dog has slight white coating and red eye??? cross posting

a few days ago my dog's behavior changed, he's not active, kind of sluggish and ive noticed that one of his eyes he cant seem to keep open, and its red and as of yesterday he has this coating over it, it just happened over night, he's mainly an inside dog sometimes he goes outside whenever we're outside, the other day he was outside with us for awhile and thats when it all started. does anyone know what this is??

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