Purpose: To evaluate the perfusion-measuring capability of the Heidelberg Laser Doppler Retinal Flowmeter (HRF) and to compare the HRF against another laser Doppler flowmeter based on the Bonner and Nossal theory (Appl Optics 20: 2097-2107, 1981). Methods: To assess the HRF zero offset, we analyzed images of static objects and rabbit choroid at IOP above systolic blood pressure and post mortem. To assess the linearity of the HRF measurement, we analyzed images of different concentrations of milk in a glass capillary tube over a range of velocities at different camera angles. Finally, we analyzed HRF images of rabbit choroid during step-increases in IOP and compared the results against similar measurements obtained with the Perimed (Pf-2b) fiber optic laser Doppler flowmeter. Results: Flow measurements on static objects and post mortem rabbit choroid ranged from 150 to 350 arbitrary units (AU). Control choroidal flow (MAP=75 mmHg; IOP=15 mmHg) varied from 200 to 700 AU at different sites. Flow and volume measurements of milk in a capillary tube (134 μm, ID) were linear (r > 0.96) with concentration-dependent slopes at velocities < 5 mm/sec, but constant at higher velocities. By contrast, the Perimed flux was linear over the same velocity range but the CMBC was not. HRF and Perimed measurements in rabbit choroid over a wide range of IOPs showed similar flow and flux responses but different volume and CMBC responses. Conclusions: Quantitative HRF flow assessments are seriously limited by site-to-site variations in the large zero offset which can only be determined when blood flow ceases after death. The HRF flow is linear, but it is unclear whether the linear range encompasses the range of RBC velocities in the retinal and choroidal microcirculations. The discrepancies between the HRF volume and the Perimed CMBC indicate fundamental differences in the two systems. The manufacturer is implementing software modifications to resolve these problems.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - Feb 15 1996|
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience