Optic Nerve Head Deformation in Glaucoma: A Prospective Analysis of Optic Nerve Head Surface and Lamina Cribrosa Surface Displacement

Vascular resistance indices are higher in the superior than inferior optic nerve head and retina

Retinal vascular resistance is of interest in glaucoma research, as a potential link between retinal ganglion cell loss and observed phenomena including disrupted vascular autoregulation, altered biomechanical stiffness, and impaired neurovascular coupling. It can now be assessed in vivo, using laser speckle flowgraphy. However, continued progress in the field requires better understanding of its physiology. In this study, we test the hypothesis of homogeneity of vascular resistance indices between regions of the retina: specifically, between superior and inferior hemifields. The resistivity index (maximum flow minus minimum flow, as a proportion of the maximum) and pulsatility index (maximum minus minimum, as a proportion of the mean) were measured in major vessels within the optic nerve head, in the remaining tissue within the optic nerve head, and in peripapillary branch retinal arteries, separated in each case into superior and inferior quadrants. This was performed in 378 eyes of 189 participants with suspected, early or moderate glaucoma; and in 99 eyes of 50 participants without any ocular pathology. In the glaucoma cohort, the resistivity index was on average 9% higher superiorly than inferiorly in vessels within the optic nerve head; 8% higher superiorly in remaining tissue; and 8% higher superiorly in peripapillary vessels (all p < 0.001). The pulsatility index was on average 11% higher superiorly in all three locations (all p < 0.001). Average flow was slightly higher superiorly in major vessels in the nerve head, but higher inferiorly elsewhere. In the healthy control cohort, resistivity index was higher superiorly by 10% in vessels and 8% in tissue within the optic nerve head; pulsatility index was 12% and 10% higher superiorly respectively (all p < 0.001). The fact that these differences were similar between the two cohorts suggests that they are not caused by the disease process. However, it is notable that glaucomatous loss most frequently occurs first in the superior visual field, corresponding with the inferior retina. The finding that vascular resistance indices are consistently higher in the superior retina warrants further investigation, both for its causes and consequences.

Effects of Deep Optic Nerve Head Structures on Bruch's Membrane Opening- Minimum Rim Width and Peripapillary Retinal Nerve Fiber Layer

PURPOSE

To explore the effects of deep optic nerve head (ONH) structures on Bruch's membrane opening (BMO)-minimum rim width (MRW) and peripapillary retinal nerve fiber layer thickness (pRNFLT) in healthy eyes.

DESIGN

Prospective cross-sectional study.

METHODS

Two hundred five healthy eyes of 141 subjects (mean ± standard deviation of age and axial length (AXL): 46.9 ± 10.0 years and 24.79 ± 1.15 mm) were enrolled. Best fit multivariable linear mixed models identified factors associated with BMO-MRW and pRNFLT. Explanatory variables included age, gender, AXL, BMO and anterior scleral canal opening (ASCO) area and ovality, magnitude of BMO and ASCO shift, peripapillary choroidal thickness, lamina cribrosa (LC) parameters, prelaminar thickness, and peripapillary scleral (PPS) angle.

RESULTS

Thinner BMO-MRW was associated with older age, smaller ASCO/BMO offset magnitude, larger BMO area, thinner prelaminar thickness, deeper LC, and thinner pRNFLT (P = .011, <.001, .004, <.001, <.001, <.001 respectively). Thinner pRNFLT was associated with shorter AXL, smaller ASCO area, a more posteriorly bowed PPS, shallower LC and thinner BMO-MRW. (P = .030, .002, .035, .012, <.001 respectively) CONCLUSIONS: BMO-MRW and pRNFLT were influenced by several deep ONH structures such as BMO and ASCO position shift, BMO or ASCO area, prelaminar thickness, PPS bowing and LC depth in addition to patient characteristics such as age and AXL. The degree and/or direction of associations varied between deep ONH structures and BMO-MRW or pRNFLT. Despite both BMO-MRW and pRNFLT being surrogate parameters for RGC loss, a complex relationship with ONH deep-layer morphology was indicated.

Aqueous humour protein dysregulation in Asian eyes with primary open angle glaucoma

The pathophysiology of Primary Open Angle Glaucoma (POAG) remains poorly understood. Through proteomic analysis of aqueous humour (AH) from POAG patients, we aim to identify changes in protein composition of these samples compared to control samples. High resolution mass spectrometry-based TMT6plex quantitative proteomics analysis is performed on AH samples collected from POAG patients, and compared against a control group of patients with cataracts. Data are available via ProteomeXchange with identifier PXD033153. 1589 proteins were quantified from the aqueous samples using Proteome Discoverer version 2.2 software. Among these proteins, 210 were identified as unique master proteins. The proteins which were up or down-regulated by ±3 fold-change were considered significant. Human neuroblastoma full-length cDNA clone CS0DD006YL02 was significantly upregulated in patients with severe POAG on >2 medications, while actin, cytoplasmic 1, V2-7 protein (fragment), immunoglobulin-like polypeptide 1 and phosphatidylethanolamine-binding protein 4 were only present in these patients with severe POAG on >2 medications. Beta-crystallin B1 and B2, Gamma-crystallin C, D and S were significantly downregulated in the severe POAG ≤2 glaucoma medications group. Beta-crystallin B2, Gamma-crystallin D and GCT-A9 light chain variable region (fragment) were significantly downregulated in the non-severe POAG group. Actin, cytoplasmic 1 was significantly upregulated in subjects with severe POAG who required more than 2 glaucoma medications. Crystallins (Beta-crystallin B1 and B2, Gamma-crystallin C, D and S) were significantly downregulated in subjects with severe POAG who required less than 2 glaucoma medications.

The Temporal Relation Between Rates of Retinal Nerve Fiber Layer and Minimum Rim Width Changes in Glaucoma

Purpose

This study aims to determine whether OCT-derived rates of change in minimum rim width (MRW) are associated with and can potentially predict corresponding alterations in retinal nerve fiber layer thickness (RNFLT) in people with glaucoma.

Methods

The rates of change between six-monthly visits were taken from 568 eyes of 278 participants in the P3 Study. Structural equation models (SEM) assessed whether one parameter was predicted by the concurrent or previous rate of the other parameter, after adjusting for its own rate in the previous time interval. Root mean square error of approximation (RMSEA, with 90% confidence intervals [CI]), Tucker Lewis index (TLI) and the comparative fit index (CFI) assessed goodness of fit.

Results

Models without a time lag provided a better fit for the data (RMSEA = 0.101 [CI, 0.089, 0.113]), compared to a model featuring a time lag in RNFLT (RMSEA = 0.114 [CI, 0.102, 0.126]) or MRW (RMSEA = 0.114 [CI, 0.102, 0.127]). The SEMs indicated that rates for both MRW and RNFLT were predicted by their own rate in the previous time interval and by the other measure's change in the concurrent time interval (P > 0.001 for all). No evidence of a clinically significant time lag for either parameter was determined.

Conclusions

MRW and RNFLT exhibit concurrent changes over time in patients with glaucoma, with no clinically significant time lag determined.

Translational Relevance

RNFLT may be more useful than MRW in early glaucoma assessment because of its previously reported lower variability and reduced sensitivity to intraocular pressure changes.

