Zeiss CIRRUS HD-OCT 500, User Manual

Page: 206 / 352

Overview
2660021169012 Rev. A 2017-12 CIRRUS HD-OCT User Manual
9-12
Table 9-2 shows describes both Vessel Density and Perfusion Density and provides
measurements for each.
Table 9-2 Vessel Density and Perfusion Density
Vessel Density vs. Capillary Perfusion
The main difference between Vessel Density and Capillary Perfusion is that in Vessel
Density, all vessels are treated equally. In Capillary Perfusion Density, larger vessels
influence the measurement more than smaller capillaries and therefore, can overshadow
loss of individual capillaries. Vessel Density attempts to provide a higher sensitivity to loss
of individual capillaries by providing the same weight to all vasculature. This attempt
occurs by replacing each vessel in the image with a vessel with thickness of 1 pixel. The
trade-off is a higher sensitivity to noise.
Foveal Avascular Zone (FAZ)
When FAZ overlay is selected, a yellow overlay is applied to the segmented FAZ area.
Values for the total calculated Area, Perimeter, and Circularity of the FAZ are shown in the
AngioPlex Metrix view and described in Table 9-3.
Name Description Units
Vessel Density Vessel Density is defined as the total length of
perfused vasculature per unit area in a region of
measurement. It is measured in units of inverse
millimeters. Vessel density can be thought of as
untangling all the vasculature in a region of tissue,
measuring its length with a ruler, then dividing it by
the area it originally occupied. The result is a
number with a minimum of 0 (no vessels) and an
unbounded maximum. mm
-1
(mm/mm
2
)
Capillary Perfusion
Density Capillary Perfusion Density is defined as the total
area of perfused vasculature per unit area in a
region of measurement. This metric is calculated by
summing up the number of pixels which contain
perfused vasculature, and dividing the sum by the
total number of pixels in the considered region
(typically a region in the ETDRS grid). The result is a
unitless number ranging from 0 (no perfusion) to 1
(fully perfused). Unitless
(mm
2
/mm
2
)