The human inhabitants of Ilus, being new to the ecosystem, are susceptible to infection by a range of pathogens, unique microorganisms that are native to planet. The first malady to occur is the Green Blindness, which first appears to affect a young boy who is part of the squatters. At first, he has some blurry vision, which then evolves a green hue dominating the vision, followed by near total blindness. When the big storm hits New Landing, the rate of people "infected" by the Green Blindness reaches nearly 100%, except Holden who seems unaffected. It is later found that Holden's cancer meds, prevent the micro-organisms from multiplying rapidly in the eye, allowing the body's natural systems to take care of the vision problem. The microorganisms may exist in the clouds above Ilus, which also have a green hue.