Histochemical interpretation of fluorescein angiogram

Summary

The characteristics of the localization of fluorescein in the iris, ciliary body and retina were studied in the monkey eye by the whole mount preparation and paraffin section methods. By incident light fluorescence microscopy and transparent fluorescence microscopy the penetration of free fluorescein into the outer retinal layer as well as into of the nonpigmented epithelium of the ciliary body is noted. The site of the permeability barrier for protein-bound fluorescein is postulated in the pigment epithelium and the ciliary epithelium. From the anatomical and embryological points of view, the two kinds of epithelium may have the same tendency as to the permeability of fluorescein.

The whole mount preparation of the posterior pole is fairly well reminiscent of the fluorescein angiogram and can demonstrate the superficial reticular, radial epipapillary, radial peripapillary and retinal capillaries. In addition to the capillary nets and typical background fluorescence, dark cracks are recognized in the retina, suggesting that the choroidal fluorescence is not responsible for background fluorescence.

Cross sections of the macula indicate that the blood-retinal barrier in the macula is highly restrictive against the inward penetration of the dye in contrast to other sites. The result is quite compatible with the assumption that the poor penetrance is one of the major contributors of the macular dark spot.