The Impact of Intraocular Pressure Elevation on Optic Nerve Head and Choroidal Blood Flow.

Purpose: To use laser speckle flowgraphy (LSFG) to assess blood flow (BF) in the optic nerve head (ONH) tissue and choroid during elevated intraocular pressure (IOP).

Methods: This prospective study included 20 eyes of 20 healthy volunteers. The testing protocol had a baseline phase, two elevated IOP phases (+10 and +20 mm Hg), and a recovery phase. IOP was elevated by pushing against the eyelid with a novel tubular device attached to the LSFG apparatus. Measurement parameters in each phase included: LSFG-derived mean blur rate (MBR) and flow acceleration index (FAI); systemic parameters, and IOP. The % change against baseline was calculated for each phase. The protocol was repeated five times to calculate the coefficient of variation (CV) for % change MBR and to determine the effect of mydriasis on % change MBR. We compared % change MBR and FAI and evaluated the relationship between % change ocular perfusion pressure (OPP) and MBR in the choroid and ONH tissue.

Results: The % change MBR was highly reproducible (CV: 6.1-8.7%) and not affected by mydriasis (P = 0.57-0.96). The % change MBR and FAI were higher in the ONH tissue than choroid during IOP elevation (P = 0.04). The % change OPP and MBR showed positive linear correlations and two-segmental linear correlations in the choroid and ONH tissue, respectively (P < 0.01).

Conclusion: Hemodynamics during IOP elevation differ in the choroid and ONH tissue. LSFG enables highly reproducible assessment of the dynamic autoregulation of ocular BF in the ONH tissue.