Mast cell stabilisers

These are called membrane stabilisers as they inhibit the degranulation of mast cells by stabilising the cell membrane. Mast cell stabilisers are the medicines which block the IgE regulated calcium channel (which is essential for the fusionof histamine vesicles with Mast-cell-stabiliserscell wall) and stabilise the cell wall thereby preventing the histamine and related mediators release. Therefore, these medicines are used to prevent and control mild to moderate allergic diseases such as asthma.

These are very safe however anti-inflammatory effect is weak and less effective then corticosteroids. This medicine can be given before come in contact with an allergen while it cannot be avoided. 
Mast cell stabilizers (disodium cromoglycate and nedocromil) are available in various forms such as inhalers for asthma, eye drops for allergic conjunctivitis, and nasal sprays for nasal allergy symptoms. This is very effective in treating ocular symptoms.
Like with many drugs, it may take several weeks before the full effects are felt.