Retinal Vessel Caliber Measurement Bias in Fundus Images in the Presence of the Central Light Reflex

Purpose

To investigate the agreement between a fundus camera and a scanning laser ophthalmoscope in retinal vessel caliber measurements and to identify whether the presence of the central light reflex (CLR) explains potential discrepancies.

Methods

For this cross-sectional study, we obtained fundus camera and scanning laser ophthalmoscope images from 85 eyes of 85 healthy individuals (aged 50-65 years) with different blood pressure status. We measured the central retinal artery equivalent (CRAE) and central retinal artery vein equivalent (CRVE) with the Knudtson-Parr-Hubbard algorithm and assessed the CLR using a semiautomatic grading method. We used Bland-Altman plots, 95% limits of agreement, and the two-way mixed effects intraclass correlation coefficient for consistency [ICC(3,1)] to describe interdevice agreement. We used multivariable regression to identify factors associated with differences in between-device measurements.

Results

The between-device difference in CRAE (9.5  µm; 95% confidence interval, 8.0-11.1  µm) was larger than the between-device difference in CRVE (2.9  µm; 95% confidence interval, 1.3-4.5  µm), with the fundus camera yielding higher measurements (both P < 0.001). The 95% fundus camera-scanning laser ophthalmoscope limits of agreement were -4.8 to 23.9  µm for CRAE and -12.0 to 17.8  µm for CRVE. The corresponding ICCs(3,1) were 0.89 (95% confidence interval, 0.83-0.92) and 0.91 (95% confidence interval, 0.86-0.94). The between-device CRAE difference was positively associated with the presence of a CLR (P = 0.002).

Conclusions

Fundus cameras and scanning laser ophthalmoscopes yield correlated but not interchangeable caliber measurements. The CLR induces bias in arteriolar caliber in fundus camera images, compared with scanning laser ophthalmoscope images.

Translational Relevance

Refined measurements could yield better estimates of the association between retinal vessel caliber and ophthalmic or systemic disease.

Retinal Oxygen Delivery and Extraction in Ophthalmologically Healthy Subjects With Different Blood Pressure Status

Purpose

To compare retinal oxygen delivery (DO2) and oxygen extraction (VO2) in ophthalmologically healthy subjects with different blood pressure (BP) status.

Methods

In this case-control study, we prospectively included 93 eyes of 93 subjects (aged 50-65 years) from a Dutch cohort (n = 167,000) and allocated them to four groups (low BP, normal BP [controls], treated arterial hypertension [AHT], untreated AHT). We estimated vascular calibers from fundus images and fractal dimension from optical coherence tomography angiography scans. We combined calibers, fractal dimension, BP, and intraocular pressure measurements in a proxy of retinal blood flow (RBF), using a Poiseuille-based model. We measured arterial and venous oxygen saturations (SaO2, SvO2) with a scanning laser ophthalmoscope. We calculated the DO2 and VO2 from the RBF, SaO2, and SvO2. We compared the DO2 and VO2 between groups and investigated the DO2-VO2 association.

Results

DO2 and VO2 were different between groups (P = 0.009, P = 0.036, respectively). In a post hoc analysis, the low BP group had lower DO2 than the untreated AHT group (P = 4.9 × 10-4). The low BP group and the treated AHT group had a lower VO2 than the untreated AHT group (P = 0.021 and P = 0.034, respectively). There was a significant DO2-VO2 correlation (Robs = 0.65, bobs = 0.51, P = 2.4 × 10-12). After correcting for shared measurement error, the slope was not significant.

Conclusions

The DO2 and VO2 were altered in ophthalmologically healthy subjects with different BP status. Future studies could elucidate whether these changes can explain the increased risk of ophthalmic pathologies in those subjects.

Translational Relevance

Understanding the baseline interplay between BP, retinal perfusion, and oxygenation allows for improved evaluation of retinal disease manifestation.

U-Shaped Effect of Blood Pressure on Structural OCT Metrics and Retinal Perfusion in Ophthalmologically Healthy Subjects

Purpose

We wanted to investigate the association of blood pressure (BP) status with the ganglion cell-inner plexiform layer (GCIPL) and retinal nerve fiber layer (RNFL) thickness of nonglaucomatous eyes and to elucidate whether this effect is related to vascular metrics proxying retinal perfusion.

