Faculty Bibliography

Purpose : Recent studies suggest that glaucoma involves trans-neuronal changes in choline metabolism in the brain's visual system. In addition, citicoline has been suggested as a potential therapeutic for neurodegenerative diseases including glaucoma, yet the underlying mechanisms remain unclear. Here, we use proton magnetic resonance spectroscopy ( H-MRS) and optokinetics to examine the effects of chronic intraocular pressure (IOP) elevation and oral citicoline treatment on brain metabolism and visual function in a novel rat model of experimental glaucoma. Methods : Twenty-three adult Long Evans rats were divided into 3 groups. In Group 1 (n=6) and Group 2 (n=7), the right eye was intracamerally injected with an optically clear crosslinking hydrogel for chronic IOP elevation; Group 2 also received daily oral citicoline dosing for 7 days prior to hydrogel injection, and every 48 hours for 14 days post-injection. The sham group (Group 3, n=7) received an intracameral injection of buffer solution only. IOP and visual acuity (VA) were measured longitudinally using a TonoLab rebound tonometer and the OptoMotry virtual reality system, respectively. H-MRS was acquired over the left and right visual cortices at 5 weeks post-injection using a 9.4T MRI scanner. Results : VA of the left, uninjured eyes remained constant over the experimental period, whereas VA of citicoline-treated right eyes appeared to deteriorate more slowly than untreated right eyes after similar levels of chronic IOP elevation (Fig 1). The left visual cortex projecting from the right, hydrogel-injected eye without citicoline treatment showed a reduced choline level compared to the contralateral right visual cortex projecting from 1 1 the left, uninjured eye. Interestingly, a higher choline level was found in the left visual cortex of citicoline-treated rats compared to untreated rats (Fig 2). No apparent metabolic change was observed in the sham group. Conclusions : Chronic IOP elevation by intracameral hydrogel injection significantly decreased visual acuity and choline-containing compounds in the visual cortex, whereas oral administration of citicoline ameliorated these effects. Our findings suggest that oral citicoline treatment may possess neuroprotective effects on the visual cortex by replenishing choline contents during glaucomatous degeneration, and H-MRS may help in monitoring such metabolic changes in the brain

Purpose : The glymphatic system has been postulated to play a crucial role in the central nervous system via metabolic waste removal from brain tissues by the cerebrospinal fluid (CSF). However, it remains unclear whether there is a direct glymphatic pathway in the visual pathway, partly due to limited in vivo methods for assessing the physiology of CSF dynamics in the optic nerve (ON). Contrast-enhanced MRI has been shown to be capable of monitoring the dynamics of glymphatic system in the brain using paramagnetic contrast agents. Investigating the same in and around the ON might give insights into the mechanisms of vision-related diseases such as glaucoma. Methods : In the present study, we infused a small molecular weight gadolinium-DTPA contrast agent intrathecally into the lumbar region (L4-L5) of 3 healthy adult C57BL/6J mice and imaged its flow, accumulation and clearance in the brain and the optic nerve over time using a 7-Tesla MRI scanner under isoflurane anesthesia. Contrast dynamics was monitored using a 3D T1-weighted imaging sequence at an isotropic resolution of 78x78x78 mum . Each scan lasted 10 min and a total of 12 continuous scans were acquired. These scans included 3 baseline acquisitions followed by 30 min of gadolinium contrast infusion using an automated pump while the scanning continued until the 12th time point. The intensity-time curves of the ON parenchyma, ON subarachnoid space (SAS), olfactory bulb, lateral ventricles and muscle tissues were generated and compared quantitatively. Data are represented as mean+/-SEM. Results : The ON parenchyma, ON-SAS, olfactory bulb and lateral ventricles showed a gradual increase in contrast enhancement (Figures 1 and 2A) with peak intensities at 92.03+/-16.21% (p<0.05), 440.50+/-39.41% (p<0.01), 210.54+/-20.69% (p<0.01) and 196.63+/-38.63% (p<0.05) respectively relative to baseline (Figure 2B). Peak intensity 3 occurred first in the olfactory bulb followed by ON-SAS, ON parenchyma and finally the lateral ventricles (Figure 2B). No apparent contrast uptake was observed in the nearby muscle tissues. Conclusions : This study illustrates direct communications between CSF and ON parenchyma and supports the evidence of the glymphatic system in the ON. In vivo imaging of CSF dynamics in and around the ON may open up new avenues for understanding ON function in health and disease with the possibility of devising novel drug delivery routes and therapeutic targets

