In Vivo Sublayer Analysis of Human Retinal Inner Plexiform Layer Obtained by Visible-Light Optical Coherence Tomography
Purpose/UNASSIGNED:Growing evidence suggests that dendrite retraction or degeneration in a subpopulation of the retinal ganglion cells (RGCs) may precede detectable soma abnormalities and RGC death in glaucoma. Visualization of the lamellar structure of the inner plexiform layer (IPL) could advance clinical management and fundamental understanding of glaucoma. We investigated whether visible-light optical coherence tomography (vis-OCT) could detect the difference in the IPL sublayer thicknesses between small cohorts of healthy and glaucomatous subjects. Method/UNASSIGNED:We imaged nine healthy and five glaucomatous subjects with vis-OCT. Four of the healthy subjects were scanned three times each in two separate visits, and five healthy and five glaucoma subjects were scanned three times during a single visit. IPL sublayers were manually segmented using averaged A-line profiles. Results/UNASSIGNED:The mean ages of glaucoma and healthy subjects are 59.6 Â± 13.4 and 45.4 Â± 14.4 years (P = 0.02.) The visual field mean deviations (MDs) are -26.4 to -7.7 dB in glaucoma patients and -1.6 to 1.1 dB in healthy subjects (P = 0.002). Median coefficients of variation (CVs) of intrasession repeatability for the entire IPL and three sublayers are 3.1%, 5.6%, 6.9%, and 5.6% in healthy subjects and 1.8%, 6.0%, 7.7%, and 6.2% in glaucoma patients, respectively. The mean IPL thicknesses are 36.2 Â± 1.5 Âµm in glaucomatous and 40.1 Â± 1.7 Âµm in healthy eyes (P = 0.003). Conclusions/UNASSIGNED:IPL sublayer analysis revealed that the middle sublayer could be responsible for the majority of IPL thinning in glaucoma. Vis-OCT quantified IPL sublayers with good repeatability in both glaucoma and healthy subjects.
A Case for The Use of Artificial Intelligence in Glaucoma Assessment
We hypothesize that artificial intelligence applied to relevant clinical testing in glaucoma has the potential to enhance the ability to detect glaucoma. This premise was discussed at the recent Collaborative Community for Ophthalmic Imaging meeting, "The Future of Artificial Intelligence-Enabled Ophthalmic Image Interpretation: Accelerating Innovation and Implementation Pathways," held virtually September 3-4, 2020. The Collaborative Community in Ophthalmic Imaging (CCOI) is an independent self-governing consortium of stakeholders with broad international representation from academic institutions, government agencies, and the private sector whose mission is to act as a forum for the purpose of helping speed innovation in healthcare technology. It was one of the first two such organizations officially designated by the FDA in September 2019 in response to their announcement of the collaborative community program as a strategic priority for 2018-2020. Further information on the CCOI can be found online at their website (https://www.cc-oi.org/about). Artificial intelligence for glaucoma diagnosis would have high utility globally, as access to care is limited in many parts of the world and half of all people with glaucoma are unaware of their illness. The application of artificial intelligence technology to glaucoma diagnosis has the potential to broadly increase access to care worldwide, in essence flattening the Earth by providing expert level evaluation to individuals even in the most remote regions of the planet.
