Tissue thickness calculation in ocular optical coherence tomography

Exploring the relationship between 24-2 visual field and widefield optical coherence tomography data across healthy, glaucoma suspect and glaucoma eyes

PURPOSE

To utilise ganglion cell-inner plexiform layer (GCIPL) measurements acquired using widefield optical coherence tomography (OCT) scans spanning 55° × 45° to explore the link between co-localised structural parameters and clinical visual field (VF) data.

METHODS

Widefield OCT scans acquired from 311 healthy, 268 glaucoma suspect and 269 glaucoma eyes were segmented to generate GCIPL thickness measurements. Estimated ganglion cell (GC) counts, calculated from GCIPL measurements, were plotted against 24-2 SITA Faster visual field (VF) thresholds, and regression models were computed with data categorised by diagnosis and VF status. Classification of locations as VF defective or non-defective using GCIPL parameters computed across eccentricity- and hemifield-dependent clusters was assessed by analysing areas under receiver operating characteristic curves (AUROCCs). Sensitivities and specificities were calculated per diagnostic category.

RESULTS

Segmented linear regression models between GC counts and VF thresholds demonstrated higher variability in VF defective locations relative to non-defective locations (mean absolute error 6.10-9.93 dB and 1.43-1.91 dB, respectively). AUROCCs from cluster-wide GCIPL parameters were similar across methods centrally (p = 0.06-0.84) but significantly greater peripherally, especially when considering classification of more central locations (p < 0.0001). Across diagnoses, cluster-wide GCIPL parameters demonstrated variable sensitivities and specificities (0.36-0.93 and 0.65-0.98, respectively), with the highest specificities observed across healthy eyes (0.73-0.98).

CONCLUSIONS

Quantitative prediction of VF thresholds from widefield OCT is affected by high variability at VF defective locations. Prediction of VF status based on cluster-wide GCIPL parameters from widefield OCT could become useful to aid clinical decision-making in appropriately targeting VF assessments.

Transfer Learning-Based Approach for Thickness Estimation on Optical Coherence Tomography of Varicose Veins

In-depth mechanical characterization of veins is required for promising innovations of venous substitutes and for better understanding of venous diseases. Two important physical parameters of veins are shape and thickness, which are quite challenging in soft tissues. Here, we propose the method TREE (TransfeR learning-based approach for thicknEss Estimation) to predict both the segmentation map and thickness value of the veins. This model incorporates one encoder and two decoders which are trained in a special manner to facilitate transfer learning. First, an encoder-decoder pair is trained to predict segmentation maps, then this pre-trained encoder with frozen weights is paired with a second decoder that is specifically trained to predict thickness maps. This leverages the global information gained from the segmentation model to facilitate the precise learning of the thickness model. Additionally, to improve the performance we introduce a sensitive pattern detector (SPD) module which further guides the network by extracting semantic details. The swept-source optical coherence tomography (SS-OCT) is the imaging modality for saphenous varicose vein extracted from the diseased patients. To demonstrate the performance of the model, we calculated the segmentation accuracy-0.993, mean square error in thickness (pixels) estimation-2.409 and both these metrics stand out when compared with the state-of-art methods.

Characterisation of the normal human ganglion cell-inner plexiform layer using widefield optical coherence tomography

PURPOSE

To describe variations in ganglion cell-inner plexiform layer (GCIPL) thickness in a healthy cohort from widefield optical coherence tomography (OCT) scans.

METHODS

Widefield OCT scans spanning 55° × 45° were acquired from 470 healthy eyes. The GCIPL was automatically segmented using deep learning methods. Thickness measurements were extracted after correction for warpage and retinal tilt. Multiple linear regression analysis was applied to discern trends between global GCIPL thickness and age, axial length and sex. To further characterise age-related change, hierarchical and two-step cluster algorithms were applied to identify locations sharing similar ageing properties, and rates of change were quantified using regression analyses with data pooled by cluster analysis outcomes.

RESULTS

Declines in widefield GCIPL thickness with age, increasing axial length and female sex were observed (parameter estimates -0.053, -0.436 and -0.464, p-values <0.001, <0.001 and 0.02, respectively). Cluster analyses revealed concentric, slightly nasally displaced, horseshoe patterns of age-related change in the GCIPL, with up to four statistically distinct clusters outside the macula. Linear regression analyses revealed significant ageing decline in GCIPL thickness across all clusters, with faster rates of change observed at central locations when expressed as absolute (slope = -0.19 centrally vs. -0.04 to -0.12 peripherally) and percentage rates of change (slope = -0.001 centrally vs. -0.0005 peripherally).

CONCLUSIONS

Normative variations in GCIPL thickness from widefield OCT with age, axial length and sex were noted, highlighting factors worth considering in further developments. Widefield OCT has promising potential to facilitate quantitative detection of abnormal GCIPL outside standard fields of view.

Anterior Scleral Thickness Profile in Keratoconus

PURPOSE

Considering that peripheral corneal thinning occurs in keratoconus (KC), the anterior scleral thickness (AST) profile was measured to compare thickness variations in healthy and KC eyes across several meridians.

METHODS

This cross-sectional case-control study comprised 111 eyes of 111 patients: 61 KC eyes and 50 age- and axial-length-matched healthy eyes. The AST was explored at three scleral eccentricities (1, 2, and 3 mm from the scleral spur) across four scleral zones (nasal, temporal, superior, and inferior) by using swept-source optical coherence tomography. The AST variations among eccentricities and scleral regions within and between groups were investigated.

RESULTS

The AST significantly varied with scleral eccentricity in healthy eyes over the temporal meridian (p = 0.009), whereas in KC eyes, this variation was observed over the nasal (p = 0.001), temporal (p = 0.029) and inferior (p = 0.006) meridians. The thinnest point in both groups was 2 mm posterior to the scleral spur (p < 0.001). The sclera was thickest over the inferior region (control 581 ± 52 μm, KC 577 ± 67 μm) and thinnest over the superior region (control 448 ± 48 μm, KC 468 ± 58 μm) in both populations (p < 0.001 for all eccentricities). The AST profiles were not significantly different between groups (p > 0.05). The inferior-superior thickness asymmetry was statistically different 2 mm posterior to the scleral spur between groups (p = 0.009), specifically with subclinical KC (p = 0.03). There is a trend where the asymmetry increases, although not significantly, with the KC degree (p > 0.05).

