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Birgit Sander, Michael Larsen, Birgitte Moldow, Henrik Lund-Andersen; Diabetic Macular Edema: Passive and Active Transport of Fluorescein through the Blood–Retina Barrier. Invest. Ophthalmol. Vis. Sci. 2001;42(2):433-438.
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purpose. To investigate the passive bidirectional and active outward transport of
fluorescein through the blood–retina barrier (BRB) in diabetic
patients with clinically significant macular edema and in healthy
methods. The passive and active transport of fluorescein through the BRB was
quantitated by vitreous fluorometry. A previously developed method was
used to model passive transport. A new simulation model was developed
and evaluated for estimation of active transport. The study included 10
eyes of 5 healthy controls and 31 eyes of 20 diabetic patients with
clinically significant diabetic macular edema (CSME) in at least one
eye, totalling 25 eyes with CSME.
results. Passive permeability of fluorescein was increased by a factor of 12 in
eyes with edema compared to healthy controls (edema, 23.7 nm/sec;
healthy subjects, 1.9 nm/sec, P < 0.01), whereas
the active transport was doubled (edema, 84.1 nm/sec; healthy subjects,
43.5 nm/sec, P < 0.01). Unlike active transport,
passive permeability was related to the degree of retinopathy, in that
eyes with severe non-proliferative diabetic retinopathy had a passive
permeability that was significantly increased compared to moderate
retinopathy (32.1 nm/sec and 14.6 nm/sec, respectively, P < 0.05). The passive movement quantitated with
vitreous fluorometry was larger for diffuse and mixed leakage compared
to focal (P = 0.07).
conclusions. Insofar as the movement of fluorescein can be taken as a probe for the
movement of electrolytes and water, the pathogenesis of diabetic
macular edema seems to involve a disruption of the BRB, presumably its
inner component. The active resorptive functions of the blood–retina
barrier appear to be compensatorily increased to counteract edema
formation, although the increase is too small to prevent edema in the
face of severe leakage through the blood–retina
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