Table 3. Factors influencing variability in vascular SO₂ by retinal oximetry.

	Co-variate	SD of SO2 Measurements	Relative Effect Size*	p-value
Between-subject variability	Un-IR group vs. IR group	2.23% vs. 3.63%	1.63	0.14
Between- vessel variability (within the same patient)	Un-IR vs. IR group	5.06% vs. 8.19%	1.62†	<0.001
	Arterioles vs. venules	2.78% vs. 5.06%	0.55‡	<0.001
	Vessel width	–	0.993	0.71
Between- vessel variability (within the same patient)	Un-IR vs. IR group
	Arterioles vs. venules
	Vessel width
Same vessel variability (repeatability of measurement)	Un-IR vs. IR group	2.39% vs. 2.48%	1.04	0.41
	Arterioles vs. venules	1.70% vs. 2.39%	0.71§	<0.001
	Vessel width	–	1.01	0.27

SD: Standard deviation; Un-IR: unirradiated group; IR: irradiated group.

^*Standard deviation of SO₂ measurements in one patient co-variate category divided by another co-variate category.

^†Between-vessel SD in the irradiated group is 1.62 times the unirradiated group for vessels of the same type and width.

^‡Between-vessel SD for arterioles is 0.55 that of venules for vessels of same width and in the same group of patients.

^§The SD of repeated measurements of the same vessel is 0.71 fold smaller for arterioles than for venules in vessels of the same width and in the same group of patients.