CONCLUSIONS

KC eyes presented significant thickness variations among eccentricities over the paracentral sclera. Although AST profiles did not differ between groups, the inferior-superior asymmetry differences demonstrated scleral changes over the vertical meridian in KC that need further investigation.

Derivation of human retinal cell densities using high-density, spatially localized optical coherence tomography data from the human retina

This study sought to identify demographic variations in retinal thickness measurements from optical coherence tomography (OCT), to enable the calculation of cell density parameters across the neural layers of the healthy human macula. From macular OCTs (n = 247), ganglion cell (GCL), inner nuclear (INL), and inner segment-outer segment (ISOS) layer measurements were extracted using a customized high-density grid. Variations with age, sex, ethnicity, and refractive error were assessed with multiple linear regression analyses, with age-related distributions further assessed using hierarchical cluster analysis and regression models. Models were tested on a naïve healthy cohort (n = 40) with Mann-Whitney tests to determine generalizability. Quantitative cell density data were calculated from histological data from previous human studies. Eccentricity-dependent variations in OCT retinal thickness closely resemble topographic cell density maps from human histological studies. Age was consistently identified as significantly impacting retinal thickness (p = .0006, .0007, and .003 for GCL, INL and ISOS), with gender affecting ISOS only (p < .0001). Regression models demonstrated that age-related changes in the GCL and INL begin in the 30th decade and were linear for the ISOS. Model testing revealed significant differences in INL and ISOS thickness (p = .0008 and .0001; however, differences fell within the OCT's axial resolution. Qualitative comparisons show close alignment between OCT and histological cell densities when using unique, high-resolution OCT data, and correction for demographics-related variability. Overall, this study describes a process to calculate in vivo cell density from OCT for all neural layers of the human retina, providing a framework for basic science and clinical investigations.

IMI-The Dynamic Choroid: New Insights, Challenges, and Potential Significance for Human Myopia

The choroid is the richly vascular layer of the eye located between the sclera and Bruch's membrane. Early studies in animals, as well as more recent studies in humans, have demonstrated that the choroid is a dynamic, multifunctional structure, with its thickness directly and indirectly subject to modulation by a variety of physiologic and visual stimuli. In this review, the anatomy and function of the choroid are summarized and links between the choroid, eye growth regulation, and myopia, as demonstrated in animal models, discussed. Methods for quantifying choroidal thickness in the human eye and associated challenges are described, the literature examining choroidal changes in response to various visual stimuli and refractive error-related differences are summarized, and the potential implications of the latter for myopia are considered. This review also allowed for the reexamination of the hypothesis that short-term changes in choroidal thickness induced by pharmacologic, optical, or environmental stimuli are predictive of future long-term changes in axial elongation, and the speculation that short-term choroidal thickening can be used as a biomarker of treatment efficacy for myopia control therapies, with the general conclusion that current evidence is not sufficient.

Choroidal Thickness Measured by Ocular Coherence Tomography (SD-OCT) and Body Mass Index in Healthy Saudi Women: A Cross-sectional Controlled Study

BACKGROUND

Obesity is one of the major public health problems globally, especially among women. Obesity is associated with glaucoma, cataract, age-related macular degeneration and diabetic retinopathy. Although it is clear that the anatomy and physiologic functions of the choroid may be affected by obesity, data investigating the effect of obesity on the choroid is limited and/or unavailable for the Saudi population.

OBJECTIVE

To assess Choroidal Thickness (CT) changes in a sample of healthy Saudi Arabian women with different Body Mass Index (BMI) using Spectral-domain Ocular Coherence Tomography (SD-OCT).

METHODS

A total of 140 healthy women aged 18-29 years (mean age ± standard deviation SD, 24.5 ± 1.7 years) with different BMI, axial length (AL) ≤ 24 ± 1.0 mm, and spherical equivalent refraction (SER) of ≤ ±2.0 dioptres were enrolled for the study. The participants were age and refractionmatched, and grouped into underweight (BMI ≤ 18.0 kg/m2) (n = 30), normal (control group) (18.5-24.9 kg/m2) (n = 43), overweight (25.0-29.9 kg/m2) (n=37), and obese study groups (≥ 30.0 kg/m2) (n = 30). SD-OCT imaging was performed on one eye of each participant. Comparisons among groups for all locations and the associations between CT and other variables were examined.

RESULTS

The mean CT at the subfoveal region (285 ± 31 μm, range: 203 μm to 399 μm) was significantly greater, and it was the lowest in the nasal region (248 ± 26 μm, range 154 to 304) compared with other locations, across all the groups (p < 0.05). Compared with the control, the subfoveal choroid was thinner in the obese group (mean difference: 22.6 μm, 95% Confidence Interval; CI: 8.6 μm to 36.6 μm; p = 0.02) and across all locations (p < 0.05) but thicker at the temporal location in the underweight group (12.4 μm, 95% CI: -23.7 μm to -1.04 μm; p = 0.01). No significant association of subfoveal CT with any of the measured parameters, including age (p-values ranged from 0.10 to 0.90), was found.

CONCLUSION

BMI may have an influence on the CT of healthy individuals and could be a cofounder in research studies on CT. It is, therefore, recommended that BMI should be evaluated in the clinical diagnosis and management of conditions associated with choroid in healthy individuals.

Application of Deep Learning Methods for Binarization of the Choroid in Optical Coherence Tomography Images

Purpose

The purpose of this study was to develop a deep learning model for automatic binarization of the choroidal tissue, separating choroidal blood vessels from nonvascular stromal tissue, in optical coherence tomography (OCT) images from healthy young subjects.

Methods

OCT images from an observational longitudinal study of 100 children were used for training, validation, and testing of 5 fully semantic networks, which provided a binarized output of the choroid. These outputs were compared with ground truth images, generated from a local binarization technique after manually optimizing the analysis window size for each individual image. The performance was evaluated using accuracy and repeatability metrics. The methods were also compared with a fixed window size local binarization technique, which has been commonly used previously.

