It appears to be a fungal infection. Though I am not certain. You need to have it treated immediately though as it will worsen quickly. He needs to be removed from the tank and put into a hospital tank for treatment and so he will not contaminate the others.
Though your tank is very pretty, it is highly advised against to house all of these different species together. Especially the frogs with the geckos. The frogs cannot compete with the lizards for food and they could be injured. I know this first hand as I rescued a Red-Eyed Leaf Frog from a pet store in which he had several scratches and puncture wounds I had to heal and he has never completely recovered and has to be force fed even still.
The temp is a bit cool for Red-Eyed Leaf Frog's. Can you warm it up a bit?
Anyway, you'll need medication to treat the eye.