Vision Underwater with Correction Lens (Instead of Swimming Goggles)
How our eyes work is that the different tissues inside act as a lens/lenses and create an image of objects on the retina. Going under water with open eyes changes the focal length of the system and the focus/image is not on the retina anymore, much further behind it.
The usual solution for this problem is swimming goggles. The goggles keep the water away from the surface of the eye and restore the original conditions.
It is possible to simulate this in an optical simulation software. There are various eye models available. In this example I will use the Arizona eye model. This is what how it works normally in air:
Now let's observe what happens if the air is replaced with water.
The distant object doesn't produce a nice spot on the retina but a much larger blurred spot. It's equivalent to being terribly long-sighted.
Just like long-sightedness, this issue can be also corrected with the proper lens. Unfortunately the usual method doesn't work here because the refractive index of the water is very low (around 1.33) and most of the glasses have a refractive index very close to this value (1.45 for instance) or even higher.
The easiest solution is to use a well shaped bubble as a lens. Well shaped because bubbles in water with their spherical shape work as negative focal length lenses. We will need a bubble which is in fact concave shape.
Bubbles are of course not easy to keep in shape without a solid enclosure so I add a 2mm thick PMMA (Acrylic) shell to it.. This is the results:
Voilà, the vision is restored.
The field of view and performance is not gonna be as good as modern prescription glasses.. but at least it's easy to construct something like this.
The lens has on both sides a 30mm radius of curvature, made of PMMA and the centre thickness of the air pocket is 5mm. The lens outer diameter is 44mm and inner diameter is 40mm, edge thickness is about 28mm. For a prototype build one needs a 60mm diameter half-sphere pair (Christmas tree deco from DIY shops) and a 40mm hollow acrylic cylinder. By heating the PMMA above 125°C it's possible to weld the pieces together.
A company did the more professional version of this concept some years ago and were selling the concept mask for $60 000 each. Our is a DIY style thing and material cost is around $10 in September 2022.
The $60k goggles:
I will eventually build a prototype and let you know on the DIY-Optics YouTube channel how it worked..
Perfect for those who like to keep their eyes OPEN under water and prefer to see too..