Snake Eyesight and Water

[longqi]

It may seem ridiculous considering how long Ive played with slitherers but I just started realising something
Land snakes and water snakes both seem to be able to follow and catch fish under water
A certain percentage of this could be vibrations from the fish??
Or scent?
But when they ambush a passing fish under water it must be their eyesight??

We have ular pelangi or sunbeam snakes here in an aquarium set up
They actively hunt the fish we drop into the aquarium
But they also sight hunt just as well on land

So the question is very simple considering that our eyesight is not bad on land but abysmal in water

Is a snakes eyesight the same on both land and water??

 

[GeckoJosh]

Id say it is as they have a lens protecting their eye so its like us wearing goggles, just a thought...

 

[longqi]

Thought about that but if we wear contacts; which would be similar to a protective lens; we still cannot see clearly under water unless we also have an air gap provided by goggles etc

 

[SteveNT]

No answers here but my Darwin has clear "bubbles" over her eyes viewed from above. What's inside I dont know.

She and the bhp love to cruise underwater, I've wondered about their uw vision and will be testing it out soon.

Mozzies are breeding in my fw crab tank so I will need to put fish in. My preference is natives but as egg layers in tight confines the crabs will find and eat the eggs. So I'm going (SHOCK HORROR) live bearing exotics.

Not sure what yet, probably mollies, but I will be popping some into the waterbowls to see if the snakes are interested.

I was really surprised to learn gts's were such good fishermen, will be interesting (they're not getting the big Jewie from the weekend!)

 

[snakeynewbie]

Crocs dont have an airgap behind the third eyelid that allows them ti see under the water, i dont believe an air gap is required for vision.

 

[longqi]

Crocs dont have an airgap behind the third eyelid that allows them ti see under the water, i dont believe an air gap is required for vision.

So exactly how do their eyes differ from ours??
Because our eyes definitely need that air gap

 

[snakeynewbie]

Our eyes dont have a third eyelid, thats the defining difference. The third eyelid protects the surface of the eye allowing them to see, in the case of snakes a scale over the eye would serve the same purpose.

Contact lenses do not work the same as a third eyelid

 

[gavman]

longqi, a few months ago I was flicking through a science mag and it had an article about how animals see. It made reference to a snake's brains ability to to switch between images generated through normal sight and infrared image data from their heat sensor systems.

The article stated that the scientist said it is possible for a snake to use both this image processing at the same time (very Psychedelic).

Could they be relying images generated through their heat sensors underwater????

 

[snakeynewbie]

Fish would ot emit heat though

 

[gavman]

Your right snakenewbie the fish snakes prey on would be ectotherms and I do agree that the spectacle scale would function as you say.

I was thinking more about metabolic heat (detectable at the gills), it would only be within a degree or so of the water temperature - would it still be detecable by the heat sensory system? If it is was, would this enhace the snakes ability to hunt and target fish or would it play no part at all?

 

[longqi]

Im not so sure about the third eyelid thing

Crocs have these and they flick up and down when surfacing or submerging if memory serves me
So their sight must alter between land and water
Whereas a snakes eyes have no eyelid so their sight must remain the same??

 

[snakeynewbie]

The third eyelid simply serves to protect the eye, it isnt a lense soitbdoesnt actually hange the way they see

 

[junglepython2]

Human's cant see underwater as the eye relies on a difference of refractive index between the cornea and its outer medium to refract the light and focus it on the retina. The cornea's refractive index is about 1.38 and air's is about 1 while water has a refractive index of 1.33 which is very simialr to the human cornea.
If snakes really can see underwater they could possibly have a higher refractive index of there refracting medium or they may have a much more powerful lens then our own to add extra power to the system. Also animals which are very short sighted will have reasonable vision underwater.

 

[slide]

Great thread/discussion

 

[slim6y]

JP2 - not sure about the short sighted comment at the end.

Longqi - I think it may have (but don't quote me on this) something to do with the Stiles-Crawford effect.

About how much light actually reaches photo-receptors from light that does not fall directly on the pupil and which receptors are stimulated.

It is possible then, that receptors in the eyes of reptiles (adapted for water hunting) are more sensitive to scattered light than direct light.

 

[Sock Puppet]

I thought we couldn't see in full 1080 HD underwater due to water pressure altering the shape of the lens on our eye.

Perhaps the spectacle covering a snake's eye is strong enough not to be affected by water pressure (especially in shallow water), keeping the lens on their eye unchanged.

 

[slim6y]

Sock Puppet - from what I gather pressure only makes up a small part of our inability to see underwater.

For example, put on goggles, go under water. The pressure is the same as without the goggles, but with the goggles you can see.

It's all to do with refraction (bending of light). Light bends when it changes from one optical medium to another.

The eye has several optical mediums designed to carry light to the retina.

Water, has is a significantly different optical medium to air and therefore light bends at a 'different' rate.

This is why you can't see out of water when you look up into the air from under water (ie looking up to the water surface from below).

The light bends away from the normal and eventually will reach what is known as the critical angle - where light rays exiting the medium run at right angles to the medium they're travelling in.

Light is an awesome science to read up on! Teaching it is fun too, there's many optical tricks you can play

My guess stands though for the reptile eye and the effect that scattered light has on receptors.

 

[junglepython2]

JP2 - not sure about the short sighted comment at the end.

Longqi - I think it may have (but don't quote me on this) something to do with the Stiles-Crawford effect.

About how much light actually reaches photo-receptors from light that does not fall directly on the pupil and which receptors are stimulated.

It is possible then, that receptors in the eyes of reptiles (adapted for water hunting) are more sensitive to scattered light than direct light.

If you are short sighted, light from infinity is focused in front of the retina instead of on it, in other words the optics of the eye is too strong or the eye is too large. If you are short sighted enough then going into water (which due to the difference in refractive index) will weaken the overall power of the eye and push the focus back towards the retina. Although this doesn’t really explain having good vision both above and below water.

 

[Scleropages]

My file snake will strike at the glass when I walk past the aquarium sometimes so I would say eyesight.

 

[longqi]

File snakes would just about be considered as a water only snake??
Seldom hear of them out of the water
So I would suspect their sight would be more adapted to water??

Or is there some reason all snakes appear to see equally well on water and land??