Faculty Bibliography

Purpose: Most reported information regarding the in vivo prelaminar tissue is based on a limited number of sampling planes on OCT volumes. In this study we used whole volume data to compute a global mean prelaminar thickness and examined its association with structural and functional parameters in subjects with moderate to advanced glaucoma. Given the low reliability of OCT and visual field (VF) to detect progression in advanced subjects, this study focuses on this subset as it could benefit most from a novel structural parameter.
Method(s): Subjects with moderate to advanced glaucoma, as indicated by a baseline spectral-domain(SD) OCT's mean RNFL thickness <=70mum, were included. All subjects had a baseline prototype swept-source(SS) OCT, VF (Humphrey Field Analyzer, Zeiss), and at least one follow-up SD-OCT (Cirrus HD-OCT, Zeiss). SS-OCT raster scan of the optic nerve head (ONH) (3.5 mmx3.5mm;400x400x861sampling points) was performed. The prelaminar tissue was manually delineated in each SS-OCT cross-section and the mean distance between the vitreous/ONH interface and the anterior lamina surface was automatically computed by averaging the thickness in every sampling point within the ONH. A random mixed effects model was used for assessing the association between baseline prelaminar thickness and cross-sectional variables, and longitudinal changes in structural and functional parameters.
Result(s): 31 eyes from 27 subjects were available for analysis (mean follow-up=20 months). Baseline prelaminar thickness was positively associated with baseline RNFL (average, superior, inferior), GCIPL (average, superior, inferior), rim area, vertical cup to disc ratio (C/D ratio), VFI and MD (p<=0.02) and negatively associated with baseline average C/D ratio and cup volume (p<=0.002;Table). Longitudinal analysis demonstrated that thicker baseline prelaminar tissue was associated with faster rate of progression for average and inferior RNFL thickness and faster enlargement of average and vertical C/D ratio (p<=0.03).
Conclusion(s): Prelaminar tissue thickness is significantly associated with ONH, peripapillary, macular and VF parameters on cross-sectional analysis. On longitudinal analysis prelaminar thickness showed association with faster rate of RNFL progression. Thorough sampling of the prelaminar tissue thickness has the potential to serve as a biomarker for both disease status and risk of progression in subjects with glaucoma. (Table presented)

Purpose : Ganglion cell-inner plexiform layer (GCIPL) and retinal nerve fiber layer (RNFL) thicknesses measured by OCT have been shown to be useful for glaucoma diagnosis and progression detection. The purpose of this study was to determine the disease severity threshold (tipping point) at which the longitudinal rate of change for RNFL and GCIPL thickness slows down; allowing to determine the preferred location to follow structural damage along the spectrum of the disease severity. Methods : Subjects with comprehensive ophthalmic examination and >= 5 visits with qualified visual field (VF; Humphrey Field Analyzer; Zeiss, Dublin, CA) and OCT (Cirrus HDOCT; Zeiss) optic nerve head and macular scans were enrolled. Piece-wise linear mixed effects model was used to identify the tipping points of RNFL and GCIPL vs. VF mean deviation (MD), respectively, and model with quadratic term for RNFL vs. GCIPL. To account for the difference in dynamic ranges, RNFL and GCIPL rate of change were standardized (normal distribution, mean=0 sd=1). Results : 177 eyes (125 open angle glaucoma, 45 glaucoma suspect, and 7 healthy eyes) of 114 subjects were analyzed. Subjects' mean age: 70 +/- 11 years, median VF MD: -1.78 dB ([Q1, Q3]; -5.8, -0.2), baseline average RNFL and GCIPL thicknesses: 73.2 +/- 14.9mum and 68.3 +/- 10.7mum, respectively, average follow-up time: 3.4 +/- 1 years, mean visits per subject: 5.6, with a grand total of 1,010 follow-up visits. Tipping point for RNFL occur at earlier stage of the disease and the rate of change is faster than for GCIPL (Table). However, after standardization, the slopes for RNFL and GCIPL were similar. When comparing the rate of change for RNFL and GCIPL, no tipping point was detected, but as RNFL and GCIPL decreased, the rate of change in RNFL became significantly smaller. Conclusions : Rate of RNFL thinning slows down at an earlier stage of functional damage than GCIPL. Different dynamic ranges give the impression that RNFL decreases faster, but accounting for the larger dynamic range, a similar rate of change to GCIPL is observed across the entire disease severity spectrum. Our results do not indicate whether RNFL or GCIPL is better for detecting progression except for very advanced stages of the disease where RNFL progression rate stalls

The lamina cribrosa is a primary site of damage in glaucoma. While mechanical distortion is hypothesized to cause reduction of axoplasmic flow, little is known about how the pores, which contains the retinal ganglion cell axons, traverse the lamina cribrosa. We investigated lamina cribrosa pore paths in vivo to quantify differences in tortuosity of pore paths between healthy and glaucomatous eyes. We imaged 16 healthy, 23 glaucoma suspect and 48 glaucomatous eyes from 70 subjects using a swept source optical coherence tomography system. The lamina cribrosa pores were automatically segmented using a previously described segmentation algorithm. Individual pore paths were automatically tracked through the depth of the lamina cribrosa using custom software. Pore path convergence to the optic nerve center and tortuosity was quantified for each eye. We found that lamina cribrosa pore pathways traverse the lamina cribrosa closer to the optic nerve center along the depth of the lamina cribrosa regardless of disease severity or diagnostic category. In addition, pores of glaucoma eyes take a more tortuous path through the lamina cribrosa compared to those of healthy eyes, suggesting a potential mechanism for reduction of axoplasmic flow in glaucoma.