Interplay between intraocular and intracranial pressure effects on the optic nerve head in vivo
Intracranial pressure (ICP) has been proposed to play an important role in the sensitivity to intraocular pressure (IOP) and susceptibility to glaucoma. However, the in vivo effects of simultaneous, controlled, acute variations in ICP and IOP have not been directly measured. We quantified the deformations of the anterior lamina cribrosa (ALC) and scleral canal at Bruch's membrane opening (BMO) under acute elevation of IOP and/or ICP. Four eyes of three adult monkeys were imaged in vivo with OCT under four pressure conditions: IOP and ICP either at baseline or elevated. The BMO and ALC were reconstructed from manual delineations. From these, we determined canal area at the BMO (BMO area), BMO aspect ratio and planarity, and ALC median depth relative to the BMO plane. To better account for the pressure effects on the imaging, we also measured ALC visibility as a percent of the BMO area. Further, ALC depths were analyzed only in regions where the ALC was visible in all pressure conditions. Bootstrap sampling was used to obtain mean estimates and confidence intervals, which were then used to test for significant effects of IOP and ICP, independently and in interaction. Response to pressure manipulation was highly individualized between eyes, with significant changes detected in a majority of the parameters. Significant interactions between ICP and IOP occurred in all measures, except ALC visibility. On average, ICP elevation expanded BMO area by 0.17mm2â€¯at baseline IOP, and contracted BMO area by 0.02â€¯mm2â€¯at high IOP. ICP elevation decreased ALC depth by 10Î¼mâ€¯at baseline IOP, but increased depth by 7â€¯Î¼mâ€¯at high IOP. ALC visibility decreased as ICP increased, both at baseline (-10%) and high IOP (-17%). IOP elevation expanded BMO area by 0.04â€¯mm2â€¯at baseline ICP, and contracted BMO area by 0.09â€¯mm2â€¯at high ICP. On average, IOP elevation caused the ALC to displace 3.3â€¯Î¼m anteriorly at baseline ICP, and 22â€¯Î¼m posteriorly at high ICP. ALC visibility improved as IOP increased, both at baseline (5%) and high ICP (8%). In summary, changing IOP or ICP significantly deformed both the scleral canal and the lamina of the monkey ONH, regardless of the other pressure level. There were significant interactions between the effects of IOP and those of ICP on LC depth, BMO area, aspect ratio and planarity. On most eyes, elevating both pressures by the same amount did not cancel out the effects. Altogether our results show that ICP affects sensitivity to IOP, and thus that it can potentially also affect susceptibility to glaucoma.
Optical Coherence Tomography and Glaucoma
Early detection and monitoring are critical to the diagnosis and management of glaucoma, a progressive optic neuropathy that causes irreversible blindness. Optical coherence tomography (OCT) has become a commonly utilized imaging modality that aids in the detection and monitoring of structural glaucomatous damage. Since its inception in 1991, OCT has progressed through multiple iterations, from time-domain OCT, to spectral-domain OCT, to swept-source OCT, all of which have progressively improved the resolution and speed of scans. Even newer technological advancements and OCT applications, such as adaptive optics, visible-light OCT, and OCT-angiography, have enriched the use of OCT in the evaluation of glaucoma. This article reviews current commercial and state-of-the-art OCT technologies and analytic techniques in the context of their utility for glaucoma diagnosis and management, as well as promising future directions.
Diffusion Tensor Imaging of Visual Pathway Abnormalities in Five Glaucoma Animal Models
Purpose:To characterize the visual pathway integrity of five glaucoma animal models using diffusion tensor imaging (DTI). Methods:Two experimentally induced and three genetically determined models of glaucoma were evaluated. For inducible models, chronic IOP elevation was achieved via intracameral injection of microbeads or laser photocoagulation of the trabecular meshwork in adult rodent eyes. For genetic models, the DBA/2J mouse model of pigmentary glaucoma, the LTBP2 mutant feline model of congenital glaucoma, and the transgenic TBK1 mouse model of normotensive glaucoma were compared with their respective genetically matched healthy controls. DTI parameters, including fractional anisotropy, axial diffusivity, and radial diffusivity, were evaluated along the optic nerve and optic tract. Results:Significantly elevated IOP relative to controls was observed in each animal model except for the transgenic TBK1 mice. Significantly lower fractional anisotropy and higher radial diffusivity were observed along the visual pathways of the microbead- and laser-induced rodent models, the DBA/2J mice, and the LTBP2-mutant cats compared with their respective healthy controls. The DBA/2J mice also exhibited lower axial diffusivity, which was not observed in the other models examined. No apparent DTI change was observed in the transgenic TBK1 mice compared with controls. Conclusions:Chronic IOP elevation was accompanied by decreased fractional anisotropy and increased radial diffusivity along the optic nerve or optic tract, suggestive of disrupted microstructural integrity in both inducible and genetic glaucoma animal models. The effects on axial diffusivity differed between models, indicating that this DTI metric may represent different aspects of pathological changes over time and with severity.
