Changes in Retinal Blood Flow in Response to an Experimental Increase in IOP in Healthy Participants as Assessed With Doppler Optical Coherence Tomography

Abstract

Purpose: Blood flow autoregulation is an intrinsic mechanism of the healthy retinal vasculature to keep blood flow constant when ocular perfusion pressure (OPP) is changed. In the present study, we set out to investigate retinal blood flow in response to an experimental decrease in OPP in healthy participants using Doppler optical coherence tomography.

Methods: Fifteen healthy participants aged between 22 and 31 years (mean, 27 ± 3 years) were included in the present open study. IOP was increased stepwise via the suction cup method to induce a decrease in OPP. Retinal blood flow in arteries and veins was assessed using a custom-built Doppler optical coherence tomography system and pressure-flow relationships were calculated to assess autoregulation.

Results: Suction cup application induced a pronounced increase in IOP with a maximum value of 50.5 ± 8.0 mm Hg at the highest level of suction. Pressure-flow relationships revealed that blood flow was autoregulated until the OPP was decreased by approximately 21 mm Hg and started to decrease significantly when the OPP was reduced by 30 mm Hg. Retinal blood flow at the last suction period decreased at a maximum of -57.0 ± 22.3% and 65.2 ± 15.4% in retinal arteries and retinal veins, respectively. These changes in retinal blood flow were less pronounced than the decrease in OPP (-75.2 ± 19.2%), indicating retinal autoregulation.

Conclusions: The results of the present study confirm that retinal blood flow is autoregulated in response to changes in the OPP. Doppler optical coherence tomography has the potential to become a clinical tool for the investigation of retinal blood flow autoregulation in the future, because of its ability to assess the blood velocities and diameter of the retinal vessels parallel and therefore also their blood flow in absolute values. (Clinicaltrials.gov number NCT03398616).

Conflict of interest statement

Disclosure: S. Puchner, None; D. Schmidl, None; L. Ginner, None; M. Augustin, None; R. Leitgeb, None; S. Szegedi, None; K. Stjepanek, None; N. Hommer, None; M. Kallab, None; R.M. Werkmeister, None; L. Schmetterer, None; G. Garhofer, None

Figures

Figure 1.

Changes in IOP, MAP and OPP during application of the suction cup. Data are presented as mean ± SD (n = 15). *Significant changes versus baseline for IOP and OPP.

Figure 2.

Relative change in OPP during application of the suction cup. Data are presented as mean ± SD (n = 15). *Significant changes versus baseline.

Figure 3.

Relative change in arterial and venous vessel diameter during application of the suction cup. Data are presented as mean ± SD (n = 15). *Significant changes versus baseline for retinal veins; #significant changes versus baseline for retinal arteries.

Figure 4.

Relative change in arterial and venous blood velocity during application of the suction cup. Data are presented as mean ± SD (n = 15). *Significant changes versus baseline for retinal arteries and veins.

Figure 5.

Pressure–flow relationship for retinal arteries and veins determined by categorized OPP and retinal blood flow during application of the suction cup. Data were sorted into groups of 15 values, each according to ascending OPP. Data are presented as mean ± SD (n = 15). *Significant changes versus baseline for retinal arteries and veins.

Figure 6.

Representative summed phase images of both channels as acquired with the bidirectional Doppler-OCT at baseline (top) and during the highest suction level (bottom). As for channel 1, the angle of the measurement beam was almost perpendicular to the vessel and the observed phase shift in channel 1 is only small. Vessel diameter was determined based on the channel with the higher phase shift (channel 2). The vessels of interest are marked in red and decrease in size upon suction.