Water

[justlearning]

why do your eyes sting and become red when you get pure, fresh water in them, but yet, they dont hurt at all (as anyone who wears contact lenses will attest) when you put "eye drops" (contact lens rinsing solution, Visine..) in them?

[sukhnidhaan]

I find a few splashes of fresh cold water rather refreshing! It usually does the trick to make me a little more saavdhaan....

But anyway, is this an actual Biology/Chemistry homework question? Initially I thought of pH changes but PURE water is neutral. I suppose if you have stuff in your eye, eg. dust/ allergens, then just water alone might produce a stinging sensation as there's actually no active ingredient in H2O to counter them; just as when you have hot spicy food it's better to drink milk/lassi which is gentle on the stomach rather than water which just washes it all down, inciting the gastric lining.

Also, anything added to the eye should be isotonic i.e. of same osmotic potential. I know that eye drops can work to restore the lubrication of the eyes (hypermellose- fake tears). Contact lenses tend to dry out the eyes and since it is an extra coating on the surface of the eye, obviously don't allow as much air to get to them (although the daiy disposable developers dispute this!) and also allow the build up of deposits: that's why you're only meant to wear the usual ones for a certain length of time and then clean them in a solution.

Hope this helps, or at least triggers you're own thinking a bit for the answer.

Just my 2 cents

[justlearning]

vwihgurU jI kw Kwlsw!

vwihgurU jI kI &iqh!!

thanks man

its so for biologyy

a lab on osmosis

and im familiar with the word isotonic

[GABROO KHALISTAN DAH]

we have a different chemical composting in our body as for water...and pure water is straight up h20 causing a ph imablance

[nanosecond]

Well the fluid that's isotonic ( means that will exert same osmotic pressure) with our body is around 0.9 % NaCl solution....or 5 % glucose. So if u put any isotonic soln, it will not draw any water from eyes....if u use hypotonic (<0.9%) it will draw water , if u use hypertonic, it will swell up ur eyes....same thing happens when u put ur hands in fresh water for long....they sort of shrink and if u put them in soap soln for long...they swell up...Hope this helps

[Khalsa4ever]

vwihgurU jI kw Kwlsw!

vwihgurU jI kI &iqh!!

I think I may disagree.

The eyeball has a coating around it which prevents direct contact with the eyeball... so pH or osmolarity have little to do with it.

Although I am not certain, I believe the answer may be that the cold water splashing your eye causes the blood vessels to vasodilate (expand), thereby passing more blood and making your eye appear red. In addition, if you splash a lot of water in your eyes, it "feels like" that there is something stuck in your eye -- even if it is only a second. You know that the body reacts similarily and the eye goes red. With drops, only a small amount of liquid doesn't cause this effect.

vwihgurU jI kw Kwlsw!

vwihgurU jI kI &iqh!!

[justlearning]

I agree with nanosecond. i've got the answer now, so don't stress out.

eye fluid has a low concentration of h20 and nacl as compared to fresh H20. When diffusion takes place, fresh h20 is being put into a hypertonic solution, causing eye fluid molecules to expand and burst. Also, ions move out of the eye, causing irritation. The "eye drops," however, have the same concentration as the eye fluids. As a result, they are isotonic. That's the reason as to why you don't feel any stings when placing eye drops and contact solutions in your eyes.

Thanks to all that helped.