Blood flow in the human optic nerve head during isometric exercise

Area of Science:

• Ophthalmology
• Neuroscience
• Physiology

Background:

• Understanding optic nerve blood flow is crucial for ocular diseases like glaucoma.
• Previous studies focused on reduced perfusion pressure's effect on optic nerve blood flow.
• The relationship between optic nerve blood flow and perfusion pressure requires further investigation.

Purpose of the Study:

• To investigate the impact of elevated perfusion pressure on optic nerve blood flow.
• To establish the complete relationship between perfusion pressure and optic nerve blood flow in humans.

Main Methods:

• Laser Doppler flowmetry (LDF) used to measure red blood cell velocity, volume, and flux in the optic nerve head (ONH).
• Measurements taken in 13 subjects during isometric squatting exercise.
• Perfusion pressure was elevated by squatting, and intraocular pressure (IOP) changes were monitored.

Main Results:

• Optic nerve blood flow (mean velocity, volume, flux) showed no significant variation across a perfusion pressure range of 56+/-4 to 80+/-5 mmHg.
• Vascular resistance within the optic nerve head increased by approximately 50% during elevated perfusion pressure.
• Intraocular pressure (IOP) significantly increased during squatting and returned to baseline during recovery.

Conclusions:

• Constant optic nerve blood flow is maintained by a compensatory increase in vascular resistance.
• This autoregulation occurs in vessels feeding or draining the ONH, or in the ophthalmic artery.
• Combined with prior research, this study elucidates the full perfusion pressure-blood flow relationship in the human optic nerve.