"[O]ral ketotifen has been used in patients with asthma, allergic rhinitis, allergic conjunctivitis, atopic dermatitis, chronic urticaria, cold-induced urticaria, cholinergic urticaria, exercise-induced urticaria, [systemic mast cell disease including mastocytosis, MCAS, allergic and nonallergic anaphylaxis, angioedema], and food allergy in Canada, Europe, and Mexico." Now available via prescription at US compounding pharmacies: "For adults and older children with asthma or allergic disease, the recommended dose of ketotifen is 1 mg twice daily." "FDA staff did recommend more extensive evaluations for management of urticaria."  
Antihistamine eye drops tend to address watery, itchy eyes. They stop the histamine chemical from building up in your eyes. Histamines are created by the immune system whenever an allergy trigger is encountered. These types of eye drops are usually recommended to be the first type of treatment you try if your allergy is reflected in your eyes. They usually provide very fast acting relief, but you will need to reapply the drops after just a few hours. This is further reason as to why you should choose preservative free drops, as you are likely to have to use them often, which could irritate the eye.