Residual Nonemulsified SO

• Role of Silicone Oil (SO) in Vitreoretinal Surgery:
• SO is commonly used as a tamponade in vitreoretinal surgery to manage complex retinal detachments.
• Postoperative emulsification of SO is a significant complication, leading to issues like glaucoma, keratopathy, and inflammation due to emulsified droplets in the anterior chamber, retina, or optic nerve.

• Residual Nonemulsified SO and Emulsification:
• Residual nonemulsified SO persists after conventional removal techniques (e.g., repeated fluid-air exchange [FAX] and passive drainage [PD]), contributing to postoperative emulsification.
• Residual nonemulsified SO ranges from 2.75 to 24.71 μL, with no significant difference between PD and repeated FAX or between 1,000 cSt and 5,000 cSt SO viscosities (P>0.05).
• Residual nonemulsified SO forms a floating slick at the air/balanced salt solution (BSS) interface due to buoyancy, which is resistant to aspiration due to high viscosity.

• Mechanisms of SO Emulsification:
• Emulsification is driven by saccadic eye movements, shear stress from BSS infusion, and biosurfactants (e.g., proteins) that lower interfacial tension at the SO/BSS interface.
• BSS infusion during repeated FAX (even at low flow rates of 5 mL/min) generates small SO droplets due to interface fluctuations, enhancing emulsification.
• Residual SO adheres to the retina, and shear stress from BSS flow deforms the SO/BSS/retina contact line, forming emulsified droplets (1–2 μm in size).

• Conventional SO Removal Techniques:
• Repeated FAX (Triple-FAX) involves alternating air and BSS to remove residual SO, with the aspiration probe ideally at the SO/BSS interface; however, it is ineffective for nonemulsified SO slick removal.
• Passive drainage (PD) involves prolonged BSS extrusion for 15 minutes but also fails to eliminate residual nonemulsified SO.
• Challenges in SO removal: High SO viscosity, adhesion to ocular surfaces, and small-gauge probes (e.g., 25-gauge) limit complete removal, leaving residual SO in surgically inaccessible areas.

• Study Methods and Findings:
• In vitro model: Simulated SO slick removal using a 25-gauge probe at three aspiration positions (within SO, at SO/BSS interface, within BSS) showed no effective removal of nonemulsified SO (P>0.05), with BSS infusion causing droplet formation.
• Ex vivo porcine eye model: Quantified residual nonemulsified SO (2.75–24.71 μL) using Fourier-transform infrared spectroscopy (FTIR) after standard 23-gauge vitrectomy, confirming persistence of both nonemulsified and emulsified SO.
• FTIR quantification: Used Si-O-Si bond absorption (1,000–1,100 cm⁻¹) to measure residual SO dissolved in dichloromethane, avoiding contamination from syringe lubricants.

• Clinical Implications:
• Residual nonemulsified SO is a source of postoperative emulsification, potentially forming 0.66–5.93 × 10⁹ emulsified droplets, leading to complications.
• Preoperative emulsification incidence is low (~5%), but postoperative detection rises to 13–24%, partly due to residual nonemulsified SO.
• Current techniques are limited by poor visualization during FAX (air flux blurs the surgical field) and SO adhesion to the retina, necessitating optimized removal strategies.

• Limitations and Future Directions:
• Study used in vitro and ex vivo models, requiring in vivo validation.
• Did not explore underlying causes of emulsification beyond BSS infusion and adhesion.
• Future improvements: Develop alternative removal techniques, optimize BSS flow rates, and enhance visualization to minimize residual SO and emulsification-related complications.
Citation
Chen Y, Li KKW, Steel DH, Chan YK. Residual Silicone Oil Does Appear After Conventional Removal and Contributes to Postoperative Emulsification. *Retina*. 2025;45(4):630-638. doi:10.1097/IAE.0000000000004091.