So I enjoy snorkeling and have recently finished the PADI Open Water Diver course, it is all awesome - despite from the fact that I can't really see much without my glasses as I have -5.5 myopia and 1.5 astigmatism in both eyes.

Some say that contact lenses can be used but for some reason my eyes don't tolerate it and also I've been told that it is not safe to use them underwater because of the risk of eye trauma and infection. Sure some people could use single-use contacts to lessen the risk of infection but where I live the cost is prohibitive.

After looking online and asking around on my dive center i found out that there are some workarounds to be able to see properly with a scuba mask.

This is my first Instructable and I hope some short-sighted people like me can enjoy the best underwater experience.

Step 1: What Options Do I Have?

If, like me, you have visual problems there are some options available to overcome it.

After some online researching I could find the following options:

Contact lenses
Stick-on lenses
Special purpose glasses frame
Replace the mask's lenses
Outside mounted custom add-on lenses
And my solution: glued-on custom lenses

Contact lenses

I have been discouraged to use this solution for 3 reasons:

It seems that there is a non-negligible risk of getting an eye trauma while diving using contact lenses
The risk of infection and contamination of the lenses is also high
Contact lenses in my country are not cheap, even the single-use ones (to decrease the infection risk)
I can't get confortable using these
There is also the risk of losing your contacts if the mask gets flooded

Some people use this option without a problem but I don't like the odds of infection or trauma.

Stick-on lenses

That is one very good option and one I'd really like to try someday, the problem is, I can't find them locally and the mailing costs by ordering it online would be too high.

Some people have said that it works great until they don't as there is the risk of it unsticking mid-dive specially if your mask gets flooded. I don't know what is the fogging behavior of these.

Special purpose glasses frame

I don't really know the correct name for this one but see in the picture. It is a frame specially designed (or improvised) to be placed inside the mask and hold your corrective lenses. I didn't really consider this one as I think I would have a lot of fogging problems as instead of 1 I would end up with 3 fogging surfaces.

Replace the mask's lenses

I think this one would be the best solution of all but also one of the most expensive.

You send your scuba mask along with your prescription to an specialized company to replace the original flat lenses for some custom made ones. If done correctly you would end up with a very good field of view and clear vision. Well, I couldn't find where to do it around here and I suspect that it would cost more than the Mask itself.

Outside mounted add-on lenses

This one is an awesome instructable by Filio Schiavina where he goes into details on how to make a contraption to be placed outside the mask with movable lenses, I highly recommend reading it, you'll learn some neat tricks on photogrammetry, 3d-printing and modeling.

I tried his approach but prescpription lenses don't take into account the refraction index of water and, at least for myopia, to account for that the lens would have to be too thick. Also, I didn't want any moving parts.

Glued-on custom lenses

That is the one this instructable is about.

Step 2: Prescription, Lenses and Glue

Ok, if you decided that this approach may be the one for you, first you have to make an appointment with your optometrist. Around here the prescription just informs the diopter (< 0 for myopia and >0 for hypermetropia) and the axis for astigmatism.

With the prescription and your mask on hand you have to find a lens manufacturer to make you a pair. He will take some measurements on the mask to find the best design of the lenses and find the correct position of your eyes to center it. But the real secret is: the new lenses have to be completely flat on the outside surface so that you use just a drop of glue.

Now you have to find the correct glue to make the bond, this is a trial and error process. I bought 3 different types of superglue and tested them with some discarded lenses that I asked from the manufacturer to test the transparency of the glue.

Put a drop of glue on one lens and press the other one on top of it and leave it to harden, test afterwards if it is clear and transparent, repeat untill you find a good one.

The best glue I could find is this UHU MAX, it is a gelatinous superglue that keeps the transparency, doesn't harden very fast and is very viscous so you have time to make some adjustments.

Step 3: Glueing

After you get your lenses from the manufacturer, it is time to test and glue it.
Try putting the lens inside the mask and see if you can find the best spot to glue it on so that you have a confortable vision afterwards. Make sure you clean both the masks lenses and your custom ones as you don't want to find a rogue strand of hair or some dust after the glue hardens. Put a drop of glue in the middle of the new lens and press it on the inside of your scuba mask in the spot you found to be more confortable. If you used the viscous glue you'll have time to put the mask on your face for a while to check if the lens is correctly placed. If you find it unconfortable, try moving the lens a little bit to correct the placement. This is the most difficult part and i found myself having to completely disassemble the mask to unglue the lens, clean everything and starting over again. If that happens don't despair, use some acetone to clean the custom lens and a blade to scrape what was left on the scuba lens. DONT SCRAPE THE CUSTOM LENS, most probably it will be made of a polymer that is not hard enough to resist damage and you'll end up with an scratched lens. After you find a good and confortable placement for your lenses it is time to let the glue harden. I bought a plastic clamp to press the lenses on the masks glass while the glue cured, try tightening it with some force so that it doesn't form air bubbles on the inside.

Leave the mask for a day or two to evaporate any residual solvent that may be there so it doesn't irritate your eyes.

Step 4: Enjoy

If all went well you can finally enjoy the amazing environment that is the ocean.
I must admit, it is not a pretty solution and you will probably end up with a rim of glue around the new lenses but, in my experience, this inconvenience is not a problem. Now I can see tha marine life, check my instruments and be more aware of my diving buddy's signs and conditions. I feel safer and happier diving now than before.