Purpose : Glaucoma is thought to involve neurochemical changes not only in the eye but also the brain's visual system. While excitotoxicity may play a role in glaucoma pathogenesis, it remains controversial whether excess glutamate occurs in this process. In the current study, we investigated alterations in the excitatory-inhibitory balance (E/I balance) in the visual cortex of glaucoma patients. In addition, we examined whether the altered neurochemical balance in the visual cortex is associated with projections of basal nucleus of Meynert (BNM), a major source of cortical cholinergic innervation in the basal forebrain. Methods : 10 glaucoma patients with a wide range of disease severity and 4 age-matched healthy subjects underwent 3-Tesla anatomical MRI, resting-state functional MRI (fMRI), and magnetic resonance spectroscopy (MRS). We used MEGA-PRESS and PRESS sequences to measure the levels of gamma-aminobutyric acid (GABA) and combined glutamate and glutamine (GLX), respectively. Both GABA and GLX were obtained from the same single voxel (2.2x2.2x2.2 cm³) placed along the calcarine sulci and fitted by LCModel software. We normalized the amount of GABA and GLX to N-acetyl-aspartate (NAA) values obtained from MEGA-PRESS, following LCModel guidelines. E/I balance was calculated by dividing the amount of GLX by the amount of GABA. The resting-state fMRI data were analyzed by CONN software. Results : Glaucoma patients had 16.51% higher E/I balance in the visual cortex compared to the healthy control group (Figure 1a). This difference in E/I balance was apparently driven by a 16.85% reduction in GABA (Figure 1b) with no apparent difference in glutamate or glutamine levels between groups (Figure 1c). Furthermore, the E/I balance in the visual cortex was correlated with the functional connectivity between BNM and the visual cortex (Figure 2). Conclusions : The current study shows that the visual cortex of glaucoma patients adopts an excitatory-dominant state that is driven by reduced GABA. This imbalance was associated with the functional connectivity between BNM and the visual cortex, suggesting that weaker projection of BNM to the visual cortex may play a role in the neurochemical changes in the visual cortex of glaucoma patients. Taken together, these findings suggest that widespread functional and metabolic alterations are involved in the brain during glaucoma pathogenesis

Purpose : Development and pre-clinical testing of glaucoma neurotherapeutics have been obfuscated by limited experimental models that provide chronic elevation of intraocular pressure (IOP) while preserving optical media clarity for structural and functional assessments over time. In this study, we developed an in vivo model system involving the use of non-invasive tonometry, optical coherence tomography (OCT) and optokinetics to characterize retinal integrity and visual behavior in a novel hydrogel-induced chronic IOP elevation model. Methods : Six adult C57BL/6J mice underwent unilateral intracameral injection of an optically clear, chemically cross-linked hydrogel composed of hyaluronic acid functionalized with vinyl sulfone and thiol groups. IOP was measured with a rebound tonometer at baseline and 1, 3, 7, 10 and 14 days after hydrogel injection. The optic nerve head (ONH) region was scanned for each eye using OCT at baseline and 2 weeks after injection, and total retinal thickness (TRT) was measured within a 0.26-0.36 mm radius ring centered on the ONH using custom-written software (Fig 1). Visual acuity (VA) was measured for each eye using an optokinetic virtual-reality system at baseline and 2 weeks after injection. Data are presented as mean+/-SEM. Results : Intracameral hydrogel injection resulted in mild-to-moderate IOP elevation throughout the 2-week experimental period (Fig 2a). TRT in the hydrogel-injected eye was 10.06+/-3.61% thinner at 2 weeks post-injection compared to baseline (p<0.01) (Fig 2b). IOP elevation also led to a decline in VA by 58.12+/-7.22% at 2 weeks post-injection compared to baseline (p<0.001) (Fig 2c). Interestingly, among the hydrogel-injected eyes, cumulative IOP measured from 0 to 14 days post-injection did not correlate with TRT or VA (p>0.05) (Fig 2d-e), whereas TRT was positively associated with VA at 2 weeks post-injection (r=0.824, p<0.05) (Fig 2f). No significant change in IOP, TRT or VA was found in the non-injected eye. Conclusions : An in vivo glaucoma model system was developed that showed a positive correlation between retinal thinning and visual behavioral deficits after chronic IOP elevation. The weak association between cumulative IOP and TRT or VA suggests additional factors apart from IOP level in contributing to glaucomatous damage after chronic IOP elevation