Methods

For this case-control study, we prospectively included 96 eyes of 96 healthy subjects (age 50–65) from a large-scale population-based cohort in the northern Netherlands (n = 167,000) and allocated them to four groups (low BP, normal BP [controls], treated arterial hypertension [AHT], untreated AHT). We measured macular GCIPL and RNFL (mRNFL) and peripapillary RNFL (pRNFL) thicknesses with optical coherence tomography (OCT). We estimated retinal blood flow (RBF), retinal vascular resistance (RVR), and autoregulatory reserve (AR) from quantitative OCT-angiography, fundus imaging, BP, and intraocular pressure. We compared structural and vascular metrics across groups and performed mediation analysis.

Results

Compared to controls, GCIPL was thinner in the low BP group (P = 0.013), treated hypertensives (P = 0.007), and untreated hypertensives (P = 0.007). Treated hypertensives exhibited the thinnest mRNFL (P = 0.001), temporal pRNFL (P = 0.045), and inferior pRNFL (P = 0.034). The association of GCIPL thickness with BP was mediated by RBF within the combined low BP group and controls (P = 0.003), by RVR and AR within the combined treated hypertensives and controls (P = 0.001, P = 0.032), and by RVR within the combined untreated antihypertensives and controls (P = 0.022).

Conclusions

Inner retinal thinning was associated with both tails of the BP distribution and with ineffective autoregulation. Longitudinal studies could clarify whether these defects can explain the reported glaucomatous predisposition of these population groups.

Combined Multi-Modal Assessment of Glaucomatous Damage With Electroretinography and Optical Coherence Tomography/Angiography

Purpose

To compare the diagnostic performance and to evaluate the interrelationship of electroretinographical and structural and vascular measures in glaucoma.

Methods

For 14 eyes of 14 healthy controls and 15 eyes of 12 patients with glaucoma ranging from preperimetric to advanced stages optical coherence tomography (OCT), OCT-angiography (OCT-A), and electrophysiological measures (multifocal photopic negative response ratio [mfPhNR] and steady-state pattern electroretinography [ssPERG]) were applied to assess changes in retinal structure, microvasculature, and function, respectively. The diagnostic performance was assessed via area-under-curve (AUC) measures obtained from receiver operating characteristics analyses. The interrelation of the different measures was assessed with correlation analyses.

Results

The mfPhNR, ssPERG amplitude, parafoveal (pfVD) and peripapillary vessel density (pVD), macular ganglion cell inner plexiform layer thickness (mGCIPL) and peripapillary retinal nerve fiber layer thickness (pRNFL) were significantly reduced in glaucoma. The AUC for mfPhNR was highest among diagnostic modalities (AUC: 0.88, 95% confidence interval: 0.75-1.0, P < 0.001), albeit not statistically different from that for macular (mGCIPL: 0.76, 0.58-0.94, P < 0.05; pfVD: 0.81, 0.65-0.97, P < 0.01) or peripapillary imaging (pRNFL: 0.85, 0.70-1.0, P < 0.01; pVD: 0.82, 0.68-0.97, P < 0.01). Combined functional/vascular measures yielded the highest AUC (mfPhNR-pfVD: 0.94, 0.85-1.0, P < 0.001). The functional/structural measure correlation (mfPhNR-mGCIPL correlation coefficient [rs]: 0.58, P = 0.001; mfPhNR-pRNFL rs: 0.66, P < 0.001) was stronger than the functional-vascular correlation (mfPhNR-pfVD rs: 0.29, P = 0.13; mfPhNR-pVD rs: 0.54, P = 0.003).

Conclusions

The combination of ERG measures and OCT-A improved diagnostic performance and enhanced understanding of pathophysiology in glaucoma.

Translational Relevance

Multimodal assessment of glaucoma damage improves diagnostics and monitoring of disease progression.

