If you suffer from eye allergies, chances are they're worse at certain times of the year. Things that are constant in your life, like dust mites, pet dander and feathers in your bedding, are the most likely culprits of your perennial allergies. These are the allergens that will affect you to some degree all year long.
Then, there are seasonal allergies. These occur at certain times of the year when specific plants and weeds grow that aggravate your particular allergy. This is typically spring through fall for most allergy sufferers. Not only are more plants, grasses and weeds growing, but you're outside more and vulnerable to exposure.