This idea occured to me today when I was driving home after running some errands this morning. Last night, due to an unplanned adventure, I was deprived of sleep. As often happens, I later suffered from dry, itchy eyes. I contemplated using Visine to reduce the dryness. Then I thought that if Visine contained caffeine, I could relieve my tired eyes and wake myself for a bit at the same time. Since caffeinated water is widely available, I suspect it wouldn't be a difficult operation.
I am also operating on the assumption that caffiene will be easily absorbed into the blood stream through the blood vessels of the eyes.-- mighty_cheese, May 26 2002 (??) The dangers of coffee http://www.jtbaker.com/msds/c0165.htm [brewmaster, May 26 2002, last modified Oct 04 2004] (??) I can't see! http://www.shortand...head-up-ass_jpg.htmWhy not look on the floor for your glasses? [reensure, May 27 2002] My dictionary defines caffeine as "a bitter white alkaloid, C8H10N4O2-H20..." The "bitter" part makes me think I "better" not put this in my eyes.-- jurist, May 26 2002 New: *Decaffeinated* Visine! All the soothing comfort you need without the harmful caffeine contained in *some* eyedrops. Now only $439.95 per 1.5 fl. oz. container.-- jester, May 26 2002 Mighty Eye-Tea? Eye Coffee? Mountain Dewdrops? -- phoenix, May 26 2002 Ocular Mocca?-- brewmaster, May 26 2002 you ought to do something about those god-damn tea-bags under your eyes, mate-- po, May 26 2002 But they go so well with my cream-colored skin....-- phoenix, May 26 2002 jurist - Caffeine may taste bitter, but I don't have taste buds in my eyes. Does your dictionary say whether or not it burns the eyes?-- mighty_cheese, May 26 2002 Mine does (see link). Maybe some other kind of stimulant might be more appropriate.-- brewmaster, May 26 2002 It would hit your blood stream faster if you snorted it. But I guess you can already do that with coffee.
[brewmaster: note that those are the dangers of *caffeine*. I don't think ingesting 10g of *coffee* is going to kill anyone.]-- DrCurry, May 27 2002 Still wouldn't fancy an eyeful of it though.-- brewmaster, May 27 2002 An old friend of mine (probably since deceased) swore that by allowing tabs of acid to dissolve under his eyelids, he greatly increased the drug's potency.-- brewmaster, May 27 2002 [brewmaster] //he greatly increased the drug's potency.// not his own though. eh?-- po, May 27 2002 ¯brewmaster: Your friend didn't hear the adage ‘acid users went blind staring at their sunshine’; had he listened to some passers of more high-test advice he'd not be too late to cry.-- reensure, May 27 2002 will your eyes turn brown?? I wonder..-- hangman, May 27 2002 I think a change of lifestyle might be better. In the eyes?-- Chris38183, May 27 2002 My peepers are sacred.-- brewmaster, May 27 2002 Here's mud in your eye?-- phoenix, May 28 2002 It's time for a long overdue baccy-chewing-revival I say.-- brewmaster, May 29 2002 does it send you to sleep for long periods?-- po, Jun 14 2004 Caffienated ear drops would be better.-- DesertFox, Jun 14 2004 //I just don't think it reviatalizes and make you more energetic.//
Well, no. It wouldn't. It's just a run-the-numbers thing. Caffeine is fairly soluble in water-based solutions, but with eye drops you're dealing with drops... say 50 microlitres (1/20th of 1 milliliter). I did a project with caffeine and remember that the solubility is in the region of 20g/liter. Which is quite good as molecules like that go, 2-10 fold better than the related paraxanthine* and theobromine. That leads to about 0.001g (1mg) in a drop. This makes you about 100 fold off a meaningful amount of caffeine. You might argue that you're delivering it right to the brain, as eyes can just be considered a specialized bit of brain tissue sticking out of the skull, but that argument isn't a very good one as caffeine is a molecule that's remarkable in it's tissue solubility/penetration... it just wanders through membranes, the blood brain barrier etc with minimal restriction, so it'd be pretty homogeneously distributed very quickly.
Other effects? Well, if you do briefly achieve high concentrations in the eye, then you'll achieve the opposite of the desired effect. Caffeine at millimolar concentrations (very achievable with the amounts discussed) is a very good inhibitor of the inositol trisphosphate receptor. This is a poorly named but very important calcium channel that turns hormone stimulation into calcium release. This is required for secretion, including in salivary glands, the pancreas and the lacrimal glands of the eye and many others. So you are at least creating a demand for eye drops with your eye drops.
Conversely, millimolar amounts of caffeine are potent stimulators of the ryanodine receptor, another poorly named and important calcium release channel. This would cause calcium release in muscle cells causing contraction, I don't know what the net effect of that would be, unpleasant, but likely temporary.
What you want in eye drops, is probably something like carbachol. This is a tougher synthetic version of the neurotransmitter acetyl choline. This will cause stimulation of muscarinic receptors, activation of the inositol trisphosphate receptor, calcium oscillations and bicarbonate/liquid secretion. Carbachol eye drops exist, I think I made my own at some point, but that's a by product of having things like carbachol hanging around in the lab.
*This stands out as caffeine is just paraxanthine with 1 more methyl group and adding methyl groups would be expected to make it less water soluble, but what do i know.-- bs0u0155, Jun 21 2023 [a1], it might not be the coffee that moistens your eye, but the cream in it.-- Sgt Teacup, Jun 21 2023 It's probably all the weeping shortly before you poured a cup of coffee over your face. Hope you are feeling better.-- mylodon, Jun 22 2023 I'm not sure I should take medical advice off Half Bakery but I'm very intrigued. Filter? Espresso? Instant?-- mylodon, Jun 30 2023 random, halfbakery