# Contact Lenses **URL:** \ **Category:** Factual Questions\ **Created:** [December 28, 2010, 10:32pm UTC](https://boards.straightdope.com/t/contact-lenses/565654 "2010-12-28T22:32:58Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![Giddiupldy](https://avatars.discourse-cdn.com/v4/letter/g/8797f3/32.png) [@Giddiupldy](https://boards.straightdope.com/u/Giddiupldy)\ **Post date:** [December 28, 2010, 10:32pm UTC](https://boards.straightdope.com/t/contact-lenses/565654/1 "2010-12-28T22:32:58Z")
My son has been wearing glasses now for five months and I would like to get him contacts. How do I translate the numbers on his card to what he actually needs? It seems that the card has more info. than what is required for the online order form. His prescription reads OD: -1.25 -1.00 x 5 and his OS ADD is -1.00 -1.25 x 175. Could someone tell me how I would order contacts for this reading. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [December 28, 2010, 10:45pm UTC](https://boards.straightdope.com/t/contact-lenses/565654/2 "2010-12-28T22:45:57Z")
Short answer: You can’t. Longer answer: The existing spectacle prescription does not contain key dimensions needed for contact lenses - the base curve and the diameter. Get these wrong, and the lenses will be uncomfortable at best, and more likely, won’t fit and stay on the eye. ---
**Author:** ![3\_20\_59\_or\_bust](https://avatars.discourse-cdn.com/v4/letter/3/47e85d/32.png) [@3\_20\_59\_or\_bust](https://boards.straightdope.com/u/3_20_59_or_bust)\ **Post date:** [December 28, 2010, 10:46pm UTC](https://boards.straightdope.com/t/contact-lenses/565654/3 "2010-12-28T22:46:23Z")
It’s usually a completely different appointment/test with the doctor and a different prescription for contacts, as compared to your normal glasses. ---
**Author:** ![purplehorseshoe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/purplehorseshoe/32/2996_2.png) [@purplehorseshoe](https://boards.straightdope.com/u/purplehorseshoe)\ **Post date:** [December 28, 2010, 10:46pm UTC](https://boards.straightdope.com/t/contact-lenses/565654/4 "2010-12-28T22:46:28Z")
How old is your son? (Contacts require more maintenance and diligent hygeine than glasses.) Why do _you_ want to get him contacts? (I was expecting it to read “… and now he wants to get contacts.”) Since there are hard, soft, gas-permeable, toric etc. contacts out there, I’d think you’d want to let an eye dr. handle things for the first time. ---
**Author:** ![barbitu8](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@barbitu8](https://boards.straightdope.com/u/barbitu8)\ **Post date:** [December 28, 2010, 10:48pm UTC](https://boards.straightdope.com/t/contact-lenses/565654/5 "2010-12-28T22:48:13Z")
You need more info for contacts than for regular glasses. Optometrists are required to give you a lens prescription, not a contact prescription. Anyway, if he hasn’t been examined for contacts, that info is not available. ---
**Author:** ![purplehorseshoe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/purplehorseshoe/32/2996_2.png) [@purplehorseshoe](https://boards.straightdope.com/u/purplehorseshoe)\ **Post date:** [December 28, 2010, 11:05pm UTC](https://boards.straightdope.com/t/contact-lenses/565654/6 "2010-12-28T23:05:51Z")
These kinds of threads always crack me up. OP thinks they have a straighforward “How do I…?” to post and barely ten minutes in people are all going “NOOOOOOO O O O !!! Don’t do it! You can’t!” ---
**Author:** ![Digital\_is\_the\_new\_Analog](https://avatars.discourse-cdn.com/v4/letter/d/a88e4f/32.png) [@Digital\_is\_the\_new\_Analog](https://boards.straightdope.com/u/Digital_is_the_new_Analog)\ **Post date:** [December 29, 2010, 1:35am UTC](https://boards.straightdope.com/t/contact-lenses/565654/7 "2010-12-29T01:35:14Z")
Agreed - it’s a different prescription. If you want more information, you could [Ask the Optometry student](http://boards.straightdope.com/sdmb/showthread.php?t=590662). -D/a ---
