What causes raised intraocular pressure (IOP) after pneumatic retinopexy with cryotherapy?

Raised Intraocular Pressure After Pneumatic Retinopexy with Cryotherapy

The primary cause of raised IOP after pneumatic retinopexy is gas bubble expansion, which occurs immediately after injection and can be exacerbated by changes in atmospheric pressure, particularly at higher altitudes or during air travel. 1, 2

Immediate Post-Injection IOP Elevation

The most common mechanism is the immediate rise in IOP following gas injection, which occurs in all patients undergoing pneumatic retinopexy:

• All eyes experience an immediate IOP spike after the 0.3 ml perfluoropropane (C3F8) gas injection, with some cases showing complete absence of central retinal artery perfusion for up to 3 minutes due to the acute pressure rise 2
• This initial pressure elevation typically resolves within 30-60 minutes after gas injection 2
• The acute IOP rise is mechanical in nature, caused by the volume of gas injected into a closed space 2

Gas Expansion-Related IOP Elevation

Expansile gas concentrations are a significant risk factor for sustained IOP elevation:

• Elevated IOP (>25 mm Hg) occurs in approximately 43% of eyes after vitreoretinal surgery with intraocular gas 3
• Expansile gas concentrations and use of C3F8 are independently associated with increased risk of postoperative IOP elevation (P < 0.001 and P = 0.01, respectively) 3
• Most IOP elevations (88%) occur within the first 24 hours and respond to aqueous suppression therapy within 24-72 hours 3

Altitude and Atmospheric Pressure Changes

Gas bubble expansion at higher altitudes represents a critical mechanism for dangerous IOP elevation:

• Driving to or ascending to altitudes more than 1000 feet above the surgical site can cause gas expansion and increased IOP, potentially resulting in arterial occlusion, wound dehiscence, or gas leakage 1
• Air travel is absolutely contraindicated until complete gas absorption occurs (typically 2-6 weeks for SF6 or C3F8) 1
• A documented case showed central retinal artery occlusion when a patient flew 2 weeks post-procedure, with the gas bubble expanding at cruise altitude (8000 ft cabin pressure), causing IOP to exceed central artery perfusion pressure 4
• Lower atmospheric pressure causes gas expansion according to Boyle's Law, which can persist for weeks to months depending on the gas type used 4

Anesthetic Agent Interaction

Nitrous oxide use represents an iatrogenic cause of dangerous IOP elevation:

• The use of nitrous oxide anesthesia in patients with intraocular gas may result in a dangerous rise in IOP 1
• Patients should wear a wristband warning that their eye contains intraocular gas and that nitrous oxide must be avoided 1

Additional Risk Factors

Several patient and procedural factors increase the risk of IOP elevation:

• Increasing patient age is significantly associated with postoperative IOP elevation (P < 0.001) 3
• Circumferential scleral buckles increase the risk of elevated IOP (P = 0.04) 3
• Eyes with pre-existing glaucoma or compromised optic nerves are at higher risk for pressure-related complications 3

Clinical Management Implications

Routine IOP-lowering medication is not indicated for uncomplicated pneumatic retinopexy:

• Once the initial IOP spike resolves (30-60 minutes post-injection), routine prophylactic IOP-lowering medication is not necessary during the subsequent 5-day period 2
• However, prophylactic treatment should be considered in high-risk eyes (advanced glaucoma, elderly patients, or when using expansile gas concentrations) 3
• IOP measurement should be performed at 1-2 days postoperatively and again at 1-2 weeks as part of routine follow-up 1

Critical Pitfalls to Avoid

• Failure to warn patients about altitude restrictions can result in catastrophic vision loss from central retinal artery occlusion 1, 4
• Patients must avoid air travel and ascending to altitudes >1000 feet above the surgical site until complete gas absorption 1
• Anesthesiologists must be informed about intraocular gas presence to avoid nitrous oxide use 1
• The duration of gas persistence varies: SF6 typically lasts 2-3 weeks, while C3F8 can persist for 6-8 weeks 1