Mapping retinal fluorescein leakage with confocal scanning laser fluorometry of the human vitreous

Objective: To demonstrate an objective, quantitative, and sensitive method of mapping retinal fluorescein leakage into the vitreous while simultaneous ly imaging the retina. Methods: A prototype Zeiss confocal scanning laser ophthalmoscope was modif ied to obtain fluorometric measurements from 18 optical planes across the r etina and cortical vitreous, separated from each other by 150 mu m, and par allel to the retinal surface. After intravenous administration of fluoresce in, an axial graphic of equivalent fluorescein concentration in the vitreou s may be obtained from any region of interest. After correcting for fluores cence levels in the retina and choroid and plasma levels of free fluorescei n, permeability values of the blood-retinal barrier to fluorescein were obt ained from 1512 regions measuring 75 x 75 mu m, from a total 3150 x 2700-mu m area of the fundus, generating a detailed map of retinal fluorescein lea kage. The method was assessed in vitro and in 7 healthy subjects who underw ent scans during separate visits. Depth resolution and influence of chorior etinal fluorescence were further tested in 2 patients with multiple drusen and in 2 eyes after vitrectomy. Fourteen eyes from 7 patients with diabetes and nonproliferative retinopathy were also examined. Lateral resolution wa s tested in 3 diabetic eyes that underwent focal photocoagulation. Four eye s from 2 patients with diabetes and minimal retinopathy were examined at 3- month intervals. All eyes examined had less than 2 diopters of astigmatism. Results: Characteristics of the modified confocal scanning laser fluoromete r included a lower limit of detection equal to 0.40 Eq ng/mL and depth prec ision of +/-15 pm. Values for the blood-retinal barrier permeability index in healthy subjects, measured 30 minutes after a single intravenous pulse o f fluorescein (14 mg/kg), ranged from 1.3 +/- 0.4 x 10(-6) cm/s over the fo veal avascular zone to 2.2 +/- 0.6 x 10(-6) cm/s over vessels in the retina . Diabetic eyes with retinopathy showed higher values, ranging from 1.4 to 15.0 x 10(-6) cm/s. Vitrectomized eyes and eyes with multiple drusen showed the validity of the correction algorithm demonstrating that measurements o f fluorescence in the vitreous are not influenced by the chorioretinal fluo rescence level. Argon laser photocoagulation burns placed in the diabetic r etina demonstrated a lateral resolution on the order of 75 to 100 mu m. Int ravisit and intervisit reproducibility was +/-10.2% and +/-13%, respectivel y. Conclusions: This new method measures localized alterations of the blood-re tinal barrier and allows for direct correlation with retinal anatomy. Its m ost interesting feature is the ability to map retinal fluorescein leakage w hile simultaneously imaging the retina. This capability is expected to impr ove our understanding and management of retinal disease.