Description of the 15 retinal vascular parameters measured for each retinal photograph and relevant retinal zone
| Parameter | Description | Retinal zone | |
|---|---|---|---|
| CRAE | Central retinal arteriolar equivalent calibre | Summary measures of vascular equivalent calibre representing the equivalent single-vessel parent width for the six largest arterioles and venules. Based on the Knudston-Parr-Hubbard formula.24 | B |
| CRVE | Central retinal venular equivalent calibre | B | |
| AVR | Arteriole–venular ratio | Defined as the ratio of CRAE to CRVE. CRAE/CRVE=AVR | B |
| FDa | Fractal dimension of arteriolar network | Global summary measure of branching complexity of the retinal vascular tree reflecting how thoroughly the branching pattern fills two-dimensional spaces. Larger values represent a more complex pattern. Calculated from the skeletonised line tracing using the box-counting method. | C |
| FDv | Fractal dimension of venular network | C | |
| TORTa | Curvature tortuosity arteriole | Integral of the curvature squared along the vessel path, normalised by the total path length. Measurements are summarised to represent the average tortuosity of arterioles and venules separately, with smaller values reflecting straighter vessels. | C |
| TORTv | Curvature tortuosity venule | C | |
| Num1stBa | Number of first branching arterioles | The number of arterioles and venules with a first bifurcation, branch or daughter vessel, in zone C. | C |
| Num1stBv | Number of first branching venules | C | |
| BCa | Branching coefficient arteriole | Calculated from average Num1st measurements. Branching coefficient reflects the relationship between parent vessels and branches. Defined as the summed square of the mean vessel widths of each branch or daughter vessel divided by the square of the mean width of the parent vessel. | C |
| BCv | Branching coefficient venule | C | |
| JEa | Junctional exponent deviation for arterioles | Calculated from average Num1st measurements. Junctional exponent deviation reflects the deviation from the optimum ratio of vessel widths at a bifurcation | C |
| JEv | Junctional exponent deviation for venules | C | |
| LDRa | Length-to-diameter ratio arteriole | Length-to-diameter ratio is the length of the vessel from the midpoint of one bifurcation to the midpoint of the next bifurcation. It is expressed as a ratio to the diameter of the parent vessel at the first bifurcation | C |
| LDRv | Length-to- diameter ratio venule | C | |
Retinal vessels within the retinal zones of interest (0.5–1.0 (zone B) and 1.0–2.0 (zone C) disc diameters away from the optic disc margin) were traced automatically by the software.