Displacement of the Lamina Cribrosa With Acute Intraocular Pressure Increase in Brain-Dead Organ Donors

Purpose

To examine deformations of the optic nerve head (ONH) deep tissues in response to acute elevation of intraocular pressure (IOP).

Methods

Research-consented brain-dead organ donors underwent imaging by spectral domain optical coherence tomography (OCT). OCT imaging was repeated while the eye was sequentially maintained at manometric pressures of 10, 30, and 50 mm Hg. Radial scans of the ONH were automatically segmented by deep learning and quantified in three dimensions by a custom algorithm. Change in lamina cribrosa (LC) depth and choroidal thickness was correlated with IOP and age by linear mixed-effect models. LC depth was computed against commonly utilized reference planes.

Results

Twenty-six eyes from 20 brain-dead organ donors (age range, 22-62 years; median age, 43 years) were imaged and quantified. LC depth measured against a reference plane based on Bruch's membrane (BM), BM opening, and an anterior sclera canal opening plane showed both a reduction and an increase in LC depth with IOP elevation. LC depth universally increased in depth when measured against a sclera reference plane. Choroidal (-0.5222 µm/mm Hg, P < 0.001) and retinal nerve fiber layer thickness (-0.0717 µm/mm Hg, P < 0.001) significantly thinned with increasing IOP. The magnitude of LC depth change with IOP was significantly smaller with increasing age (P < 0.03 for all reference planes).

Conclusions

LC depth changes with IOP reduce with age and are significantly affected by the reference plane of choice, which highlights a need for standardizing LC metrics to properly follow progressive remodeling of the loadbearing tissues of the ONH by OCT imaging and for the definition of a reference database.

Risk Factors Associated With a Large Vertical Cup-to-Disc Ratio: Korean National Health and Nutritional Examination Survey

PRCIS

Higher intraocular pressure, higher systolic blood pressure, and higher serum aspartate transaminase to alanine aminotransaminase level were risk factors associated with a large vertical cup-to-disk ratio (vCDR).

PURPOSE

To identify risk factors for a large vCDR using data from the Korea National Health and Nutritional Examination Survey (2008-2012).

MATERIALS AND METHODS

Out of the total 29,322 participants aged 20 or older who participated in Korea National Health and Nutrition Survey (KHANES) from the year 2008 to 2012, this study was conducted on 21,780 participants, excluding 1449 of them without fundus photographs and 6093 of them with missing values. To identify the risk factors associated with a large vCDR, the participants were divided into 2 groups: ≥0.6 and <0.6.

RESULTS

Of the 21,780 subjects, 2357 of them had a vCDR ≥0.6 and 19,423 had a vCDR <0.6. There were significant differences in age, sex, and educational levels between the 2 groups. After adjusting age, sex, education level, and survey year by propensity score matching, in the group having vCDR ≥0.6, intraocular pressure (IOP) was high, systolic blood pressure (SBP) was high, and serum aspartate transaminase to alanine aminotransaminase level (AST/ALT ratio) was high ( P <0.001, P <0.001, and P <0.001). The results of multiple logistic regression analyses revealed that high IOP, high SBP, high myopia, and high AST/ALT ratio were risk factors for vCDR ≥0.6 ( P <0.001, P =0.006, P =0.005, P <0.001).

CONCLUSIONS

In this study, risk factors associated with large vCDR were analyzed. Higher IOP, higher SBP, and higher AST/ALT ratio were related to vCDR ≥0.6.

Dynamic Ranges of Retinal Nerve Fiber and Optic Nerve Head Parameters Measured Using Optical Coherence Tomography in Glaucoma: A Longitudinal Study

PURPOSE

To evaluate the dynamic range of retinal nerve fiber layer (RNFL) and optic nerve head (ONH) parameters measured using optical coherence tomography (OCT) in conditions ranging from nonglaucomatous status to advanced glaucoma by longitudinal observation.

METHODS

A total of 15 eyes from 12 participants with glaucoma progression from a nonglaucomatous status to advanced glaucoma were included. The RNFL and ONH parameters were compared between the nonglaucomatous and advanced stages within the same eye. The absolute and relative changes in OCT parameters were analyzed.

RESULTS

The median highest intraocular pressure was 42.5 mmHg (interquartile range, 37.5 to 54.5 mmHg), and the final mean deviation of the visual field test was -24.68 dB (interquartile range, -23.93 to -31.13 dB). The median relative changes in RNFL thickness were -40.6% in the overall area, and -51.9%, -21.4%, -51.1%, and -41.8% in the superior, nasal, inferior, and temporal quadrants, respectively (all p < 0.05). Relative changes in the rim area, disc area, average cup to disc ratio, vertical cup to disc ratio, and cup volume were -56.64%, 0.59%, 62.10%, 66.0%, and 337.90%, respectively (all p < 0.05, except for disc area with a p-value of 0.753).

CONCLUSIONS

The dynamic range of the RNFL thickness ranged from 40.6% to 51.9%, and the dynamic range of the ONH parameters ranged from 56.64% to 337.90%. During the course of glaucoma progression, the cup volume showed the widest dynamic range. However, the disc area did not show significant changes.

A high-accuracy and high-efficiency digital volume correlation method to characterize in-vivo optic nerve head biomechanics from optical coherence tomography

In-vivo optic nerve head (ONH) biomechanics characterization is emerging as a promising way to study eye physiology and pathology. We propose a high-accuracy and high-efficiency digital volume correlation (DVC) method to characterize the in-vivo ONH deformation from optical coherence tomography (OCT) volumes. Using a combination of synthetic tests and analysis of OCTs from monkey ONHs subjected to acutely elevated intraocular pressure, we demonstrate that our proposed methodology overcame several challenges for conventional DVC methods: First, a pre-registration technique was used to remove large ONH rigid body motion in OCT volumes which could lead to analysis failure; second, a modified 3D inverse-compositional Gaussian Newton method was used to ensure sub-voxel accuracy of displacement calculations despite high noise and low image contrast of some OCT volumes; third, a tricubic B-spline interpolation method was applied to improve computational efficiency; fourth, a confidence parameter was introduced to guide the searching path in the displacement calculation; fifth, a confidence-weighted strain calculation method was applied to further improve the accuracy. The proposed DVC method had displacement errors smaller than 0.037 and 0.028 voxels with Gaussian and speckle noises, respectively. The strain errors in the three directions were less than 0.0045 and 0.0018 with Gaussian and speckle noises, respectively. Compared with the conventional DVC method, the proposed method reduced the errors of displacement and strain calculations by up to 70% under large body motions, with 75% lower computation time, while saving about 30% memory. Our study demonstrates the potential of the proposed technique to investigate ONH biomechanics. STATEMENT OF SIGNIFICANCE: The biomechanics of the optic nerve head (ONH) in the posterior pole of the globe play a central role in eye physiology and pathology. The application of digital volume correlation (DVC) to the analysis of optical coherence tomography (OCT) images of the ONH has emerged as a promising way to quantify ONH biomechanics. Conventional DVC methods, however, face several important challenges when analyzing OCT images of the ONH. We introduce a high-accuracy and high-efficiency DVC method to characterize in vivo ONH deformations from OCT volumes. We demonstrate the new method using synthetic tests and actual OCT data from monkey ONHs. The new method also has the potential to be used to study other tissues, as OCT applications continue to expand.

