This invention relates to novel physiological oxysteroids and oxysteroid hormones which are C27 modified sterols, particularly derivatives of intermediates in cholesterol synthesis, including lanosterol, zymosterol and desmosterol, including C27 diol and C27 acid derivatives, as well as related compounds and analogs thereof. The invention relates to treatment of cholesterol-related conditions by modulating the rate of cholesterol synthesis or cholesterol metabolism by administration of the oxysteroids, analogs or antagonists thereof. Methods are provided for ameliorating, treating or preventing macular degeneration by administering an agent which stimulates the expression or activity of steroid sulphotransferase (SLUT2), particularly SLUT2B1b, or which stimulates the expression or activity of CYP27A1 or sterol 27-hydroxylase. Assays for identification of analogs, antagonists or modulators of the oxysteroids or of sterol 27-hydroxylase are provided.