When we dive under water, vision is blurred unless we wear goggles.
Why don't fish have blurred vision ?

Dear michaelpollak-ga;

Thank you for allowing me to answer your interesting question. Simply
put, fishes have eyes adapted to underwater vision. Their eyes can
compensate for the density of the environment, low light and what
humans perceive as distorted light refraction. Therefore a fish?s eyes
can focus in a way that allows them to see under such conditions. Out
of water, a fish is believed to have distorted vision similar to the
problems humans have underwater.

STRAIGHT DOPE
http://www.straightdope.com/mailbag/mwaterblur.html

Why is this so? Well, most fish have fixed, spherical lens shapes, and
their ability to focus is achieved by telescoping the lens (similar to
the way a camera focuses). By adjusting the eye?s lenses back and
forth at will as needed, a fish can compensate for the visual
disturbances and depth perception caused by the water, whereas a human
cannot physically do this.

WIKIPEDIA ? EYE
http://en.wikipedia.org/wiki/Eye


I hope you find that my answer exceeds your expectations. If you have
any questions about my research please post a clarification request
prior to rating the answer. Otherwise I welcome your rating and your
final comments and I look forward to working with you again in the
near future. Thank you for bringing your question to us.

Best regards;
Tutuzdad-ga ? Google Answers Researcher



INFORMATION SOURCES

WHAT DO FISH SEE?
http://www.pressrepublican.com/outdoors/lib/05262002out1.htm


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Fish

Eyes

See

Vision

Lens

They do, in the air.

because the eye of each creature was "developed" by evolution to be
more adapted to its medium.
when light crosses from one material to another it's trajectory gets
bended (refraction). when using a lens to focus something it's
critical how much it gets bended to point all the light of an image to
a particular point.
how much it gets bended depends on both materials (the one outside,
air or water, and the one inside the eye). Look up Snell's law.
And well, I guess your next question might be why we don't get blurry
vision when underwater with goggles, it's because the surface of the
goggles is flat, instead our eyes are round.
The light we try to focus comes from in front of us, according to
Snell's law, how much the light's trajectory gets bended depends on
the angle the initial trajectory has with the surface separating the
two materials.
So with the flat surface the angle is almost nothing but with our eyes
it's gathered from different points in the eye surface that are not
perpendicular with the direction that the ray comes from.

The eye cannot "evolve". It must be complete to function at all. The
theory of Evolution is just that, a "theory". The Biblical answer,
that all things were created, makes more sense. Genesis 1; 22,23 ". 22
With that God blessed them, saying: ?Be fruitful and become many and
fill the waters in the sea basins, and let the flying creatures become
many in the earth.? 23 And there came to be evening and there came to
be morning, a fifth day". A created eye, underwater or not, is a fully
functioning eye.

The links in the answer are very good.  The straightdope one gives an
excellent explanation.  However, the paragraph

"Why is this so? Well, most fish have fixed, spherical lens shapes, and
their ability to focus is achieved by telescoping the lens (similar to
the way a camera focuses). By adjusting the eye?s lenses back and
forth at will as needed, a fish can compensate for the visual
disturbances and depth perception caused by the water, whereas a human
cannot physically do this."

is misleading.  The difference in mechanisms by which human and fish
eyes focus is irrelevant to the present question.  There is no reason
why fish could not have human-type eyes, which focus by changing the
shape of the lens.  There is no advantage to a fish-type focussing
mechanism in terms of visual acuity underwater.  Most fish don't have
binocular vision, so their depth perception sucks, but that again has
nothing to do with the focussing mechanism.  Water absorbs/scatters
light much more strongly than air, so fish likely gauge distance
mostly by 'dimness' of the object and by apparent size relative to
actual size (when actual size is known).

Pug, do you actually believe that garbage?