Microvasculature Recovery Detected Using Optical Coherence Tomography Angiography and the Rate of Visual Field Progression After Glaucoma Surgery

Purpose

We evaluated microvascular changes using optical coherence tomography angiography (OCT-A) in glaucoma patients who underwent glaucoma surgery.

Methods

The macula and optic nerve head were imaged using an OCT-A device at one day before surgery and at one week, one month, three months, and six months after surgery. Measurements of vessel density (VD) were made in the intradisc region and macula, and the area of the foveal avascular zone (FAZ) was measured in both superficial and deep vascular layers. A mean deviation (MD) slope value of < −1.0 decibel/y was considered to be indicative of VF progression.

Results

A significant increase in VD was observed postoperatively in the deep vascular layer of the intradisc area (P < 0.001), and a significant decrease in the FAZ area was evident in the deep vascular layer (P = 0.018). An increase in the intradisc deep VD (17.48% ± 5.63%) was statistically significant in glaucoma eyes without progression, compared with those with progression (−1.27% ± 2.19%). Worse preoperative MD of the VF (P = 0.006), lower preoperative intradisc VD (P < 0.001), and fewer changes in the intradisc deep VD after surgery (P < 0.001) were significantly associated with MD slope.

Conclusions

We found deep VD changes in the laminar region of the optic nerve head and the macular area at up to postoperative one month after glaucoma surgery. An increase in the deep VD in the laminar region was beneficial to VF progression in glaucoma patients after surgery.

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 0.17 mm² at baseline IOP, and contracted BMO area by 0.02 mm² at high IOP. ICP elevation decreased ALC depth by 10 μm at baseline IOP, but increased depth by 7 μm at high IOP. ALC visibility decreased as ICP increased, both at baseline (-10%) and high IOP (-17%). IOP elevation expanded BMO area by 0.04 mm² at baseline ICP, and contracted BMO area by 0.09 mm² at high ICP. On average, IOP elevation caused the ALC to displace 3.3 μm anteriorly at baseline ICP, and 22 μm 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.

Racial Differences in the Rate of Change in Anterior Lamina Cribrosa Surface Depth in the African Descent and Glaucoma Evaluation Study

Purpose

The purpose of this study was to determine if the rate of change in the depth of the surface of the lamina cribrosa due to glaucomatous remodeling differs between glaucoma patients of African descent (AD) and European descent (ED).

Methods

There were 1122 images taken longitudinally over an average of 3 years (range = 0.9-4.1 years) from 122 patients with glaucoma followed in the African Descent and Glaucoma Evaluation Study (ADAGES) and Diagnostic Intervention and Glaucoma Study (DIGS) were automatically segmented to compute anterior lamina cribrosa surface depth (ALCSD). The rate of ALCSD change was compared across racial groups after adjusting for baseline characteristics known to be associated with ALCSD or disease progression (visual field, ALCSD, corneal thickness, optic disk size, and age).

Results

After adjusting for all other covariates, the ED group had significantly greater ALCSD posterior migration (deepening) than the AD group (difference = 2.57 µm/year, P = 0.035). There was a wider range of ALCSD change in the ED compared with the AD group, and more individuals had greater magnitude of both deepening and shallowing. No other covariates measured at baseline had independent effects on the longitudinal changes in ALCSD (baseline visual field severity, baseline ALCSD, corneal thickness, Bruch's membrane opening [BMO] area, or age).

Conclusions

Glaucomatous remodeling of the lamina cribrosa differs between AD and ED patients with glaucoma. Unlike the cross-sectional associations seen with aging, in which a deeper ALCSD was seen with age in the ED group, glaucomatous remodeling in this longitudinal study resulted in more posterior migration of ALCSD in ED compared to AD patients.

Elucidation of the role of the lamina cribrosa in glaucoma using optical coherence tomography

Glaucoma is a chronic and progressive optic neuropathy characterized by the death of retinal ganglion cells and corresponding visual field loss. Despite the growing number of studies on the subject, the pathogenesis of the disease remains unclear. Notwithstanding, several studies have shown that the lamina cribrosa (LC) is considered an anatomic site of glaucomatous optic nerve injury, thus having a key role in the pathophysiology of glaucoma development and progression. Different morphological alterations of the LC have been described in vivo in glaucomatous eyes after the evolution of optical coherence tomography (OCT) devices. The most relevant findings were the reduction of laminar thickness, the presence of localized defects, and the posterior LC displacement. These new laminar parameters documented through OCT are not only promising as possible additional tools for glaucoma diagnosis and monitoring, but also as predictors of disease progression. In spite of the advance of technology, however, proper evaluation of the LC is not yet viable in all eyes. We describe OCT-identified LC changes related to the development and progression of glaucoma and provide future directions based on a critical data analysis, focusing on its clinical relevance and applicability.

The Relationship Between Corneal Hysteresis and Retinal Ganglion Cells - A Step Forward in Early Glaucoma Diagnosis

BACKGROUND Glaucoma is a major cause of irreversible visual field (VF) loss across the world. Many studies have assessed the accuracy of glaucoma diagnostic tests for a more precise diagnosis to quickly identify patients with higher risk of progression. MATERIAL AND METHODS We conducted a study that included 214 eyes divided into 3 groups: 79 eyes from patients diagnosed with primary open-angle glaucoma (POAG), 68 eyes from patients diagnosed with ocular hypertension (OH), and 67 eyes from normal individuals (normal eyes, NE). All patients included in the study received a complete checkup. RESULTS In POAG patients, means of central corneal thickness (CCT), corneal hysteresis (CH), corneal resistance factor (CRF), mean defect (MD), visual field index (VFI), peripapillary retinal nerve fiber layer (pRNFL), and ganglion cell complex (GCC) are lower than in OH patients, and in NE are higher than in both groups. Also, we found a statistically significant direct correlation between CH and GCC thickness. Further statistical analysis revealed that both pRNFL thickness and GCC thickness are significantly influenced by CH value in a precise manner. CONCLUSIONS The first cell type affected in glaucoma is the retinal ganglion cell. We found a positive correlation between GCC thickness and CH, suggesting that CH might be a parameter to consider in the evaluation of all glaucoma patients from their first examination. Moreover, both pRNFL thickness and GCC thickness are influenced by CH, suggesting the utility of monitoring the value of CH at every checkup to detect its decrease in glaucoma patients.

Changes in corneal biomechanics in patients with diabetes mellitus: a systematic review and meta-analysis

AIMS

To determine the changes in corneal biomechanical parameters in patients with diabetes mellitus (DM) in comparison with controls.

METHODS

Pertinent studies were identified by comprehensively search of PubMed, Embase, the Web of Science, the Cochrane Library, Scopus, the China National Knowledge Infrastructure and the Chinese biomedical disc (CBM) databases. Pooling analyses by random models using the D-L method were performed for corneal hysteresis (CH), the corneal resistance factor (CRF), corneal-compensated intraocular pressure (IOPcc) and Goldmann-correlated intraocular pressure (IOPg).

