Iridotomy Requirement with Vitrectomy and Silicone Oil Placement
An iridotomy (peripheral iridectomy) is strongly recommended but not universally required with vitrectomy and silicone oil placement; the decision depends on lens status, with aphakic and pseudophakic eyes having the highest risk of pupillary block and requiring prophylactic iridotomy in most cases.
Risk-Based Approach to Iridotomy
High-Risk Situations Requiring Iridotomy
Aphakic eyes undergoing silicone oil tamponade should routinely receive an inferior peripheral iridectomy to prevent pupillary block glaucoma 1, 2. The American Academy of Ophthalmology guidelines identify silicone oil with forward displacement of the lens-iris diaphragm as a posterior pushing mechanism causing secondary angle closure 1.
- In aphakic patients, silicone oil can migrate anteriorly and cause pupillary block, leading to acute angle closure and severe intraocular pressure elevation 2, 3
- Historical surgical series performing routine inferior iridectomy in all aphakic eyes demonstrated a positive impact with low incidence of secondary glaucoma (6%) 2
- Case reports document acute glaucoma from silicone-induced pupillary block that required laser iridectomy for treatment 3
Intermediate-Risk Situations
Pseudophakic eyes have lower but still significant risk, with silicone oil entering the anterior chamber in 6% of phakic and pseudophakic eyes 2. Consider prophylactic iridotomy based on:
- IOL position and stability
- Anterior chamber depth
- History of angle closure disease
- Expected duration of silicone oil tamponade (>6 months increases risk) 4
Lower-Risk Situations
Phakic eyes have the lowest risk of pupillary block from silicone oil, as the intact crystalline lens provides a natural barrier preventing anterior migration 2, 3. However, these eyes universally develop cataracts requiring subsequent surgery, which changes the risk profile 1.
Mechanism and Pathophysiology
The pupillary block mechanism with silicone oil differs from primary angle closure:
- Silicone oil acts as a posterior pushing force, displacing the lens-iris diaphragm anteriorly 1
- Unlike primary pupillary block where aqueous cannot flow from posterior to anterior chamber, silicone oil physically blocks the pupil 1, 5
- Parasympathomimetic (miotic) treatment is ineffective when silicone oil or the IOL is blocking the pupil; mydriatics may be more effective in these secondary cases 1
Surgical Technique Considerations
When performing iridotomy with silicone oil surgery:
- Inferior peripheral iridectomy is the preferred location to allow aqueous flow while preventing silicone oil migration through the iridotomy 2
- The iridectomy must be adequate size, as closure of the inferior iridectomy occurred in 6% of cases in one large series 2
- If iridectomy becomes occluded with fibrous tissue postoperatively, Nd:YAG laser iridotomy or surgical revision may be required 5
Postoperative Complications
Even with prophylactic iridotomy, monitor for:
- Intraocular pressure changes occur frequently during silicone oil endotamponade and after removal, especially in the early postoperative period 4
- A 2022 meta-analysis found significantly higher rates of intraocular hypertension with silicone oil compared to other tamponade agents (OR = 1.66, p = 0.0002) 6
- Glaucoma developed in 6% of patients in a large consecutive series despite routine inferior iridectomy in aphakic eyes 2
Critical Pitfalls to Avoid
- Do not assume a patent iridotomy will remain patent—fibrous tissue can occlude the opening, requiring intervention 5
- Do not rely on miotics to break pupillary block when silicone oil is the cause; these are ineffective and mydriatics may be more appropriate 1
- In cases refractory to Nd:YAG laser iridotomy, consider 30-gauge needle transfixion technique to restore aqueous flow 5
- Inadequate sclerotomy closure is a common cause of hypotony; meticulous closure with mattress sutures using long scleral passes is essential 7