The following post from the ROP list defines the term "phthisis". The ROP list was moderated by Dr. Scott Richards until August, 2002. The list has closed now. For more information about lists of interest to people with visual impairments, please visit the email list index.
Date: Wed, 2 Dec 1998 From: Scott Richards
Phthisis is an involution of the eye, usually caused by inflammation. After longstanding inflammation, unrepaired retinal detachment, or unusually high or low intraocular pressures, some eyes just seem to "quit". They start to shrink, pull back into the orbit, and may become painful. Usually if you see someone with a whitened, shrunken eye, it is phthisis. Phthisis is more of a description than a true diagnosis - it is the end result of a number of different problems with eyes.