"A sight for sore eyes" is something, or someone, that is a relief to see after a long absence.
A person who makes a journey to another country for an extended period of time will say this to express joy at returning home.
Howard is an American who has been working overseas, in Europe, for a period of ten months. Only now is he returning to the United States by airplane. As his plane flies to an international airport in New Jersey, he sees land through his window. He sees America.
In his mind, he thinks to himself, "That sure is a sight for sore eyes." Howard is happy to be back in America after so long.