This releases inflammatory mediators from the
mast cells, which make the
eye red, swollen, and more itchy
. I do not know why this only happens in 1 eye. Contact lenses may be a factor if you wear them. You should see an ophthalmologist for a complete exam. Until then, a chilled artificial tear can provide relief and be very soothing; try Refresh or Optive. If you are sensitive to preservatives, then look for the single-use vials, which are preservative-free.