Results

The tested deep learning methods provided a good performance in terms of accuracy and repeatability. With the U-Net and SegNet networks showing >96% accuracy. All methods displayed a high level of repeatability relative to the ground truth. For analysis of the choroidal vascularity index (a commonly used metric derived from the binarized image), SegNet showed the closest agreement with the ground truth and high repeatability. The fixed window size showed a reduced accuracy compared to other methods.

Conclusions

Fully semantic networks such as U-Net and SegNet displayed excellent performance for the binarization task. These methods provide a useful approach for clinical and research applications of deep learning tools for the binarization of the choroid in OCT images.

Translational Relevance

Deep learning models provide a novel, robust solution to automatically binarize the choroidal tissue in OCT images.

Regional Distribution of Choroidal Thickness and Diurnal Variation in Choroidal Thickness and Axial Length in Young Adults

Purpose

To examine the regional distribution of choroidal thickness (ChT) and the diurnal variation in ChT and axial length (AL) over a wide range of myopic refractive error.

Methods

ChT was measured in thirty-four healthy young adults (age mean ± SD: 25.2 ± 2.8, range: 18-35 years) using spectral-domain optical coherence tomography and AL using an IOL-Master 500. Participants were divided into three refractive groups: emmetropes, myopes, and high myopes. We evaluated ChT in macular (foveal, parafovea, and perifovea) and peripheral regions (6-mm from the foveal pit) in four quadrants (superior, temporal, inferior, and nasal). To assess the diurnal variation, three measurement sessions of ChT and AL were taken at 8 AM, 12 PM, 4 PM.

Results

ChT thins progressively towards the periphery. Superior and nasal quadrants exhibited the thickest (277 ± 73 µm) and thinnest (218 ± 89 µm) choroid, respectively. Higher myopic eyes showed an overall thinner choroid (237 ± 48 µm) compared to myopic eyes (264 ± 78 µm) (P < 0.05). Higher myopes exhibited a significant choroidal thinning in all quadrants except in the temporal quadrant (all p < 0.05). Both ChT and AL underwent a significant diurnal variation (p < 0.05). The ChT and AL diurnal variation amplitudes in higher myopes were significantly reduced (ChT: 14.6 ± 11, AL: 14.5 ± 13 µm), compared to those in emmetropes (ChT: 21.4 ± 15, AL: 21.3 ± 8.5 µm) and myopes (ChT: 19 ± 17, AL: 19 ± 9.7 µm). Diurnal variation amplitude in ChT did not differ significantly across quadrants and choroidal eccentricity regions (p > 0.05).

Conclusion

ChT distribution varies based on quadrant and eccentricity; superior choroid exhibited the thickest, and nasal showed the thinnest choroid. Higher myopes experience a reduced diurnal variation in ChT and AL.

Ganglion cell-inner plexiform layer measurements derived from widefield compared to montaged 9-field optical coherence tomography

CLINICAL RELEVANCE

With equivalent inner retinal thickness measurements compared to a more conventional composite optical coherence tomography (OCT) protocol, Widefield optical coherence tomography (WF-OCT) is a clinically viable, time-saving option facilitating detection of ocular pathologies within the central 55° of the retina.

PURPOSE

To compare ganglion cell-inner plexiform layer (GCIPL) thicknesses obtained using a single WF-OCT scan and standard composite OCT scans acquired in 9 fields of gaze (9F-OCT).

METHODS

Thirteen healthy participants underwent WF-OCT and 9F-OCT using the Spectralis OCT. The GCIPL was automatically segmented with a manual review for 9F-OCT and was manually segmented for WF-OCT. After registration, differences in GCIPL thicknesses were compared using 95% confidence intervals computed from one-sample t-tests and Bland-Altman analyses. Location-specific differences in B-scan tilt were analysed using Spearman correlations and linear regression models. To determine whether B-scan tilt influences GCIPL measurements, regression models of tilt versus differences between perpendicular and axial GCIPL thickness were applied.

RESULTS

While scattered locations demonstrated significant GCIPL thickness differences between WF-OCT and 9F-OCT, most differences did not exceed the axial pixel resolution of the instrument of 3.87 µm. Bland-Altman analyses indicated no notable bias using WF-OCT. Moderate correlations indicating significant location-specific differences in B-scan tilt were observed for temporal, central and inferior B-scans (r = -0.62 to 0.72), with linear regression models predicting a maximum difference in the tilt of 4.65°. The quadratic regression model indicated that at tilts greater than 27.3°, perpendicular GCIPL measurements become increasingly thin relative to axial measurements.

CONCLUSIONS

GCIPL thicknesses and B-scan tilts from WF-OCT are comparable to 9F-OCT, indicating that WF-OCT can be applied clinically to obtain valid inner retinal OCT measurements over 55° of the central retina with relative ease. However, for peripheral locations, B-scan tilt may need to be considered when measuring GCIPL thicknesses.

Prevention of Choroidal Thinning by 0.01% Atropine Administered 24 h Before Exposure to Hyperopic Blur in Young Myopes

Purpose: To evaluate the persistence of atropine's effect upon choroidal thickness and ocular biometrics and its interaction with hyperopic blur in a population of young adult myopes. Methods: Twenty young (aged 18-35 years) myopic participants with spherical equivalent refractive error of -0.75 to -6.00 D (mean ± SD -2.85 ± 1.64 D) had subfoveal choroidal thickness (SFCT) measurements derived from scans collected from the right eye only with a SD-OCT instrument (Copernicus SOCT-HR) before, as well as 60 min following the introduction of 3 testing conditions: (1) placebo/hyperopic (-3 D) blur, (2) placebo/hyperopic blur one day after administration of 0.01% atropine, and (3) placebo/no blur. Each combination of blur and pharmacological agent was tested on a separate day at approximately the same time of day between 9 am and 2 pm. Results: Repeated measures ANOVA revealed that hyperopic blur and placebo were associated with a decrease in choroidal thickness (mean change: -10.7 ± 2.7 μm, P < 0.001 after 60 min), whereas administration of 0.01% atropine one day before the introduction of hyperopic blur prevented the thinning of the choroid (mean change of +1.1 ± 3.7 μm after 60 min) compared to baseline (both, P > 0.05). There was also no significant difference between the baseline choroidal thickness measurements for any of the conditions tested. Conclusion: Low dose atropine can inhibit signals associated with hyperopic defocus that cause thinning of the choroid for at least 24 h after initial instillation.

