Japan-based Astellas Pharma has agreed to buy US drugmaker Iveric Bio for about $5.9 billion in its biggest acquisition, giving it access to a range of ophthalmology treatments.

The deal marks the fifth major overseas acquisition by Astellas, Japan's third-biggest drugmaker by sales, since 2019 in a push to shore up its pipeline as its main sellers lose patent protection.

New Jersey-based Iveric, formerly branded as Ophthotech, is focussed on developing treatments for retinal diseases, which fits with Astellas' focus on blindness and regeneration therapies.

Through Berry Merger Sub, a wholly-owned subsidiary of Astellas US Holding, the Japanese company agreed to acquire Iveric for $40 per share in cash, Astellas said in a release.