As the result of a preoperative and postoperative study of a series of intracranial tumors, I was impressed with my own difficulty in accurately measuring the degree of papilledema by ophthalmoscopic examination. That this difficulty was not altogether confined to my limitations in ophthalmologic training was emphasized by the discrepancies in the measurements of diopters of swelling made by competent ophthalmologists on the same patients. Therefore, at the suggestion of Dr. Brown Pusey, I undertook first to study the graphs of the blind spots of patients with intracranial tumors taken before and after operation and, secondly, to determine if possible the actual mechanism involved in the enlargement of the blind spots due to an increase in intracranial pressure.
In 1668, Mariotte1 described the simple, perhaps crude, but wholly satisfactory experiment which demonstrated the existence of the blind spot:
I fastened on an obscure wall, about the height of my