Meeting Highlights: AAO

Pulsatile Aqueous Flow: Implications, Imaging and Clinical Relevance

Aqueous outflow is pulsatile, involving continuous movement of the trabecular meshwork (TM) in synchrony with transients, such as the ocular pulse.^1,2 This movement slows in glaucoma.³ To allow exploration of TM movement, Ricky Wang, MD, in the department of bioengineering at the University of Washington has developed a novel optical coherence tomography (OCT) technology. The imaging does not characterize structure, as does traditional OCT, but rather, movement and thus function of the TM.

This optical trabeculogram is noninvasive and objective and can be adapted to an office environment. The imaging technology is unique in assessing functional behavior associated with the TM elasticity and compliance necessary for pressure regulation, permitting us to achieve real-time measurement of pulse-dependent TM movement in eyes in the laboratory and in human subjects (Figure).

Click here for larger version of Figure.

Where could this lead us? We are currently developing a normative database of trabecular meshwork movement in humans. Comparison with movements in glaucomatous eyes may provide a new tool for early assessment of outflow system dysfunction.

Medications improving pulsatile aqueous outflow do so within minutes.^2,3 Before prescribing, real-time measurements in the office could permit identification of non-responders based on measurements of TM movement. Patients may thus be spared unnecessary costs and visits.

Decisions about initiating, adding or changing medications could be made based on objective measurements of function, thus enhancing patient care. Progressive reduction in TM movement with time could signal trends toward worsening regulation of function, thus accelerating decision-making.³

Severe reductions in TM movement could inform us of the need to consider earlier surgical intervention.³ The likely outcome of minimally invasive Schlemm’s canal surgery could be better predicted, eliminating those with a high probability of failure, and surgical locations could be better selected, potentially improving the outcome of procedures.

By shedding new light on the machinery of pressure regulation, we anticipate that this technology may lead to improved medical and surgical approaches to pressure management in glaucoma.

Murray Johnstone, MD

References

Johnstone MA. The aqueous outflow system as a mechanical pump: evidence from examination of tissue and aqueous movement in human and non-human primates. J Glaucoma. 2004:13:421-438.
Johnstone MA, Martin E, Jamil A. Pulsatile flow into the aqueous veins: Manifestations in normal and glaucomatous eyes. Exp Eye Res. 2011;92:318-327.
Johnstone MA. A new model describes an aqueous outflow pump and explores causes of pump failure in glaucoma. In: Essentials in Glaucoma II. Grehn F, Stamper R (eds) Heidelberg: Springer; 2007.