Microcirculatory model predicts blood flow and autoregulation range in the human retina: in vivo investigation with laser speckle flowgraphy

In this study, we mathematically predict retinal vascular resistance (RVR) and retinal blood flow (RBF), we test predictions using laser speckle flowgraphy (LSFG), we estimate the range of vascular autoregulation, and we examine the relationship of RBF with the retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC). Fundus, optical coherence tomography (OCT), and OCT-angiography images, systolic/diastolic blood pressure (SBP/DBP), and intraocular pressure (IOP) measurements were obtained from 36 human subjects. We modeled two circulation markers (RVR and RBF) and estimated individualized lower/higher autoregulation limits (LARL/HARL), using retinal vessel calibers, fractal dimension, perfusion pressure, and population-based hematocrit values. Quantitative LSFG waveforms were extracted from vessels of the same eyes, before and during IOP elevation. LSFG metrics explained most variance in RVR (R² = 0.77/P = 6.9·10^-9) and RBF (R² = 0.65/P = 1.0·10^-6), suggesting that the markers strongly reflect blood flow physiology. Higher RBF was associated with thicker RNFL (P = 4.0·10^-4) and GCC (P = 0.003), thus also verifying agreement with structural measurements. LARL was at SBP/DBP of 105/65 mmHg for the average subject without arterial hypertension and at 115/75 mmHg for the average hypertensive subject. Moreover, during IOP elevation, changes in RBF were more pronounced than changes in RVR. These observations physiologically imply that healthy subjects are already close to LARL, thus prone to hypoperfusion. In conclusion, we modeled two clinical markers and described a novel method to predict individualized autoregulation limits. These findings could improve understanding of retinal perfusion and pave the way for personalized intervention decisions, when treating patients with coexisting ophthalmic and cardiovascular pathologies.NEW & NOTEWORTHY We describe and test a new approach to quantify retinal blood flow, based on standard clinical examinations and imaging techniques, linked together with a physiological model. We use these findings to generate individualized estimates of the autoregulation range. We provide evidence that healthy subjects are closer to the lower autoregulation limit than thought before. This suggests that some retinas are less prepared to withstand hypoperfusion, even after small intraocular pressure rises or blood pressure drops.

Quantification and Repeatability of Vessel Density and Flux as Assessed by Optical Coherence Tomography Angiography

Purpose

To determine the intrasession repeatability (test-retest variability) of parafoveal and peripapillary perfused capillary density (PCD) and normalized flux index (NFI) as assessed with Canon OCT-HS100 angiography.

Methods

Pairs of optical coherence tomography angiography (OCT-A) images were obtained from the parafoveal and peripapillary region of 30 eyes of 30 healthy subjects. PCD and NFI were calculated using generic image-processing software. Macular ganglion-cell complex thickness (GCC) and peripapillary retinal nerve fiber layer thickness (RNFLT) were also recorded. Bland-Altman analysis was performed and the coefficient of repeatability (CoR) and intraclass correlation coefficient (ICC) were calculated. Correlations of parafoveal PCD/NFI with GCC and of peripapillary PCD/NFI with RNFLT were also computed.

Results

Mean (standard deviation) parafoveal and peripapillary PCD were 40.0% (1.8%) and 44.5% (1.3%), respectively. Corresponding values for NFI were 151.2 (6.8) and 164.2 (3.9). For PCD, ICC was 0.76 for parafoveal and 0.79 for peripapillary measurements; corresponding CoRs were 2.7% and 1.8%. Corresponding values for NFI were 0.62 and 0.67 for ICC and 13.3 and 7.0 for CoR. Average measures ICC was 0.87/0.88 and 0.76/0.80 for the parafoveal/peripapillary PCD and NFI, respectively. PCD and NFI were weakly correlated with GCC (r = 0.39, P = 0.035; r = 0.33, P = 0.077) and moderately correlated with RNFLT (r = 0.43, P = 0.017; r = 0.55, P = 0.002).

Conclusions

Repeatability of a commercially available OCT-A with generic image-processing software was good (NFI) to excellent (PCD). Our results indicate that changes surpassing the variability in healthy subjects should be easily detectable in a clinical setting.

Translational Relevance

Repeatability estimates provide information regarding the relevance of changes in retinal perfusion.