The APOSTEL 2.0 Recommendations for Reporting Quantitative Optical Coherence Tomography Studies
OBJECTIVE:To update the consensus recommendations for reporting of quantitative optical coherence tomography (OCT) study results, thus revising the previously published Advised Protocol for OCT Study Terminology and Elements (APOSTEL) recommendations. METHODS:To identify studies reporting quantitative OCT results, we performed a PubMed search for the terms "quantitative" and "optical coherence tomography" from 2015 to 2017. Corresponding authors of the identified publications were invited to provide feedback on the initial APOSTEL recommendations via online surveys following the principle of a modified Delphi method. The results were evaluated and discussed by a panel of experts, and changes to the initial recommendations were proposed. A final survey was recirculated among the corresponding authors to obtain a majority vote on the proposed changes. RESULTS:One hundred sixteen authors participated in the surveys, resulting in 15 suggestions, of which 12 were finally accepted and incorporated into an updated 9-point-checklist. We harmonized the nomenclature of the outer retinal layers, added the exact area of measurement to the description of volume scans; we suggested reporting device-specific features. We advised to address potential bias in manual segmentation or manual correction of segmentation errors. References to specific reporting guidelines and room light conditions were removed. The participants' consensus with the recommendations increased from 80% for the previous APOSTEL version to greater than 90%. CONCLUSIONS:The modified Delphi method resulted in an expert-led guideline (evidence class III, GRADE criteria) concerning study protocol, acquisition device, acquisition settings, scanning protocol, fundoscopic imaging, post-acquisition data selection, post-acquisition analysis, nomenclature and abbreviations, and statistical approach. It will still be essential to update these recommendations to new research and practices regularly.
Variability in schlemm canal anatomical measurements [Meeting Abstract]
Purpose : Schlemm canal (SC) is characterized by high local variations in morphology. Previously, we reported characteristics of SC using SC area measurements by optical coherence tomography (OCT) in healthy eyes. Herein, we examine the interobserver variability of SC height, width, and area in glaucomatous and healthy eyes. Methods : The anterior segment of six eyes from three subjects (1 female, 2 male) were imaged using OCT (Cirrus HD-OCT, Zeiss, Dublin, California, USA). A 4x4mm volumetric image of the limbus (depth of 2mm) was acquired with the Anterior Segment Cube scan protocol, comprised of 128 horizontal B-scans composed of 512 A-scans. SC was positioned to the side of the image to maximize visualization of aqueous humor vessel crossings. Scans were processed to maximize visualization of SC; image volumes were averaged (3x3x3 kernel) and contrast was enhanced with the local histogram algorithm using Fiji (version 2.10/1.53c). A cross-sectional B-scan and the two B-scans +/-5 frames were identified as three reference frames, based on best visualized SC location (Fig. 1). Three independent observers performed manual segmentation to measure SC width, height, and cross-sectional area for these three reference frames per volume. Width was defined as the longest measure of SC and height as perpendicular to the line used for width measurement. The observers performed these measurements on 15 volumes for a total of 45 analyzed frames each. The coefficient of variation was calculated based on standard deviations estimated using hierarchical multi-level random-effects models. Interobserver variability was quantified with a two-way ANOVA to calculate the intraclass correlation coefficient (ICC). Results : Participants had a mean age of 72.0 +/- 7.47 years (range: 66 to 82) and consisted of one healthy subject and two with primary open angle glaucoma. Measurement means and variation are presented in Table 1. The ICCs for interobserver variability are excellent for width measurements and low to moderate for height and area (Table 2) Conclusions : Excellent ICC for interobserver variability of SC width suggests it is suitable for use in clinical trials
Normative OCT optic nerve head parameters of rhesus macaques [Meeting Abstract]
Purpose : Rhesus macaques are a common animal model in ophthalmology because of the high similarity of their eyes and visual pathway to human. The characterization of optic nerve head (ONH) and peripapillary region in monkeys reported so far mostly involved a manual process which is laborious and subjected to operator errors. It is also usually generated from a cohort of similar age group. In this cross-sectional observational study, we deploy automated and manual segmentations to evaluate the OCT retinal nerve fiber layer (RNFL) thickness, ONH and lamina cribrosa (LC) microstructure parameters in a cohort of free roaming macaques. Methods : In-vivo ONH spectral-domain OCT scans (Leica, Chicago, IL) were obtained by a single experienced operator after excluding eyes with any retinal pathologies. The margins of the optic disc were drawn manually and the resultant scans were analyzed using an automated segmentation software of