The Very Large Telescope, or VLT, is the biggest of its kind in the world. It is located in Cerro Paranal in Chile, where the air is extremely dry. Its sights are directed towards the depths of space, but dust is blurring the telescope's vision.The scientists who maintain the telescope say that it has glaucoma. That is why the coating on the mirrors must be polished and renewed every 18 months. It is a painstaking procedure that takes several weeks. And it requires special care, because the enormous mirrors must be removed and transported for cleaning.