Distribution of Aqueous Solutions Injected Suprachoroidally (SC) in Rabbits

Abstract

Purpose : We previously reported the effect of endothelin-1 (ET-1) on choroidal blood flow (ChBF) when injected suprachoroidally in 11 rabbits (ARVO 2019, #1637). As measured by non-recirculating microspheres, reduction in ChBF did not occur evenly throughout the eyes. We wanted to determine if this was due to variable concentration of the ET-1 or incomplete coverage by the initial SC injections. We also wanted to know if single or double injections provided better distribution as well as the effect, if any, of intraocular pressure on distribution.

Methods : To visualize the distribution of injected aqueous solutions directly, we chose to use New Zealand White rabbits (albinos) and 0.1% sodium fluorescein mixed with balanced salt solution (BSS). For the SC injections, 34 gauge needles with a stop permitting exposure of 700 µm of the needle tip were used. A single injection of 50 µL was given 5 mm posterior to the corneal limbus in the superotemporal quadrant. The fundus was then imaged with a Topcon camera with barrier and excitation filters appropriate for fluorescein. The fundus was also imaged with a Heidelberg scanning laser ophthalmoscope (SLO) using a 488 nm laser. A second injection was then done in the inferonasal quadrant in a similar manner. Prior to the SC injections, the intraocular pressure (IOP) was adjusted to 30 mmHg in the right eye by injecting BSS into the vitreous. The IOP in the left eye was lowered to 10 mmHg by manually pressing on the globe. To confirm that the observed fluorescence was not immediately transient, another set of rabbits were injected SC with 50 µl of a viral like particle (VLP) conjugated with Alexa Fluor 488, (which serves as an surrogate (analog) for Aura Biosciences AU-011, viral VLP conjugated with IRDye® 700DX) and imaged at 30 minutes and 24 hours post-dose with a Heidelberg SLO.

Results : As with the ET-1 study, the distribution of all single injections was incomplete although the coverage was greater at the 10 mmHg than the 30 mmHg IOP. Most of the unlabeled portions of the choroid was successfully labeled after the second injection. 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 : Incomplete distribution of SC injected aqueous solutions in the rabbit eye is somewhat dependent on IOP but can be improved by a second injection in the opposite quadrant regardless of the IOP.

This is a 2020 ARVO Annual Meeting abstract.