our own design. The LC microstructure parameters were obtained through a previously described segmentation algorithm. The other parameters of ONH, namely the cup-to-disc (C/D) ratio and minimum rim width (MRW) were assessed manually. Wilcoxon rank sum test was used to test the association of LC parameters, C/D ratio and MRW with age, while the rest of the parameters were analyzed using mixed effects model accounting for age, sex and intra-subject correlation. Results : 29 eyes from 19 monkeys (11 females, 8 males) with age ranging from 4.2 to 23.8 years were analyzed. Males were overall bigger and significantly heavier than females in our cohort (Table 1). Superior RNFL was thicker in male and is the only RNFL parameter that was associated with age or sex in this healthy cohort. No significant association was detected for any of the ONH parameters with age or sex. LC was more visible and thicker in male with higher beam to pore ratio and connective tissue fraction than in female. Conclusions : The characterization of normal macaque eyes from a cohort of free roaming animals is useful as a standard reference to assess pathological changes in future experimental studies
Optimal retinal nerve fiber layer sampling location with OCT in rhesus monkeys [Meeting Abstract]
Purpose : To investigate the least variable sampling location for OCT retinal nerve fiber layer (RNFL) thickness measurements on rhesus macaque monkeys, for determining the preferred sampling location. Methods : In vivo three-dimensional spectral-domain OCT scans (Leica, Chicago, IL) were obtained as raster scan data (400x400x1024) in a 5x5x1.6 mm region (human equivalent, not the actual size in the monkey eye) centered on the optic nerve head (ONH) of 33 healthy adult rhesus macaques (19 males, 14 females; ages 3.0-10.7 years). The ONH scans of 48 eyes were analyzed using OCT segmentation software of our own design to calculate point-by-point RNFL thickness measurements. Mean RNFL thickness was computed on consecutive concentric circles within the scan window, centered on the geometric ONH center and starting at the optic disc margin (between 64-119 circles). The least variable RNFL measurement area was identified in the vicinity of the RNFL peak within the 2 mum deviation. Results : The least variable RNFL was observed in between 98.88+/-11.82 and 114.4+/-11.32 pixels from the ONH center with the peak RNFL at 106.42+/-11.55 pixels (Figure 1). Note that the number of available eyes in each sampling location varied as detailed in Figure 2. For comparison, the radius of the OCT scan circle conventionally used in humans is 1.7 mm, or 136 pixels, from the center of the ONH. Conclusions : In order to obtain less variable circumpapillary RNFL thickness measurements on rhesus macaque monkey eyes, it is recommended to use a sampling circle with a radius of approximately 106 pixels from the ONH center, which is smaller than the human equivalent
Under pressure: Response of the lamina cribrosa pore tortuosity to acute pressure changes [Meeting Abstract]
Purpose : Lamina cribrosa (LC) deformation is hypothesized to be a major cause of glaucoma. The LC undergoes different forms of stress both anteriorly from intraocular pressure (IOP), as well as posteriorly and circumferentially from subarachnoid cerebrospinal fluid pressure (CSFP) and the sclera. The purpose of this study was to determine possible in vivo changes in the path of the lamina pores under different IOP settings while maintaining fixed CSFP. Methods : Spectral-domain OCT scans (Leica, Chicago, IL) of the optic nerve head (ONH) were acquired in vivo under different pressure settings from healthy rhesus monkeys. IOP was controlled using a gravity-based perfusion system through a needle inserted into the anterior chamber. CSFP was maintained at the baseline opening pressure via gravitybased perfusion system through cannulation of the brain's lateral ventricle (range 8- 12mmHg). Scans were acquired at baseline IOP (15mmHg), high (30 mmHg) and very high IOP (40-50 mmHg) and registered in 3D. Pores from shared regions were automatically segmented using a previously described segmentation algorithm. The path of each pore was tracked based on the calculated geometric centroid of each pore. The tortuosity of each pore path was defined as the total actual distance of the centroid path divided by the minimal distance between the first (most anterior) and last (most posterior) pore centroids. Results : 7 eyes from 6 healthy adult Rhesus macaque were analyzed. The mean value of the pore path tortuosity varies between eyes at baseline IOP levels (range: 1.16-1.68; Table). Two main overall patterns of pore path tortuosity were detected in response to increased IOP at fixed CSFP: 4 eyes became more tortuous (M2, M5, M8, M11); in the rest of the eyes (M6 OD, M6 OS, M10) the pore paths remained either unchanged or showed a variable response. No statistically significant change (p > 0.05) was observed in this small sample in either the subject-specific analysis or the analysis of the pooled combined values of the pore path tortuosity. Conclusions : Baseline pore tortuosity as well as the response of the pores to acute IOP increase varies between eyes. Further investigation is warranted to determine if these differences are associated with glaucoma susceptibility