RESULTS

A total of 15 studies were included in the final analysis, involving 1506 eyes in the diabetic group and 2190 eyes in the control group. The diabetic group had significantly higher CH, CRF, IOPg and IOPcc values than the control group. The pooled mean differences were 1.34 mmHg (95% confidence interval [CI] 0.60-2.08 mmHg, P < 0.001) for IOPg and 0.85 mmHg (95% CI 0.18-1.51 mmHg, P = 0.013) for IOPcc, 0.38 mmHg (95% CI 0.01-0.75, P = 0.047) for CH and 0.63 mmHg (95% CI 0.27-0.98, P = 0.001) for the CRF. Sensitivity analyses using the leave-one-out method showed a consistent significant difference between the groups (all P < 0.001).

CONCLUSIONS

Corneal biomechanics changed in the patients with DM. High CH, CRF, IOPcc and IOPg values may be associated factors for diabetes mellitus. Future studies are warranted to clarify the underlying mechanisms and explore the relationship between corneal biomechanics, glaucoma and diabetes mellitus.

REGISTRATION

PROSPERO registration No CRD4201705465.

Investigation of the Optic Nerve Head Morphology Influence to the Optic Nerve Head Biomechanics - Population Specific Model

Glaucoma is an eye disorder potentially leading to permanent blindness through the damage of optic nerves at the optic nerve head (ONH). As a critical region of optic nerve damage, the porous Lamina Cribrosa (LC) in the ONH plays a critical role in determining whether optic nerves passing through will experience apoptosis in response to shear stress. The primary cause of shear stress to the LC is the increase in intraocular pressure (IOP). Since morphology governs how mechanical stresses distributes, LC morphology could be an important factor in determining the risks of glaucoma development and progression. The current project aims at investigating how anterior LC surface morphology impacts its response to shear stress caused by IOP. Results of the current study show that steeper LC morphologies could be associated with increased average shear stress on the anterior LC surface. The effect of LC morphology was comparable to that of IOP. This highlights the potential significance of LC morphology on the distribution of IOP-induced shear stress and calls for further investigation in this area.

Relationship of Corneal Hysteresis and Anterior Lamina Cribrosa Displacement in Glaucoma

PURPOSE

To investigate the relationship between corneal hysteresis (CH) and anterior lamina cribrosa surface (ALCS) displacement over time in a cohort of patients with glaucoma.

DESIGN

Prospective observational case series.

METHODS

In this study, 147 eyes from 96 glaucoma or glaucoma suspect patients were followed for a mean of 3.5 years and 7.9 visits. Baseline CH measurements were obtained using the Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments Inc, Depew, New York, USA). The mean anterior lamina cribrosa surface depth (ALCSD) and choroidal thickness were by automated segmentation of spectral-domain optical coherence tomography (SD-OCT) scans. The rate of change of ALCSD was calculated using linear mixed effects models. Relationship between baseline CH and follow-up ALCSD rate of change was adjusted for confounding factors, including age, intraocular pressure (IOP), and choroidal thickness.

RESULTS

The mean baseline CH was 9.4 mm Hg (95% confidence interval [CI] 9.1-9.7). Overall, the ALCS was displaced posteriorly at a rate of 0.78 μm/y (95% CI -1.82, 0.26). Seventeen eyes (11.5%) showed a significant posterior displacement of ALCS, whereas 22 eyes (15.0%) showed a significant anterior displacement of ALCS. The choroidal thickness thinned at a rate of -1.09 μm/y during the follow-up (P = .001). Multivariable mixed modeling showed that choroidal thinning, lower IOP change, and lower corneal hysteresis were significantly associated with posterior ALCS displacement over time (P = .034, P = .037, and P = .048). Each 1 mm lower CH was associated with 0.66 μm/y posterior displacement of the ALCS.

CONCLUSIONS

Lower corneal hysteresis was significantly associated with posterior displacement of the anterior lamina cribrosa over time. These data provide additional support for lower corneal hysteresis being a risk factor for glaucoma progression.

Racial Differences in the Association of Anterior Lamina Cribrosa Surface Depth and Glaucoma Severity in the African Descent and Glaucoma Evaluation Study (ADAGES)

Purpose

To determine if variation in anterior lamina cribrosa surface depth (ALCSD) differs between glaucoma patients of African (AD) and European descent (ED).

Methods

A total of 178 eyes from 123 glaucoma patients in the African Descent and Glaucoma Evaluation Study (ADAGES) and Diagnostic Innovations in Glaucoma Study (DIGS) were included. ALCSD and choroidal thickness were measured using the San Diego Automated Layer Segmentation Algorithm (SALSA). ALCSD was defined by both Bruch's membrane opening (BMO)-based (ALCSD-BMO) and scleral-based (ALCSD-Scl) reference planes. Racial differences in ALCSD were evaluated using cross-sectional univariate and multivariable models.

Results

A deeper ALCSD-Scl was found in males (52.4 μm, P = 0.0401), AD individuals (78.6 μm, P = 0.0004), younger individuals (−3.1 μm/year, P < 0.0213), and eyes with larger discs (81.0 μm/mm², P = 0.024), increased visual field loss (mean defect, MD: −6.4 μm/dB [decibel], P = 0.0106), and higher intraocular pressure (IOP: 14.1 μm/mm Hg, P = 0.0256). Significant deepening of ALSCD was observed with increasing IOP and visual field severity only in the AD group. Race modified the relationship between ALCSD-Scl and age (P = 0.0145) with ALCSD-Scl in AD individuals becoming more shallow with increasing age (−3.1 μm/year, P = 0.0213), while there was no significant association in the ED group (2.1 μm/mm Hg, P < 0.2026).

Conclusions

This study demonstrates that a deeper ALCSD, regardless of the ALCSD reference plane used, is associated with more severe glaucoma and higher IOP in the ADAGES cohort, particularly in individuals of AD. These results suggest that characterizing ALCSD morphology and its relationships to IOP, aging, and glaucoma progression may help explain racial differences in disease susceptibility.

A Deep Learning Approach to Denoise Optical Coherence Tomography Images of the Optic Nerve Head

Optical coherence tomography (OCT) has become an established clinical routine for the in vivo imaging of the optic nerve head (ONH) tissues, that is crucial in the diagnosis and management of various ocular and neuro-ocular pathologies. However, the presence of speckle noise affects the quality of OCT images and its interpretation. Although recent frame-averaging techniques have shown to enhance OCT image quality, they require longer scanning durations, resulting in patient discomfort. Using a custom deep learning network trained with 2,328 'clean B-scans' (multi-frame B-scans; signal averaged), and their corresponding 'noisy B-scans' (clean B-scans + Gaussian noise), we were able to successfully denoise 1,552 unseen single-frame (without signal averaging) B-scans. The denoised B-scans were qualitatively similar to their corresponding multi-frame B-scans, with enhanced visibility of the ONH tissues. The mean signal to noise ratio (SNR) increased from 4.02 ± 0.68 dB (single-frame) to 8.14 ± 1.03 dB (denoised). For all the ONH tissues, the mean contrast to noise ratio (CNR) increased from 3.50 ± 0.56 (single-frame) to 7.63 ± 1.81 (denoised). The mean structural similarity index (MSSIM) increased from 0.13 ± 0.02 (single frame) to 0.65 ± 0.03 (denoised) when compared with the corresponding multi-frame B-scans. Our deep learning algorithm can denoise a single-frame OCT B-scan of the ONH in under 20 ms, thus offering a framework to obtain superior quality OCT B-scans with reduced scanning times and minimal patient discomfort.

