Fluorescein in the human optic disc,

1. Compressing the globe to intraocular pressure values even higher than the systolic ophthalmica pressure does not totally empty the capillaries of the disc. 2. Almost only the plasma layer at the wall of the retinal and papillary vessels is the source of vessel fluorescence seen after intravenous fluorescein injection. Therefore small vessels fluoresce almost as much as big ones and extravasates appear as very brilliant patches. 3. Fluorescein diffuses into the disc tissue mostly from the surrounding tissues (uvea, ev. sclera). 4. The blood circulation in the disc diminishes more than that of the retinal vessels if the eye is compressed, 5. Fluorescein is not especially appropriate for the measurement of the circulation in the disc.