Thank you for the additional info and very good job with proper caregiving by the way.
This sounds like it could be one of two (or even both) infections that are pretty common in cats.
Even though you're not seeing sneezing or typical respiratory symptoms, an upper respiratory infection will many times show up with excessive ocular discharge that crusts like you're describing.
The typical viruses are Rhinotracheitis, sometimes Calicivirus; these may be chronic and recurring. Feline Herpes Virus can also be the cause of a URI.
A separate problem or even a part of the same problem could be conjunctivitis.
Most cases of conjunctivitis are Feline Herpes Virus (FHV). There is no cure, but there are treatments that usually target the secondary (bacterial) infections that result and may help speed recovery from the actual viral infection. http://www.eyevet.info/herpes.html
In many cats, the recurrence is more frequent when they're young and seem to reduce as they get older. We have found this to be true in all of our rescues and usually note that after a year or 1 ½ years old, some never have another outbreak.
To answer the question you may be wondering: No, a human or non-feline cannot catch feline herpes virus.
If the infection is bacterial, some of these may be zoonotic (transferable to people and other animals), which is another reason to have a vet check it and diagnose it for sure. You wouldn't want this yourself, right?
Some of the things that may trigger an outbreak in any aged cat are stress, other illness or injury.
For an eye wash you can use plain, clean water on clean cotton balls to wipe out; or saline solution that you'd normally use for rinsing contact lenses. Another ‘recipe' is Boric Acid solution: 1 tablespoon boric acid + 1 quart of water. Bring to a boil and then let cool. Use on clean cotton balls to wipe eyes as needed.
There may be any number of other things going on and the only way to know for sure is with a hands on veterinary exam with appropriate tests.
By the way, in all of these cases, you might be seeing the loose stool as well.
This isn't to say that's not even a third problem, but going back to the type of care you're providing, I'm not prone to thinking you're dealing with a parasite. Unless, however, you've had even a single flea in the home (that's all it takes).
you can try offering the cat a half teaspoon or so of unflavored, no sugar, plain yogurt to help balance intestinal bacteria. Also, Immodium AD (.1 to .2 mg per kg of weight once a day or every 12 hours) is an option or a small amount of psyllium (Metamucil tm). A kg = 2.2 lbs
There are measuring droppers and delivery devices available for babies in most pharmacy/medication sections of stores that are good to have on hand whenever there's a pet in the house.
Now, finally, it's prudent to mention that you might be seeing a food allergy (would account for all symptoms).
Food allergies can occur at any time, even after years on the same brand.
As much as we don't think we're changing foods, it doesn't mean the manufacturers aren't. They change ingredients without telling us - and in their efforts to provide the cheapest product that they can charge the most money for, sometimes our animals suffer. This became painfully apparent during the pet food recall in '07, the largest in history with the most pet deaths.
If you take a look at the ingredients in the food you'll find that just plain meat or fish isn't in the top three ingredients. In fact, it's usually 'ground yellow corn; brewers rice; chicken by product meal', which translates to filler+filler+beaks, feet, bones ground up into even more filler.
The best way to start with ideal nutrition is to read ingredients on the cans (yes, canned foods are better overall). Name brands are not important, but ingredients are. Meat or fish should be in the first couple ingredients and not plant products and no ‘meal' or ‘by-products' should be listed until after the third ingredient (preferably not at all, but that's not likely).
Not all proteins are the same either. Looking for the protein percentage on the label is deceiving if most or all of it is from plant material or by-products.
Even if you choose a kibble to supplement the canned foods it needs to have a real meat in the first two ingredients.
For more comprehensive information on feline nutrition, by a vet who specializes in this research - check this site: http://www.catinfo.org/ (it is not a sales site).
You need to trust your own judgement on this - you know your cat and you know what you're seeing. These are a few possibilities and options that might take care of it or at least get you through until Monday.
Good luck and keep up the good work!