In 1953, Goldmann observed that outflow resistance increases in an underperfused meshwork and concluded that only continuous perfusion keeps the outflow channels open. In primary open-angle glaucoma densifications occur beneath the inner wall of Schlemm's canal. They consist of fine fibrillary material and various glycoproteins. In order to see if densifications with reduced flow exist in clinical cases three possible examination techniques are proposed. (1) Doppler ultrasound: A transmitter with a very divergent beam could be placed on the cornea and the limbus probed with a small-diameter receiver. If the meshwork is perfused radially some Doppler frequencies might be generated and rendered audible in the usual way. Over densifications without perfusion they would be absent. (2) Doppler laser: If monochromatic light were used in a gonioscope and the light returned from the angle mixed with the original, it might be possible to observe Doppler frequencies. However, present-day lasers are not sufficiently monochromatic. (3) Observation of albumin-bound fluorescein entering the chamber from the canal. The canal is filled retrogradely with blood. Gonioscopy with polarized excitant light and observation through a polarized filter.