the evaluations are complicated and require careful interpretation [11, 12].

20.5.4  Laser Doppler Flowmetry

The measurements in laser Doppler flowmetry are of a relative nature. Since there is variation in vascular density and vessel orientation within the tissue sampled, inter-individual comparisons are generally not recommended. It is difficult to interpret the data since measured Doppler shifts may be from both the retinal or choroidal vasculature [38].

20.5.5  Retinal Vessel Analyzer

This technique only provides retinal vessel diameter in relation to time and location. The measurements of retinal vessel diameters are restricted to larger vessels and should be performed in subjects with clear ocular media (Fig. 20.4).

Fig. 20.4  Retinal oximetry. A spectral retinal oximeter consists of a modified fundus camera and an image splitter, which divides the image into individual narrow band images for measurements. Therefore, it directly measures oxygenation within the retinal tissue vasculature.

20.5.6  Scanning Laser Ophthalmoscopy

Angiography

Measurements of volumetric blood flow by SLO angiography are currently not feasible. The analysis of these measurements is time consuming and requires trained graders [16].

20.5.7  Pulsatile Ocular Blood Flowmeter/

Pascal Dynamic Contour

Tonometer

Currently, POBF and Pascal DCT are available for clinical use to assess certain ocular hemodynamic parameters [39]. Since they measure global pulsatile choroidal hemodynamics, their measurements may not correlate with the blood supply to the optic nerve. Despite the correlation between OPA and visual field indices, POBF/Pascal DCT is not proven to provide guidance in the clinical management of glaucoma patients.

Summary for the Clinician:

››Interpretation of ocular hemodynamics is complex, since no technique provides the measurement of blood flow itself.

››Color Doppler imaging: Peak systolic and end diastolic blood flow velocities, which move in the same direction, represent a change in volumetric blood flow.

››Heidelberg retinal flowmeter interpretation may be difficult, as the volume of tissue from which the data is collected may vary.

››Scanning laser ophthalmoscopy angiography permits velocity and dye circulation time calculation. Interpretation of these parameters in relation to the global retinal blood flow is not clear.

››POBF/Pascal DCT: Although more practical for clinical use, further research is necessary for their use to guide clinical management in glaucoma.