# Why are there numbers on my contact lenses?
**URL:** https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743
**Category:** Factual Questions
**Created:** [February 6, 2009, 7:44pm UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743 "2009-02-06T19:44:59Z")
**Posts on this page:** 19
**Page:** 1
### Author:  [@not\_alice](https://boards.straightdope.com/u/not_alice)
#### Post date: [February 6, 2009, 7:44pm UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/1 "2009-02-06T19:44:59Z")
I just noticed yesterday when cracking open a new pair of disposable lenses that there are tiny numbers engraved on each one. They don’t seem to match any of the numbers on the packaging (but they are small, and I don’t have my lenses in to be able to see well, so…)
What are they, and what effect do they have on my vision?
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### Author:  [@Morbo](https://boards.straightdope.com/u/Morbo)
#### Post date: [February 6, 2009, 8:04pm UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/2 "2009-02-06T20:04:47Z")
If they’re 123, they’re there so you know which way to put them in. If the 123 aren’t backwards while you’re holding it on your fingertip, you know it isn’t inside-out.
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### Author:  [@Athena](https://boards.straightdope.com/u/Athena)
#### Post date: [February 6, 2009, 8:18pm UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/3 "2009-02-06T20:18:44Z")
Yup. I wear AccuVue brand contacts, and they each have AV on them so you can tell if they’re inside out.
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### Author:  [@not\_alice](https://boards.straightdope.com/u/not_alice)
#### Post date: [February 6, 2009, 8:31pm UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/4 "2009-02-06T20:31:13Z")
> [@Athena](#):
>
> Yup. I wear AccuVue brand contacts, and they each have AV on them so you can tell if they’re inside out.
I don’t think it is that - I have had contact lenses for most of the period since 1979. No one ever told me about this, and I never have inside out problems - The shape of the lens on my finger tells me that, and if it doesn’t, the pain in my eye will. I am guessing I have made that mistake maybe 3-5 times in 30 years.
Asking people to see near microscopic numbers when they are badly nearsighted hardly seems like the right answer to me.
It seems to me I once had some prescription where there was a blue dot on the right one (probably before disposable), but I can tell left from right by careful tracking, and both pain and incorrect correction should I mix them up. So I don’t think it is that either.
I am more inclined to think it is some sort of manufacturing batch tracking number, but then I would expect a longer number then 2-3 characters.
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### Author:  [@ChrisBooth12](https://boards.straightdope.com/u/ChrisBooth12)
#### Post date: [February 6, 2009, 8:33pm UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/5 "2009-02-06T20:33:00Z")
I doubt this to i wear contacts and it is very easy to tell if they are inside out before you even put them in your eyes
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### Author:  [@dangermom](https://boards.straightdope.com/u/dangermom)
#### Post date: [February 6, 2009, 8:46pm UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/6 "2009-02-06T20:46:55Z")
Some of them come with letters or numbers on them anyway, so you can tell. Mine say 123, and I just look at them very close-up before I put them in. Or with my glasses on. The cardboard package will have a little diagram, showing wrong and right.
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### Author:  [@Athena](https://boards.straightdope.com/u/Athena)
#### Post date: [February 6, 2009, 8:54pm UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/7 "2009-02-06T20:54:40Z")
> [@not\_alice](#):
>
> I don’t think it is that - I have had contact lenses for most of the period since 1979. No one ever told me about this, and I never have inside out problems - The shape of the lens on my finger tells me that, and if it doesn’t, the pain in my eye will. I am guessing I have made that mistake maybe 3-5 times in 30 years.
Er, no. The call it an inside-out marker. Even the [Acuvue website](http://www.acuvue.com/wearing-apply-remove.htm#put-in) talks about it - check out Step 3.
I’ve worn contacts since the early 80s, and I used to be able to tell if they were inside out from the shape, but the Acuvues are so thin that it’s difficult. And sure, you _can_ tell from the pain in your eye, but I just check the inside-out marker cuz I’m just not a big fan of pain!
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### Author:  [@aerodave](https://boards.straightdope.com/u/aerodave)
#### Post date: [February 6, 2009, 9:30pm UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/8 "2009-02-06T21:30:52Z")
The inside-out markers are definitely there for that purpose. That’s because while it’s easy to tell for some lenses, it’s not so easy for others. I have fairly flat lenses, and my disposables are quite thin. The combination of these two factors means that I actually have trouble telling the difference between inside-out and right-side-in. I used to have an easier time with older lenses.
Then again, I wonder sometimes if it matters. If I can’t see the difference, is there a difference? There must be, because I can feel an inside-out lens even when I can’t see it.
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### Author:  [@Athena](https://boards.straightdope.com/u/Athena)
#### Post date: [February 6, 2009, 10:20pm UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/9 "2009-02-06T22:20:21Z")
> [@not\_alice](#):
>
> I don’t think it is that - I have had contact lenses for most of the period since 1979. No one ever told me about this, and I never have inside out problems - The shape of the lens on my finger tells me that, and if it doesn’t, the pain in my eye will. I am guessing I have made that mistake maybe 3-5 times in 30 years.
:smack: I realized after I wrote my first reply that you were talking about YOUR lenses, not mine.
What brand do you wear? Maybe you can look at the web site for them and find more info about the numbers.
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### Author:  [@not\_alice](https://boards.straightdope.com/u/not_alice)
#### Post date: [February 6, 2009, 10:22pm UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/10 "2009-02-06T22:22:46Z")
> [@Athena](#):
>
> Er, no. The call it an inside-out marker. Even the [Acuvue website](http://www.acuvue.com/wearing-apply-remove.htm#put-in) talks about it - check out Step 3.
