Muddy Brown Sclera

Gambit has a muddy sclera - has had it since he was a puppy. The sclera is the white of his eye. His right eye isn't white, it's got a brown patch over most of it. This doesn't seem to affect his vision at all, and the vet has looked at it a few times and while she hasn't told me what it IS, she says it's not harmful.

Essentially, it looks like someone poked the pupil of his eye and his eye leaked brown colour into the white of his eye. Like when you poke an egg. It isn't a "Spot" it's like a leak or stain. From an angle it even takes on a reddish tint. I have had this looked at repeatedly by the vet, and she assures me it's not a concern. I was just wondering if anyone has ever seen this before in a dog?

I'm just curious to know if anyone knows what it is or if anyone has seen a dog with this before. He still sees fine, and though it got more prominent as he grew, it hasn't changed shape or anything in about two years.

It's hard to get a good shot of it since you have to look at his eye at a certain angle to catch the discoloration.

Behind the cut because it needs to be big to show the eye. This was him and baby Daisy about a year ago, it's the best shot of his eye that I have.