Characterization of human retinal vessel arborisation in normal and amblyopic eyes using multifractal analysis

The role of magnification correction in macular vessel density assessment: a contralateral eye study in anisometropia patients

Background

Investigating the impact of magnification correction in macular vessel density using optical coherence tomography angiography (OCTA) in patients with anisometropia.

Methods

Cross-sectional study. Totally 47 patients (11 male, 36 female) aged >18 years with high myopia were analyzed. All patients underwent evaluation of visual acuity, subjective refraction, and axial length. Anisometropia (n=37) was defined as a refraction difference between paired eyes ≥0.75 D. The control group (n=10) consisted patients with a refraction difference ≤0.5 D. Superficial vessel density was performed using 3 mm × 3 mm Cirrus-HD OCTA protocol. The vessel length density (VLD) and foveal avascular zone area (FAZA) were analyzed before and after magnification correction using Bennett’s formula.

Results

The mean spherical equivalent (SE) was −10.54±3.47 D in the more myopic eye and −8.05±3.47 D in the contralateral eye (P<0.001). Before magnification correction, the mean perfusion density (PD) and VLD were both significantly lower in the more myopic eyes. After magnification correction, the VLD and PD did not differ between paired eyes. No statistical difference was found in terms of the FAZA between paired eyes regardless of magnification correction. The magnification-induced differences in both VLD and PD were positively correlated with the difference in SE (both r=0.86, P<0.001).

Conclusions

In OCTA analysis, magnification correction should be performed to reduce refraction error-induced image error, which deserves attention in the clinical application.

Investigating Vascular Complexity and Neurogenic Alterations in Sectoral Regions of the Retina in Patients With Cognitive Impairment

Evidence is accumulating that cognitive function, and visual impairment may be related. In this pilot study, we investigated whether multifractal dimension and lacunarity analyses performed in sectoral regions of the retina may reveal changes in patients with cognitive impairment (CI) that may be masked in the study considering the whole retinal branching pattern. Prospective age-matched subjects (n = 69) with and with no CI and without the presence of any ophthalmic history were recruited (age > 55+ years). The Montreal Cognitive Assessment (MoCA) was used to measure CI, and full-field electroretinogram (ERG) was performed. Also, visual performance exams were conducted using the Rabin cone contrast test (CCT). Quantification of the retinal structure was performed in retinal fundus images [45^o field of view (FOV), optic disk centered] with excellent quality for all individuals [19 healthy controls (HC) and 20 patients with CI] after evaluating the inclusion and exclusion criteria in all study participants recruited (n = 69). The skeletonized vasculature network that comprised the whole branching pattern observable in the full 45° FOV was obtained for each image and divided into nine equal regions (superotemporal, superior, superonasal, macular, optic disk, nasal, inferotemporal, inferior, and inferonasal). The multifractal behavior was analyzed by calculating the generalized dimension Dq (Do, D1, and D2), the lacunarity parameter (Λ), and singularity spectrum f(α) in the nine sectoral skeletonized images as well as in the skeletons that comprised the whole branching pattern observable in the full 45° FOV. The analyses were performed using the ImageJ program together with the FracLac plug-in. Independent sample t-tests or Mann Whitney U test and Pearson correlation coefficient were used to find associations between all parameters in both groups. The effect size (Cohen’s d) of the difference between both groups was also assessed. A p-value < 0.05 was considered statistically significant. Significant correlations between multifractal and Λ parameters with the MoCA and implicit time ERG-parameter were observed in the regional analysis. In contrast, no trend was found when considering the whole retinal branching pattern. Analysis of combined structural-functional parameters in sectoral regions of the retina, instead of individual retinal biomarkers, may provide a useful clinical marker of CI.

Quantitative analysis of macular and peripapillary microvasculature in adults with anisometropic amblyopia

INTRODUCTION

The aim of this study was to compare the macular and peripapillary capillary vessel density (CVD) and foveal avascular zone (FAZ) in amblyopic eyes of adults with their fellow eyes and with eyes of healthy controls using optical coherence tomography-angiography (OCT-A).

METHODS

A total of 34 eyes of 17 patients with anisometropic amblyopia and 80 eyes of 40 age- and gender-matched healthy controls were included. CVD in superficial (SCP) and deep retinal capillary plexuses (DCP), peripapillary region, and FAZ were analyzed by OCT-A.

RESULTS

The median ages were 31 years (range 20-64) in patients with amblyopia and 34.5 years (range 24-65) in healthy controls (p = 0.242). The mean FAZ area measured was 0.329 ± 0.024 mm² in amblyopic eyes, 0.332 ± 0.025 mm² in fellow eyes, and 0.269 ± 0.015 mm² in control eyes (p < 0.05). The amblyopic eye of participants showed a decrease in CVD of SCP and DCP (p < 0.001, for all). The inside optic disk CVD measurements were lower in the amblyopic eyes than in the fellow eyes (p = 0.001) and healthy subjects (p = 0.015).

CONCLUSION

Significant differences in macular and peripapillary microvasculature were found in anisometropic amblyopic patients. The clinical significance of the results requires further investigation.