Wide-field choroidal thickness and vascularity index in myopes and emmetropes

PURPOSE

To study regional variations in choroidal thickness (CT), luminal thickness and stromal thickness of the choroid, and choroidal vascularity index (CVI) in low myopic and emmetropic eyes using wide-field optical coherence tomography (OCT).

METHODS

Sixty-nine healthy young adults between 20 and 38 years of age participated in this study, including 40 low myopes (mean ± SD spherical equivalent (MSE) refractive error: -3.00 ± 1.39 D, range: -6.00 to -0.62 D) and 29 emmetropes (MSE: -0.05 ± 0.09 D, range: -0.25 to +0.12 D). Wide-field CT, luminal thickness, stromal thickness and CVI were measured across five eccentricities (fovea, parafovea, perifovea; near-periphery and periphery) and four quadrants (nasal, temporal, inferior and superior), in vertical and horizontal meridians, while controlling for a range of extraneous factors potentially influencing the CT. Custom-written software was used to segment and binarize the OCT images.

RESULTS

Wide-field CT, luminal thickness and stromal thickness, averaged across all participants, exhibited significant topographical variation, with the foveal (379 ± 8 µm, 200 ± 4 µm, 179 ± 4 µm, respectively) and peripheral (275 ± 8 µm, 161 ± 4 µm, 114 ± 4 µm, respectively) regions presenting the thickest and thinnest regions (all p < 0.001). Wide-field CVI showed a progressively higher percentage (greater vascularity) with increasing eccentricity from the fovea towards the periphery (p < 0.001). Macular CT and stromal choroidal thickness were significantly thinner in myopes compared to emmetropes (p < 0.05). Myopes (55.7 ± 0.3%) showed a slightly higher CVI compared with emmetropes (54.4 ± 0.4%) (p < 0.05).

CONCLUSIONS

Low myopia in young adults was associated with significant choroidal thinning across the macular, but not extramacular regions, with this decrease in choroidal thickness mostly attributed to thinning in the stromal component of the choroid, rather than the luminal (vascular) component.

Choroidal thickness measurements in different ethnicities using swept source optical coherence tomography: repeatability and assessment

Clinical relevance: Swept-source optical coherence tomography may not provide reliable measurements of choroidal thickness for pigmented subjects.Background: The repeatability of choroidal thickness measurements in young healthy adults was investigated using swept source optical coherence tomography.Methods: Choroidal thickness was measured using swept source optical coherence tomography in 98 healthy subjects (49 South Asian and 49 Caucasian) aged between 19 and 28 years old. Repeated radial scan images centred on the fovea were obtained from the right eye with 5 min between measurements. Choroidal thickness values were obtained from the built-in automated segmentation algorithm for the 9 subfields defined by the Early Treatment Diabetic Retinopathy Study. Interclass correlation coefficients and Bland-Altman methods were used to assess test-retest repeatability.Results: The mean ± standard deviation sub-foveal choroidal thickness was 316.53 ± 63.36 µm for the Caucasian group and 292.70 ± 60.13 µm for the South Asian group. Bland-Altman analysis showed smaller test-retest variability for choroidal thickness measurements in the Caucasian group (mean difference ± SD = -0.01 ± 6.59 µm) compared to the South Asian group (mean difference ± SD = -2.38 ± 12.20 µm). No relationship was found between the mean choroidal thickness and mean spherical equivalent of refractive error for both subject groups.Conclusion: Swept source optical coherence tomography is capable of obtaining choroidal thickness measurements with good repeatability. However, test-retest limits of agreement are substantially greater in South Asian subjects, suggesting that successful identification of the choroidal scleral interface may be affected by the amount of pigmentation present in the retinal and choroidal tissues.

Anterior scleral thickness dimensions by swept-source optical coherence tomography

Clinical relevance: Given the association of scleral characteristics with many ophthalmological diseases, there is an important need to measure the anterior scleral thickness (AST).Background: This study examined the AST by swept-source optical coherence tomography (SS-OCT) in a large healthy population, assessing also the reproducibility of AST measurements and the correlation with different parameters.Methods: Cross-sectional study in 605 eyes of 605 subjects. AST measurements were made in the temporal and nasal quadrants at 1 (AST1) and 3 mm (AST3) from the scleral spur using SS-OCT. These dimensions were then assessed for associations in a multivariate model with the factors age, sex, refractive error, conjunctival-Tenon capsule thickness (CTT), anterior chamber angle (ACA), intraocular pressure (IOP), iris thickness (IT), limbus-sulcus distance (LSD), and ciliary muscle thickness (CMT). The reproducibility of the AST measurements was determined in 30 of the participants.Results: The mean age was 42.6 ± 17.3 years (range 5 to 86 years). The following means were recorded: AST1 was 522.3 ± 65.7 µm (355 to 761) and 558.4 ± 71.5 µm (357 to 889); AST2 was 513.3 ± 67.3 µm (343 to 732) and 574.4 ± 71.6 µm (389 to 789), and AST3 548.8 ± 71.9 µm (356 to 762) and 590.1 ± 76.6 µm (414 to 873) in the temporal and nasal quadrants respectively, being thicker the nasal quadrant (all p < 0.001). A positive correlation was detected between AST and age, sex, temporal ACA and LSD (all p ≤ 0.043), being negative the correlation with CMT (p ≤ 0.044). No correlation was observed between AST measurements and refractive error, CTT and IT (p ≥ 0.064). The reproducibility of AST measurements was excellent (intraclass correlation coefficient ≥0.951).Conclusions: SS-OCT allows for in vivo AST measurements. Our data contained a wide range of measurements, showing an association between AST and age, sex, ACA, LSD and CMT.

Deep feature loss to denoise OCT images using deep neural networks

SIGNIFICANCE

Speckle noise is an inherent limitation of optical coherence tomography (OCT) images that makes clinical interpretation challenging. The recent emergence of deep learning could offer a reliable method to reduce noise in OCT images.

AIM

We sought to investigate the use of deep features (VGG) to limit the effect of blurriness and increase perceptual sharpness and to evaluate its impact on the performance of OCT image denoising (DnCNN).

