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It is recommended that "daily" contact lenses are to be disposed of after about 8 hours of use. I understand that daily lenses are made from a different material than, say, monthly ones; they are softer and apparently not suitable for cleaning.

However, what stops me from buying a lens case, some sterilising lens liquid and simply storing them in the case for a couple more days?

I asked a salesperson at the opticians today, but they declined to answer, and have a financial bias.

I have tried it once before (I kept some of the solution the lenses came in, placed the lenses in it after a day's wear and used them the next day) and it I didn't feel that my eyes were irritated, though I did notice that they became drier faster than usual.

Why I shouldn't do this; what happens to the material/my eyes?

Oddthinking
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turnip
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  • The salesperson was probably not a doctor, so he/she did the right thing not giving you medical advice... – nico Jun 07 '14 at 18:57
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    See also: [Are disposable contacts unsafe beyond their recommended time limits?](http://skeptics.stackexchange.com/questions/5809/are-disposable-contacts-unsafe-beyond-their-recommended-time-limits) – User Nov 19 '15 at 13:07

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Truth be told, all contacts are prone to buildup of biological materials. I could find no data on whether temporary lenses are more prone to buildup, or are more difficult to clean. To get FDA approval, the companies must have their product tested for the duration of usage, frequency of replacement, and conditions treated. A full list of approved contact lens products and what the FDA has certified them for can be found here. The FDA definition of "disposable" contact lenses is for them to be used once and discarded, but sellers are also allowed to market extended use contacts as "disposable". Any use past that period is not FDA-approved usage of the product and thus is outside of the usual scope of safety.

Reuse of temporary lenses is shown to cause problems for users.

Thirty-nine percent (154/398) had some qualifying criterion: reduced comfortable wearing time (CWT), 20%; dryness, 20%; irritation, 5%; corneal staining, 8%; and hyperaemia, 7%. After refitting with [daily dispoables (DDs)], the prevalence of reduced CWT was decreased from 65% to 51% (P=0.0039), dryness from 60% to 41% (P<0.0001) and corneal staining from 28% to 21% (P=0.04). There was no significant change in the prevalence of irritation, or hyperaemia. Some differences were noted between the two lens materials.

Ultimately, it's a matter of risk-benefit. Some people don't produce as much build-up. Some people are less susceptible to infections. But when it comes to your eye health, consider that the risks could be serious including permanent blindness. Is that worth saving a few bucks even if that's the rare worst case?

Sean Duggan
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  • Maybe same materials, but from my own observations, one-day lenses are significantly thinner than longer term ones. – Compro01 Jun 06 '14 at 14:26
  • Your first link doesn't provide references, so we can't check on it. The second link is about contact lens cases, and neither argues for or against the claim. Please provide references that (a) the different lenses are made from the same materials, and that this matters, (b) long-term lenses can be washed better and (c) that the risk-benefits differ for daily and long-term lenses. – Oddthinking Jun 06 '14 at 15:08
  • I removed the reference to different materials since I couldn't find anything official other than a difference between pHEMA and silicone hydrogel lenses in terms of ease of cleaning. Since both are used in disposable and more extended contact lenses, it didn't seem relevant. – Sean Duggan Jun 06 '14 at 16:15
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    The question here is: `is reusing "daily" lenses worse than reusing "two-week" (or longer) lenses?` The link "Reuse of temporary lenses is shown to cause problems for users" doesn't answer this question. It suggests that no reuse is better than reuse, but says nothing about dailies reuse being worse than non-dailies reuse. – User Nov 19 '15 at 13:06
  • @User: I'm confused... that's not the question at all. The question is "Can daily disposable contact lenses be safely re-used?" – Sean Duggan Nov 19 '15 at 13:28
  • @SeanDuggan which is another way of saying is there something about daily disposable contacts that makes reusing them worse for your eyes than reusing lenses that are designed for reuse. If the answer to the question "Can daily disposable contact lenses be safely re-used?" is no, then the answer to "are they worse for reuse" is: yes. In any case, even taking the question as stated "Can daily disposable contact lenses be safely re-used?" the linked to study does not answer this, which is my main point. – User Nov 19 '15 at 14:01
  • I'll disagree with you on that. The study shows that daily use does cause problems. The links to the FDA pages show that there is no medical standard for "daily" temporary lenses versus "two-week" temporary lenses. Anything marked as "disposable" is judged by the standard of health impact of wearing them once and at the time, I found no data indicating that there was a difference. That's all in my answer. If you have better data, feel free to edit my answer or add your own. – Sean Duggan Nov 19 '15 at 14:14