Purpose : The presence of s zone peripapillary atrophy (PPA) has been associated with glaucoma. We performed a retrospective longitudinal study to evaluate s zone PPA area as a predictor for glaucomatous structural and functional progression. Methods : Subjects with glaucoma and >4 visits were included. Subjects had Humphrey visual field (Zeiss, Dublin, CA) testing, spectral-domain OCT (Cirrus HD-OCT; Zeiss) optic nerve head (ONH) and macula scans. s zone PPA was manually delineated on the baseline en face ONH scan as the area contiguous with the optic disc with the presence of hyper-and hyporeflectivity. Mixed effects linear models accounting for intra-subject correlation, follow-up time, scan's signal strength and ethnicity, were performed to determine if baseline PPA area was associated with glaucoma severity. Subsequent models incorporating the interaction term between time and baseline PPA area were performed to determine if baseline PPA area affected the rate of change in parameters of glaucoma over time. Results : 81 eyes (56 subjects) aged 62.8+/-14.1 years with an average follow-up time 3.9+/-1.3 years were analyzed. PPA was significantly associated with mean deviation (MD), visual field index (VFI), and inferior retinal nerve fiber layer (RNFL), (p=0.033, 0.038, and 0.034, respectively), but not with average RNFL, or macular ganglion cell inner plexiform layer (GCIPL) global and sectoral measurements and ONH parameters. No significant association was detected between s zone PPA area and the rate of progression for any parameter except for VFI (p =0.035). Conclusions : Although baseline s zone PPA area is associated with some indicators of glaucoma severity, it is not a significant predictor of the rate of glaucomatous progression (except for VFI)

PURPOSE: Congenital retinal macrovessels are large aberrant retinal blood vessels that cross the horizontal raphe and can traverse the central macula. Using multimodal imaging and optical coherence tomography angiography, we describe 2 cases of congenital retinal macrovessel associated with macroaneurysms. METHODS: Two patients presented for evaluation and were found to have congenital retinal macrovessels associated with macroaneurysms. Color photography, optical coherence tomography, fundus autofluorescence fluorescein angiography, and optical coherence tomography angiography were performed and used to establish the diagnosis and monitor resolution at follow-up visits. RESULTS: The first patient presented with central vision loss in the right eye and was noted to have a ruptured macroaneurysm and scattered microaneurysms along the course of a venous macrovessel. After 3 months of observation, the patient's vision improved. The second patient presented for evaluation of a cataract in her left eye and was incidentally found to have an arterial macrovessel in her right eye with an associated macroaneurysm. Both cases demonstrated an intricate capillary network in the central macula best visualized on optical coherence tomography angiography. CONCLUSION: Macroaneurysms can occur on both arterial and venous macrovessels. After rupture of these lesions, hemorrhage and exudation can resolve with observation alone. Macrovessels can also present with microaneurysms. Optical coherence tomography angiography can effectively image the complex capillary network associated with these vascular anomalies.

Purpose : Oxygen concentration in retinal blood vessels (sO ) can be critical biomarkers for diabetic retinopathy and glaucoma, leading causes of blindness worldwide. We previously demonstrated sO2measurements in rodent and human retinas with spectroscopic visible-light optical coherence tomography (vis-OCT). However, reliable measurements of sO2in a clinical setting remains an open challenge due to constraints on light exposure, imaging time, patient motion, and variation in eye geometry. Spectral calibration to optimize sO2measurements under these non-ideal imaging conditions is needed. Here, we investigate, develop, and implement such calibration. Methods : We developed vis-OCT processing software to optimize sO2measurements in humans. First, we identified an optimal spectral range for spectral measurement in which sO2was most stable. Next, we developed methods to account for alterations induced by the imaging system and eye optics. Specifically, we accounted for depth-dependent variations in the measured spectrum, such as absorption contrast, spectrally-dependent roll-off, chromatic aberrations, and eye morphology. We then imaged the retinas of 12 healthy subjects aged 22 to 60 at Northwestern Medical Hospital in Chicago, IL, and Langone Medical Center in New York, NY. All imaging was approved by the respective IRBs and strictly adhered to the Declaration of Helsinki. Light exposure in the eye was no higher than 250 muW and imaging time was no longer than 5 s. We extracted sO2from vessels larger than 50 mum in diameter using an automated version of our vis-OCT processing software. Results : We measured the sO2in 89 vessels (53 arteries and 36 veins). We found the mean sO2in arteries was 97.70 +/-4.75 % in arteries and mean sO2in veins was 53.11 +/-6.85 %. Conclusions : We developed analytical methods for depth-dependent alterations to the measured spectrum in vis-OCT retinal oximetry. Our measurements yielded spectra that are highly consistent with those reported in literature, despite variations in imaging conditions. Our results indicate a clear path forward for clinical adoption of vis-OCT

