Application of an OCT data-based mathematical model of the foveal pit in Parkinson disease

Spatial characterization of the effect of age and sex on macular layer thicknesses and foveal pit morphology

Characterizing the effect of age and sex on macular retinal layer thicknesses and foveal pit morphology is crucial to differentiating between natural and disease-related changes. We applied advanced image analysis techniques to optical coherence tomography (OCT) to: 1) enhance the spatial description of age and sex effects, and 2) create a detailed open database of normative retinal layer thickness maps and foveal pit shapes. The maculae of 444 healthy subjects (age range 21-88) were imaged with OCT. Using computational spatial data analysis, thickness maps were obtained for retinal layers and averaged into 400 (20 x 20) sectors. Additionally, the geometry of the foveal pit was radially analyzed by computing the central foveal thickness, rim height, rim radius, and mean slope. The effect of age and sex on these parameters was analyzed with multiple regression mixed-effects models. We observed that the overall age-related decrease of the total retinal thickness (TRT) (-1.1% per 10 years) was mainly driven by the ganglion cell-inner plexiform layer (GCIPL) (-2.4% per 10 years). Both TRT and GCIPL thinning patterns were homogeneous across the macula when using percentual measurements. Although the male retina was 4.1 μm thicker on average, the greatest differences were mainly present for the inner retinal layers in the inner macular ring (up to 4% higher TRT than in the central macula). There was an age-related decrease in the rim height (1.0% per 10 years) and males had a higher rim height, shorter rim radius, and steeper mean slope. Importantly, the radial analysis revealed that these changes are present and relatively uniform across angular directions. These findings demonstrate the capacity of advanced analysis of OCT images to enhance the description of the macula. This, together with the created dataset, could aid the development of more accurate diagnosis models for macular pathologies.

Foveal Pit Morphology Characterization: A Quantitative Analysis of the Key Methodological Steps

Disentangling the cellular anatomy that gives rise to human visual perception is one of the main challenges of ophthalmology. Of particular interest is the foveal pit, a concave depression located at the center of the retina that captures light from the gaze center. In recent years, there has been a growing interest in studying the morphology of the foveal pit by extracting geometrical features from optical coherence tomography (OCT) images. Despite this, research has devoted little attention to comparing existing approaches for two key methodological steps: the location of the foveal center and the mathematical modelling of the foveal pit. Building upon a dataset of 185 healthy subjects imaged twice, in the present paper the image alignment accuracy of four different foveal center location methods is studied in the first place. Secondly, state-of-the-art foveal pit mathematical models are compared in terms of fitting error, repeatability, and bias. The results indicate the importance of using a robust foveal center location method to align images. Moreover, we show that foveal pit models can improve the agreement between different acquisition protocols. Nevertheless, they can also introduce important biases in the parameter estimates that should be considered.

The Fovea in Retinopathy of Prematurity

Purpose

Because preterm birth and retinopathy of prematurity (ROP) are associated with poor visual acuity (VA) and altered foveal development, we evaluated relationships among the central retinal photoreceptors, postreceptor retinal neurons, overlying fovea, and VA in ROP.

Methods

We obtained optical coherence tomograms (OCTs) in preterm born subjects with no history of ROP (none; n = 61), ROP that resolved spontaneously without treatment (mild; n = 51), and ROP that required treatment by laser ablation of the avascular peripheral retina (severe; n = 22), as well as in term born control subjects (term; n = 111). We obtained foveal shape descriptors, measured central retinal layer thicknesses, and demarcated the anatomic parafovea using automated routines. In subsets of these subjects, we obtained OCTs eccentrically through the pupil (n = 46) to reveal the fiber layer of Henle (FLH) and obtained adaptive optics scanning light ophthalmograms (AO-SLOs) of the parafoveal cones (n = 34) and measured their spacing and distribution.

Results

Both VA and foveal depth decreased with increasing ROP severity (term, none, mild, severe). In severe subjects, foveae were broader than normal and the parafovea was significantly enlarged compared to every other group. The FLH was thinner than normal in mild (but not severe) subjects. VA was associated with foveal depth more than group. Density of parafoveal cones did not differ significantly among groups.

