GD-DTPA enhanced MRI of ocular transport in a rat model of chronic glaucoma.

Glaucoma is a neurodegenerative disease of the visual system characterized by the elevation of intraocular pressure. While this elevated pressure is related to an increased resistance to the outflow of aqueous humor from the eye, their impacts to the etiology and pathogenesis of the disease are not fully understood. This study aims to employ in vivo Gd-DTPA enhanced magnetic resonance imaging to evaluate the ocular transport following an induction of ocular hypertension in a rat model of chronic glaucoma. An experimental ocular hypertension model was induced in adult rats using an argon laser to photocoagulate the episcleral and limbal veins on the surface of the eyeball. The enhancements of the MRI signal intensity in the anterior chamber and vitreous body were measured as a function of time following systemic administration of Gd-DTPA solution at 3 mmol/kg. Results showed a progressive T1-weighted signal increase in the vitreous body of the glaucomatous eye but not the control eye. This increase occurred earlier in the anterior vitreous body than the preretinal vitreous. Further, there was an earlier Gd-DTPA transport into the anterior chamber in the majority of glaucomatous eyes. Our findings revealed the leakage of Gd-DTPA at the aqueous-vitreous interface, which was likely resulted from increased permeability of blood-aqueous or aqueous-vitreous barrier. These may explain the sources of changing biochemical compositions in the glaucomatous chamber components, which may implicate the cascades of neurodegenerative processes in the retina and the optic nerve.