**Author:** ![bleibtreu](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bleibtreu](https://boards.straightdope.com/u/bleibtreu)\ **Post date:** [December 29, 2010, 6:36am UTC](https://boards.straightdope.com/t/contact-lenses/565654/8 "2010-12-29T06:36:38Z")
> [@gotpasswords](#): > > Longer answer: The existing spectacle prescription does not contain key dimensions needed for contact lenses - the base curve and the diameter. That prompts me to ask: can you go in the other direction, using a contact lens prescription to create eyeglasses? I’m assuming so, based on recent personal experience. My eyeglasses are a few years old, but I’ve updated my contact lens prescription every year. I last did that about two months ago, and when I went to pick up the lens order a week or so after my exam I took along a pair of plain-glass lenses in designer frames that I happen to have come into possession of. I like the way they look, so was wondering if I could get prescription lenses placed in them. I asked the guy who rang me up, who I believe is one of the owners of this neighborhood store – but not an optometrist himself. He looked at them and said, “Yeah, that’s a nice frame. If you want them, we have your prescription so just let us know.” So I should have confirmed that, but it left me wondering… did he think that I have had a specific eyeglass exam, or is it really the case that the info from my contact lens exam is all I need to get lenses fitted for these? Obviously the base curve and diameter are meaningless for eyeglass lenses, but is there anything that’s missing from my current prescription that I’d need for glasses? Or should I ask the optometry student? 😉 ---
**Author:** ![Rhiannon8404](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rhiannon8404/32/17929_2.png) [@Rhiannon8404](https://boards.straightdope.com/u/Rhiannon8404)\ **Post date:** [December 29, 2010, 6:45am UTC](https://boards.straightdope.com/t/contact-lenses/565654/9 "2010-12-29T06:45:49Z")
My son recently switched from glasses to contacts. I took him in to the optometrist who fitted him with contacts. He’s 12 and adjusted to them very well. As other’s have said…he needs to be fitted. The nice thing about this is, an optometrist can fit him with a pair of contacts and if he really hates the way they feel, you haven’t paid for a whole box. ---
**Author:** ![bleibtreu](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bleibtreu](https://boards.straightdope.com/u/bleibtreu)\ **Post date:** [December 29, 2010, 6:52am UTC](https://boards.straightdope.com/t/contact-lenses/565654/10 "2010-12-29T06:52:45Z")
> [@Rhiannon8404](#): > > The nice thing about this is, an optometrist can fit him with a pair of contacts and if he really hates the way they feel, you haven’t paid for a whole box. Yep. My experience has been that they fit you with the lenses and you leave wearing a sample pair. You can place an order right away, or wait a couple of days to see if you’re comfortable with them first. ---
**Author:** ![Any\_Other\_Name](https://avatars.discourse-cdn.com/v4/letter/a/f17d59/32.png) [@Any\_Other\_Name](https://boards.straightdope.com/u/Any_Other_Name)\ **Post date:** [December 30, 2010, 5:50pm UTC](https://boards.straightdope.com/t/contact-lenses/565654/11 "2010-12-30T17:50:23Z")
I’ve worn contacts for years and have a pretty fair understanding off the specifications. I’ve read that a given base curve and diameter can vary from brand to brand; that is, base curve of 8.5 and diameter of 14.5 may fit ell in one brand but not in another. And most brands only offer 1-3 different values of base curve and diameter. I’ve read that there to some extent it’s a case of try something close and see how it feels. but all of this is a moot point because it seems that no one will sell contact lenses without a prescription less than one year old. I order online from 1-800-contacts and they seem to ship with just a Doctors name and fax number. I’ve been told that by law the vendor is required to request confirmation of prescription but if there is no response from the doctor within 48 hours, the vendor is able to ship. Do glasses and contacts require a valid prescription? Why are they required? ---
