Saline is problem your best option until you get to the vet.  If you kitten
tolerates it, you might try a hot pack (just warm) for 5-10 minutes at a
time.  Sounds as though he has an eye infection which will require antibiotic
ointment or drops.  It's good that you're getting to vet soon.  Eye
infections, particularly in kittens, can cause permanent damage.

It's most likely from the salt. Did you ever rub salt into your own eye and
see what it feels like?
The only thing to use is fennel tea, undiluted, you can use the teabag
directly on the eye, gently.

Carola

I have just treated Angus (14 week burmese) for the same problem. He
will probably need ointment for a week or so. Salt water is fine as
long as it is dilute but warm tap water is ok too. My vet gave me some
very good advice - give puss a treat after EVERY treatment. After a
couple of days Angus was much better and within the week completely
better. Hope it goes well.
Kate

Oh, one more thing. I wouldn't reuse any topical medication as it may
become contaminated with the original infective agent and you could
reinfect the cat.
Kate