Retinal hemodynamic oxygen reactivity assessed by perfusion velocity, blood oximetry and vessel diameter measurements

Abstract

ABSTRACT.Purpose: To test the oxygen reactivity of a fundus photographic method of measuring macular perfusion velocity and to integrate macular perfusion velocities with measurements of retinal vessel diameters and blood oxygen saturation. Methods: Sixteen eyes in 16 healthy volunteers were studied at two examination sessions using motion-contrast velocimetry and retinal oximetry with vessel diameter corrections. To test oxygen reactivity, participants were examined during normoxia, after 15 min of hyperoxia and finally after 45 min of normoxia. Repeatability was assessed by intraclass correlation coefficients (ICC) and limits of agreement. Results: Fifteen minutes of hyperoxia was accompanied by mean reductions in arterial and venous perfusion velocities of 14% and 16%, respectively (p = 0.0080; p = 0.0019), constriction of major arteries and veins by 5.5% and 8.2%, respectively (p < 0.0001), increased retinal arterial oxygen saturation from 95.1 AE 5.0% to 96.6 AE 6.4% (p = 0.038) and increased retinal venous oxygen saturation from 62.9 AE 6.7% to 70.3 AE 7.8% (p = 0.0010). Parameters returned to baseline levels after subsequent normoxia. Saturation and vessel diameter ICCs were 0.88-0.98 (range). For perfusion velocities, short-term ICCs were 0.79-0.82 and long-term ICCs were 0.06-0.11. Intersession increases in blood glucose were associated with reductions in perfusion velocities (arterial p = 0.0067; venous p = 0.018). Conclusion: Oxygen reactivity testing supported that motion-contrast velocimetry is a valid method for assessing macular perfusion. Results were consistent with previous observations of hyperoxic blood flow reduction using blue field entoptic and laser Doppler velocimetry. Retinal perfusion seemed to be regulated around individual set points according to blood glucose levels. Multimodal measurements may provide comprehensive information about retinal metabolism.

Comparison of Retinal Microvessel Blood Flow Velocities Acquired with Two Different Fields of View

“…Of the 12 available previously published studies that measured the BFV of healthy eyes with the RFI, 9 studies used the 20-degree FOV [1, 4, 11–14, 16, 17, 24], which yielded arteriolar BFVs ranging from 3.15 to 4.45 mm/s and venular BFVs ranging from 2.50 to 3.20 mm/s. On the other hand, 4 studies used the 35-degree FOV [18–21], which yielded arteriolar BFVs ranging from 3.16 to 4.70 mm/s and venular BFVs ranging from 3.15 to 3.20 mm/s.…”

“…For example, the 35-degree FOVs were acquired and followed by the 20-degree FOVs. Klefter et al reported the short-term variability with the LoA up to 1.1 mm/s [16]. Further studies are needed to test the repeatabilities with different FOVs in different imaging orders which may validate the viewpoint.…”

“…Further studies are needed to test the repeatabilities with different FOVs in different imaging orders which may validate the viewpoint. It would be worth noting that the difference between the 20-degree FOVs and trimmed 20-degree FOVs was only ~3–5%, which is relatively small compared to the changes by hyperoxia (~15% in both arterioles and venules) [16] and in diseased conditions such as multiple sclerosis (~20%) [4]. …”

The effect of intravitreal vascular endothelial growth factor on inner retinal oxygen delivery and metabolism in rats

“…(Linsenmeier, 1986; Linsenmeier and Braun, 1992; Pournaras, 1995; Wanek et al, 2012; Yu and Cringle, 2001) However, the validity of this assumption is questionable in the inner retina except under certain experimental conditions. (Alder et al, 1990; Braun et al, 1995) Methods to assess retinal oxygenation including MRI and oximetry have yielded great contributions to our understanding of retinal oxygenation, (Choudhary et al, 2013; Hammer et al, 2009; Hardarson, 2013; Kashani et al, 2014; Klefter et al, 2014; Man et al, 2013; Shahidi et al, 2013; Trick and Berkowitz, 2005; Yi et al, 2013; Zhang et al, 2011) but these do not quantify MO 2 . Recently, Palkovits and coworkers have published results obtained by the combined use of retinal vascular oximetry, vessel caliber analysis and blood velocity measurements using laser Doppler velocimetry in healthy subjects.…”

Impaired retinal microcirculation in multiple sclerosis

“…18 RFI is cleared by the US Food and Drug Administration (FDA). 19 The system uses hemoglobin in red blood cells as the intrinsic motion contrast agent for measuring the velocity of the red blood cells in retinal arterioles and venules. No contrast agent is needed and therefore the method is non-invasive.…”