Conclusions

Foveal structure is associated with loss of VA in ROP. The preserved FLH in severe (relative to mild) eyes suggests treatment may help cone axon development. The significantly larger parafovea and increased outer nuclear layer (ONL) thickness in ROP hint that some developmental process affecting the photoreceptors is not arrested in ROP but rather is supranormal.

The intrinsically restructured fovea is correlated with contrast sensitivity loss in Parkinson's disease

Foveal structure that is specified by the thickness, depth and the overall shape of the fovea is a promising tool to qualify and quantify retinal pathology in Parkinson's disease. To determine the model variable that is best suited for discriminating Parkinson's disease eyes from those of healthy controls and to assess correlations between impaired contrast sensitivity and foveal shape we characterized the fovea in 48 Parkinson's disease patients and 45 control subjects by optical coherence tomography (OCT). The model quantifies structural changes in the fovea of Parkinson's disease patients that are correlated with a decline in contrast sensitivity. Retinal foveal remodeling may serve as a parameter for vision deficits in Parkinson's disease. Whether foveal remodeling reflects dopaminergic driven pathology or rather both dopaminergic and non-dopaminergic pathology has to be investigated in longitudinal studies.

Myopia induces meridional growth asymmetry of the retina: a pilot study using wide-field swept-source OCT

Myopic axial eye growth has mechanical implications on ocular structures, such as the retinal and foveal shape integrity or choroidal thickness. The current study investigated myopia-related changes of retinal radius of curvature, foveal width, depth, slope and choroidal thickness. Wide-field swept-source OCT line and volume scans were performed on 40 young adult participants in horizontal and vertical directions. OCT scans were corrected for their scan display distortions before automated extraction of retinal and foveal shape parameters. All findings were correlated to refractive error and axial length. The horizontal retinal radius of curvature and the directional ratio between horizontal and vertical retinal shape correlated significantly with axial length ([Formula: see text] and [Formula: see text]). Vertical retinal shape and foveal pit parameters neither showed any significant correlations with axial length nor refractive error (all [Formula: see text] 0.05). Choroidal thickness correlated significantly with refractive error in all analyzed regions ([Formula: see text]), but less with axial length ([Formula: see text] to - 0.37). Horizontal retinal shape and choroidal thickness, but not foveal pit morphology, were altered by myopic eye growth. Asymmetries in horizontal versus vertical retinal shape with increasing myopia were detected. These parameters could act as promising biomarkers for myopia and its associated complications.

Direct modeling of foveal pit morphology from distortion-corrected OCT images

Inherent distortions affect the spatial geometry of optical coherence tomography (OCT) images and consequently the foveal pit dimensions. Distortion correction provides an accurate anatomical representation of the retinal shape. A novel approach that automatically extracts foveal pit metrics from distortion-corrected OCT images using a sum of Gaussian function is presented. Foveal width, depth and slope were determined in 292 eyes with low fitting errors and high repeatability. Comparisons to undistorted scans revealed significant differences. To conclude, the internal OCT distortions affect the measurements of the foveal pit with their correction providing further insights into the role of foveal morphology in retinal pathologies and refractive development.

The role of Optical Coherence Tomography in Parkinsonism: A critical review

Optical coherence tomography (OCT) has been evaluated as a tool to assess retinal changes in various neurodegenerative disorders. Parkinson's disease (PD), is a neurodegenerative disorder wherein dopaminergic deficiency results in some of the symptoms. As retina also has high concentration of dopamine, it would be of interest for both the clinician as well as the basic scientist to know if there is a correlation between the clinical features and the retinal changes. The objective of this review is to critically evaluate the literature and study the utility of OCT as a tool to evaluate retinal changes in PD.

Assessing Retinal Structure in Patients with Parkinson's Disease

Objective:

The retina is an extension of the central nervous system (CNS), and ocular symptoms can precede manifestations of CNS disorders. Given that several neurodegenerative conditions that affect the brain exhibit ocular symptoms, the retina may be an accessible biomarker to monitor disease progression. Dopamine, the key neurotransmitter related to Parkinson’s disease (PD), is contained in amacrine and interplexiform cells, which reside in specific retinal layers. Understanding how loss of dopaminergic cells affects retinal anatomy could be relevant for monitoring disease progression. Here, our objective is to evaluate retinal structure (foveal pit morphology and thickness) in patients with PD.

