In a statement on Monday, Biogen said that it will acquire Nightstar for $25.50 per share pending customary closing conditions. The deal, which values Nightstar at $800 million after expenses, is an all-cash acquisition that will give Biogen a foothold in both gene therapy and eye care.

Nightstar has several gene therapy assets, but Biogen called one, the “NSR-REP1,” the most important of the bunch. NSR-REP1 is a possible treatment for a rare disorder of the retina called choroideremia that leads to blindness. There are currently no approved treatments for choroideremia, but Nightstar’s NSR-REP1 has shown improvement in the treatment of choroideremia in trials and could be the first approved treatment for the disorder at some point in the future.

Biogen CEO Michel Vounatsos said in a statement that “ophthalmology is an emerging growth area” for the company, which made Nightstar and its NSR-REP1 an attractive acquisition target. Nightstar also has candidates in its pipeline to address a variety of other eye disorders.

Biogen said that the deal still requires Nightstar shareholder approval, but doesn’t require the approval of Biogen’s shareholders. It’s using its current cash on hand to acquire Nightstar. The companies hope to close the deal by the middle of 2019.