Quantitative confocal optical coherence elastography for evaluating biomechanics of optic nerve head using Lamb wave model

The mechanosensitivity of the optic nerve head (ONH) plays a pivotal role in the pathogenesis of glaucoma. Characterizing elasticity of the ONH over changing physiological pressure may provide a better understanding of how changes in intraocular pressure (IOP) lead to changes in the mechanical environment of the ONH. Optical coherence elastography (OCE) is an emerging technique that can detect tissue biomechanics noninvasively with both high temporal and spatial resolution compared with conventional ultrasonic elastography. We describe a confocal OCE system in measuring ONH elasticity in vitro, utilizing a pressure inflation setup in which IOP is controlled precisely. We further utilize the Lamb wave model to fit the phase dispersion curve during data postprocessing. We present a reconstruction of Young's modulus of the ONH by combining our OCE system with a Lamb wave model for the first time. This approach enables the quantification of Young's modulus of the ONH, which can be fit using a piecewise polynomial to the corresponding IOP.

Relationship between corneal deformation amplitude and optic nerve head structure in primary open-angle glaucoma

The purpose of the study was to investigate the relationship between corneal deformation amplitude (DA), which is the amount of corneal displacement at highest degree of concavity measured by Corvis Scheimpflug Technology (ST), and various optic nerve head parameters in patients with primary open-angle glaucoma (POAG).Fifty-eight POAG patients were included in this observational study. For each patient, DA with Corvis ST, color optic disc photography, and optic nerve head imaging by enhanced depth imaging with a Heidelberg spectralis optical coherence tomography (OCT), Cirrus OCT, and Heidelberg retina tomograph (HRT) were obtained. Pearson correlation was used to analyze the relationship between DA and optic nerve head parameters before and after adjusting for age, intraocular pressure, central corneal thickness, and axial length.Corneal DA was negatively associated with lamina cribrosa (LC) depth (r = -0.390, P = .003) after adjusting for confounders. It showed positive relationship with parapapillary atrophy (PPA) area (r = 0.321, P = .046). In addition, the corneal DA was negatively correlated with cup volume (r = -0.351, P = .017) and mean cup depth (r = -0.409, P = .005) measured by HRT.Corneal DA is related with optic nerve head parameters in patients with POAG. Patients with lower corneal DA showed greater LC depth, greater cup area, deeper cup, and smaller PPA than those with higher corneal DA.

Automatic Assessment of Biometric Parameters in Optic Nerve Head Area by "Zhongshan ONH Calculator (ZOC)"

PURPOSE

To test the repeatability and reproducibility of the Zhongshan ONH Calculator (ZOC) software in terms of selected optic nerve head (ONH) parameters commonly used in clinical research of glaucoma.

MATERIALS AND METHODS

Forty-two horizontal single-line scans were selected to test the repeatability and reproducibility of the ZOC software. Clinically relevant 2D parameters of the ONH area were selected to test repeatability of ZOC, including length of BMO, minimum rim thickness on both sides (RIML and RIMR), optic cup depth (OCD), and depth of the anterior surface of the LC (ALCD).

RESULTS

Intraobserver test showed higher the intra-class correlation coefficient (ICC) of BMO ((0.991 vs. 0.777), RIML (0.988 vs. 0.890), RIMR (0.972 vs. 0.846), OCD (0.997 vs. 0.992), and ALCD (0.993 vs. 0.949) by single researcher using ZOC software than manual measurement. BA analysis showed acceptable agreement between automatic and manual measurements. SDs and limits of agreement (95% CI) of BMO, RIML, RIMR, OCD, and ALCD were 0.05 (-0.13, 0.07), 0.03 (-0.05, 0.05), 0.03 (-0.06, 0.07), 0.015 (-0.035, 0.024), and 0.04 (-0.07, 0.08), respectively.

CONCLUSION

This study presented the design and development of software for the automatic measurement of OCT images of ONH area with good reproducibility. In the future, with advances of OCTs and improvements to the resolution of the LC, ZOC will become a powerful tool in glaucoma research.

Anatomical Characterization of an Optic Disc Notch Using SD-OCT in Glaucoma

PURPOSE

To characterize anatomical dimensions of a disc notch using novel methods using spectral domain optical coherence tomography (SD-OCT).

PARTICIPANTS

All age- and severity-matched glaucoma patients with disc notch (defined as complete loss of neural rim with no residual rim between disc and cup) seen from 2014 to 2015 who underwent enhanced depth imaging with SD-OCT (Cirrus HD-OCT version 6.5, Carl Zeiss, USA) were included for this retrospective observational study.

METHODS

Using known dimensions of the 200 * 200 optic disc cube (6 * 6 mm), the notch width was calculated from the margins of the notch on either side using ImageJ software. The height was calculated from the lowest margin of the cup to the lowest point of the defect on the optic disc. These were compared with the quadrant retinal nerve fiber layer (qRNFT) and sectoral retinal nerve fiber layer (sRNFLT) thickness in notch and the sector 2 clock hours adjacent to the notch region (SaRNFLT).

RESULTS

The height and width of the notch in 31 eyes of 27 patients were 2.6 ± 0.48 mm and 2.23 ± 0.31 mm. The RNFL thickness in the same sector as that of the notch was 41 ± 21.06 µm while the adjacent two sectors measured 62 ± 26.5 and 64 ± 26.5 µm on either sides of the sector of the notch. The difference between the sRNFLT and s_aRNFLT ranged from -9 to 67 and -13 to 50 µm, respectively. This difference was significantly associated with height of the notch (R² = 20.8, p = 0.01).

CONCLUSION

Automated analysis of a notch and RNFL thickness in that sector can help in precise glaucoma monitoring in the region of interest.

DRUNET: a dilated-residual U-Net deep learning network to segment optic nerve head tissues in optical coherence tomography images

Given that the neural and connective tissues of the optic nerve head (ONH) exhibit complex morphological changes with the development and progression of glaucoma, their simultaneous isolation from optical coherence tomography (OCT) images may be of great interest for the clinical diagnosis and management of this pathology. A deep learning algorithm (custom U-NET) was designed and trained to segment 6 ONH tissue layers by capturing both the local (tissue texture) and contextual information (spatial arrangement of tissues). The overall Dice coefficient (mean of all tissues) was 0.91 ± 0.05 when assessed against manual segmentations performed by an expert observer. Further, we automatically extracted six clinically relevant neural and connective tissue structural parameters from the segmented tissues. We offer here a robust segmentation framework that could also be extended to the 3D segmentation of the ONH tissues.

Lamina cribrosa position and Bruch's membrane opening differences between anterior ischemic optic neuropathy and open-angle glaucoma

PURPOSE:

To compare the optic nerve head morphology among primary open-angle glaucoma, non-arteritic anterior ischemic optic neuropathy eyes, their fellow healthy eyes and control eyes, using spectral-domain optical coherence tomography with enhanced depth imaging.

METHODS:

Observational cross-sectional study including 88 eyes of 68 patients. In this study, 23 non-arteritic anterior ischemic optic neuropathy eyes, 17 fellow unaffected eyes, 25 primary open-angle glaucoma eyes, and 23 age-matched control eyes were included. Peripapillary retinal nerve fiber layer thickness and optic disk area were evaluated. Bruch's membrane opening diameter, optic cup depth, anterior lamina cribrosa depth, and prelaminar tissue thickness were assessed.