**Author:** ![Motorgirl](https://avatars.discourse-cdn.com/v4/letter/m/e36b37/32.png) [@Motorgirl](https://boards.straightdope.com/u/Motorgirl)\ **Post date:** [December 30, 2010, 7:21pm UTC](https://boards.straightdope.com/t/contact-lenses/565654/12 "2010-12-30T19:21:59Z")
> [@bleibtreu](#): > > That prompts me to ask: can you go in the other direction, using a contact lens prescription to create eyeglasses? > > I’m assuming so, based on recent personal experience. You probably couldn’t. I am basing this on my eyeglass presecription, vs my contact lens prescription. My eyeglass prescription has a significantly higher sphere than my contact prescription (diopters in the -5s vs the -4s, respectively). My optometrist says this is due to the distance between the eye and the lens for the different methods of correction. And the difference between the glasses and contact prescriptions are not equal for my right eye and my left eye. There is a greater difference for my left eye than my right. I can’t recall what differences might exist for cylinder and axis. ---
**Author:** ![Motorgirl](https://avatars.discourse-cdn.com/v4/letter/m/e36b37/32.png) [@Motorgirl](https://boards.straightdope.com/u/Motorgirl)\ **Post date:** [December 30, 2010, 7:23pm UTC](https://boards.straightdope.com/t/contact-lenses/565654/13 "2010-12-30T19:23:50Z")
> [@gotpasswords](#): > > Short answer: You can’t. > > Longer answer: The existing spectacle prescription does not contain key dimensions needed for contact lenses - the base curve and the diameter. Get these wrong, and the lenses will be uncomfortable at best, and more likely, won’t fit and stay on the eye. And at worst can result in corneal ulcers and blindness. ---
**Author:** ![bleibtreu](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bleibtreu](https://boards.straightdope.com/u/bleibtreu)\ **Post date:** [December 30, 2010, 11:17pm UTC](https://boards.straightdope.com/t/contact-lenses/565654/14 "2010-12-30T23:17:10Z")
> [@Any\_Other\_Name](#): > > Do glasses and contacts require a valid prescription? Why are they required? Contact lenses do, because they are considered medical devices by the FDA. Federal regulations set the expiration at one year, but a longer period can be set by state law. ---
**Author:** ![Any\_Other\_Name](https://avatars.discourse-cdn.com/v4/letter/a/f17d59/32.png) [@Any\_Other\_Name](https://boards.straightdope.com/u/Any_Other_Name)\ **Post date:** [December 30, 2010, 11:58pm UTC](https://boards.straightdope.com/t/contact-lenses/565654/15 "2010-12-30T23:58:33Z")
> [@bleibtreu](#): > > Contact lenses do, because they are considered medical devices by the FDA. Federal regulations set the expiration at one year, but a longer period can be set by state law. Eyeglasses do not though? Stores that sell eyeglasses always seem to represent hat prescriptions are required. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [December 31, 2010, 12:05am UTC](https://boards.straightdope.com/t/contact-lenses/565654/16 "2010-12-31T00:05:30Z")
> [@Any\_Other\_Name](#): > > Eyeglasses do not though? Stores that sell eyeglasses always seem to represent hat prescriptions are required. This almost certainly depends state-by-state in the US by law I’d think. My optometrist told me that stores selling eyeglasses “require” current prescriptions prescriptions to protect themselves against complaints. For example they have people coming in asking for new glasses because their old ones are now old and complaining when they get them that they are no better. Apparently they think glasses wear out or something and you simply need new ones rather than their prescription has changed. ---
**Author:** ![Siam\_Sam](https://avatars.discourse-cdn.com/v4/letter/s/d78d45/32.png) [@Siam\_Sam](https://boards.straightdope.com/u/Siam_Sam)\ **Post date:** [December 31, 2010, 2:38am UTC](https://boards.straightdope.com/t/contact-lenses/565654/17 "2010-12-31T02:38:06Z")
Make sure your son can actually wear contacts. I can’t but wish I could. Tried them in high school. I think contacts were still pretty new back then, and thus expensive. They may not have come out with “soft” lenses at that time, can’t remember. But for whatever reason, the doctor prescribed hard lenses, and they were sheer torture. I had to give them up after a few months of trying. Other eye doctors since then have told me I can’t even wear contacts at all, due to the shape of my eyeball from astigmatism, which is rather severe in my case. ---
**Author:** ![BigT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bigt/32/12044_2.png) [@BigT](https://boards.straightdope.com/u/BigT)\ **Post date:** [December 31, 2010, 3:05am UTC](https://boards.straightdope.com/t/contact-lenses/565654/18 "2010-12-31T03:05:12Z")
I had to give up contacts because my eyes are too small for the larger lenses.