Blood reflux into Schlemm's canal during suction gonioscopy was seen more frequently in eyes with low pressures or high outflow facilities than in eyes with high pressures or low outflow facilities. The blood reflux pattern could be altered in some eyes by drug-induced increases or decreases in intraocular pressure. Blood reflux was also seen more frequently in eyes of patients previously classified nn-ng (intraocular pressure less than 32 mm Hg after six weeks of topically administered dexamethasone 0.1%) than in eyes of gg patients (intraocular pressure greater than 31 mm Hg after six weeks of topically administered dexamethasone 0.1%). This difference was independent of intraocular pressure. The low frequency of blood reflux in eyes of gg individuals was similar to the low frequency of reflux in eyes with glaucoma (typical field loss).
Phelps CD, Asseff CF, Weisman RL, Podos SM, Becker B. Blood Reflux Into Schlemm's Canal. Arch Ophthalmol. 1972;88(6):625–631. doi:10.1001/archopht.1972.01000030627011