MEASUREMENT OF BLOOD-RETINAL BARRIER BREAKDOWN IN ENDOTOXIN-INDUCED ENDOPHTHALMITIS

Purpose. Endophthalmitis is a severe inflammatory disorder with profou nd visual consequences. Treatment of this disorder has been limited by the lack of quantitative information regarding retinal responses to s evere inflammation. The purpose of this study was to measure the effec t of endotoxin-induced endophthalmitis on blood-retinal barrier (BRB) function in vivo using contrast-enhanced magnetic resonance imaging (M RI). Methods. Endophthalmitis was produced by injecting Escherichia co li endotoxin into the mid-vitreous of pigmented rabbits. Contrast-enha nced MRI was performed at selected intervals thereafter. In all cases, a clinical grading system was used to assess the severity of inflamma tion before imaging. In a dose-response experiment, total vitreous pro tein was measured from vitreous specimens obtained 1 day after endotox in injection and immediately after the imaging procedure. Results. At 1 day after injection, endotoxin produced a selective breakdown of the inner BRB at all doses evaluated (0.01 mu g to 500 mu g). Permeabilit y-surface area product normalized to the area of leaky retina (PS') in creased from 1.35 +/- 0.78 X 10(-4) cm/minute (mean +/- SEM, n = 4 eye s) at a dose of 0.01 mu g to 8.15 +/- 2.22 X 10(-4) cm/minute (n = 4 e yes) at a dose of 10 mu g. Inner BRB integrity was restored by day 28 after injection. In general, changes in PS', blood-aqueous barrier lea kage, mean clinical score, and vitreous protein concentration were fou nd, but the correlation between any two of these parameters was poor. Conclusion. Leakage of contrast appears early in the course of endotox in-induced endophthalmitis and is a self-limited process. In future st udies, these quantifiable changes in BRB permeability should prove use ful in the assessment of various therapeutic interventions.