This is made by attaching an iris diaphragm to an asbestos chimney. The amount of light passing through the opening in the diaphragm is controlled by an ivory-tipped lever at the left-hand side. An index at the periphery records the diameter of the opening in millimeters, from one to thirty.
When using the Maddox rod for muscle testing, the light streak can be made thread-like, or very broad, by regulating the size of the opening in the diaphragm.
While this screen may be of use in otology, laryngology, and in general ophthalmology, yet it is primarily for retinoscopy; simplicity and great convenience in controlling the amount of light being it points of merit.
To Messrs. Wall & Ochs I am indebted for their careful workmanship and skill in making a diaphragm the leaves of which are not affected by the heat.
120 South Eighteenth Street.