RESULTS:

Non-arteritic anterior ischemic optic neuropathy and primary open-angle glaucoma eyes had similar visual field mean deviation and peripapillary retinal nerve fiber layer thickness (P = 0.6 and P = 0.56, respectively). Bruch's membrane opening diameter was significantly larger in primary open-angle glaucoma eyes than in control eyes (P = 0.02). Lamina cribrosa and disk cup were deeper in eyes with primary open-angle glaucoma than both control and non-arteritic anterior ischemic optic neuropathy eyes (P < 0.001). Prelaminar tissue thickness was significantly thinner in primary open-angle glaucoma eyes than in non-arteritic anterior ischemic optic neuropathy eyes (P < 0.001). Lamina cribrosa was shallower in both non-arteritic anterior ischemic optic neuropathy and unaffected fellow eyes compared to healthy eyes (P < 0.001 and P = 0.04, respectively). No differences were found in the optic disk area.

CONCLUSION:

A forward lamina cribrosa placement and not a smaller disk could be involved in the pathogenesis of non-arteritic anterior ischemic optic neuropathy. A significantly larger Bruch's membrane opening diameter was found in primary open-angle glaucoma eyes compared with control eyes. This issue has clinical implications because Bruch's membrane opening has been considered a stable reference for disk-related measures.

Clinical Implications of In Vivo Lamina Cribrosa Imaging in Glaucoma

The lamina cribrosa (LC) is a multilayered, collagenous, sieve-like structure at the deep optic nerve head, and is presumed to be the primary site of axonal injury. According to biomechanical theory, intraocular pressure-induced posterior deformation of the LC causes blockage of axonal transport and alters the ocular blood flow, so that the axons of the retinal ganglion cells lead to apoptosis, which results in glaucomatous optic disc change. Although most of the research on the LC to date has been limited to experimental animal or histologic studies, the recent advances in optical coherence tomography devices and image processing techniques have made possible the visualization of the LC structure in vivo. LC deformation in glaucoma typically has been evaluated in terms of its position from a structural reference plane (LC depth), entire curvature or shape, thickness, or localized structural change (focal LC defects or LC pore change). In this review, we highlight the methods of assessing LC deformation from in vivo optical coherence tomography scans, and we discuss the clinical implications of the recent investigations of the in vivo structure of LC in glaucoma.

Thick Prelaminar Tissue Decreases Lamina Cribrosa Visibility

Purpose

Evaluation of the effect of prelaminar tissue thickness on visualization of the lamina cribrosa (LC) using optical coherence tomography (OCT).

Methods

The optic nerve head (ONH) region was scanned using OCT. The quality of visible LC microstructure was assessed subjectively using a grading system and objectively by analyzing the signal intensity of each scan's superpixel components. Manual delineations were made separately and in 3-dimensions quantifying prelaminar tissue thickness, analyzable regions of LC microstructure, and regions with a visible anterior LC (ALC) boundary. A linear mixed effect model quantified the association between tissue thickness and LC visualization.

Results

A total of 17 healthy, 27 glaucoma suspect, and 47 glaucomatous eyes were included. Scans with thicker average prelaminar tissue measurements received worse grading scores (P = 0.007), and superpixels with low signal intensity were associated significantly with regions beneath thick prelaminar tissue (P < 0.05). The average prelaminar tissue thickness in regions of scans where the LC was analyzable (214 μm) was significantly thinner than in regions where the LC was not analyzable (569 μm; P < 0.001). Healthy eyes had significantly thicker average prelaminar tissue measurements than glaucoma or glaucoma suspect eyes (both P < 0.001), and glaucoma suspect eyes had significantly thicker average prelaminar tissue measurements than glaucoma eyes (P = 0.008). Significantly more of the ALC boundary was visible in glaucoma eyes (63% of ONH) than in healthy eyes (41%; P = 0.005).

Conclusions

Thick prelaminar tissue was associated with impaired visualization of the LC. Healthy subjects generally had thicker prelaminar tissue, which potentially could create a selection bias against healthy eyes when comparing LC structures.

Displacement of the Lamina Cribrosa in Response to Acute Intraocular Pressure Elevation in Normal Individuals of African and European Descent

Purpose

To assess if the in vivo mechanical displacement of the anterior laminar cribrosa surface (ALCS) as a response of an acute elevation in intraocular pressure (IOP) differs in individuals of European (ED) and African descent (AD).

Methods

Spectral-domain optical coherence tomography (SDOCT) scans were obtained from 24 eyes of 12 individuals of AD and 18 eyes of 9 individuals of ED at their normal baseline IOP and after 60 seconds IOP elevation using ophthalmodynamometry. Change in depth (displacement) of the LC and to the prelaminar tissue (PLT) were computed in association with the change (delta) in IOP (Δ IOP), race, age, corneal thickness, corneal rigidity (ocular response analyzer [ORA]), and axial.

Results

In the ED group for small IOP elevations (Δ IOP < 12 mm Hg), the ALCS initially displaced posteriorly but for larger increase of IOP an anterior displacement of the lamina followed. Inversely, in the AD group the ALCS did not show a significant posterior displacement for small Δ IOP, while for larger IOP increases the ALCS significantly displaced posteriorly. Posterior displacement of the lamina cribrosa (LC) was also significantly correlated with longer axial length, higher corneal thickness, and ORA parameters. Prelaminar tissue posteriorly displaced for any magnitude of Δ IOP, in both groups.

Conclusions

The African descent group demonstrated a greater acute posterior bowing of the LC after adjustment for age, axial length, Bruch's membrane opening (BMO) area, and ORA parameters. Greater PLT posterior displacement was also seen in the AD group with increasing IOP, which was tightly correlated with the displacement of the LC.

Effect of acute intraocular pressure elevation on the minimum rim width in normal, ocular hypertensive and glaucoma eyes

BACKGROUND

To estimate and compare changes in the Bruch's membrane opening-minimum rim width (BMO-MRW) and area in normal, ocular hypertensive and glaucoma eyes following acute elevations in intraocular pressure (IOP).

METHODS

The optic nerve heads (ONHs) of 104 subjects (31 normals, 20 ocular hypertension (OHT) and 53 with primary glaucoma) were imaged using Spectral-domain optical coherence tomography (OCT; Spectralis, Heidelberg Engineering, Germany). IOP was raised twice by applying a force (0.64 n then 0.9 n) to the anterior sclera using an ophthalmo-dynamometer. After each IOP increment, IOP was held constant, measured with a Tonopen (AVIA applanation tonometer, Reichert, Depew, New York, USA), and ONH was rescanned with OCT. In each OCT volume, BMO-MRW and area were calculated and at each IOP increment.

RESULTS

The baseline MRW was significantly smaller in glaucoma subjects (174.3±54.3 µm) compared with normal (287.4±42.2 µm, p<0.001) and OHT subjects (255.4±45.3 µm, p<0.001). MRW of glaucoma subjects was significantly thinner at the first and second IOP elevations than that at baseline (both p<0.01), but no significant change was noted in normal and OHT subjects. There was no significant change of BMO area at acute IOP elevations from baseline in all diagnoses (all p>0.05).

