Flow Heterogeneity and Factors Contributing to the Variability in Retinal Capillary Blood Flow

Area of Science:

• Ophthalmology
• Biomedical Engineering
• Physiology

Background:

• Capillary flow is crucial for neural tissue health and can be non-invasively imaged in the human retina.
• Understanding normal retinal capillary flow patterns is limited by current imaging resolution.

Purpose of the Study:

• To investigate the characteristics of capillary blood flow in the living human retina.
• To analyze patterns of erythrocyte velocity and flow variability in retinal capillaries.

Main Methods:

• Employed high-resolution adaptive optics ophthalmoscopy in three healthy young adults.
• Captured retinal capillary imaging at 200-300 frames per second to observe red blood cell flow.
• Measured erythrocyte velocities in 72 parafoveal capillary vessels per subject.

Main Results:

• Observed significant variability in capillary flow parameters (velocity, pulsatility) within and between subjects.
• Local factors like vessel diameter, tortuosity, and hematocrit did not fully explain the observed flow heterogeneity.
• A moderate correlation between erythrocyte velocity and hematocrit suggested plasma redistribution within vessels.

Conclusions:

• Findings advance the fundamental understanding of normal capillary physiology in the human retina.
• The study highlights unexplained flow heterogeneity, suggesting potential network-level effects influencing capillary function.