Red Blood Cell Distribution and Volume Changes at Capillary Junctions in the Living Human Retina

Area of Science:

• Ophthalmology
• Physiology
• Biomedical Engineering

Background:

• Understanding red blood cell (RBC) behavior in retinal microcirculation is crucial for diagnosing and treating eye diseases.
• Capillary junctions are critical sites where blood flow dynamics and cell distribution are altered.

Purpose of the Study:

• To characterize red blood cell (RBC) distribution and cell size changes at capillary junctions in the living human neural retina.
• To evaluate existing RBC partitioning models and propose new ones for retinal capillaries.

Main Methods:

• Cell-resolved blood flow was measured in 60 retinal capillary junctions of 6 healthy subjects using adaptive optics at 200-400 fps.
• Empirical RBC partitioning models, including the Pries model, were compared for predictive accuracy.

Main Results:

• Updated Pries model coefficients for human retinal capillaries were provided.
• A new linear model for RBC flow distribution was proposed.
• RBC volume decreased by 5.5% in branch vessels compared to the main vessel, with increased spacing and reduced hematocrit, suggesting water transfer.

Conclusions:

• This is the first noninvasive in vivo characterization of RBC partitioning in human retinal capillaries.
• Subtle fluid exchange between RBCs and plasma may optimize oxygen delivery in the retina.