“The Fall of the House of Usher” is the story of a sick man whose fears manifest themselves through his supernatural, sentient family estate. (Sentient means able to perceive things.) The story explores both physical and mental illness, and the effect that such afflictions have on the people closest to those who are sick. One interpretation is that much of the seeming “madness” of the main character does turn out, in fact, to be the cause of truly supernatural events. That is, he’s not crazy – his house really is haunted, and his sister really is back from the dead. Another interpretation is that the madness really is imaginary.
Madeline is just a manifestation of Roderick’s fear.
Roderick's acute sensitivity to light, sound, and touch result from his psychological illness rather than a true physical illness.