Controlled injection pressure prevents damage during subretinal injections in pigs

Abstract

Purpose : Injections into the subretinal space with manual controlled injection pressure has previously shown to damage the retinal pigment epithelium (RPE) and outer neuro-retina. We hypothesized that machine controlled injection pressure prevents damage and provides a safe delivery to the subretinal space. Flow rate was investigated at different injection pressures, in order to determine safe and efficient delivery of subretinal treatment.

Methods : In full anesthesia, 12 pigs were vitrectomized and received a vitrector controlled, subretinal injection through a 41G cannula. Preliminary measurements determined that the flow in a 41 G cannula shifts from laminar to tubular at 32 psi (pounds per square inch), and that the manual controlled flow is tubular and erratic. Four subretinal injections of 300 microliters were machine controlled and injected at 14, 24, and 32 psi (96.5, 165.5, and 220.5 kPa). Prior to surgery (baseline) and two and four weeks after surgery, the animals were examined by multifocal electroretinogram (mfERG), fundus photographs, and optical coherence tomography (OCT). At the final evaluation, the animals were enucleated for histological examination. A multivariable test was used for statistical analysis.

Results : Only minor histopathological changes were found in the RPE and photoreceptors. In both the 24 and 32 psi group, two out of four pigs developed a retinal fold affecting the histology of the inner retinal layers. No significant differences in retinal histology or function measured with mfERG were observed between the three different psi-groups.

Conclusions : A vitrector-controlled system with injection pressure lower than 32 psi provides a safe delivery to the subretinal space. Machine controlled injections have a significant lower flow rate than manual injections and are easier to control. Large amount of fluid injected into the subretinal space may create lasting retinal folds.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.