Mine are not accuvue, but rather [these](http://www.bausch.com/en_US/downloads/ecp/visioncare/general/SLtoric_PIB.pdf) (pdf)
No mention there of these engraved numbers.
[This page](http://www.bausch.com/en_US/downloads/consumer/visioncare/general/sftoricinsert.pdf) (also pdf) for the doctors seems to indicate there are lines on the edges, but doesn’t mention numbers. I will have to take a closer look tomorrow.
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### Author:  [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)
#### Post date: [February 6, 2009, 11:50pm UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/11 "2009-02-06T23:50:07Z")
I’m almost certain they’ll be inside out markers as well. They’re put on regardless of how easy it is to tell if a particular type of lens is inside out or not. I’ve used Acuvues and Bausch & Lomb lenses and both had these markings, the optometrist also briefed me on their use. It can be useful to someone who’s new to lenses.
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### Author:  [@not\_alice](https://boards.straightdope.com/u/not_alice)
#### Post date: [February 7, 2009, 1:29am UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/12 "2009-02-07T01:29:58Z")
[quote=“1920s Style “Death Ray”, post:11, topic:484743”]
I’m almost certain they’ll be inside out markers as well. They’re put on regardless of how easy it is to tell if a particular type of lens is inside out or not. I’ve used Acuvues and Bausch & Lomb lenses and both had these markings, the optometrist also briefed me on their use. It can be useful to someone who’s new to lenses.
[/QUOTE]
Well, wouldn’t their existence be on, say, the instructions, then? :dubious:
I should also note that I don’t think the string of numbers is the same on both lenses, and that of the ones I could identify so far, I have seen 1, 0, “.” and 2.
None of which would be a whole lot different when viewed from the other side. 😕
What do the indicators look like on the Accuvues?
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### Author:  [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)
#### Post date: [February 7, 2009, 2:42am UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/13 "2009-02-07T02:42:22Z")
“123”
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### Author:  [@AquaPura](https://boards.straightdope.com/u/AquaPura)
#### Post date: [February 7, 2009, 11:26am UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/14 "2009-02-07T11:26:10Z")
These numbers are usually used by the patient to tell if the lens is inside out or not, however they are further used by optical providers as a lens identifier and in some cases, a fitting guide.
~Aqua
Optican
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### Author:  [@Athena](https://boards.straightdope.com/u/Athena)
#### Post date: [February 7, 2009, 1:06pm UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/15 "2009-02-07T13:06:12Z")
> [@not\_alice](#):
>
> What do the indicators look like on the Accuvues?
It just says AV. If they’re inside out, they say VA. So it’s really the ordering of the letters, not the letters themselves, that tell you it’s inside out.
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### Author:  [@not\_alice](https://boards.straightdope.com/u/not_alice)
#### Post date: [February 8, 2009, 12:54am UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/16 "2009-02-08T00:54:49Z")
> [@AquaPura](#):
>
> These numbers are usually used by the patient to tell if the lens is inside out or not, however they are further used by optical providers as a lens identifier and in some cases, a fitting guide.
>
> ~Aqua
> Optican
No way these are inside out indicators. They are too small and hard to see. Anyone that can see them does not need lenses 🙂
I just had to study veryu closely to see what they are.
Each lens is different.
One says |N|S|, the other |1|5| (I think). These are right when seen form the outside, meaning if you stare deep into my eyes you will see them and be able to read them.
Precisely the angle you would not want them at if I was trying to see if they are inside out or not routinely. that took far too much handling to figure out.
Anyway, what I indicated as “|” angles towards the center, and the letters/numbers are probably 3 points high. As small a letter as you will ever see with your bare eyes.
That somewhat aligns with one of the docs I lined above regarding alignment measuring, but that one only mentions the lines, not the letters.
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### Author:  [@AquaPura](https://boards.straightdope.com/u/AquaPura)
#### Post date: [February 8, 2009, 12:06pm UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/17 "2009-02-08T12:06:29Z")
> [@not\_alice](#):
>
> No way these are inside out indicators. They are too small and hard to see. Anyone that can see them does not need lenses 🙂
>
> I just had to study veryu closely to see what they are.
>
> Each lens is different.
>
> One says |N|S|, the other |1|5| (I think). These are right when seen form the outside, meaning if you stare deep into my eyes you will see them and be able to read them.
>
> Precisely the angle you would not want them at if I was trying to see if they are inside out or not routinely. that took far too much handling to figure out.
>
> Anyway, what I indicated as “|” angles towards the center, and the letters/numbers are probably 3 points high. As small a letter as you will ever see with your bare eyes.
>
> That somewhat aligns with one of the docs I lined above regarding alignment measuring, but that one only mentions the lines, not the letters.
Ahhh… It seems you have yourself a pair of toric lenses there. The teensy numbers and slashes you see are a fitting guide for us providers. They help us see if your contacts are lining up properly on your eyes for the best correction. Also, they are usually unique to brand, so we may be able to tell what type of lenses you are wearing.
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### Author:  [@not\_alice](https://boards.straightdope.com/u/not_alice)
#### Post date: [February 11, 2009, 3:09am UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/18 "2009-02-11T03:09:08Z")
So is it that toric lenses have a variable thickness, and that blinking will rotate them to the proper position?
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### Author:  [@AquaPura](https://boards.straightdope.com/u/AquaPura)
#### Post date: [February 12, 2009, 1:54am UTC](https://boards.straightdope.com/t/why-are-there-numbers-on-my-contact-lenses/484743/19 "2009-02-12T01:54:39Z")
In most cases yes. A Blink or an eyeroll will shift the toric lenses into proper alignment.