Methods:

Thirty-three Caucasian subjects diagnosed with PD and 40 age-matched Caucasian control subjects underwent retinal imaging with spectral-domain optical coherence tomography (SD-OCT). Axial length measurements were used to correct the lateral scale of each macular volume scan. From these corrected volumes, foveal morphology was quantified with previously described algorithms, and Early Treatment Diabetic Retinopathy Study (ETDRS) grids of retinal thickness were generated and incorporated into a logistic regression model to predict PD.

Results:

Interocular foveal morphology measurements were highly symmetrical in PD patients and control subjects. There were no significant differences in foveal pit morphology between PD patients and control subjects. Using a model incorporating sex and axial length corrected ETDRS regions, we generated a receiver operating characteristic curve with a C-statistic of 0.80.

Conclusion:

Our study, which to our knowledge is the first to properly scale OCT measurements when quantifying retinal thickness, demonstrates that PD patients retain foveal symmetry between eyes. When constructing a model to predict PD, sex, along with the center 1 mm and temporal outer ETDRS regions, were significant predictors of PD. In addition to proper scaling of OCT measures, gender and racial differences in retinal anatomy should be considered in building future predictive PD models when using OCT.

Outer Retinal Assessment Using Spectral-Domain Optical Coherence Tomography in Patients With Alzheimer's and Parkinson's Disease

Purpose

To investigate outer retinal parameters among patients with various chronic neurodegenerative disorders by using spectral-domain coherence tomography (OCT) in a prospective cross-sectional cohort study.

Methods

A total of 132 participants were enrolled following a comprehensive diagnostic evaluation with neurologic, neuropsychology, and magnetic resonance imaging volumetric evaluations. Participants were 50 years or older, either diagnosed with Alzheimer's disease (AD) dementia, amnestic mild cognitive impairment (MCI), non-AD dementia, Parkinson's disease (PD), or age- and sex-matched controls. All participants underwent a macular cube scan for both eyes by using the Cirrus 4000 HD-OCT (Zeiss, Oberkochen, Germany). The OCT image with the best quality was selected for further analysis. Outer retinal parameters including ellipsoid zone mapping and outer nuclear layer metrics were evaluated with a novel software platform.

Results

One hundred twenty-four eyes of 124 participants with AD dementia (24 eyes), amnestic MCI (22 eyes), non-AD dementia (20 eyes), PD (22 eyes), and age- and sex-matched controls (36 eyes) were included in the analysis. Eight eyes were excluded either due to the presence of macular disease or poor quality of the OCT image. The mean ages of participants were 65.9 ± 8.9 years. The outer retinal thickness measures did not show any statistical significance between the groups. However, ellipsoid zone to retinal pigment epithelium volume correlated with cognitive testing scores in all study participants.

Conclusions

There were no identifiable differences in the outer retinal metrics across neurodegenerative disease groups and controls. The relationship between the degree of cognitive impairment and ellipsoid zone to retinal pigment epithelium volume warrants further study.

CuBe: parametric modeling of 3D foveal shape using cubic Bézier

Optical coherence tomography (OCT) allows three-dimensional (3D) imaging of the retina, and is commonly used for assessing pathological changes of fovea and macula in many diseases. Many neuroinflammatory conditions are known to cause modifications to the fovea shape. In this paper, we propose a method for parametric modeling of the foveal shape. Our method exploits invariant features of the macula from OCT data and applies a cubic Bézier polynomial along with a least square optimization to produce a best fit parametric model of the fovea. Additionally, we provide several parameters of the foveal shape based on the proposed 3D parametric modeling. Our quantitative and visual results show that the proposed model is not only able to reconstruct important features from the foveal shape, but also produces less error compared to the state-of-the-art methods. Finally, we apply the model in a comparison of healthy control eyes and eyes from patients with neuroinflammatory central nervous system disorders and optic neuritis, and show that several derived model parameters show significant differences between the two groups.

