Controlled Subretinal Injection Pressure Prevents Damage in Pigs

Abstract

Introduction Administration of retinal gene- and stem cell therapy in patients with retinal degenerative diseases (RDD) is in many cases dependent of a subretinal approach. It has been indicated that manual subretinal injection is associated with outer retinal damage, which may be explained be high flow rate in the injection cannula. In the present porcine study, we evaluated flow-related retinal damage after controlled subretinal injection at different flow rates. Methods Flow rate through a 41G cannula was estimated at different injection pressures (6-48 PSI (pounds per square inch)) in an in-vitro setup. A linear correlation between flow rate and injection pressure was found from 6-32 PSI. In full anesthesia, 12 pigs were vitrectomized and received a controlled subretinal injection of 300 microliters balanced saline solution at injection pressures of either 14, 24 and 32 PSI (four in each group). Prior to surgery and two and four weeks after surgery, the eyes where examined by multifocal electroretinogram (mfERG) and fundus photographs. At the end of follow-up, the eyes were enucleated for histology. Results The in vitro flow study determined that the flow in a 41 G cannula shift from laminar to tubular at 32 PSI, and that the manual injection flow is tubular. In the porcine study we showed a significant difference in retinal pigment epithelium (RPE) damage between the three pressure groups (p = 0.0096). There was no significant difference in damage to the outer retina (p = 0.1526), but the high-pressure group (32 PSI) had most outer retinal damage. The middle-pressure group (24 PSI) showed minimum retinal damage. There was no significant change in the mfERG ratios during follow-up. Discussion/Conclusion This study indicates that an injection pressure at approximately 24 PSI might be safe for subretinal delievery. Retinal damage at low injection pressures may be explained by mechanical damage to the RPE due to prolonged needle time in the subretinal space, whilst retinal damage at high pressures can be related to high flow in the injection cannula. Controlled subretinal injection pressure of 24 PSI showed minimum mechanical and flow-related damage to the porcine retina.

Dose-Dependent Progression of Chorioretinal Atrophy at the Injection Site After Subretinal Injection of rAAV2/8 in Nonhuman Primates

“… 3 , 13 Increased injection pressures have been known to cause atrophy at the injection site in both monkeys 14 and pigs. 15 , 16 Therefore, many gene therapy treatment centers try to minimize injection pressures through the use of injection systems with pneumatic-assisted foot pedals. 17 Although spontaneous enlargement of mechanical RPE defects is not unheard of (e.g., in myopes), this type of mechanical atrophy would be presumed to be mostly stationary or self-limiting 14 rather than progressive and be present in both sham and AAV-treated groups.…”

The Role of Subretinal Injection in Ophthalmic Surgery: Therapeutic Agent Delivery and Other Indications

“…The identification of the optimal injection pressure is crucial for the safety of this technique as both low and high injection pressure may be associated with mechanical RPE/retinal damage due to a prolonged permanence of the needle in the subretinal space and the high flow generated, respectively [ 22 ]. In this regard, a recent study on porcine eyes in vivo reported that injection pressure up to 24 psi might be safe, resulting in minimal retinal damage and no functional changes on the multifocal electroretinogram [ 22 ]. To note, the injection pressure to initiate the bleb formation is higher than that required for the bleb propagation [ 21 ].…”

Liquid-Driven Microinjection System for Precise Fundus Injection

“…For CRAO/CRVO or submacular hemorrhage caused by AMD, the intra-vascular injection of tissue plasminogen activator solution (tPA) or subretinal injection of air and tPA has emerged as a new therapeutic approach [5,6]. Subretinal drug delivery involves directly injecting the drug into the subretinal space, allowing the drug to directly act on the retina and retinal pigment epithelium (RPE) [7]. For intra-vascular injection in retinal artery cannulation and retinal vein cannulation, the surgeons inject thrombolytic drugs into the occluded retinal arteries or veins to lyse the thrombus, thereby restoring blood circulation to the retinal vessels [8,9].…”