CONCLUSION

Acute IOP elevation leads to compression of the nerve fibre layers of neuroretinal rim in glaucoma subjects only without changing ONH size. This suggests that the neural and connective tissues at ONH level in glaucoma subjects are more susceptible to acute IOP episodes than OHT or normal controls.

Glaucoma: the retina and beyond

Over 60 million people worldwide are diagnosed with glaucomatous optic neuropathy, which is estimated to be responsible for 8.4 million cases of irreversible blindness globally. Glaucoma is associated with characteristic damage to the optic nerve and patterns of visual field loss which principally involves the loss of retinal ganglion cells (RGCs). At present, intraocular pressure (IOP) presents the only modifiable risk factor for glaucoma, although RGC and vision loss can continue in patients despite well-controlled IOP. This, coupled with the present inability to diagnose glaucoma until relatively late in the disease process, has led to intense investigations towards the development of novel techniques for the early diagnosis of disease. This review outlines our current understanding of the potential mechanisms underlying RGC and axonal loss in glaucoma. Similarities between glaucoma and other neurodegenerative diseases of the central nervous system are drawn before an overview of recent developments in techniques for monitoring RGC health is provided, including recent progress towards the development of RGC specific contrast agents. The review concludes by discussing techniques to assess glaucomatous changes in the brain using MRI and the clinical relevance of glaucomatous-associated changes in the visual centres of the brain.

Relationship between Intraocular Pressure and Anterior Lamina Cribrosa Depth: A Cross-Sectional Observational Study in a Healthy Portuguese Population

Purpose

To investigate the association between anterior lamina cribrosa depth (ALCD), determined with enhanced depth imaging spectral-domain optical coherence tomography (EDI-OCT), and intraocular pressure (IOP) in a healthy Portuguese population.

Methods

In this cross-sectional observational study conducted between January and July 2015, 2 optic nerve head (ONH)–centered EDI-OCT cross-scans were performed and ALCD was defined as the perpendicular distance between the line connecting both edges of Bruch's membrane opening and the anterior border of the lamina cribrosa at the maximum depth point. A multivariate regression model was performed to assess the association of IOP and ALCD.

Results

The studied population included 59 subjects (35 women) with a mean age of 61.7 ± 15.1 years. Mean vertical and horizontal maximum ALCD was 444.5 ± 92.2 μm and 427.6 ± 82.7 μm, respectively. When controlling for age and spherical equivalent, maximum vertical and horizontal ALCD were positively correlated with intraocular pressure (R2>0.20) by 8.58 μm (95% confidence interval [CI] 2.80-14.36 μm; p<0.01) and 8.25 μm (95% CI 2.71-13.78 μm; p<0.01) per mm Hg of IOP, respectively.

Conclusions

Our sample of healthy subjects presented a statistically significant positive correlation between IOP and ALCD when controlling for possible confounding factors. These results may trigger further studies to better elucidate the role of IOP in the morphologic and functional dynamics of the ONH.

Anterior Displacement of Lamina Cribrosa during Valsalva Maneuver in Young Healthy Eyes

Purpose

To investigate lamina cribrosa (LC) displacement during the Valsalva maneuver in young healthy eyes using enhanced depth imaging (EDI) spectral-domain optical coherence tomography (SD-OCT).

Methods

Forty-eight eyes of 48 young healthy volunteers (age range: 20–34 years) underwent intraocular pressure (IOP) measurement by Goldmann applanation tonometry as well as Cirrus HD-OCT scans before and during the Valsalva maneuver. The optic nerve head (ONH) parameters (average retinal nerve fiber layer thickness, rim area, disc area, average C/D ratio, vertical C/D ratio, cup volume), anterior LC depth (LCD), subfoveal and peripapillary choroidal thickness, and neural canal opening diameter were measured on compensated OCT and compared during Valsalva challenge. The subjects were asked to take a five-minute break after each Valsalva maneuver.

Results

During the Valsalva maneuver, the IOP significantly increased, from 12.7 ± 3.0 mmHg to 16.0 ± 3.2 mmHg (P < 0.001), while the LCD sharply decreased, from 463.4 ± 118.8 μm to 427.3 ± 106.4 μm (P < 0.001). The subfoveal choroidal thickness (300.7 ± 90.6 vs. 309.6 ± 93.5 μm), peripapilllary choroidal thickness (152.2 ± 55.4 vs. 150.8 ± 49.3 μm), neural canal opening diameter (1651.8 ± 204.2 vs. 1651.0 ± 217.6 μm), and all of the ONH parameters did not change significantly (all P > 0.05).

Conclusions

The Valsalva maneuver induced anterior displacement of the LC, but did not alter the choroidal thickness or ONH morphology. The data describe the positional characteristics of the LC in response to the Valsalva maneuver in young healthy eyes.

What is a typical optic nerve head?

Whereas it is known that elevated intraocular pressure (IOP) increases the risk of glaucoma, it is not known why optic nerve heads (ONHs) vary so much in sensitivity to IOP and how this sensitivity depends on the characteristics of the ONH such as tissue mechanical properties and geometry. It is often assumed that ONHs with uncommon or atypical sensitivity to IOP, high sensitivity in normal tension glaucoma or high robustness in ocular hypertension, also have atypical ONH characteristics. Here we address two specific questions quantitatively: Do atypical ONH characteristics necessarily lead to atypical biomechanical responses to elevated IOP? And, do typical biomechanical responses necessarily come from ONHs with typical characteristics. We generated 100,000 ONH numerical models with randomly selected values for the characteristics, all falling within literature ranges of normal ONHs. The models were solved to predict their biomechanical response to an increase in IOP. We classified ONH characteristics and biomechanical responses into typical or atypical using a percentile-based threshold, and calculated the fraction of ONHs for which the answers to the two questions were true and/or false. We then studied the effects of varying the percentile threshold. We found that when we classified the extreme 5% of individual ONH characteristics or responses as atypical, only 28% of ONHs with an atypical characteristic had an atypical response. Further, almost 29% of typical responses came from ONHs with at least one atypical characteristic. Thus, the answer to both questions is no. This answer held irrespective of the threshold for classifying typical or atypical. Our results challenge the assumption that ONHs with atypical sensitivity to IOP must have atypical characteristics. This finding suggests that the traditional approach of identifying risk factors by comparing characteristics between patient groups (e.g. ocular hypertensive vs. primary open angle glaucoma) may not be a sound strategy.

Clinical Factors Associated with Lamina Cribrosa Thickness in Patients with Glaucoma, as Measured with Swept Source Optical Coherence Tomography

Purpose

To investigate the influence of various risk factors on thinning of the lamina cribrosa (LC), as measured with swept-source optical coherence tomography (SS-OCT; Topcon).

Methods

This retrospective study comprised 150 eyes of 150 patients: 22 normal subjects, 28 preperimetric glaucoma (PPG) patients, and 100 open-angle glaucoma patients. Average LC thickness was determined in a 3 x 3 mm cube scan of the optic disc, over which a 4 x 4 grid of 16 points was superimposed (interpoint distance: 175 μm), centered on the circular Bruch’s membrane opening. The borders of the LC were defined as the visible limits of the LC pores. The correlation of LC thickness with Humphrey field analyzer-measured mean deviation (MD; SITA standard 24–2), circumpapillary retinal nerve fiber layer thickness (cpRNFLT), the vertical cup-to-disc (C/D) ratio, and tissue mean blur rate (MBR) was determined with Spearman's rank correlation coefficient. The relationship of LC thickness with age, axial length, intraocular pressure (IOP), MD, the vertical C/D ratio, central corneal thickness (CCT), and tissue MBR was determined with multiple regression analysis. Average LC thickness and the correlation between LC thickness and MD were compared in patients with the glaucomatous enlargement (GE) optic disc type and those with non-GE disc types, as classified with Nicolela’s method.