APPROACH

Fifty-one macula-centered OCT pairs were used in training of the network. Another set of 20 OCT pair was used for testing. The DnCNN model was cascaded with a VGG network that acted as a perceptual loss function instead of the traditional losses of L1 and L2. The VGG network remains fixed during the training process. We focused on the individual layers of the VGG-16 network to decipher the contribution of each distinctive layer as a loss function to produce denoised OCT images that were perceptually sharp and that preserved the faint features (retinal layer boundaries) essential for interpretation. The peak signal-to-noise ratio (PSNR), edge-preserving index, and no-reference image sharpness/blurriness [perceptual sharpness index (PSI), just noticeable blur (JNB), and spectral and spatial sharpness measure (S3)] metrics were used to compare deep feature losses with the traditional losses.

RESULTS

The deep feature loss produced images with high perceptual sharpness measures at the cost of less smoothness (PSNR) in OCT images. The deep feature loss outperformed the traditional losses (L1 and L2) for all of the evaluation metrics except for PSNR. The PSI, S3, and JNB estimates of deep feature loss performance were 0.31, 0.30, and 16.53, respectively. For L1 and L2 losses performance, the PSI, S3, and JNB were 0.21 and 0.21, 0.17 and 0.16, and 14.46 and 14.34, respectively.

CONCLUSIONS

We demonstrate the potential of deep feature loss in denoising OCT images. Our preliminary findings suggest research directions for further investigation.

Anterior scleral thickness and shape changes with different levels of simulated convergence

PURPOSE

Convergence plays a fundamental role in the performance of near visual tasks. We measured the effect of two levels of convergence on anterior scleral thickness and shape in emmetropes, low to moderate myopes and high myopes.

METHODS

Forty-five healthy young adults aged between 18 and 35 years including 15 emmetropes, 15 low/moderate myopes, and 15 high myopes were recruited. Anterior segment optical coherence tomography and eye surface profilometry were used to evaluate the anterior scleral thickness (nasal only, n = 42) and shape (n = 40), before and during two visual tasks involving 9° and 18° convergence, in those participants with complete and reliable data.

RESULTS

Convergence led to a thickening of the total anterior eye wall (5.9 ± 1.4 μm) and forward movement (10 ± 2 μm) of the nasal anterior scleral surface (both p < 0.001). Larger changes were found at 18° than at 9° convergence and in more peripheral nasal scleral regions. There was a significant association between total wall thickening and forward movement of the scleral surface. Refractive group was not a significant main effect, but there were significant interactions between refractive group and the thickness changes with convergence in different scleral regions.

CONCLUSION

During convergence, the biomechanical forces acting on the eye lead to nasal anterior scleral thickening and forward movement of the nasal scleral surface.

Custom extraction of macular ganglion cell-inner plexiform layer thickness more precisely co-localizes structural measurements with visual fields test grids

We aimed to evaluate methods of extracting optical coherence tomography (OCT)-derived macular ganglion cell-inner plexiform layer (GCIPL) thickness measurements over retinal locations corresponding to standard visual field (VF) test grids. A custom algorithm was developed to automatically extract GCIPL thickness measurements from locations corresponding to Humphrey Field Analyser 10-2 and 30-2 test grids over Goldmann II, III and V stimulus sizes from a healthy cohort of 478 participants. Differences between GCIPL thickness measurements based on VF test grids (VF-based paradigms) and the 8 × 8 grid, as per instrument review software, were analyzed, as were impacts of fovea to optic disc tilt and areas over which GCIPL thickness measurements were extracted. Significant differences between the VF-based paradigms and the 8 × 8 grid were observed at up to 55% of locations across the macula, with the greatest deviations at the fovea (median 25.5 μm, 95% CI 25.24–25.72 μm, P < .0001). While significant correlations with fovea to optic disc tilt were noted at up to 33% of locations distributed 6°–8° from the foveal center, there were no marked differences in GCIPL thickness measurements between VF-based paradigms using different stimulus sizes. As such, standard high-density OCT measurement paradigms do not adequately reflect GCIPL measurements at retinal locations tested with standard VF patterns, with the central macular region contributing most to the observed differences and with further correction required for fovea to optic disc tilt. Spatial direction of GCIPL thickness measurements will improve future comparisons of structure and function, thereby improving methods designed to detect pathology affecting the inner retina.

Retinal Boundary Segmentation in Stargardt Disease Optical Coherence Tomography Images Using Automated Deep Learning

Purpose

To use a deep learning model to develop a fully automated method (fully semantic network and graph search [FS-GS]) of retinal segmentation for optical coherence tomography (OCT) images from patients with Stargardt disease.

Methods

Eighty-seven manually segmented (ground truth) OCT volume scan sets (5171 B-scans) from 22 patients with Stargardt disease were used for training, validation and testing of a novel retinal boundary detection approach (FS-GS) that combines a fully semantic deep learning segmentation method, which generates a per-pixel class prediction map with a graph-search method to extract retinal boundary positions. The performance was evaluated using the mean absolute boundary error and the differences in two clinical metrics (retinal thickness and volume) compared with the ground truth. The performance of a separate deep learning method and two publicly available software algorithms were also evaluated against the ground truth.

Results

FS-GS showed an excellent agreement with the ground truth, with a boundary mean absolute error of 0.23 and 1.12 pixels for the internal limiting membrane and the base of retinal pigment epithelium or Bruch's membrane, respectively. The mean difference in thickness and volume across the central 6 mm zone were 2.10 µm and 0.059 mm³. The performance of the proposed method was more accurate and consistent than the publicly available OCTExplorer and AURA tools.

Conclusions

The FS-GS method delivers good performance in segmentation of OCT images of pathologic retina in Stargardt disease.

Translational Relevance

Deep learning models can provide a robust method for retinal segmentation and support a high-throughput analysis pipeline for measuring retinal thickness and volume in Stargardt disease.

Short-term effects of atropine combined with orthokeratology (ACO) on choroidal thickness

PURPOSE

To analyse the one-month change in subfoveal choroidal thickness (SFChT) of myopic children treated with 0.01 % atropine, orthokeratology (OK), or their combination.