Purpose/UNASSIGNED:To introduce an experimental approach for direct comparison of the primate optic nerve head (ONH) before and after death by exsanguination. Method/UNASSIGNED:The ONHs of four eyes from three monkeys were imaged with spectral-domain optical coherence tomography (OCT) before and after exsanguination under controlled IOP. ONH structures, including the Bruch membrane (BM), BM opening, inner limiting membrane (ILM), and anterior lamina cribrosa (ALC) were delineated on 18 virtual radial sections per OCT scan. Thirteen parameters were analyzed: scleral canal at BM opening (area, planarity, and aspect ratio), ILM depth, BM depth; ALC (depth, shape index, and curvedness), and ALC visibility (globally, superior, inferior, nasal, and temporal quadrants). Results/UNASSIGNED:All four ALC quadrants had a statistically significant improvement in visibility after exsanguination (overall P < 0.001). ALC visibility increased by 35% globally and by 36%, 37%, 14%, and 4% in the superior, inferior, nasal, and temporal quadrants, respectively. ALC increased 4.1%, 1.9%, and 0.1% in curvedness, shape index, and depth, respectively. Scleral canals increased 7.2%, 25.2%, and 1.1% in area, planarity, and aspect ratio, respectively. ILM and BM depths averaged -7.5% and -55.2% decreases in depth, respectively. Most, but not all, changes were beyond the repeatability range. Conclusions/UNASSIGNED:Exsanguination allows for improved lamina characterization, especially in regions typically blocked by shadowing in OCT. The results also demonstrate changes in ONH morphology due to the loss of blood pressure. Future research will be needed to determine whether there are differences in ONH biomechanics before and after exsanguination and what those differences would imply.

Although elevated intraocular pressure (IOP) and age are major risk factors for glaucoma, their effects on glaucoma pathogenesis remain unclear. This study examined the onset and progression of glaucomatous changes to ocular anatomy and physiology, structural and physiological brain integrity, and visuomotor behavior in the DBA/2J mice via non-invasive tonometry, multi-parametric magnetic resonance imaging (MRI) and optokinetic assessments from 5 to 12 months of age. Using T2-weighted MRI, diffusion tensor MRI, and manganese-enhanced MRI, increasing IOP elevation at 9 and 12 months old coincided with anterior chamber deepening, altered fractional anisotropy and radial diffusivity of the optic nerve and optic tract, as well as reduced anterograde manganese transport along the visual pathway respectively in the DBA/2J mice. Vitreous body elongation and visuomotor function deterioration were observed until 9 months old, whereas axial diffusivity only decreased at 12 months old in diffusion tensor MRI. Under the same experimental settings, C57BL/6J mice only showed modest age-related changes. Taken together, these results indicate that the anterior and posterior visual pathways of the DBA/2J mice exhibit differential susceptibility to glaucomatous neurodegeneration observable by in vivo multi-modal examinations.

Purpose/UNASSIGNED:Sex hormones may be associated with primary open-angle glaucoma (POAG), although the mechanisms are unclear. We previously observed that gene variants involved with estrogen metabolism were collectively associated with POAG in women but not men; here we assessed gene variants related to testosterone metabolism collectively and POAG risk. Methods/UNASSIGNED:We used two datasets: one from the United States (3853 cases and 33,480 controls) and another from Australia (1155 cases and 1992 controls). Both datasets contained densely called genotypes imputed to the 1000 Genomes reference panel. We used pathway- and gene-based approaches with Pathway Analysis by Randomization Incorporating Structure (PARIS) software to assess the overall association between a panel of single nucleotide polymorphisms (SNPs) in testosterone metabolism genes and POAG. In sex-stratified analyses, we evaluated POAG overall and POAG subtypes defined by maximum IOP (high-tension [HTG] or normal tension glaucoma [NTG]). Results/UNASSIGNED:In the US dataset, the SNP panel was not associated with POAG (permuted P = 0.77), although there was an association in the Australian sample (permuted P = 0.018). In both datasets, the SNP panel was associated with POAG in men (permuted P ≤ 0.033) and not women (permuted P ≥ 0.42), but in gene-based analyses, there was no consistency on the main genes responsible for these findings. In both datasets, the testosterone pathway association with HTG was significant (permuted P ≤ 0.011), but again, gene-based analyses showed no consistent driver gene associations. Conclusions/UNASSIGNED:Collectively, testosterone metabolism pathway SNPs were consistently associated with the high-tension subtype of POAG in two datasets.

