What could have does this to his eye? (warning: very graphic)

Just a few hours ago I was checking on my rats and getting ready to do a quick handling session with my new holdbacks. However, when I opened my top tub I was alarmed to find this poor top eared Russian Blue male running around with a mutilated eye.
http://i50.tinypic.com/2cnjza8.jpg

After this picture he was immediately fed off to end the poor thing's suffering.

The only ones in his tub are his mom and other 4 week old litter mates. His tub was cleaned yesterday morning and when he was moved and from the holding tub he seemed fine, nothing out of the ordinary. Whatever did this must had to have happened in the last 36 hours.

Does anyone know what could have caused this terrible injury to his eye? An accident during play with on of his siblings maybe?

Was there blood anywhere? Poor thing, the only hing I would think would happen is over grooming from other cage mates or over zealous playfighting. When was the last time you checked on them?

Maybe got a little to frisky with mom and she chomped him.

An accident bc of trauma like a bite or an infection maybe? Thats yucky and painful looking. My eyes started watering just looking at it lol.

I too am thinking some sort of trauma then infection. I have had one or two of those and it just breaks my heart. They are so good at hiding it when they are feeling bad.

I've seen something like this happen to a kitten in the past. A litter mate got it in the eye pretty bad and ruptured it while they were playing. A ruptured eye on its own is generally pretty nasty but the mother immediately went to go clean the injury herself resulting in more aggravation, swelling, and bruising so the end result looked close to this. I'm guessing that since he was with his siblings and mother, the situation was similar.

There wasn't any blood anywhere else in the tub. As I said in the original post he was last examined 36 hours prior to the discovery of the injury and looked fine at that time so I don't think a eye infection could have progressed that quickly to the result pictured above (although I'm not 100% sure, I'm not a vet).

I examined the tub area to make sure there were no sharp points sticking out anywhere but didn't see anything. My best guess is the eye was injured somehow during their play fighting. I've just never seen this kind of injury as a result.

Aww, poor thing. I agree with you, it was most likely play fighting.

My friend breed rats and one day he found a pinky with half its skull bit off. Brain and everything. Surprisingly it scabbed up and started to heal and didnt seem to hinder the rat. He eventually fed it off but i was crazy seeing the damage that was done

Damage done, time to feed it :(

Poor lil guy was playing too rough or getting played with too roughly looks like a trauma injury. At least you did the nice thing and ended his pain. I had a hedge hog when I was little puncture his eye socket it ended up looking like this but with blood :(

Ugh, that earns the vote of most disturbing pic I've seen yet today. Poor thing, glad you found him quick and fed him off.