Monitoring retinal responses to acute intraocular pressure elevation in rats with visible light optical coherence tomography

Abstract

Elevated intraocular pressure (IOP) is an important risk factor for glaucoma. However, the role of IOP in glaucoma progression, as well as retinal physiology in general, remains incompletely understood. We demonstrate the use of visible light optical coherence tomography to measure retinal responses to acute IOP elevation in Brown Norway rats. We monitored retinal responses in reflectivity, angiography, blood flow, oxygen saturation (sO 2), and oxygen metabolism over a range of IOP from 10 to 100 mmHg. As IOP was elevated, nerve fiber layer reflectivity was found to decrease. Vascular perfusion in the three retinal capillary plexuses remained steady until IOP exceeded 70 mmHg and arterial flow was noted to reverse periodically at high IOPs. However, a significant drop in total retinal blood flow was observed first at 40 mmHg. As IOP increased, the venous sO 2 demonstrated a gradual decrease despite steady arterial sO 2 , which is consistent with increased arterial-venous oxygen extraction across the retinal capillary beds. Calculated total retinal oxygen metabolism was steady, reflecting balanced responses of blood flow and oxygen extraction, until IOP exceeded 40 mmHg, and fell to 0 at 70 and 80 mmHg. Above this, measurements were unattainable. All measurements reverted to baseline when the IOP was returned to 10 mmHg, indicating good recovery following acute pressure challenge. These results demonstrate the ability of this system to monitor retinal oxygen metabolism noninvasively and how it can help us understand retinal responses to elevated IOP.

Visible-Light Optical Coherence Tomography Fibergraphy for Quantitative Imaging of Retinal Ganglion Cell Axon Bundles

“… 53 Additionally, studies have shown that the increased intraocular pressure levels associated with glaucoma lead to reduced perfusion of the retina. 54 Therefore, vis-OCT fibergraphy could be applied to investigate what percentage of a decrease in capillary density corresponds to a decrease in RGC axon bundles.…”

Retinal capillary oximetry with visible light optical coherence tomography

“…Compared to standard OCT operating in the near-infrared band, visible-light OCT (vis-OCT) (24, 25) produces higher axial resolution (26,27) and higher spectral contrast between oxy-and deoxy-hemoglobin (8). Using vis-OCT, oximetry on major vessels in rodents and humans has been successfully demonstrated (24,(28)(29)(30)(31) and used to monitor how progressive hypoxic challenge (32) or intraocular pressure (IOP) elevation (33,34) affects retinal oxygen metabolism. Advances in automated detection of posterior vascular boundaries (29), acquisition of multiple circumpapillary scans (31), and quantitative quality controls (35) have been made to improve retinal oximetry on major vessels.…”

Retinal blood flow in critical illness and systemic disease: a review

“…Retinal circulation lacks autonomic innervation [39] and is dependent on local vasogenic factors acting on the neurovascular unit [39,40]. Despite the absence of sympathetic activation, retinal blood flow is able to remain constant over a range of intraocular pressures (IOP), which naturally fluctuates in daily life [38], although an elevated IOP above 40 mmHg reduces retinal blood flow [41]. Local metabolic factors mediating retinal autoregulation include endothelin-1 which is secreted by EC and acts as a vasoconstrictor, affecting retinal vascular endothelium, pericytes and the choroid [39].…”