Retinal degeneration in progressive supranuclear palsy measured by optical coherence tomography and scanning laser polarimetry

This cross-sectional study compared the retinal morphology between patients with progressive supranuclear palsy (PSP) and healthy controls. (The retinal nerve fiber layer (RNFL) around the optic disc and the retina in the macular area of 22 PSP patients and 151 controls were investigated by spectral domain optical coherence tomography (SD-OCT). Additionally, the RNFL and the nerve fiber index (NFI) were measured by scanning laser polarimetry (SLP). Results of RNFL measurements with SD-OCT and SLP were compared to assess diagnostic discriminatory power. Applying OCT, PSP patients showed a smaller RNFL thickness in the inferior nasal and inferior temporal areas. The macular volume and the thickness of the majority of macular sectors were reduced compared to controls. SLP data showed a thinner RNFL thickness and an increase in the NFI in PSP patients. Sensitivity and specificity to discriminate PSP patients from controls were higher applying SLP than SD-OCT. Retinal changes did not correlate with disease duration or severity in any OCT or SLP measurement. PSP seems to be associated with reduced thickness and volume of the macula and reduction of the RNFL, independent of disease duration or severity. Retinal imaging with SD-OCT and SLP might become an additional tool in PSP diagnosis.

A sloped piecemeal Gaussian model for characterising foveal pit shape

PURPOSE

High-quality optical coherence tomography (OCT) macular scans make it possible to distinguish a range of normal and diseased states by characterising foveal pit shape. Existing mathematical models lack the flexibility to capture all known pit variations and thus characterise the pit with limited accuracy. This study aimed to develop a new model that provides a more robust characterisation of individual foveal pit variations.

METHODS

A Sloped Piecemeal Gaussian (SPG) model, consisting of a linear combination of a tilted line and a piecemeal Gaussian function (two halves of a Gaussian connected by a separate straight line), was developed to fit retinal thickness data with the flexibility to characterise different degrees of pit asymmetry and pit bottom flatness. It fitted the raw pit data between the two rims of the fovea to improve accuracy. The model was tested on 3488 macular scans from both eyes of 581 young adults (376 myopes and 206 non-myopes, mean (S.D.) age 21.9 (1.4) years). Estimates for retinal thickness, wall height and slope, pit depth and width were derived from the best-fitting model curve. Ten variations of Gaussian and Difference of Gaussian models were fitted to the same scans and compared with the SPG model for goodness of fit (by Root mean square error, RMSE), model complexity (by the Bayesian Information Criteria) and model fidelity.

RESULTS

The SPG model produced excellent goodness of fit (mean RMSE = 4.25 and 3.89 μm; 95% CI: 4.20, 4.30 and 3.86, 3.93 for fitting horizontal and vertical profiles respectively). The SPG model showed pit asymmetry, with average nasal walls 17.6 (11.6) μm higher and 0.96 (0.61)^° steeper than temporal walls and average superior walls 7.0 (12.2) μm higher and 0.41 (0.65)^° steeper than the inferior walls. The SPG model also revealed a continuum of human foveal shapes, from round bottoms to extended flat bottoms (up to 563 μm). 49.1% of foveal profiles were best fitted with a flat bottom >30 μm wide. Compared with the other tested models, the SPG was the preferred model overall based on the Bayesian Information Criteria.

CONCLUSIONS

The SPG is a new parsimonious mathematical model that improves upon other models by accounting for wall asymmetry and flat pit bottoms, providing an excellent fit and more faithful characterisation of typical foveal pit shapes and their known variations. This new model may be helpful in distinguishing normal foveal shape variations by refractive status as well by other characteristics such as sex, ethnicity and age.

The Association between Foveal Morphology and Macular Pigment Spatial Distribution: An Ethnicity Study

Purpose

Macular pigment (MP) spatial distribution varies considerably among individuals. We investigated ethnic variations in MP spatial distribution in relation to foveal architecture.