METHODS

This is a prospective, randomized controlled trial. One hundred fifty-four children aged between 8 and 12 years with a spherical equivalent (SE) of -1.00 to -6.00 diopters were enrolled. Subjects were randomly assigned to receive 0.01 % atropine and orthokeratology (ACO, n = 39), 0.01 % atropine and single vision glasses (atropine, n = 42), orthokeratology and placebo (OK, n = 36), or placebo and single vision glasses (control, n = 37). SFChT was assessed using optical coherence tomography (OCT). Ocular parameters, including axial length (AL), were measured using a Lenstar LS 900.

RESULTS

SFChT significantly increased in the ACO (14.12 ± 12.88 μm, p < 0.001), OK (9.43 ± 9.14 μm, p < 0.001) and atropine (5.49 ± 9.38 μm, p < 0.001) groups, while it significantly decreased in the control group (-4.81 ± 9.93 μm, p = 0.006). The one-month change in SFChT was significantly different between the control and treatment groups (p < 0.001). The results of pairwise comparisons among the treatment groups showed that the magnitude of the SFChT change was larger in the ACO group than in the atropine group (p = 0.002). The changes in the ACO and OK groups were not significantly different (p = 0.326).

CONCLUSION

The combination of OK and atropine induced a greater increase in SFChT than monotherapy with atropine, which might indicate a better treatment effect for childhood myopia control.

Myopia and Regional Variations in Retinal Thickness in Healthy Eyes

Purpose

To investigate the effects of refraction on retinal thickness measurements at different locations and layers in healthy eyes of Saudi participants.

Methods

Thirty-six randomly selected adults aged 27.0 ± 5.7 years who attended a Riyadh hospital from 2016 to 2017 were categorized into three groups: non-myopic (spherical equivalent refraction [SER], +1.00 to –0.50 diopters [D]), low myopic (SER, –0.75 to –3.00D), and moderate to high myopic (SER ≤ –3.25D). Full, inner, and outer retinal thicknesses were measured at nine locations by spectral-domain stratus optical coherence tomography (Optovue Inc., Fremont, CA, USA) and were compared according to refractive group and sex.

Results

The mean SERs for the non-myopia, low myopia, and moderate to high myopia groups were 0.2 ± 0.6, –1.5 ± 0.5, and –7.5 ± 1.9 D, respectively. Refractive error, but not sex, had significant effects on the retinal layer thickness measurements at different locations (P < 0.05). The parafoveal and outer retinal layers were significantly thicker than the perifoveal and inner retina layers in all groups (P < 0.05). The full foveal thickness was higher and the full parafoveal and perifoveal regions were thinner in moderate to high myopic eyes than in the non-myopic eyes (P < 0.05), but were similar to those in the low myopic eyes (P > 0.05). The foveal thicknesses measured in the inner and outer layers of the retina were higher but the thicknesses measured at the inner and outer layers of the parafoveal and perifoveal regions were lower in moderate to high myopic eyes.

Conclusion

There were regional differences in the retinal layer thicknesses of healthy Saudi eyes, which was dependent on the central refractions. This is important when interpreting retinal nerve fiber layer thicknesses in myopia and disease management in Saudi participants.

Posterior Choroidal Stroma Reduces Accuracy of Automated Segmentation of Outer Choroidal Boundary in Swept Source Optical Coherence Tomography

Purpose

To determine the influence of choroidal boundary morphology on the accuracy of automated measurements of subfoveal choroidal thickness (SFCT) in swept source optical coherence tomography (SSOCT).

Methods

A retrospective image analysis of foveal-centered horizontal line scans from normal and diseased eyes using the Topcon DRI OCT-1 Atlantis SSOCT was conducted. Subfoveal choroid-scleral junction (CSJ) and retina-choroidal junction (RCJ) morphologies were graded by two observers. Automated SFCT (A-SFCT) was compared with manual SFCT (M-SFCT) measurements from Bruch's membrane to the posterior limits of choroidal vessel, hyperreflective stroma, and hyporeflective lamina fusca. Agreement in boundary grading was assessed by Cohen's kappa. A-SFCT and M-SFCT were compared using Bland-Altman analysis and paired t-tests.

Results

A total of 200 eyes of 100 patients with a mean (SD) age of 62 (18) years were included. The choroidal vessel, stromal, and lamina fusca boundaries were visible in 100%, 58%, and 38% of the eyes, respectively. Interobserver agreement in RCJ and CSJ grading was high (kappa = 0.974 and 0.851). Mean A-SFCT differed from M-SFCT by only 2 μm at posterior choroidal vessel boundary (P = 0.801). A-SFCT overestimated SFCT at the posterior vessel wall boundary by 17 μm (P = 0.026) and 23 μm (P = 0.001) in the presence of a visible posterior choroidal stroma and lamina fusca, respectively.

Conclusions

Automated outer choroidal boundary segmentation tends to identify the posterior limit of the choroidal vessel. Agreement between A-SFCT and M-SFCT is reduced by the presence of posterior stromal layer and lamina fusca. A-SFCT should be interpreted with RCJ and CSJ boundary grading.

Wide-field choroidal thickness in myopes and emmetropes

There is a paucity of knowledge regarding the normal in-vivo thickness of the choroid beyond the macula (~17°). In this study, the choroidal thickness of 27 healthy young adults was examined across the macular (the central 5 mm including the fovea, parafovea, and perifovea) and extra-macular (a 5-14 mm annulus including the near-periphery and periphery) regions using wide-field optical coherence tomography, and compared between emmetropes (n = 14) and myopes (n = 13). The choroid progressively thinned beyond the parafovea (350 ± 86 µm) towards the periphery (264 ± 44 µm), and was thickest superiorly (355 ± 76 µm) and thinnest nasally (290 ± 79 µm). Choroidal thickness also varied with refractive error; myopes exhibited a thinner choroid than emmetropes in the macular region (311 ± 88 vs. 383 ± 66 µm), however, this difference diminished towards the periphery (251 ± 48 vs. 277 ± 37 µm). Meridional variations in choroidal thickness were not different between myopes and emmetropes. In conclusion, the choroid was thickest within the perifovea; thinned substantially towards the periphery, and exhibited the minimum and maximum peripheral thinning superiorly and nasally across a 55° region respectively. Choroidal thinning associated with myopia was more pronounced in the macular than extra-macular regions.

