In Vivo Assessment of Aqueous Humor Dynamics Upon Chronic Ocular Hypertension and Hypotensive Drug Treatment Using Gadolinium-Enhanced MRI

Abstract

Gadolinium-enhanced MRI allows spatiotemporal and quantitative evaluation of altered AH dynamics and ocular tissue permeability for better understanding the physiological mechanisms of ocular hypertension and the efficacy of antiglaucoma drug treatments.

Long-Term Effects of Neonatal Hypoxia-Ischemia on Structural and Physiological Integrity of the Eye and Visual Pathway by Multimodal MRI

“…After systemic Gd administration, Gd may mimic soluble aqueous humor components and readily pass the highly permeable blood-aqueous barrier into the anterior chamber but not the less permeable aqueous-vitreous or blood-retinal barrier into the vitreous body. 14,15,[22][23][24] In this study, Gd-MRI showed similar Gd enhancement patterns and comparable aqueous humor dynamics in the anterior chamber of both eyes after unilateral neonatal HI injury. However, significant Gd enhancement was observed in the vitreous body of the ipsilesional eye but not the contralesional eye by the end of the 1-hour Gd-MRI experiment.…”

“…The T1-weighted signal intensities in the anterior chamber and vitreous body of each eye in Gd-MRI, 23,24 in the retina of each eye in Cr-MRI, 20 and in the optic nerve and superior colliculus of each hemisphere in Mn-MRI 27,28 were measured using ImageJ v1.43u (http://imagej.nih.gov/ij/; provided in the public domain by the National Institutes of Health, Bethesda, MD, USA) based on the anatomical landmarks in the MR images and the rat brain atlas. 39 We calculated the relative signal enhancement of Gd and Cr via dividing the signal intensity at each time point by that at the earliest time point acquired.…”

“…Although it is not clear whether such a change in metabolic environment in the vitreous body from neonatal HI might possess causal effect on the pathogenesis of chronic retinal injury and visual impairment in the adult rats, similar Gd-MRI findings on the compromise of aqueous-vitreous or bloodocular barrier integrity have been observed in the experimental chronic glaucoma models, whereby the retina and optic nerve fibers of the adult rats were concurrently injured. 23,24 Gadolinium-enhanced MRI has been used to evaluate the efficacy of therapeutic drugs on anterior uveitis across the blood-ocular barriers. 15 Future studies are envisioned that elucidate the relations of ocular tissue permeability to retinal health and visual function.…”

“…Within the eyeball, systemic administration of the gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) MR contrast agent allowed noninvasive assessments of the aqueous humor dynamics and the permeability of the blood-aqueous, aqueous-vitreous, and blood-retinal barriers in different ocular compartments simultaneously in both eyes. 14,15,[22][23][24] Local administration of potassium dichromate (K 2 Cr 2 O 7 ) and manganese chloride (MnCl 2 ) MR contrast agents may help assess the biochemical properties of the retina and the active axonal transport in the visual pathway. 17,18,20,[25][26][27][28][29] Diffusion tensor MR imaging (DTI) probes the anisotropic property of tissue water 30,31 and has been successfully used to reveal the microstructural integrity of the optic nerve and optic tract in normal, developing, and injured brains.…”

A Magnetic Microbead Occlusion Model to Induce Ocular Hypertension-Dependent Glaucoma in Mice

“…In many of these models, glaucoma is induced by disrupting aqueous humour dynamics, resulting in the elevation of IOP. Occlusion models, in which microbeads or other substances are injected into the anterior chamber of the eye to block aqueous drainage, have gained popularity in recent years partly due to their relative ease to increase IOP [4][5][6][7][8][9][10][11][12][13][14] .…”