Evaluation of therapeutic effectiveness using MR imaging in a rabbit model of anterior uveitis

Magnetic resonance imaging (MRI) has been used to examine conditions that alter the permeability of the blood-retinal barrier. Our goal was to determine if blood-aqueous barrier permeability could be similarly assessed, because MRI offers the theoretical advantage of providing quantitative data directly from inflamed uveal tissues rather than from the aqueous humor into which the inflammatory reaction spills. As an additional challenge, we sought to use MRI to measure differences between the inflamed uveal tissues of corticosteroid-treated and placebo-treated uveitic eyes. Anterior uveitis was induced in one eye of eight rabbits by subcutaneous injection of Mycobacterium tuberculosis, followed after 10 days with intravitreal challenge. One rabbit of each pair was treated with topical 1% prednisolone acetate while control rabbits were treated with artificial tears. Contrast-enhanced MRI studies were performed prior to uveitis induction, one day after induction and then weekly for at least 2 weeks. MR image data were analyzed to determine percent change in peak enhancement of the ciliary body and anterior chamber. The initial rate of change of enhancement of the anterior chamber was also measured. Extensive contrast agent-induced MR image enhancement of both the anterior chamber and the ciliary processes was measured following the induction of uveitis. More rapid improvement was measured for the 1% prednisolone acetate-treated rabbit eyes (P < 0.001). MR signal enhancement data obtained from the ciliary processes proved to be the most reliable indicator of disease activity in this rabbit model of uveitis. Such data can only be obtained using MRI.