Underwater vision

[nVy]

I don't like to be to dependent on googles everytime I'm out diving og swimming. I've noticed I have really poor vision underwater, I feel like I'm almost blind sometimes, I do have a little bad vision on land too but does it have that huge impact on my vision underwater? Is there something I could do to improve the vision without using googles?

My vision is about -1.5 on the left and -1.0 on the right. I'm taking an eye operation in a few weeks though..

[Pezman]

There is not much that you can do "mechanically" because the index of refraction of the eye lens is almost identical to water. This means that the muscles in our eyes that are responsible for focusing are essentially unable to do anything when our eyes are immersed in water -- and that your operation is unlikely to have any impact on your underwater vision.

The good news is that almost everyone has equally bad eyesight underwater, independent of their vision on land -- the matched index of refraction between water and the eye's cornea/lens etc. basically wipes out most common vision problems -- we are all infinitely farsighted underwater. This is why fluid goggles use high-index lenses with very short focal lengths (about 20mm). An interesting side-note is that even if you have problems like astigmatism etc., you should be able to see perfectly with fluid goggles.

I'm going to guess that some folks may be able to see a little better underwater than others if their eyeball is elongated and there were threads suggesting that children who spend a lot of time underwater can learn to process the blurry images better over time.

[efattah]

The more elongated your eyeball is, the better you see underwater. People who are very nearsighted may or may not have longer than normal eyeballs.

However, regardless, if you strain to 'focus up close' when underwater, you vision improves. If you can train yourself to focus on a point just 2cm from your eye (on land), then in theory you would see virtually perfectly underwater.

Try an experiment, see how close you can bring an object to your eye and still focus clearly on it.


Eric Fattah
BC, Canada

[efattah]

WARNING: Focusing up close can cause nearsightedness, which is why seals & marine mammals are nearsighted!

Eric Fattah
BC, Canada

[noa]

I've been diving without a mask for two months now. it started because i forgot my mask one day, so i dove anyway. it felt uncomfortable the first time, especialy the water up the nose. next time i dove again without a mask but using a nose clip to solve that issue. to make a long story short, i got used to diving without a mask now and really enjoy the feeling of water on my face, it feels very "free" and it's one less piece of equipment to stand between me and the ocean. two days ago i dove with a mask again because i wanted to see some fish better and guess what...i really didn't like the feeling. it felt like having some restraining object on my face. also in this time it feels like my vision without the mask has improved although i know it's just that i have gotten used to seeing blury, but the psychological factor does make a difference. so i now think most of my diving might be maskless. how would the near focusing training work, could that really lead to seeing well underwater and at the cost of seeing well on land ?
Delphicly,
Noa

[efattah]

It is well established that the extrinsic eye muscles (oblique & recti muscles) are far stronger than they need to be -- assuming they are only there to point your eye in different directions.

However, in marine mammals, the same extrinsic muscles are used in a forceful manner (fully using the muscle's strength) to change the shape of the eyeball, allowing vision above and below the water.

An innovative researcher named Dr. William Bates postulated in the early 1900's that human extrinsic eye muscles can also change the shape of the eye. Bates speculated that during close up work, the ciliary muscle (which bends the lens) becomes tired, so the extrinsic muscles lengthen the eyeball, so the ciliary muscle can relax. The problem is, with excessive use, this adaptaton can become semi permanent, resulting in a permanently elongated eyeball, due to chronic tension in the extrinsic muscles. This led to 'natural vision therapy' which Bates developed to try to reverse the chronic tension in the extrinsic muscles, in order to reverse certain cases of nearsightedness.

Regardless, with close up focus training, according to the above ideas, it is possible that your extrinsic eye muscles will learn to change the shape of your eyeball, elongating it. The ciliary muscle may also become stronger.

Bates found that with children, permanent nearsightedness could be prevented by occasionally focusing on hard-to-see far objects, such as an eye chart. In several schools this idea was implemented, and kids were made to look at an eye chart and read the lowest line they could see, once every few hours. The cases of nearsightedness in those schools were zero. However, traditional opthalmologists intervened and changed the schools policy, claiming there was no basis etc....

Eric Fattah
BC, Canada

[Pezman]

Cool to see this thread growning - it's an interesting topic.
I think that I may have discovered the ultimate in cheap fluid-goggles -- a pinhole. I cuts out a lot of light, so it would only be useful in shallow-water w/ bright light, but think that a pair of swim goggles:

- w/ holes in them to allow water in,
- painted black to cut out ambient light
- w/ pinholes right in front of the center of the eye

would allow you to see to some extent in well-lit water.

I rigged up an experiment with some speedo goggles and a sheet of paper and I was able to focus quite close -- not 20mm, but 30mm was doable w/ some straining.

I'll try it at the pool tonight.

[efattah]

Been there, done that! I have 'pinhole' glasses that are popular with natural vision therapists. I had the idea of cheap pinhole goggles for divers everywhere -- I tried my pinhole glasses underwater and couldn't see hardly anything. Perhaps smaller pinholes would work.


Eric Fattah
BC, Canada

[skarz]

i wish i could swim without a mask..... stupid contacts.

[Pezman]

I made a simple prototype by making a pinhole in a piece of heavy, opaque paper -- one piece of junk-mail that actually proved to be useful. I just made a "lens" for one eye and held my other eye closed under water.

Holdig the lens close to my eye, I was able to see reasonably well straight ahead. Peripheral vision was terrible, things were fuzzy around the edges and it was a little dark, but I could see individual objects pretty well. When I removed the "lens", things were much brighter but much blurrier.

Another strange effect is that very small movements in the pinhole cause the projected image on my retina to jump disproportionately, so the image tended to be shaky.

I think that the pinhole glasses don't have much application for freediving because of the limited quality of the image, but it was a fun experiment.

After the pinhole-glasses test, I tried some tests w/ just squinting and straining my eyes to focus and that cleard things up noticeably (though still blurry).

[noa]

So could what kind of "eye training regiment" could there be in order to help underwater vision ?
Delphicly,
Noa

[nVy]

Originally posted by skarz
i wish i could swim without a mask..... stupid contacts.

An operation, LASIK or LASEK would do the trick

[Pezman]

Surgery won't help. Just take out the contacts when you are in the water. Because the lens and corna have an index of refraction that is almost the same as water, refractive focusing does not work at all underwater.

BTW, I found that you can see reasonably well underwater if you make a pin-hole lens with your fingers. For example, you can make a very small circle with your thumb and forefinger (pin-hole sized) and look through that. This is a nice trick if you need to see underwater "in a pinch" (hey, I made a pun ). For example, you might use this trick to retrieve a lost mask or fnd some other critical item in a SCUBA emergency.

[Fenixxx]

Here is a link to some research about this:

http://theses.lub.lu.se/postgrad/sea...format=display

In short it says that it is possible to develope better underwater visual acuity by accommodation and concurrent pupil constriction which can be learned in 4-6 months.

[DeepThought]

A thing I used to do when I was younger was to look downwards, put my palms on the forhead and the side of my eyes (like I'm protecting my eyes from the sun), and fill it with bubbles from my nose.
If you seal it with with your hands, you get an airspace infront of your eyes, and can see as clear as with a mask.
But you can only look downwards...