Effect of patch size and network architecture on a convolutional neural network approach for automatic segmentation of OCT retinal layers

Deep learning strategies, particularly convolutional neural networks (CNNs), are especially suited to finding patterns in images and using those patterns for image classification. The method is normally applied to an image patch and assigns a class weight to the patch; this method has recently been used to detect the probability of retinal boundary locations in OCT images, which is subsequently used to segment the OCT image using a graph-search approach. This paper examines the effects of a number of modifications to the CNN architecture with the aim of optimizing retinal layer segmentation, specifically the effect of patch size as well as the network architecture design on CNN performance and subsequent layer segmentation. The results demonstrate that increasing patch size can improve the performance of the classification and provides a more reliable segmentation in the analysis of retinal layer characteristics in OCT imaging. Similarly, this work shows that changing aspects of the CNN network design can also significantly improve the segmentation results. This work also demonstrates that the performance of the method can change depending on the number of classes (i.e. boundaries) used to train the CNN, with fewer classes showing an inferior performance due to the presence of similar image features between classes that can trigger false positives. Changes in the network (patch size and or architecture) can be applied to provide a superior segmentation performance, which is robust to the class effect. The findings from this work may inform future CNN development in OCT retinal image analysis.

Changes in retina and choroid after haemodialysis assessed using optical coherence tomography angiography

BACKGROUND

Reports of choroidal and retinal changes before and after haemodialysis are few and have been controversial. Traditional imaging modalities are insufficient for quantitative assessment. This study aims to use optical coherence tomography angiography to monitor the short-term vascular density and thickness changes in retina and choroid before and after haemodialysis.

METHODS

Seventy-seven eyes of 77 patients with end-stage kidney disease undergoing haemodialysis were included. Ophthalmologic examinations including optical coherence tomography angiography were performed one hour before and after haemodialysis. The vascular density of retina and choroid were measured and calculated by optical coherence tomography angiography. The retinal thickness and subfoveal choroidal thickness were measured manually using Image J software. The relationships between the changes in ocular and systemic parameters after haemodialysis were evaluated.

RESULTS

The systolic blood pressure decreased from 123.7 ± 19.7 to 116.9 ± 24.6 mmHg (p < 0.05) in all patients. The mean ocular perfusion pressure decreased significantly after haemodialysis in both diabetic and non-diabetic groups (p < 0.05). Mean retinal thickness decreased from 204.7 ± 22.4 μm to 200.8 ± 22.8 μm (p < 0.05) after haemodialysis in all patients. The vascular density of outer retina was decreased from 38.8 ± 5.5 per cent to 37.5 ± 3.4 per cent (p < 0.05) after haemodialysis in all patients. The changes in diastolic blood pressure, intraocular pressure, subfoveal choroidal thickness, vascular density of the superficial capillary plexus, deep capillary plexus and choriocapillaris were insignificant. There was no significant correlation between systolic blood pressure and the vascular density of the outer retina.

CONCLUSION

In optical coherence tomography angiography, the retinal thickness became thinner and the vascular density in the outer retina decreased after haemodialysis in patients with end-stage kidney disease. The change of subfoveal choroidal thickness showed no significance after haemodialysis. The decreased volume in the retinal vascular bed and deficient choroidal autoregulatory control of ocular blood flow might be involved in the mechanism of these changes.

Choroidal thickness and axial length changes in myopic children treated with orthokeratology

PURPOSE

To analyze the change in subfoveal choroidal thickness (SFChT) and its relationship with changes in axial length (AL) in myopic children treated with Orthokeratology (Ortho-k).

METHODS

Fifty myopic children participated in this study: 29 subjects were treated with Ortho-k lenses and 21 with single vision distance spectacles. The SFChT and ocular biometrics, including AL, were measured at baseline, one month, and six months after lens wear in both groups.

RESULTS

AL significantly increased in both groups over time. In the Ortho-k group, SFChT also increased; however, there was no significant change in SFChT in the control group over time. At the six-month visit, the magnitude of eye growth was significantly reduced in the Ortho-k group compared to the control group (0.06±0.10mm vs. 0.17±0.10mm, P<0.001). SFChT was significantly thicker in the Ortho-k group compared to the control group at the one-month and six-month visits (15.78±11.37μm vs. -2.98±8.96μm, P<0.001 (one-month visit); 21.03±12.74μm vs. -2.50±14.43μm, P<0.001 (six-month visit)), although there was no significant difference between the two follow-up visits (P=0.102 for the Ortho-k group; P=0.898 for the control group). Changes in the large choroidal vascular layer (LCVL) accounted for the majority of subfoveal choroidal thickening (approximately 77% and 80% at one-month and six-month visits, respectively).

CONCLUSION

Ortho-k treatment induced significant choroidal thickening and a slowing of eye growth. LCVL thickening accounted for the majority of SFChT thickening. However, its potential mechanism in myopia control requires further investigation.

Automatic Choroidal Layer Segmentation Using Markov Random Field and Level Set Method

The choroid is an important vascular layer that supplies oxygen and nourishment to the retina. The changes in thickness of the choroid have been hypothesized to relate to a number of retinal diseases in the pathophysiology. In this paper, an automatic method is proposed for segmenting the choroidal layer from macular images by using the level set framework. The three-dimensional nonlinear anisotropic diffusion filter is used to remove all the optical coherence tomography (OCT) imaging artifacts including the speckle noise and to enhance the contrast. The distance regularization and edge constraint terms are embedded into the level set method to avoid the irregular and small regions and keep information about the boundary between the choroid and sclera. Besides, the Markov random field method models the region term into the framework by correlating the single-pixel likelihood function with neighborhood information to compensate for the inhomogeneous texture and avoid the leakage due to the shadows cast by the blood vessels during imaging process. The effectiveness of this method is demonstrated by comparing against other segmentation methods on a dataset with manually labeled ground truth. The results show that our method can successfully and accurately estimate the posterior choroidal boundary.

Variability of Retinal Thickness Measurements in Tilted or Stretched Optical Coherence Tomography Images

Purpose

To investigate the level of inaccuracy of retinal thickness measurements in tilted and axially stretched optical coherence tomography (OCT) images.

