Okay guys, this is about the weirdest thread I have ever seen on ScubaBoard. First, you cannot see more clearly with pupil dilation, because (as mentioned above) the depth-of-field is very shallow. You have more light-gathering ability, but reduced focus depth.
Second, while with a great amount of training, you may be able to dialate the pupils, why would you want to. It is precisely because this is reflexive, and not dependent on the mind's control, that we can seamlessly go from very dim light to bright light. But try to reverse that, and you'll find that it takes about 15 minutes to become fully dark adapted. This is because we have both rod and cone cells in our eyes for light perception. The rods are for night vision, and provide very good vision, once adapted, to the night. Cones are color-perception get cells, and function optimally in bright light.
Cone cell - Wikipedia
Third, there is this thing about our eyes being adapted to seeing in air, but not in water, due to the different refractive indexes of the two mediums. The only way that the human eye can see well underwater is to put an air barrier onto the eye; this means a mask or goggles must npbe used. If any other method was available, it would already have been invented. In my high school days, I undertook life guarding training. We learned how to see clearly without a mask or goggles when we had to float almost motionless for 15 minutes. Boredom overtook use, and we learned to use our hands to capture an air bubble around our eye socket/cupped hands and see clearly with our heads underwater. But again, in order for this to work, we needed an eye/air interface.
The idea that controlling eye dilitation can somehow overcome the physics of the eye/water refractive index change is bogus. Dilitation doesn't change this index, only makes the eye even less adapted to water by reducing the depth-of-field focus problems the eye experiences in the water. (The wider the pupil dialates, the narrower the depth of field; but the refractive index of the eye/water interface remains the same.)
Refraction can be seen when looking into a bowl of water. Air has a refractive index of about 1.0003, and water has a refractive index of about 1.3333. If a person looks at a straight object, such as a pencil or straw, which is placed at a slant, partially in the water, the object appears to bend at the water's surface. This is due to the bending of light rays as they move from the water to the air.
Refraction - Wikipedia
The only way possible for the human eye to adapt is not to dialate the pupil, but to distort the eyeball itself; however I think the differences are such that such a distortion to change the focal distance would be rather painful and not something any of us would wish to do. Appropriate contact lenses have been developed and use daily underwater, but then you have the other problem of seeing out of the water.
SeaRat
John C. Ratliff, MSPH
