Unexpectedly large enhancement of a severely constricted field with reversed Galilean telescopes.

A 25-year-old female presented with severely constricted visual fields secondary to stroke associated with mitral valve prolapse. Repeatably measured central fields of less than 4 degrees diameter showed an unexpected enlargement up to 20 to 40 degrees diameter, when fitted with reversed full field 1.3x and 1.7x Galilean telescopes. Although initial tests indicated no psychogenic component, fields of approximately 20 degrees diameter were eventually obtained through an imitation telescope made with 2 plano lenses. This technique may be useful in determining whether there is a psychogenic component to inexplicable field results in other patients.