Methods

A consecutive series of 50 eyes of 50 patients with age-related macular degeneration were included in this study, and Cirrus HD-OCT images through the foveal center were used for the analysis. The foveal thickness was measured in three ways: (1) parallel to the orientation of the A-scan (Tx), (2) perpendicular to the retinal pigment epithelium (RPE) surface in the instrument-displayed aspect ratio image (Ty), and (3) thickness measured perpendicular to the RPE surface in a native aspect ratio image (Tz). Mathematical modeling was performed to estimate the measurement error.

Results

The measurement error was larger in tilted images with a greater angle of tilt. In the simulation, with axial stretching by a factor of 2, Ty/Tz ratio was > 1.05 at a tilt angle between 13° to 18° and 72° to 77°, > 1.10 at a tilt angle between 19° to 31° and 59° to 71°, and > 1.20 at an angle ranging from 32° to 58°. Of note with even more axial stretching, the Ty/Tz ratio is even larger. Tx/Tz ratio was smaller than the Ty/Tz ratio at angles ranging from 0° to 54°. The actual patient data showed good agreement with the simulation.

The Ty/Tz ratio was greater than 1.05 (5% error) at angles ranging from 13° to 18° and 72° to 77°, greater than 1.10 (10% error) angles ranging from 19° to 31° and 59° to 71°, and greater than 1.20 (20% error) angles ranging from 32° to 58° in the images axially stretched by a factor of 2 (b/a = 2), which is typical of most OCT instrument displays.

Conclusions

Retinal thickness measurements obtained perpendicular to the RPE surface were overestimated when using tilted and axially stretched OCT images.

Translational Relevance

If accurate measurements are to be obtained, images with a native aspect ratio similar to microscopy must be used.

Quantifying Variability in Longitudinal Peripapillary RNFL and Choroidal Layer Thickness Using Surface Based Registration of OCT Images

Purpose

To assess within-subject variability of retinal nerve fiber layer (RNFL) and choroidal layer thickness in longitudinal repeat optical coherence tomography (OCT) images with point-to-point measurement comparison made using nonrigid surface registration.

Methods

Nine repeat peripapillary OCT images were acquired over 3 weeks from 12 eyes of 6 young, healthy subjects using a 1060-nm prototype swept-source device. The RNFL, choroid and the Bruch's membrane opening (BMO) were segmented, and point-wise layer thicknesses and BMO dimensions were measured. For each eye, the layer surfaces of eight follow-up images were registered to those of the baseline image, first by rigid alignment using blood vessel projections and axial height and tilt correction, followed by nonrigid registration of currents-based diffeomorphisms algorithms. This mapped all follow-up measurements point-wise to the common baseline coordinate system, allowing for point-wise statistical analysis. Measurement variability was evaluated point-wise for layer thicknesses and BMO dimensions by time-standard deviation (tSD).

Results

The intraclass correlation coefficients (ICCs) of BMO area and eccentricity were 0.993 and 0.972, respectively. Time-mean and tSD were computed point-wise for RNFL and choroidal thickness and color-mapped on the baseline surfaces. tSD was less than two coherence lengths of the system 2ℓ = 12 μm at most vertices. High RNFL thickness variability corresponded to the locations of retinal vessels, and choroidal thickness varied more than RNFL thickness.

Conclusions

Our registration-based end-to-end pipeline produced point-wise correspondence among time-series retinal and choroidal surfaces with high measurement repeatability (low variability). Blood vessels were found to be the main sources contributing to the normal variability of the RNFL thickness measure. The computational pipeline with a measurement of normal variability can be used in future longitudinal studies to identify changes that are above the threshold of normal point-wise variability and track localized changes in retinal layers in high spatial resolution.

Translational Relevance

Using the registration-based approach presented in this study, longitudinal changes in retinal and choroidal layers can be detected with higher sensitivity and spatial precision.

Macular thickness in healthy Saudi adults. A spectral-domain optical coherence tomography study

Objectives:

To determine the macular thickness in the eyes of healthy Saudi adults using spectral-domain optical coherence tomography (SD-OCT).

Methods:

This is a prospective, cross-sectional study, including 158 healthy participants between August and December 2015. Mean subject age was 29.9 ± 7.85 years old. All participants underwent full ophthalmic evaluation, including SD-OCT imaging, and axial length measurement. Data from the right eye were included. Mean retinal thickness was determined. Correlations between retinal thickness and gender, age, axial length, and spherical equivalence were analyzed.

Results:

Mean central retinal thickness was 244.76 ± 23.62 µm, mean axial length was 23.8 ± 1.062 mm (range: 20.5-29 mm) and mean spherical equivalent was -0.31 ± 1.75 diopters (D) (range: -5.50 to +4.25 D). Central subfield (CSF) thickness and foveal volume were significantly lower in women than in men (both p<0.001). Data from the various age groups did not show statistically significant differences in the CSF thickness (p=0.389) or foveal volume (p=0.341). A positive correlation between CSF thickness and axial length (p<0.001) was observed.

Conclusion:

The normal macular thickness values in healthy Saudi individuals is different from that reported in other ethnic groups, as obtained by SD-OCT. Saudi men had thicker CSF than Saudi women and axial length was positively correlated to the central foveal thickness.

Anterior eye tissue morphology: Scleral and conjunctival thickness in children and young adults

The sclera and conjunctiva form part of the eye's tough, protective outer coat, and play important roles in the eye's mechanical protection and immune defence, as well as in determining the size and shape of the eye globe. Advances in ocular imaging technology now allow these tissues in the anterior eye to be imaged non-invasively and with high resolution, however there is a paucity of data examining the dimensions of these tissues in paediatric populations. In this study, we have used optical coherence tomography (OCT) imaging to examine the normal in vivo thickness profile of the anterior sclera and overlying conjunctiva in 111 healthy young participants, including a large proportion of paediatric subjects. We demonstrate that the thickness of the anterior sclera varies significantly with measurement location and meridian. Tissue thickness also varied significantly with age, with younger subjects exhibiting significantly thinner scleras and significantly greater conjunctival thickness. Males were also found to exhibit significantly greater scleral thickness. Refractive error however was not significantly associated with either scleral or conjunctival thickness in this population. These findings provide new data describing the normative dimensions of anterior eye tissues in children and the factors that can influence these dimensions in young populations.