U66858, also known as Bunaprolast, is primarily used in the field of ophthalmology for its anti-inflammatory properties. It is commonly applied in the treatment of allergic conjunctivitis, where it helps to reduce inflammation and alleviate symptoms such as redness, itching, and swelling of the eyes. The compound works by inhibiting the release of histamine and other inflammatory mediators from mast cells, which are key players in allergic reactions. This makes it an effective option for managing eye discomfort caused by allergens. Additionally, its localized application in the form of eye drops ensures targeted action with minimal systemic side effects, making it a preferred choice for patients suffering from seasonal or perennial allergic eye conditions.