and see how it goes. I did consider the contacts-as-diffs idea, but then I’d have to buy some new contacts, although I would be able to use them later as norms, when/if I reach that point.

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I completely agree. I do want to learn from other people’s mistakes. I’m not looking for hacks, just looking for flexibility and options.

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It sounds like the -9.5 contacts are too strong to just use distance as the only tool to get the computer screen to the edge of blur since the screen has to be more than a meter away to avoid having to use accommodation.

If I were you I’d try to make up some comfortable single vision plus glasses in a few strengths (+0.5,+0.75, +1), those would let you move in closer to the screen and still be at the edge of blur. Maybe you could start out with the +0.5 and in a month or two if you’re having to roll your chair back too far from your desk to get to the blur horizon you could switch to the +0.75. When you drop to -9 contacts you probably wouldn’t need plus lenses for the computer screen at first.

You could keep using those glasses for the next number of years while you’re slowly working your way down through the contact lenses. If I remember correctly the contact lenses only come in half-diopter steps, so you’ll probably want to be using lenses over them for “fine tuning” to deal with being able to keep the screen at a comfortable working distance, and being able to add on enough correction to drive, etc.

-9.5 contacts are kind of in an awkward “no mans land” for you right now where they’re just too strong for near work, and not strong enough for distance vision.


Funny you should suggest that I get a bunch of plus glasses, because I do have those already (+0.75, +1.0, +1.5). I haven’t been able to find +0.5 glasses yet. Today, I started the day with the +1.0, but then by midday, I had to use the +0.75. Then a few hours later, I had to sit closer to the monitor with the +0.75, since I don’t have +0.5. I completely agree about the “no man’s land” reference. I can’t wait to drop to -9.0. In fact, I have those contacts already and wore them all day Saturday just to see how they feel as norms. (No close-up work on the weekends.) They were perfectly fine. I even saw 20/20 in the morning, right after putting them on. But then I read a post on this forum about how someone reduced their norms too quickly and developed a double-vision situation. So, I’ll just be patient and wait a few more weeks.

Thanks for all your advice. It’s much appreciated.


Wow! How are people here feasibly standing this far away from their screens? I’ve never seen a desk that deep.

I use differentials +1.25 over my norms. With my norma I can see 20/50. I think you’re in a good place now. You just need to be sure to give your eyes a challenge but not too much that you quit in 6 months.
The glasses over contacts worked well for me but I eventually got tired of the distortion and lower quality plus glasses. So I just good anti-reflective glasses for the diff and this made all the difference in my daily enjoyment of work.


Yea, my desk is pretty deep but I also put my wireless keyboard on my lap, which allows me to scoot my chair back from my desk. But based on the suggestions in response to my post, I’ve decided sit closer and wear +1.0 glasses over my contacts to get that blur challenge.

May I ask what “distortion” you’re referring to when said you used plus glasses over your contacts? Maybe I should be investing in plus glasses with anti-reflective coating? I’m using cheap plus glasses from Target.


Those might be OK if they fit you well, but if I were you I’d measure your PD (if you don’t know it already) and have some glasses made up from CR-39 lenses for about $5 to $20 per pair that fit you.

If your lenses aren’t centered properly (wrong pupilary distance) it induces prism that you probably don’t want. Personally, I would get the premium anti-reflective coatings, too. [Anything you can do to reduce eye strain is good, getting outside and away from the screen is even better.]


I do know my PD from one of my opto appts a few years ago. I’m assuming it wouldn’t have changed. I’ve never heard of CR-39, so I’ll definitely check it out. I usually get polycarbonate for my high myopia distance glasses, as I need to do everything I can to reduce the weight and thickness of the lenses.

I just checked Zenni, and it looks like they offer CR-39 lenses as their standard lenses.

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CR-39 is just the cheap plastic, but it has the best optical quality, one of those happy times when cheap is good. The higher index lenses are thinner and a lot more expensive but the optical quality is worse. (But it makes sense if your prescription is -9 like for your distance glasses.)

Since the readers are low powered +1 you don’t need the higher index for them. If the Target readers work well for you there’s nothing wrong with that, I’m just thinking some bigger and more comfortable glasses made for you with the nice coatings would be ideal for long hours in front of the computer.

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