Respiratory and circulatory influence on photopapillometry.

Respiratory and circulatory conditions that could have an influence on measurements of pallor of the papilla were evaluated with our photopapillometer in a controlled study on canines. The brightness of the papilla rim and the width of the arterioles emerging from the optic nerve head were measured in six anesthetized dogs under normal, hypertensive, and hypotensive circulatory conditions, as well as under various respiratory manipulations, and the parameters were compared for statistical correlation. Both brightness and vessel width remained constant for a wide range of arterial pressures when the rest of the experimental conditions were kept stable at naturally occurring levels. If respiration and circulation were brought to extreme levels, however, there was a statistical tendency for the brightness of the papilla to be dependent on arterial and pulmonary arterial blood pressure. The importance of these findings is discussed with regard to their influence on objective measurements of fundus brightness.