How natural? Artificial tears made of salt water & Cellulose will soothe the symptoms of eye allergy. Cromolyn eye drops (crolom) is an herbal medication derived from the khella plant (ammi visnaga) that grows in egypt. It is purified but not altered. This remedy was used by the ancient eqyptians. Its very effective for allergic eyes. By my reckoning its as close as you're going to get to a natural remedy.
A natural answer. Most natural products haven't been studied as well as fda approved products but if you want to try something natural, bhi products which handle heel products of germany, is a fine homeopathic retailer that has natural eye drops as well as allergy tablets. Look on the internet for bhi homeopathic products.
Check thyroid. Any chronic allergy is silent zinc deficiency which is inhibiting liver from priming the nuclear receptor cells by not producing enough vit a and vit d for the thyroid hormone to work efficiently - in the long run causes increased t cell response with increase in incidience of allergies - check for organix profile with metametrix and find out where the body is stuck. Replace iodine, zinc, vit a+d.