Ocular imaging has been heavily incorporated into glaucoma management and provides important information that aids in the detection of disease progression. Longitudinal studies have shown that the circumpapillary retinal nerve fiber layer is an important parameter for glaucoma progression detection, whereas other studies have demonstrated that macular parameters, such as the ganglion cell inner plexiform layer and optic nerve head parameters, also are useful for progression detection. The introduction of novel technologies with faster scan speeds, wider scanning fields, higher resolution, and improved tissue penetration has enabled the precise quantification of additional key ocular structures, such as the individual retinal layers, optic nerve head, choroid, and lamina cribrosa. Furthermore, extracting functional information from scans such as blood flow rate and oxygen consumption provides new perspectives on the disease and its progression. These novel methods promise improved detection of glaucoma progression and better insight into the mechanisms of progression that will lead to better targeted treatment options to prevent visual damage and blindness.

Primary open-angle glaucoma (POAG) is the most common chronic optic neuropathy worldwide. Epidemiological studies show a robust positive relation between intraocular pressure (IOP) and POAG and modest positive association between IOP and blood pressure (BP), while the relation between BP and POAG is controversial. The International Glaucoma Genetics Consortium (n=27 558), the International Consortium on Blood Pressure (n=69 395), and the National Eye Institute Glaucoma Human Genetics Collaboration Heritable Overall Operational Database (n=37 333), represent genome-wide data sets for IOP, BP traits and POAG, respectively. We formed genome-wide significant variant panels for IOP and diastolic BP and found a strong relation with POAG (odds ratio and 95% confidence interval: 1.18 (1.14-1.21), P=1.8 x 10-27) for the former trait but no association for the latter (P=0.93). Next, we used linkage disequilibrium (LD) score regression, to provide genome-wide estimates of correlation between traits without the need for additional phenotyping. We also compared our genome-wide estimate of heritability between IOP and BP to an estimate based solely on direct measures of these traits in the Erasmus Rucphen Family (ERF; n=2519) study using Sequential Oligogenic Linkage Analysis Routines (SOLAR). LD score regression revealed high genetic correlation between IOP and POAG (48.5%, P=2.1 x 10-5); however, genetic correlation between IOP and diastolic BP (P=0.86) and between diastolic BP and POAG (P=0.42) were negligible. Using SOLAR in the ERF study, we confirmed the minimal heritability between IOP and diastolic BP (P=0.63). Overall, IOP shares genetic basis with POAG, whereas BP has limited shared genetic correlation with IOP or POAG.European Journal of Human Genetics advance online publication, 30 August 2017; doi:10.1038/ejhg.2017.136.

Advances in imaging have made it increasingly common to study soft tissues without first embedding them in plastic or paraffin and without using labels or stains. The process, however, usually still involves fixation and cryosectioning, which could deform the tissues. Our goal was to quantify the morphological changes of ocular tissues caused by formalin fixation and cryosectioning. From each of 6 porcine eyes, 4 regions were obtained: cornea, equatorial and posterior sclera, and posterior pole containing the optic nerve head. Samples were imaged using visible light microscopy fresh, 1-minute and 24-hours post-fixation, and post-cryosectioning. Effects were assessed by 14 parameters representing sample size and shape. Overall, formalin fixation and sectioning caused only minimal changes to the ocular tissues, with average percentage parameter differences of 0.1%, 1%, and 1.2% between fresh and post-fixing by 1 minute, 24 hours, and post-cryosectioning, respectively. Parameter changes were not directional, and were only weakly dependent on the duration of fixation and the region of the eye. These results demonstrate that formalin fixation and cryosectioning are good choices for studying ocular tissue morphology and structure, as they do not cause the large tissue shrinkage or distortions typically associated with other, more complicated, techniques.

Glaucoma is a leading cause of blindness that leads to characteristic changes in the optic nerve head (ONH) region, such as nasalization of vessels. It is unknown whether the spatial location of this vessel shift inside the ONH occurs within the lamina cribrosa (LC) or the prelaminar tissue. The purpose of this study was to compare the location of the central retinal vessel trunk (CRVT) in the LC and prelaminar tissue in living healthy and glaucomatous eyes. We acquired 3-dimensional ONH scans from 119 eyes (40 healthy, 29 glaucoma suspect, and 50 glaucoma) using optical coherence tomography (OCT). The CRVT location was manually delineated in separate projection images of the LC and prelamina. We found that the CRVT in glaucoma suspect and glaucomatous eyes was located significantly more nasally compared to healthy eyes at the level of the prelamina. There was no detectable difference found in the location of the CRVT at the level of the LC between diagnostic groups. While the nasal location of the CRVT in the prelamina has been associated with glaucomatous axonal death, our results suggest that the CRVT in the LC is anchored in the tissue with minimal variation in glaucomatous eyes.