Methods

We measured MP optical density (MPOD) using heterochromatic flicker photometry (MAP test, City, University of London) in 76 white, 80 South Asian and 70 black volunteers (18 to 39 years). MPOD spatial profiles were classified objectively as exponential, ring-like or central dip, based on deviations away from an exponential fit. Measurements including total retinal thickness (RT), inner retinal layer (IRL), inner and outer plexiform layer (IPL and OPL) thickness, foveal width and foveal pit slope were taken from Spectralis SD-OCT (Heidelberg, Germany) scans.

Results

Integrated MPOD up to 1.8° (MPODint) was higher in South Asian (0.84±0.26) and black (0.84±0.31) than whites (0.63±0.24, P<0.0005). Ethnicity explained around 10% of the variance while gender played no significant role. MPOD profile phenotypes were associated with ethnicity: 58% with ring profiles were South Asian and 43% with dip profiles were black (χ²(4,226) = 13.4, P = 0.009). MPODint was lower in exponential (0.66±0.21) compared to ring-like (0.96±0.26) and central dip (1.00±0.32, P<0.0005) groups. White subjects had thicker IRL at 0° (130±21μm) than South Asian (123±16μm) and blacks (116±14μm; F(2) = 12.4, P<0.0005), with comparable results for IPL (P<0.0005) and OPL (P = 0.03). There was no significant difference in IRL, IPL or OPL (from 0 to 3.8° retinal eccentricity) or foveal width between MP profile groups (P>0.05).

Conclusion

We report a significant difference in the amount and distribution of MP between ethnicities that is not explained by variations in foveal morphology.

Evaluation of Retinal Vessel Morphology in Patients with Parkinson's Disease Using Optical Coherence Tomography

PURPOSE

The retina has been found affected in Parkinson's disease (PD). It is unclear if this is due to neurodegeneration of local dopamine-dependent retinal cells, a result of central nervous degeneration including the optic nerve or retinal small vessel disease. This study aimed to detect changes of the retinal vasculature in PD patients compared to controls.

METHODS

We examined 49 PD patients and 49 age- and sex-matched healthy controls by spectral domain optical coherence tomography (SD-OCT) with a circular scan centred at the optic disc. Vessels within the retinal nerve fibre layer were identified by an automated algorithm and thereafter manually labelled as artery or vein. Layer segmentation, vessel lumen and direct surrounding tissue were marked automatically with a grey value and the contrast between both values in relation to the surrounding tissue was calculated. The differences in these grey value ratios among subjects were determined and used as an indicator for differences in vessel morphology. Furthermore, the diameters of the veins and arteries were measured and then compared between the groups.

RESULTS

The contrast of retinal veins was significantly lower in PD patients compared to controls, which indicates changes in vessel morphology in PD. The contrast of arteries was not significantly different. Disease duration, disease stage according to Hoehn and Yahr or age did not influence the grey value ratios in PD patients. Vessel diameter in either veins or arteries did not differ between subject groups. The contrast of retinal veins contralateral to the clinically predominant and first affected side was significantly lower compared to the ipsilateral side.

CONCLUSION

Our data show a potential difference of the retinal vasculature in PD patients compared to controls. Vascular changes in the retina of PD patients might contribute to vision-related complaints in PD.

From Imaging the Brain to Imaging the Retina: Optical Coherence Tomography (OCT) in Schizophrenia

Optical Coherence Tomography (OCT) is a noninvasive imaging method, which provides an in vivo image of the retina. It allows for quantitative measurements of retinal and macular thickness, including single-layer analysis. Because the retinal nerve fibre layer comprises the first axons of the visual pathway and is unmyelinated, it can be considered a unique anatomical model, which may provide insight into the pathophysiological processes of diseases with a neurodegenerative character. In fact, past OCT studies have emphasized the role of the visual pathway as an ideal structure for exploring neurodegeneration and have demonstrated the potential of the method as an instrument for longitudinally monitoring structural changes in neurological disorders such as multiple sclerosis. Progress in signal processing and advancements to the OCT technique enables the illustration of structural changes in the retinal layers in a quick, reproducible, and objective manner with a spatial resolution comparable to those of histological slices.Findings from computer-based magnetic resonance imaging analyses and neuropathological studies support the hypothesis of a degenerative component of certain psychiatric disorders such as schizophrenia. Studies in schizophrenia incorporating OCT are currently rare and have yielded further heterogeneous results. This article elucidates the method of OCT and the retina's role as a "window to the brain". Furthermore, in delineating the degenerative components of schizophrenia, we discuss the possible applications of OCT in the schizophrenia population.

