Faculty Bibliography

Purpose/UNASSIGNED:To validate the ability of visible-light optical coherence tomography (vis-OCT) in imaging the full Schlemm's canal (SC) and its surrounding limbal vascular network in mice in vivo through a compound circumlimbal scan. Methods/UNASSIGNED:We developed an anterior segment vis-OCT system and a compound circumlimbal scanning method, which montages eight rotated raster scans. We calibrated the circumlimbal scan geometry using a three-dimensional printed phantom eyeball before imaging wild-type C57BL/6J mice. We measured SC size by segmenting SC cross sections from vis-OCT B-scan images and imaged the limbal microvascular network using vis-OCT angiography (vis-OCTA). To introduce changes in SC size, we used a manometer to adjust the intraocular pressure (IOP) to different levels. To create additional optical scattering contrast to enhance SC imaging, we surgically increased the episcleral venous pressure (EVP) and caused blood reflux into SC. Results/UNASSIGNED:Using the compound circumlimbal scan, our anterior segment vis-OCT noninvasively imaged the full SC and limbal microvascular network in mouse for the first time. We observed an average 123% increase in SC volume when we decreased the IOP by 10 mm Hg from the baseline IOP of 7 to 10 mm Hg and an average 72% decrease in SC volume when the IOP level was elevated by 10 mm Hg from the baseline IOP. We also observed location-dependent SC size responses to IOP changes. Blood reflux caused by increased EVP enabled vis-OCTA to directly visualize SC, which matched well with the segmented SC. Conclusions/UNASSIGNED:Vis-OCT and vis-OCTA can accurately image the entire SC and limbal microvascular network in vivo using the compound circumlimbal scan. Vis-OCT is also able to quantitatively measure SC responses to changing IOP levels.

Purpose: Rigorous clinical testing has established that Schlemm"™s canal cross-sec-tional area (SC-CSA) is reduced in glaucomatous eyes. However, to date, it is unclear whether trabecular bypass procedures impact the morphology of the proximal aqueous outflow tract, or if the introduction of a local region of low outflow resistance adversely affects SC-CSA elsewhere, specifically presenting as SC diminution. This study quantifies changes in the morphology of the distal outflow pathway after iStent Trabecular Micro-Bypass stent (Glaukos Corp, Laguna Hills, CA, USA) implantation in living eyes by anterior segment optical coherence tomography (OCT). Design: This was a prospective observational study. Subjects: This study included six patients (eight eyes) with primary-open angle glaucoma. Methods: Patients underwent iStent placement in the nasal anterior chamber angle quadrant. OCT imaging was obtained of both nasal and temporal eye quadrants before and after surgery. For each SC parameter, an average of ten consecutive, evenly spaced measurements were manually obtained over a 1 mm segment of SC on FIJI ImageJ. Linear mixed effects modeling quantified the effect of the iStent on these parameters. Main outcome measures: Main outcome measures were changes in SC-CSA, inner-to-outer wall distance (IOD), and trabecular meshwork (TM) thickness following iStent placement. Results: Following iStent placement, total SC-CSA increased an average of 1,039.12 µm² (P = 0.05). Individually, there were no significant changes in SC-CSA in the nasal or temporal quadrants. Total SC-IOD and nasal SC-IOD increased an average of 2.35 µm (P = 0.01) and 2.96 µm (P = 0.04), respectively. There were no significant changes in temporal quadrant SC-IOD. There were no significant changes in TM thickness in either quadrant. Conclusions: Implantation of the iStent Trabecular Micro-Bypass stent significantly increases SC-IOD in the nasal quadrant at the location of implant, with no evidence of SC diminution in the temporal quadrant. It remains unclear how these observa-tions relate to the surgical efficacy of trabecular bypass procedures.

Purpose/UNASSIGNED:The purpose of this study was to develop a machine learning model to forecast future circumpapillary retinal nerve fiber layer (cpRNFL) thickness in eyes of healthy, glaucoma suspect, and glaucoma participants from multimodal temporal data. Design/UNASSIGNED:Retrospective analysis of a longitudinal clinical cohort. Participants/UNASSIGNED:Longitudinal clinical cohort of healthy, glaucoma suspect, and glaucoma participants. Methods/UNASSIGNED:(LTBE). Main Outcome Measures/UNASSIGNED:The mean absolute difference and Pearson's correlation coefficient between the true and forecasted values of the cpRNFL in the healthy, glaucoma suspect, and glaucoma patients. Results/UNASSIGNED:< 0.01) for the 3 groups, respectively. Conclusions/UNASSIGNED:The performance of the proposed forecasting model for cpRNFL is consistent across glaucoma suspect and glaucoma patients, which implies the robustness of the developed model against the disease state. These forecasted values may be useful to personalize patient care by determining the most appropriate intervisit schedule for timely interventions.

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 : 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: 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 : 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

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 : 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