Results

We found that average LC thickness in the 16 grid points was significantly associated with overall LC thickness (r = 0.77, P < 0.001). The measurement time for this area was 12.4 ± 2.4 minutes. Average LC thickness in this area had a correlation coefficient of 0.57 with cpRNFLT (P < 0.001) and 0.46 (P < 0.001) with MD. Average LC thickness differed significantly between the groups (normal: 268 ± 23 μm, PPG: 248 ± 13 μm, OAG: 233 ± 20 μm). Multiple regression analysis showed that MD (β = 0.29, P = 0.013), vertical C/D ratio (β = -0.25, P = 0.020) and tissue MBR (β = 0.20, P = 0.034) were independent variables significantly affecting LC thickness, but age, axial length, IOP, and CCT were not. LC thickness was significantly lower in the GE patients (233.9 ± 17.3 μm) than the non-GE patients (243.6 ± 19.5 μm, P = 0.040). The correlation coefficient between MD and LC thickness was 0.58 (P < 0.001) in the GE patients and 0.39 (P = 0.013) in the non-GE patients.

Conclusion

Cupping formation and tissue blood flow were independently correlated to LC thinning. Glaucoma patients with the GE disc type, who predominantly have large cupping, had lower LC thickness even with similar glaucoma severity.

In Vivo 3-Dimensional Strain Mapping of the Optic Nerve Head Following Intraocular Pressure Lowering by Trabeculectomy

PURPOSE

To map the 3-dimensional (3D) strain of the optic nerve head (ONH) in vivo after intraocular pressure (IOP) lowering by trabeculectomy (TE) and to establish associations between ONH strain and retinal sensitivity.

DESIGN

Observational case series.

PARTICIPANTS

Nine patients with primary open-angle glaucoma (POAG) and 3 normal controls.

METHODS

The ONHs of 9 subjects with POAG (pre-TE IOP: 25.3±13.9 mmHg; post-TE IOP: 11.8±8.6 mmHg) were imaged (1 eye per subject) using optical coherence tomography (OCT) (Heidelberg Spectralis, Heidelberg Engineering GmbH, Heidelberg, Germany) before (<21 days) and after (<50 days) TE. The imaging protocol was repeated for 3 controls in whom IOP was not altered. In each post-TE OCT volume, 4 tissues were manually segmented (prelamina, choroid, sclera, and lamina cribrosa [LC]). For each ONH, a 3D tracking algorithm was applied to both post- and pre-TE OCT volumes to extract IOP-induced 3D displacements at segmented nodes. Displacements were filtered, smoothed, and processed to extract 3D strain relief (the amount of tissue deformation relieved after TE). Strain relief was compared with measures of retinal sensitivity from visual field testing.

MAIN OUTCOME MEASURES

Three-dimensional ONH displacements and strain relief.

RESULTS

On average, strain relief (averaged or effective component) in the glaucoma ONHs (8.6%) due to TE was higher than that measured in the normal controls (1.07%). We found no associations between the magnitude of IOP decrease and the LC strain relief (P > 0.05), suggesting biomechanical variability across subjects. The LC displaced posteriorly, anteriorly, or not at all. Furthermore, we found linear associations between retinal sensitivity and LC effective strain relief (P < 0.001; high strain relief associated with low retinal sensitivity).

CONCLUSIONS

We demonstrate that ONH displacements and strains can be measured in vivo and that TE can relieve ONH strains. Our data suggest a wide variability in ONH biomechanics in the subjects examined in this study. We further demonstrate associations between LC effective strain relief and retinal sensitivity.

Clinical Assessment of Lamina Cribrosa Curvature in Eyes with Primary Open-Angle Glaucoma

Purpose

Quantitative evaluation of lamina cribrosa (LC) posterior bowing in primary open-angle glaucoma (POAG) eyes using swept-source optical coherence tomography.

Methods

Patients with POAG (n = 123 eyes) and healthy individuals of a similar age (n = 92 eyes) were prospectively recruited. Anterior laminar insertion depth (ALID) was defined as the vertical distance between the anterior laminar insertion and a reference plane connecting the Bruch’s membrane openings (BMO). The mean LC depth (mLCD) was approximated by dividing the area enclosed by the anterior LC, the BMO reference plane, and the two vertical lines for ALID measurement by the length between those two vertical lines. The LC curvature index was defined as the difference between the mLCD and the ALID. The factors influencing the LC curvature index were evaluated.

Results

The ALID and mLCD were significantly larger in POAG eyes than in healthy controls (P < 0.05). The LC curvature index was significantly larger in POAG eyes than in healthy controls on both the horizontal (85.8 ± 34.1 vs. 68.2 ± 32.3 μm) and vertical meridians (49.8 ± 38.5 vs. 32.2 ± 31.1 μm, all P < 0.001). Multivariate regression showed significant associations of greater disc area (P < 0.001), vertical C/D ratio (P < 0.001) and mLCD (P < 0.001), smaller rim area (P = 0.001), thinner average RNFLT (P < 0.001), and myopic refraction (P = 0.049) with increased LC curvature index. There was no difference in the LC curvature index between mild (MD > –6 dB) and moderate-to-advanced glaucoma (MD < –6 dB, P = 0.95).

Conclusions

LC posterior bowing was increased in POAG eyes, and was significantly associated with structural optic nerve head (ONH) changes but not with functional glaucoma severity. Quantitative evaluation of LC curvature can facilitate assessment of glaucomatous ONH change.

Optical Coherence Tomography Imaging for Glaucoma - Today and Tomorrow

Digital imaging technologies for glaucoma diagnostics have evolved rapidly over the recent years. From time-domain optical coherence tomography (OCT) to spectral-domain and swept-source OCTs, the application of OCT for analysis of the anterior chamber angle and the optic nerve head (ONH) is expanding. The second-generation anterior segment swept-source OCT is able to image the configuration of the anterior chamber angle in 3 dimensions in less than 1 second and perform 360-degree analysis of the anterior chamber angle width for detection of angle closure. The morphology, density, and dimensions of the crystalline lens in relation to the anterior chamber can now be examined from the anterior corneal surface to the posterior lens surface, facilitating the investigation of the involvement of the crystalline lens in primary angle closure. Spectral-domain and swept-source OCTs have improved the measurement reliability of the lamina cribrosa and the neuroretinal rim configurations. Studying the deformation of the lamina cribrosa and ONH surfaces is relevant to decipher the mechanisms of ONH damage in the development and progression of glaucoma. Software and algorithms for automatic analysis of the anterior chamber angle dimensions and deformation of the ONH and lamina cribrosa surfaces are required to process large volumetric data sets, and they are under active development. It is expected that new imaging technologies will improve the detection and risk assessment of angle-closure and open-angle glaucomas.