Scanning laser polarimetry and spectral domain optical coherence tomography for the detection of retinal changes in Parkinson's disease

PURPOSE

Whether retinal degeneration is part of the degenerative processes in patients with Parkinson's disease (PD) is still unclear. This cross-sectional study was undertaken to compare the retinal morphology of patients with PD and healthy controls using spectral domain optical coherence tomography (SD-OCT) and scanning laser polarimetry (SLP).

METHODS

Both eyes of patients with PD (n = 108) and healthy controls (n = 165) were examined using SD-OCT and SLP on the same day. Data on the thickness of the retinal nerve fibre layer (RNFL) of all quadrants and the macular area were acquired by OCT (Cirrus, Zeiss). The SLP device (Glaucoma diagnostics (GDx), Zeiss) measured the RNFL and calculated the nerve fibre index (NFI). All patients and probands were checked for concomitant ocular disorders by an ophthalmologist. Visual acuity, intraocular pressure (IOP), objective refraction and the anterior and posterior segment were assessed.

RESULTS

Patients with PD showed a reduced macular volume and a reduced central subfield thickness in OCT examinations. The RNFL in the different quadrants did not differ significantly from that of controls. SLP data showed a reduced average RNFL thickness, a decreased thickness of the inferior quadrant and an increase of the NFI in patients with PD.

CONCLUSION

PD may be associated with reduced thickness and volume of the macula and a reduced thickness of the RNFL in the inferior quadrant of the retina. Investigations using SD-OCT and SLP revealed distinct but significant differences between patients with PD and healthy controls.

A novel retinal biomarker for Parkinson's disease: Quantifying the foveal pit with optical coherence tomography

BACKGROUND

Optical coherence tomography offers a potential biomarker tool in Parkinson's disease (PD). A mathematical model quantifying symmetry, breadth, and depth of the fovea was applied.

METHODS

Nintey-six subjects (72 PD and 24 healthy controls) were included in the study. Macular scans of each eye were obtained on two different optical coherence tomography devices: Cirrus and RTVue.

RESULTS

The variables corresponding to the cardinal gradients of the fovea were the most sensitive indicators of PD for both devices. Principal component analysis distinguished 65% of PD patients from controls on Cirrus, 57% on RTVue.

CONCLUSION

Parkinson's disease shallows the superior/inferior and to a lesser degree nasal-temporal foveal slope. The symmetry, breadth, and depth model fits optical coherence tomography data derived from two different devices, and it is proposed as a diagnostic tool in PD.

Measuring hemoglobin levels in the optic disc of Parkinson's disease patients using new colorimetric analysis software

Objective. To evaluate a new method of measuring hemoglobin (Hb) levels and quantifying the color changes in the optic nerve head of Parkinson's disease (PD) patients. We also compared differences in retinal nerve fiber layer (RNFL) thicknesses obtained using spectral domain optical coherence tomography (OCT) device between PD group and healthy group. Methods. One hundred and fifty-five PD patients and 91 sex- and age-matched healthy subjects were included in this cross-sectional study. OCT examinations and one photograph of the optic disc were performed. The Laguna ONhE (“optic nerve hemoglobin”; Insoft SL, Tenerife, Spain) software was used to analyze the Hb level on the acquired optic disc photographs. Results. PD patients exhibited significantly reduced mean optic disc Hb percentages (57.56% in PD, 67.63% in healthy subjects; P = 0.001) as well as reduced Hb in almost all analyzed sectors, with the largest differences detected in the inferior and nasal sectors. RNFL parameters were significantly reduced in PD patients compared with healthy subjects, especially in the inferior quadrant. Conclusions. Measurements of optic disc Hb levels obtained with the Laguna ONhE software had good ability to detect optic nerve color changes (more papillary paleness and consequently this could suggest optic atrophy and axonal loss) in PD patients.