Correlation Between Laser Speckle Flowgraphy and OCT-Derived Retinal and Choroidal Metrics in Healthy Human Eye

Abstract

Purpose: To investigate the correlation between laser speckle flowgraphy (LSFG) signals and the quantitative metrics derived from optical coherence tomography (OCT) in normal eyes.

Methods: LSFG, OCT, and OCT angiography (OCTA) imaging were performed on normal participants using a custom-designed LSFG system and a commercial swept-source OCT system. Mean (PWM) and amplitude (PWA) of the LSFG pulse waveform were selected to quantify the LSFG signals. Retinal and choroidal maps were obtained using the standard 6 × 6 mm OCT and OCTA scans. Structural and vascular metrics maps, including thickness, vessel area density, vessel skeleton density, and vessel diameter index of the retina, and choroidal thickness (CT), choroidal vessel volume (CVV) and choroidal vessel index (CVI), were employed to quantify the retinal and choroidal properties. Correlation analysis was then performed between the LSFG, retinal, and choroidal metrics maps.

Results: Twelve healthy participants aged 23 to 36 years were enrolled in this study. The spatial distribution of the PWM and PWA values was highly correlated with that of the CT and CVV metrics. On average, Spearman correlation coefficients (ρ) were 0.80 and 0.78 (all P < 0.001) for the correlations between PWM and CT and CVV, respectively, and were 0.61 and 0.63 (all P < 0.05) for the correlations between PWA and CT and CVV, respectively. In comparison, both PWM and PWA were generally weak or not correlated with all the retinal metrics and CVI.

Conclusions: LSFG signals were positively correlated with the choroidal thickness and vessel volume, suggesting choroidal blood flows dominate the LSFG signals at the area absent of large retinal vessels.

Translational relevance: This study illustrates the dominant source of the LSFG signals in the eye.

Figure 1.

(A) Representative OCT B-scan after attenuation correction and the corresponding segmentations of the ILM, BM, and choroidal–scleral interface layers. (B) Representative 6-mm × 6-mm OCTA map of retina generated by the commercial OCT system. (C) Same OCTA map of retina as in (B) but with large retinal vessels and the ONH region removed (black areas). (D) Representative choroidal vasculature map generated from the attenuation-corrected OCT choroid slab as shown in (A). The black areas indicate the large retinal blood vessels and ONH region were eliminated from the choroidal data. (E) Overlay of retinal OCTA and LSFG maps after image registration. (F) LSFG map of the ROI with the large retinal blood vessels and ONH region eliminated (black areas). (G) The ROI was separated into 8 × 8 subregions to facilitate the topographic correlation study. (H) Representative pulse waveforms of LSFG. The black and red waveforms show the averaged signals from the subregions indicated by black and red rectangles in (G), respectively. MDR, mean decorrelation rate. Red arrowheads in (C) and (F) show portions of large retinal vessels that were not identified. Asterisks in (D–F) show the location of fovea. Vertical and horizontal scale bars represent 200 µm and 1 mm, respectively.

Figure 2.

Representative maps of LSFG, retinal, and choroidal measurements with ROI centered at the perifovea. (A) Retinal OCTA map of the ROI. (B) PWM and (C) PWA map of LSFG. (D–G) Retinal thickness (RT) map, vessel area density (VAD) map, vessel skeleton density (VSD) map, and vessel diameter index (VDI) map of the retina. (H–J) CT map, CVV map, and CVI map. The regions correspond to the large blood vessels, and ONH was removed from measurements.

Figure 3.

Representative maps of LSFG, retinal, and choroidal measurements with ROI centered at the fovea. (A) Retinal OCTA map of the ROI. (B) PWM and (C) PWA map of LSFG. (D–G) RT, VAD, VSD, and VDI maps of the retina. The regions correspond to the large blood vessels, and ONH as removed from measurements. (H–J) CT, CVV, and CVI map.

Figure 4.

Representative correlations between the mean value of the LSFG PWM and the OCT retinal and choroidal metrics. (A–D) Correlations between PWM and RT, VAD, VSD, and VDI. (E–G) Correlations between PWM and CT, CVV, and CVI. The red lines represent the linear fitting of the scatters in each plot. Data were analyzed through Spearman's correlation analysis. Significance level was determined as P < 0.05.

Figure 5.

Representative correlations between the amplitude of the LSFG PWA and the OCT retinal and choroidal metrics. (A–D) Correlations between PWA and retinal thickness, VAD, VSD, VCI, VDI, and VPI. (E–G) Correlations between PWA and choroidal thickness, CVV, and CVI. The red lines represent the linear fitting of the scatters in each plot. Data were analyzed through Spearman's correlation analysis. Significance level was determined as P < 0.05.

Figure 6.

Correlation analysis between the LSFG PWM and retinal and choroidal metrics, obtained from 12 participants. Correlations between PWM and RT (A), VAD (B), VSD (C), VCI (D), VDI (E), VPI (F), CT (G), CVV (H), and CVI (I). The x- and y-axes represent Spearman's correlation coefficient and the P value. The vertical red-dashed lines represent ρ = −0.5 and 0.5 strength level of the correlation. The horizontal red-dashed lines illustrate the P = 0.05 significance level of the correlation. SCC, Spearman's correlation coefficient. P values are displayed on a logarithmic scale.

Figure 7.

Correlation analysis between the LSFG PWA and retinal and choroidal metrics, obtained from 12 participants. Correlations between PWA and RT (A), VAD (B), VSD (C), VDI (D), CT (E), CVV (F), and CVI (G). The x- and y-axes represent Spearman's correlation coefficient and the P value, respectively. The vertical red-dashed lines represent the ρ = −0.5 and 0.5 strength level of the correlation. The horizontal red-dashed lines illustrate the P = 0.05 significance level of the correlation. P values are displayed on a logarithmic scale.