Effect of intraocular pressure (IOP), volume and location on the distribution of aqueous solutions injected into the suprachoroidal (SC) space

Abstract

Purpose : We previously reported variable distribution of endothelin-1 effects on choroidal blood flow when injected suprachoroidally (ARVO 2019, #1637). We wanted to determine if this was due differences in IOP at the time of injection. We also wanted to know if a larger volume or splitting the same volume in opposite quadrant injections provided more complete distribution.

Methods : For the SC injections, 34-gauge needles with a stop exposing 700 µm of the needle tip were used. New Zealand White rabbits were injected with 0.0074% indocyanine green (ICG) in balanced salt solution. A single injection of 50 µL was given 5 mm posterior to the corneal limbus in the superotemporal quadrant. The fundus was imaged with a Heidelberg scanning laser ophthalmoscope. The IOP was adjusted to 10 mmHg in one eye and either 35 mmHg or 55 mmHg in the fellow eye manometrically. Six rabbits with a crossover design were used for the 35 mmHg study and three rabbits for the 55 mmHg study. The distribution of ICG in the inferonasal quadrant was measured. In a separate study, two 50 µl injections with ICG and 0.1% fluorescein in opposing quadrants assessed coverage. Single injections of 100 µL were also done. To confirm that the observed fluorescence was not immediately transient, another set of rabbits were injected SC with 50 µL of a virus like particle (VLP) derived from HPV16 conjugated with Alexa Fluor 488 and imaged at 30 minutes and 24 hours post-dose.

Results : IOP did not significantly affect the distribution of ICG given as a single superotemporal SC injection. A single injection of 100 µL had better but still incomplete coverage than 50 µL. Two injections of 50 µL each (one of ICG and one of fluorescein) in opposite quadrants provided nearly complete SC coverage although some overlap and small gaps were present. Labeling with VLP*Alexa Fluor 488 was also incomplete following 50 µL injections and there was no change in the labeling pattern after 24 hours.

Conclusions : Distribution of aqueous solution SC injection is not dependent on IOP but on injection parameters including volume, number, and location of injections. A 100 µL single injection provides improved coverage compared to 50 µL and there is further improvement when two injections are administered in opposite quadrants of 50 µL each.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.