Hypertonicity hypotonicity

[Jorges69]

I have been reading a lot, also trying to calculate osmolarity, osmolality etcetc which can be done. Now, isotonicity is less easy as this depends on the permeability of the membrane. I wondered if anyone can tell me a few things about this.
First of all: suppose you have a eyedrop that is not isotonic but hypo/hypertonic. I know what it can do with cells, but most things I read refer to blood. What happens if you have an eyedrop that is 95% water and 5% other stuff readily found in contact lens fluid, like hypromellose, EDTA, PMHB, Borate and NaCl and other stuff I find in my contactlens fluid and it is NOT isotonic. Will this (permanently) damage the eye? Seems difficult to grasp as there is so much water in it and it is just one drop or may be a bit more for contactlenses?

With burning things in your eyes (NaOH or so), you need to flush it out with special water. Is the same true in this case? Never actually read about someone destroying their eyes with hypo- or hypertonic water or so. Or is winking your eye a few times enough?

I also found that saline (basic) is 99,1% water and 0,9% NaCl. And you keep reading this or they make eye drops with 2% borax. Does this mean it does not matter what you put in there, as long as you use this or do they mean in combination with sterilized water only which seems very obvious but still...?

What I also find difficult to understand is that I read that borax is also used to titrate the pH levels of some eydrops so it becomes less acidic. But does this not mean that the solution also gets more or less hypo/hypertonic?

Sorry for the many questions, but I wondered. I read quite a bit about it but I wonder if it truelly is that dangerous as I never read about any accidents based on this in eyes. I can understand that in blood, where you put something in but cannot easily get it out things are quite different.





I also read that with some cases the do not make them isotonic because the purpouse is to make it enter the cells.

[John C Hagan III, MD, FACS, FAAO]

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[Jorges69]

I understand. But I am taling about lensfluid and that kind of stuff. let's talk about oceanwater. I swim in the ocean and it is salty. I looked it up, it is about 3,5% or more depending on which one. That is well beyong the 0,9% in a saline solution. Yet I never ever had a signle problem with looking in it for prolonged times. I never came across problems with this, but there is ample info on getting acid or alkaline solutions in the eye.

So out of curiosity my question. Again: I do understand you are no expert on this one. So I'll will look elsewhere or may be leave it here. It is not that important. Thanks for your time!

[John C Hagan III, MD, FACS, FAAO]

I mean when we do surgery inside the eye. If the anterior chamber is filled with water the cornea swells and the cells burst. Everything is isotonic that we put inside the eye.

Balanced salt solution link
http://www.eyeworld.org/ascrs08livesurgery/pdf/ProductBriefStatements_10.30.pdf

JCH MD

[Jorges69]

Do you mean "inside the eye" as "inside the vitreous and aqueous humor"? That seems impossible unless you have a permeability enhancer I guess. Most eyedrops won't have those in them. So I guess you mean on top of the cornea.

I fully understand what acid or alkaline can do. But I have never read about people having serious damage because of something hypertonic/hypotonic in their eye. But I understand it is not your expertise so thanks for the ansers you did provide!

[John C Hagan III, MD, FACS, FAAO]

I can't answer all the things you asked authoritatively so I will not answer some aspects.  You can do serious damage putting water in the inside of the eye. Solutions inside the eye are called balanced salt solutions. On the surface of the eye some solutions/ointments are hypertonic to pull fluid out of the cornea example Muro 128 hypertonic   most artificial tears are hypotonic (examply hypotears) because a "dry" eye is hypertonic. Obviously strong acids or bases accidently instilled in the eye can do permanent damage

JCH MD