Automated Machine Learning Diagnostic Support System as a Computational Biomarker for Detecting Drug-Induced Liver Injury Patterns in Whole Slide Liver Pathology Images

Drug-induced liver injury (DILI) is a challenging disease to diagnose, a leading cause of acute liver failure, and responsible for drug withdrawal from the market. There is no symptom, no biomarker or test for detection, no therapy, but discontinuation of the drug. Pharmaceutical companies spend huge money, time, and scientific research efforts to test DILI effects and drug efficacy. A preclinical diagnostic support system is designed and proposed for DILI detection and classification on liver biopsy histopathology images. Heterogeneity features and automated machine learning (AutoML) models were tested to classify DILI injury patterns on whole slide image. Fractal and lacunarity values were used to detect hepatocellular necrotic injury patterns caused on a rat liver (in vivo) by 10 drugs at four dose levels. Correlations between fractal and lacunarity values were statistically analyzed for the 10 drugs; the Pearson correlation (r = 0.9809), p-value (1.6612E-06), and R2 (0.9582) were found to be high in the case of carbon tetrachloride. The AutoML model was tested to understand the injury patterns on a subset of 1,277 histology images. The AutoML algorithm was able to classify necrotic injury patterns accurately with an average precision of 98.6% on a score threshold of 0.5.

Distinguishing cognitive impairment by using singularity spectrum and lacunarity analysis of the retinal vascular network

The development of effective therapies for cognitive impairment (CI), especially due to Alzheimer's disease, demands diagnosing the condition during the prodromal phase. The diagnosis of CI involves expensive and invasive methods, such as positron emission tomography and cerebrospinal fluid assessment via spinal tap. Hence, a comparatively lower cost and noninvasive method of diagnosis is imperative. The human retina is an extension of the brain characterized by similarities in vascular and neural structures. The complications of CI are not only limited to the brain but also affect the retina for which the loss of retinal ganglion cells has been associated with neurodegeneration in the brain. The loss of retinal ganglion cells in individuals with CI may be related to reduced vascular demand and a potential remodeling of the retinal vascular branching complexity. Retinal imaging biomarkers may provide a low cost and noninvasive alternative for the diagnosis of CI. In this study, the retinal vascular branching complexity of patients with CI was characterized using the singularity spectrum multifractal dimension and lacunarity parameter. A reduced vascular branching complexity was observed in subjects with CI when compared to age- and sex-matched cognitively healthy controls. Significant associations were also found between retinal vascular and functional parameters.

Analysis of Macular Vessel Density and Foveal Avascular Zone in Adults with Amblyopia

Purpose: To quantify and compare the foveal avascular zone (FAZ) and the whole, parafoveal and foveal vessel density of superficial (SCP) and deep capillary plexus (DCP) in amblyopic eyes of adults and age-matched controls.Methods: This cross-sectional study involved 52 eyes from 34 subjects aged 18 to 45 years. Optical coherence tomography angiography (OCTA) was performed to all participants and SCP, DCP and FAZ were evaluated. SPSS (Statistical Package for the Social Sciences) 23 was used for data analysis.Results: Eighteen of 34 subjects (52,9%) were amblyopic and 16 (47,1%) of them controlled. Mean subject age was 31.2 years in the amblyopia group and 28.3 years in the control group. The mean FAZ measurements were 0.28 ± 0.08 in amblyopic eyes, 0.29 ± 0.08 in fellow eyes and 0.3 ± 0.11 in control eyes. The whole, foveal and parafoveal vessel density of SCP in both 3x3-mm and 6x6-mm scans were not statistically different in amblyopic eyes, fellow eyes and control eyes. In 6x6-mm scans, the whole, and parafoveal vessel density of DCP were significantly lower in amblyopic eyes than controls. There was no statistically significant difference in 3x3-mm scans about DCP.Conclusion: OCTA revealed lower vessel density in DCP of amblyopic eyes than fellow eyes and controls in adults.

Analysis of normal human retinal vascular network architecture using multifractal geometry

AIM

To apply the multifractal analysis method as a quantitative approach to a comprehensive description of the microvascular network architecture of the normal human retina.

METHODS

Fifty volunteers were enrolled in this study in the Ophthalmological Clinic of Cluj-Napoca, Romania, between January 2012 and January 2014. A set of 100 segmented and skeletonised human retinal images, corresponding to normal states of the retina were studied. An automatic unsupervised method for retinal vessel segmentation was applied before multifractal analysis. The multifractal analysis of digital retinal images was made with computer algorithms, applying the standard box-counting method. Statistical analyses were performed using the GraphPad InStat software.

RESULTS

The architecture of normal human retinal microvascular network was able to be described using the multifractal geometry. The average of generalized dimensions (Dq ) for q=0, 1, 2, the width of the multifractal spectrum (Δα=αmax - αmin ) and the spectrum arms' heights difference (|Δf|) of the normal images were expressed as mean±standard deviation (SD): for segmented versions, D0 =1.7014±0.0057; D1 =1.6507±0.0058; D2 =1.5772±0.0059; Δα=0.92441±0.0085; |Δf|= 0.1453±0.0051; for skeletonised versions, D0 =1.6303±0.0051; D1 =1.6012±0.0059; D2 =1.5531±0.0058; Δα=0.65032±0.0162; |Δf|= 0.0238±0.0161. The average of generalized dimensions (Dq ) for q=0, 1, 2, the width of the multifractal spectrum (Δα) and the spectrum arms' heights difference (|Δf|) of the segmented versions was slightly greater than the skeletonised versions.

CONCLUSION

The multifractal analysis of fundus photographs may be used as a quantitative parameter for the evaluation of the complex three-dimensional structure of the retinal microvasculature as a potential marker for early detection of topological changes associated with retinal diseases.