Needing a prescription for glasses is a bit absurd to begin with. The worst case of wearing the wrong prescription is that you'll get a headache. I suppose it could be a bit dangerous if some drivers were slightly disoriented, but I can't imagine glasses being more dangerous than something like Tylenol.

I... can't form a coherent response. How do you even know which prescription to get? Do you have astigmatism? How do you measure that?

It's not a scam. It's just overpriced in the US, because they can't get their stuff together in the health department.

If I need a new pair of glasses with the same prescription I have now (Say, for example, I fall and break my glasses), I shouldn't be required to go get examined to get a new pair simply because it has been more than a year. I want the same thing I've been wearing, and the worst possible outcome from me getting them is that (if my prescription has worsened, which it hasn't in 4+ years) I can't see quite as clearly at long range as I ought to.

That would be weird, good thing you are not required to get examined in order to buy glasses. I don't know why you think you are required.

You are required to get a new prescription because your original prescription expired.

It's by state.

Not for contact lenses (16 CFR 315.5):

https://www.law.cornell.edu/cfr/text/16/315.5

That doesn't make much sense because adult vision doesn't change much. It should be perfectly valid to use an old prescription unless you want to re-check your vision. I've never seen this law in Asia or Europe and people are living just fine.

I just had an eye test and both of my eyes had changed enough after two years to make a very noticable difference to my prescription.

You don't technically need an Rx. You can go to Zenni and just start plugging in numbers if you want. I'm not sure what that gains you, though.

It gains you the ability to replace a broken pair of glasses for just the cost of the glasses, rather than also having to pay for another eye exam.

> The worst case of wearing the wrong prescription is that you'll get a headache.

Doesn't using the wrong prescription worsen eyesight faster?

At least, it's been my general experience that when a child is curious about people's glasses and is given the glasses so they can experience the effect, they only let them try it for a couple seconds and are explained that using them for too long can cause damage to their eyesight (because it's the wrong prescription for them who have perfect eyesight). Is that a myth?

Yes, it's a myth in the sense that you would need to wear the glasses several orders of magnitude longer and/or consistently for there to be any negative effects. Some people seem to think that even looking through the glasses will unleash demons into the healthy eye.

Modern research does point in the direction of the eye remodelling itself based on what kind of input you give it on a longer scale, though. This includes the amount of light seen during the day and whether it is able to focus rays or not. There are indications these play a role in the development of myopia.

The eyes don't care about what's in front of it. The brain does the image processing, so that's the only thing that's affected by a bad prescription. If your glasses are so wrong that it causes eye strain, it may cause damage, but you'd have to purposefully put yourself into that ordeal.

https://mayoclinichealthsystem.org/locations/la-crosse/servi...

The eye very much does care what's in front of it. Look up "emmetropization".

Try a web search for neuroplasticity.

The real reason is they don't want grubby hands smudging up their glasses :)

No... It's not like I've seen it only once or never talked about it with other people. It's general common sense or a common belief, even if it turns out to be false.

Plus wearing glasses with a slightly different power than your own is infinitely safer than not wearing them at all.

Tylenol (acetaminophen) is probably a pretty good example. They both seem pretty safe in reasonable situations (a slight difference in prescription value, a couple hundred extra MG dose) but can be hugely problematic at greater levels (lethal/permanent liver damage or completely unable to see anything with a terrible prescription)

Which brings up another benefit of using an online eyewear vendor: they let you type your own prescription in. If you are personally fine with using a two-year-old prescription, do it.

When I ordered glasses a year ago, I also played around with the idea of eliminating astigmatism from my prescription by adjusting the cylinder value to 0 (it was only .25 in one eye and .50 in the other) and offsetting the sphere value by half of the difference. Because their buy-one get-one free sale, I got one pair with astigmatism and one without, and got to decide which I liked better.

That's awesome. Anything more than about a half diopter and you'll probably not get away with that in glasses. Contacts can go a little higher. I'm personally astigmatism sensitive, so I have to be spot on for degree and diopter.

To be legally above board, an online provide must attempt to confirm the Rx you enter is correct AND still valid. But few if any do because its a race to the bottom on quality and price. At Topology Eyewear, we spare no expense to ensure you get the best custom frames (like a custom suit) AND the best optics money can buy. We take 100% compensated Rx very seriously!

We're already aware you're enthusiastic about your business. Kindly leave the self-endorsement out of every comment.

It depends on the vendor. Warby Parker, for example, requires you to scan/upload the prescription given by your doctor, which obviously has a date on it. I guess it's always possible to just edit out or change the date on it though.

In many states it doesn't - you can ask for an extension to 2 years and in some states you can ask for a longer timeframe than that.

The length actually varies by state and it ranges from 1 to 10 years.

It varies by retailer and also contacts vs glasses.

If I remember correctly, thr Warby Parker storefront near me accepted a glasses prescriptions given out less than either five or ten years prior.

My insurance fully covers annual exams, so that doesn't bother me too much. If the period between covered exams was longer than the prescription period, yeah, I'd be peeved.

I wonder if that depends on state and/or who prescribes it?

I got a new prescription in 2017-07-07, and just took a look at it. It says it expires 2019-07-07.

I'm in Washington, and got it at Walmart.

I thought it was a state thing. But it's apparently an FTC rule that started with contacts and was expanded to glasses as some point.

Not that I would advocate anyone taking shortcuts on eye exams, but assuming online US providers insist on appropriate documentation and doctors' names, there's always ordering from Canada.

2 years in many if not all places. And I assume online places don't worry about that.

my glasses prescription doesn't have an expiration date on it. Zenni and Coastal don't care if I order new glasses using my old prescription. I haven't tried with contacts... I think my last prescription had an expiration date.

Note on contacts: because you're physically inserting a medical device into your eye, part of your annual exam is making sure that you are not causing any (potentially permanent) damage do your eye. While hopefully you are not abusing your contacts, even in normal use, sometimes the eyes can be harmed, which can cause major problems down the road for you. In my opinion, the expiration is probably a good thing if you're proponent of trying to protect people's eye health.

Yeah, I'm fine with it for contacts. It's just protectionism on glasses unless the prescribee has some degenerative condition.

That varies by state. My NJ prescription lasts for 6 years IIRC.

Depends on your doctor.

In NJ mine always dates a year, so I got fed up and found a supplier to buy from that doesn't give a shit what my prescription says.

You actually need a prescription to buy glasses in the US? 0o

That's maybe Fair given the potential rate of change.

You can go decades without a change, or a significant change (more than half a diopter).

Significant change isn't just the RX, it is other things that can go wrong in the eye as well. IF caught early it can be corrected, otherwise you may not notice until you are half blind.

That's true of everything, though. Your grocery store doesn't say, "sorry, you haven't been to the dentist in 6 months, we can't sell you food", even though there are many dental issues that can be life-threatening if not treated and eating food makes it worse. It's not their business to care.

Yeah, and others may go months, or years too.