title: An evaluation of the photographs of William H. Crisp, MD.
abstract: The popularity of the Jackson cross cylinder is based on the assumption that its end points are "equal" to each other. Crisp's photographs, showing equal end points, popularized the Jackson cross cylinder technique. Photographs presented in this study show the anamorphic distortions of Snellen letters induced by the Jackson cross cylinder and suggest that Crisp's photographs were in error. His photographs do not represent the images seen by the patient when the Jackson cross cylinder refraction technique is used with Snellen letters.
mesh_terms: D001251:Astigmatism / Q000175:diagnosis / Q000503:physiopathology; D049673:History, 20th Century; D006801:Humans; D010781:Photography / Q000266:history*; D014481:United States; D014787:Vision Tests / Q000266:history*