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Yuhua Zhang, Boyu Gu, Xiaolin Wang, Michael D Twa, Johnny Tam, Christopher A Girkin, Srinivas R Sadda; In vivo characterization of the acceleration process of erythrocytes within human retinal capillaries. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4612. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize the dynamic movement of erythrocytes within human retinal capillaries and to assess the mechanical properties of the retinal microvasculature at the individual capillary level.
We imaged erythrocytes flowing in retinal capillaries of human subjects of different ages under physiologic conditions, using a high-speed adaptive optics near-confocal ophthalmoscope. We measured the continuous velocity of the erythrocytes with custom image processing software, and thereby, derived the acceleration rate of the erythrocytes. We calculated the correlation between the erythrocyte acceleration and pulsations that were simultaneously recorded from the fingertip of the subject during velocity measurement, and also measured the maximum acceleration rate (Fig.1). We studied subjects who were in normal health substratified into 2 age groups: 20-25 years old (n=8) and 52-57 years old (n=4). We further examined a hypertensive group (58-63 years old, n=3) who had long-standing hypertension (> 5 years), but were otherwise healthy.
We measured erythrocyte velocity in 104 capillaries (young: 63; old: 32; hypertensive: 9) in 15 eyes of 15 subjects. The correlation coefficients between the pulse wave and the first derivative of the velocity were 0.95 ± 0.03, 0.94 ± 0.03, 0.92 ± 0.04 for the young, old, and the hypertensive group, respectively. The maximum acceleration values were 18.04 ± 9.53 (mm/s2), 12.86 ± 4.63 (mm/s2), 11.16 ± 3.58 (mm/s2), for the young, old, and the hypertensive group, respectively. The acceleration rates of the erythrocytes in the healthy older group and the hypertensive group were significantly lower than that of the young subjects (p=0.010 and p=0.044, respectively). However, we did not find a significant difference between the age-similar groups of normal and hypertensive subjects (p=0.8338). This may be partly due to the small number of subjects.
The acceleration waveform bears a strong resemblance to that of the pulse wave, indicating that the acceleration of the erythrocytes may reflect the overall mechanical performance of the retinal capillary and the erythrocytes within. This metric may have the potential for quantifying the health of the retinal microcirculation system.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Fig. 1 Erythrocyte dynamics in human retinal capillaries.
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