dorettas@iddic.UUCP (Doretta Schrock) (01/09/86)
> I have recently purchased a set of soft, daily wear contact lenses. > A friend of mine, who has a pair of soft, daily wear, toric lenses tells > me that he uses distilled water to rinse his lenses after cleaning them > instead of saline solution in order to save money. I asked my fitter > about this was told that using distilled water, even for rinsing, would > damage the lenses by bloating them with water and increasing their size. > This strikes me as odd since saline is primarily water and since the > enzymatic solution which the lenses must be routinely soaked in is in part > composed of distilled water. > > What gives here? *Is* pure distilled water harmful to soft lenses, or does > my fitter have stock in a company that produces saline solution? > > I have also run into a number of people who wear their daily wear lenses > as if they were extended wear lenses, siting that the only difference between > the two types of lenses is thickness (and not a very significant difference). > I wouldn't mind leaving my lenses in over night once in a while, but all > those warnings that I read about my eyes falling out if I don't clean them > every day keep me from trying. > > Jim Curl There is a very real difference between saline and distilled water. Saline solution has a small amount of salt (at least sodium and chloride ions, probably potassium and others as well) in it, while distilled water has been processed to remove all ions and other contaminants from it. Your body fluids (including tears) contain ions in similar quantities to the saline solution used for your washing your contact lenses, and the lenses, to be compatible with your body, are also adjusted to this level of salinity. If you expose cells to distilled water (red blood cells are particularlly dramatic), they burst. This is due to the water rushing into the cell in an attempt to equallize the concentration of salts (and other materials) that is higher inside than outside the cell. The same will basically be true of your lenses. While they may not burst, they will swell, doing undoubtably strange things to their optic properties. If nothing else, washing your contacts in distilled water will probably make your eyes hurt more, as the salinity of the outside of your eyes will change and have to readjust. While the difference between saline solution and distilled water may seem small, it does not take much to affect our finely-tuned physiochemistry. As an extreme example, the threshold of calcium ion concentration in muscles between contracting and non-contracting is between 10E-8 and 10E-7 moles/liter. This difference is so small as to be almost unmeasurable by us, and yet it makes the difference between a muscle fiber contracting or not. 2) As to wearing your contacts for long periods of time, the thickness *can* make a difference. The cornea of your eye has no blood vessels going to it; it receives all its nourishment from the fluid behind it, and does all its gas exchange with that fluid and the air around it. The thicker lenses inhibit the normal exhange of gases between the cornea and the air, and this could damage the cornea. You would probably feel eye discomfort before you suffocated them completely, though. The extended wear lenses, in addition, are made to be oxygen-permeable (and presumably CO2 permeable as well), and thus avoid this problem. Mike Sellers P.S. I have rather pronounced lenticular astigmatism and near-sightedness, so I haven't yet been able to get contact lenses (sigh).