Fresh water and contact lenses

  • Context: Undergrad 
  • Thread starter Thread starter kjl
  • Start date Start date
  • Tags Tags
    Contact Lenses Water
Click For Summary

Discussion Overview

The discussion revolves around the experiences of participants wearing contact lenses while kitesurfing and windsurfing in fresh and salt water. Participants explore the differences in how contact lenses behave in these two types of water, particularly focusing on the effects of osmolarity and the tear film on lens stability.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that while kitesurfing in salt water, their contact lenses remain stable even during intense conditions, whereas in fresh water, the lenses often shift or come off.
  • Another participant suggests that the difference may be due to the semi-permeable nature of contact lenses, which could cause them to adhere more strongly in salt water.
  • Some participants propose that osmosis might play a role, with salt water potentially drawing moisture out of the tear film, thus "cementing" the lenses to the eyes, while fresh water may disrupt this bond.
  • One participant mentions the osmolarity of tear film compared to fresh and salt water, indicating that fresh water is hypotonic and may disrupt the tear film more than hypertonic salt water.
  • There is a shared observation that even minor splashes of fresh water can cause lenses to dislodge, while salt water does not seem to have the same effect.

Areas of Agreement / Disagreement

Participants generally agree that there is a noticeable difference in how contact lenses behave in fresh versus salt water, but the reasons for this difference remain debated and unresolved. Multiple competing views on the mechanisms at play are presented.

Contextual Notes

Participants reference osmolarity values and the composition of the tear film, but the discussion does not resolve the underlying mechanisms or assumptions regarding the behavior of contact lenses in different water types.

Who May Find This Useful

Individuals interested in kitesurfing, windsurfing, or contact lens use in aquatic environments may find this discussion relevant.

kjl
Messages
23
Reaction score
1
I kitesurf a lot in both fresh water and salt water. I wear well-fitting contact lenses that do not shift around or come out, even if I rub my eyes.

In SALT WATER: I can crater from 20 feet in the air with a thunderous crash and get dragged through and tumbled by waves with my eyes open underwater and come up with no problems.

In FRESH WATER: I will often get a few drops of water in my eyes, kicked up from the board or dripping down from my eyebrows or hair, feel that my contact lens feels "funky", blink my eyes once, and the contact lens will have slid off my pupil, perhaps stuck under my eyelid, sometimes folded in half (in which case the next blink helpfully ejects the lens into the river). Sometimes I can get the lens back in my blinking a lot and waiting for it to reseat itself, though it takes much longer than it would if there was no water in my eye.

Any ideas on why fresh water would want to pry my contact lens out of my eye? I assume there's some boundary layer thing going on between the fresh water and the salty tear fluid in my eye, but I don't really know anything about it, or why it should matter.

A quick wikipedia search at http://en.wikipedia.org/wiki/Tears says that the film on eyes are actually 3 layers (from inside to outside: a hydrophilic mucus layer that allows for an even coating of the tear film, an aqueous layer with proteins... and salt, I assume, since it tastes salty, and a hydrophobic lipid layer). I don't know where the contact lens fits into the picture, whether it sits on top of all 3 layers, sandwiched in between two of the layers, or disrupts one or more of the layers.

Anybody have any idea why salt water and fresh water would behave so differently?


Curious minds want to know. Perhaps I should spray my eyes with Rain-X first! (Kidding)
 
Science news on Phys.org
As a Long-standing windsurfer... :biggrin:

I wear contact lenses too and I'm well aware of and very grateful for this effect.

It's so strong, I've had difficulty removing my lenses at the end of the day.

I always put it down to the lenses being semi-permeable and shrinking onto the cornea.
But I realize that's a corny explanation. :smile:(Exits left laughing helplessly.):smile:
 
Huh, interesting - I had been thinking there was some funky process at work that made fresh water want to peel my contacts off my eyes, but perhaps your way of thinking about it is more correct: that the funky process is actually the one that cements the contacts to my eyes in salt water!

I wonder if it's as simple as osmosis:

In salt water, the very salty bay/ocean water sucks the water out of the less salty tear film from underneath my contact lenses through the semi-permeable contact lens, basically vacuum-cementing the contact to my eyes (ha). You are right; sometimes it is like they are superglued on there afterwards :)

In fresh water, either the water simply sloshes around with the tear film and the contact comes off as you would normally expect any two items to come apart when immersed in water, or the slightly saltier tear film pulls water across the semi-permeable contact lens, pushing the contact lens out further from my eye until it wants to slide off.

Interesting.

Maybe before kitesurfing in fresh water I should put in super, super salty water eye drops to cement the lens to my eyes first, and hope that it takes a little longer for the water volume back there to build up as I start getting splashed :)
 
I'm not surprised you experience a difference between salt and fresh water, and I appreciate the thoughtful post.

You are correct, the tear film is more than just water (or saline). It's measured osmolarity of around 315 mOsm is isotonic to most bodily fluids:

http://www.iovs.org/cgi/content/full/47/10/4309

should be compared with sea water (2000 mOsm) and fresh water (20 mOsm). Contact lenses are stored in nearly isotonic solutions, so they are essentially 315 mOsm as well.

Honestly, I would have expected more problems in sea water than fresh water. I suppose the hypotonic fresh water is more likely to disrupt the tear film (absorption of water) than hypertonic sea water (loss of water), but I can't think of a good reason why opening your eyes in sea water causes no problems.
 
Andy Resnick said:
I can't think of a good reason why opening your eyes in sea water causes no problems.

I don't know about actually opening your eyes underwater, It's rare to spend more than a few seconds actually below the surface and you tend to have your eyes screwed shut because you just hit the water totally out of control and from a height/ moving fast. It's a reflex to clamp every orifice shut.

Even trapped under a sail as sometimes happens windsurfing, you are too busy frantically clawing for escape to open your eyes and look.

It's more a case of the odd little splash in the face catching you by surprise...

And the effect lasts for an hour or two at least. I've driven home after sailing, more than an hour after packing and stowing gear, and still had difficulty prising the darn things off my eyes.
 
I rarely open my eyes underwater, but sometimes I've opened them while clawing for my control bar and seen just a huge mess of bubbles and rushing water. I think when you fall on your windsurfing rig you don't need to do much but surface and get back on; when I fall kitesurfing, I need to make sure my kite doesn't fall into the water or get eaten by a wave, so I still have to be manipulating stuff that may or may not be in my hands at the time :)

But it turns out, opening your eyes under salt water is just fine with contacts. Weird! But the odd splash in fresh water is enough to cause them to fall out.

I agree that sometimes that trying to take my contacts out multiple hours after having been in the water, they will still be glued to my eyes!


Thanks for the numbers, Andy. I had not realized tear film was so much, uh, less salty (hypotonic?) in comparison to seawater.

Perhaps I will experiment a little (the kind of experiment that reinforces ideas but proves nothing :) ) and, next time my contacts are glued to my eyes, try splashing fresh water in them to see if I can get some pulled underneath the lense, and perhaps before kiting in fresh water, putting in a few super salty drops.
 

Similar threads

Graduate Avalanche photon detectors
  • · Replies 0 ·
Replies
0
Views
847
Medical Is it Safe to Make Your Own Costume Contact Lenses Using Gelatine?
  • · Replies 15 ·
Replies
15
Views
8K