Laboratory-made Needle for Suprachoroidal Injections in Living Animals and Human Eye Bank Eyes

Abstract

Purpose : Suprachoroidal (SC) administration of pharmaceuticals is a relatively new route of ocular drug delivery. Triamcinolone acetonide has now been approved for the treatment of uveitic macular edema. However, it must be dosed using a proprietary injector system that is not generally available for pre-clinical drug development. Here we describe a simple lab-based protocol for fabricating SC needles for use in ex vivo and in vivo preclinical studies.

Methods : To make the SC needles, 0.2 x 0.9 mm (STERiJECT^TM TSK, Japan, approx. 34 ga) with a sharp tip beveled at 12.5^o were used. A 25 ga microvitrectomy cannula (Alcon^TM valved entry system, 5 mm long) was slid over the 34 ga needle such that the plastic (colored) valved end was distal to the tip of the needle. The metal end of the microvitrectomy cannula was adjusted to leave either 700 µm or 900 µm of the 34 ga needle tip exposed. Epoxy resin was then applied connecting the plastic valved end of the microvitrectomy cannula to the hub of the 34 ga needle (Figure 1). The SC needles were used to inject 50-100 µl of either sodium fluorescein (0.1%), indocyanine green (0.0074%), or 1.0 µm fluorescent (645 nm) polystyrene microspheres. Anesthetized New Zealand white rabbits, rhesus, and cynomolgus monkeys were injected 4 to 6 mm posterior to the corneal limbus superotemporally and/or inferonasally. We also injected enucleated pig eyes and a human eye. After SC injection, the cadaveric eyes were fixed in 4% paraformaldehyde and opened 4 mm posterior to the cornea. Potassium permanganate and oxalic acid were used to bleach the ocular melanin. Six radial cuts allowed the eyes to be flattened between two microscope slides. They were imaged with an epifluorescence microscope with a motorized stage and image stitching software.

Results : We have now done approximately 40 in vivo rabbit (ARVO 2022, #4152), and 40 monkey (rhesus or cynomolgus) ocular injections. There were only 2 or 3 occasions during which the SC needle needed to be slightly repositioned. There were no instances of inadvertent intravitreal injection.

Conclusions : Although not appropriate for clinical studies, laboratory-made SC needles are reliable, cost-effective, and convenient for use in pre-clinical drug development studies.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

SC needle with 700 µm of the exposed 34 ga tip pointing downward.

 

Human eye following SC injection (asterisk) of microspheres and melanin bleaching.