Fig. 3.13  The fluorescein from either a suprachoroidal (top row) or intravitreal injection (bottom row) must diffuse (left column at 0 h, middle column at 1 h, and right column at 4 h) to the central vitreous before the fluorophotometer can measure the fluorescence)

to as tailing. After 4 h, fluorescein has diffused out of the retina and into the vitreous. As the vitreous fluorescein reaches the optical axis of the eye, the fluorophotometer scan measures an increase in the vitreous fluorescein (Fig. 3.13, top row, right column). The cornea, aqueous humor, and lens fluorescence have not increased.

3.6  Retrobulbar Fluorescein Injection

A series of rabbits received retrobulbar injections to demonstrate the fluorescein distribution in the eye. The retrobulbar injection of sodium fluorescein (100 mL of 25 mg/mL) was through the lower eyelid of NZW rabbits with 3–4 kg body weight. Care was taken to avoid penetrating the globe and the conjunctiva. The Fluorotron Master fluorophotometer (OcuMetrics, Mountain View, CA) with the standard objective lens was used to scan the fluorescence through the entire globe to measure tissue fluorescence (ng/mL).

Eight minutes after the retrobulbar injection of fluorescein, the cornea and retinal florescence increased significantly. Relative to the autofluorescence in Fig. 3.14a,

Fig. 3.14  The natural fluorescence of the ocular tissue of the rabbit is <6 ng/mL (a). The midvitreous value (4 ng/mL) was considered to be located 37% from the retina to the cornea/aqueous peak. Eight minutes after the retrobulbar injection of fluorescein, the ocular fluorescence is greatly increased (b). The corneal peak value is 230 ng/mL and the retinal peak is 254 ng/mL

the retinal fluorescein increased may be attributed to a vascular increase in fluorescein­ (Fig. 3.14b). The corneal increase may be caused by fluorescein leaking from the injection site or the conjunctival vessels into the tear film.

The fluorophotometer scans taken from the same unanesthetized rabbit 30 min postretrobulbar injection shows a continual rise in retinal fluorescence with tailing into the

Fig. 3.15  (a) Captured at 30 min postretrobulbar injection. (b) Captured at 90 min postretrobulbar injection. The aqueous humor peak has been masked by the large retinal fluorescence

vitreous­ (Fig. 3.15a). The corneal did not have the same relative increase in fluorescence. There is a slight increase in aqueous humor fluorescence, which is the secondary peak adjacent to the corneal peak. By 90-min postretrobulbar injection, the tailing curve from the large retinal fluorescence peak has masked the aqueous humor peak (Fig. 3.15b).

Fig. 3.16  (a) Captured at 180 min postretrobulbar injection and (b) was captured at 420 min postretrobulbar injection

The character of the retinal, vitreous, and aqueous fluorescence curves have not changed, but only their magnitude at 180 min following the retrobulbar injection (Fig. 3.16a). By 420 min postinjection (Fig. 3.16b), the magnitude of the ocular fluorescence has decreased sufficiently to observe normal lens fluorescence, but the vitreous retained the fluorescein. There is still an above-baseline fluorescence in the aqueous humor.

Fig. 3.18  The euthanized rabbit has received a retrobulbar injection of sodium fluorescein (a). The contralateral eye did not receive a retrobulbar injection (b). The baseline values for cornea, vitreous, and retina are indicated by dashed lines (n = 5, mean ± standard deviation)

effect of vascular circulation on the uptake and release of a retrobulbar fluorescein injection, a series of euthanized rabbits (in situ) received retrobulbar injections (Fig. 3.18). The retrobulbar fluorescein injection concentration was 100 mL of 25 mg/mL. The mid-vitreous values were defined as the fluorescence value is 37% from the retina to the corneal aqueous peak: