Mechanisms of Gas-Induced Posterior Vitreous Detachment: A Look Behind the Bubble Using Optical Coherence Tomography in Prone Position

<b>Objectives:</b> We aimed to visualize the interaction of intravitreal gas with the adjacent vitreomacular interface by using prone position (PP) SD-OCT and suggest possible mechanisms of action behind gas-induced posterior vitreous detachment (PVD) in pneumatic vitreolysis (PV). <b>Methods:</b> This was a descriptive-interpretative morphological study. Spectral domain OCT imaging in PP was carried out using a flexible scanning module (SD-OCT-Flex, Heidelberg Engineering) originally designed for bedside imaging. Routine imaging in sitting position was carried out using a regular SD-OCT-device (Heidelberg Engineering). Patients with symptomatic vitreomacular traction (VMT) scheduled for PV with perfluoropropane (C3F8, 0.3 mL) received both sitting and PP imaging immediately before and at regular follow-up visits during the first 3 post-procedural weeks, beginning 3 h after PV. Imaging was reviewed for positional changes of the gas bubble, posterior hyaloid membrane (PHM), VMT configuration, and retrohyaloidal fluid (RHF). <b>Results:</b> Three consecutive patients with VMT were included (age: 79, 80, 82 years). Before the procedure, no positional alterations were detected. After the intravitreal injection of gas, PP allowed for the precise discrimination of the PHM and the posterior border of the gas bubble. In contrast to regular SD-OCT in sitting position, PP imaging showed a flattened VMT by the gas bubble with consecutive displacement of RHF from the macular region to the midperiphery. <b>Conclusions:</b> This exploratory study describes PP imaging as a tool for the assessment of the morphologic dynamics between the posterior hyaloid membrane, retina, and gas bubble in pneumatic vitreolysis. PP in pneumatic vitreolysis causes the gas bubble to flatten the VMT and to push retrohyaloidal fluid to the midperiphery, possibly allowing for the release of persistent vitreoretinal adhesions and consequent PVD induction.