Purpose: The purpose of the present study was to quantify test-retest reproducibili-ty of measurements of stiffness of the human trabecular meshwork (HTM) by atomic force microscopy (AFM).
Method(s): Eleven 40 mum radial limbal cryostat sections from a fresh human donor rim were mounted on charged slides and rehydrated at room temperature. Stiffness at four TM locations (anterior to posterior along Schlemm's canal) was measured by AFM. At each location, a 6 x 6 grid was sampled. Indentation points were evenly distributed over a 20 mum x 20 mum area, with a rate of one load/unload cycle per second. Measurements were then repeated for calculation of test-retest variability.
Result(s): The test-retest coefficients of variation for the four measurement locations (anterior to posterior) were 24.39, 25.28, 12.74, and 14.26%, respectively, with a notable drop in the two posterior locations compared to the anterior. The test-retest coefficient for the sections was 19.17%. For the entire eye, the test-retest coefficient of variation for the measurement of the TM stiffness was 17.13%. Young's moduli consistently decreased from anterior to posterior location.
Conclusion(s): Wide regional variation suggests that single value does little to fully describe the complex array of TM stiffness levels within the eye, and future studies of TM stiffness assessed by AFM should include multiple tissue samples from each eye, with documentation of the anterior-posterior location of each measurement.
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Purpose : In mild glaucoma, RNFL thinning and visual field (VF) loss are often localized, but structure-function modeling is impeded by variability due to individual eye anatomy. We perform high-resolution spatial correlations of RNFLT maps for each VF location to identify relevant areas and study further improvements by geometrically aligning RNFLT maps based on artery trajectories. Methods : In 419 SITA Standard 24-2 Humphrey VFs with at most mild glaucoma (mean deviation >=-3dB) with accompanying circumpapillary Cirrus HD-OCT RNFLT maps, we computed pixel-wise correlations (52 VF locations x 40401 pixels). We then performed an alignment operation, ensuring that the two major retinal arteries follow the same lines in all scans. We piecewise linearly approximated the trajectories of the arteries on 4 concentric circles around ONH (Fig. 1a), determined the necessary rotation for each pixel, and morphed the images accordingly (Fig. 1b). Results : For the pre-alignment RNFLT (correlation maps Fig. 2 top) we observed: (1) relatively high correlations (max 0.29); (2) most of the high-correlation regions are highly localized around the median trajectories of the major arteries at most VF locations, possibly due to the stacked character of the fiber bundles close to ONH, which impedes precise spatial mapping to the VF. This observation suggests general retinal vulnerability zones rather than highly VF location-specific areas as assumed by many previous structure-function models. Accordingly, morphing the RNFLT maps by aligning the eyespecific artery locations increased the maximal correlations on 25 of the 52 VF locations (Fig. 2 bottom, marked in green), particularly in nasal and inferior VF, with improvements of up to 0.1 (inferior arcuate region of VF). At many locations, aligned vulnerability areas become substantially more conspicuous (e.g. the location enlarged on the top left) and might have been missed without aligning. Conclusions : High-resolution structure-function correlations reveal retinal vulnerability zones in mild glaucoma. At many VF locations, these zones become better correlated with VF regions when RNFLT maps are aligned along the arteries. Specific attention to RNFL thinning in these zones in glaucoma suspects may improve the detection of initial VF loss glaucoma

Purpose : Predicting progression of primary open angle glaucoma (POAG) continues to be a challenge. Recent studies have shown that macular parameters may predict glaucoma progression and disease onset equally as well or even better than the traditionally used optic nerve head (ONH) retinal nerve fiber layer (RNFL) thickness. We performed a retrospective longitudinal study to identify structural parameters which best predicted visual field (VF) loss. Methods : Subjects with POAG with at least 5 qualified Cirrus OCT (Zeiss, Dublin, CA) macular and optic nerve head (ONH) scans and 5 qualified 24-2 Humphrey VF tests (Zeiss) were enrolled to this study. All parameters from the OCT's report of the macula and ONH scans were used in the analysis. We identified subjects who were OCT ONH progressors or VF progressors using both event and trend based definitions of progression based on the Guided Progression Analyses. Students t-test was used to assess differences in baseline characteristics between groups, and mixed-effects model was used in longitudinal analysis to compare the rate of parameter change between groups. Results : 263 eyes (180 subjects) with a mean follow-up time of 2.4+/-1.8 years were included in the study. Twenty-three eyes were identified as ONH progressors, 25 eyes were identified as VF progressors, and of these, 6 eyes were both VF and ONH progressors. At baseline, only macular average RNFL and macular inferior RNFL were significantly thinner in ONH progressors compared to non-progressors. Between the VF progressors and non-progressor groups, all OCT parameters were significantly thinner at baseline in the progressors except for four focal macular measurements and disc area. Mixed-effects modeling showed that both focal macular and ONH parameters thinned at a significantly greater rate in VF progressors compared to non-progressors (Table 1). Conclusions : Focal macular retinal segmentations and focal ONH parameters thin significantly more per year in VF progressors, and VF progressors tend to have thinner baseline structural parameters