eye discharge

Question
Info:  
Rain is a female originally acquired from a pet store as a companion for Snow, another rat.  Snow and Rain did NOT get along.  Rain was given to my son by her original owner.  MY son reenlisted in the Marines and Rain came to live with me.
Rain is at least 18 months old, unspayed.  She originally lived in an aquarium but for the last six months has had a two and a half level wire cage.  
Bedding: Kaytee Soft-Sorbent and shredded white tissue paper.  
Food: various Kaytee mixes /Brown's Tropical Carnival / other rat/mouse mixes from Petco.  Supplemented w/apple bits, walnut pieces, (the raw kind that I by at the grocery still in their shells for baking).  She is fed free choice.  I put a little food in her dish and when I see it is gone, I put a little more.   

I try to play with Rain daily for at least thirty minutes.  Sometimes we hang longer, sometimes we skip a day.    Usually put her on my bed and allow her to run around, climb on me or whatever.  

Problem:  Lately I have noticed that Rain sleeps a little more and maybe has a little less energy than she used to.  Her eyes seem a little less big and brite than previously - or maybe that is just my imagination.  For the last few days her eyes (primarily the right) has run a little.  She has a little crust around each eye in the evening.  Kind of medium brown in color.  

This is the first rodent I have had in over 30 years.  I used to have hamsters and once had a G. Pig but have never had a rat.  Any advice you have would be appreciated.

Answer
You know, it could just be that she's slowing down; but I'd almost guess she has some sort of upper respiratory infection brewing if you're noticing runny eyes all of a sudden. Check her skin and coat and look for anything buggy or open sores, as well.. sometimes mites or lice will cause a behavior change and they're a fairly common thing on rats. Has her eating and drinking habits changed? If not, you'd do best to keep a close, close eye on her and then take her to the vet if they DO change.. if her habits have changed, especially dramatically, I'd take her to the vet and have a wellness visit done just to see if they can figure it out. Make sure they check her lungs very well -- and be sure this vet KNOWS rats, and doesn't simply "see" them, as so many vets say they do and really know absolutely nothing about rodents.