Miosis during ocular surgery—particularly cataract procedures—poses significant surgical challenges. Intraoperative miosis refers to the constriction of the pupil that can occur during surgery despite initial pharmacologic dilation. It restricts visibility and access to intraocular structures, increasing the risk of complications such as capsular rupture, vitreous loss, and increased operative time.
The primary mechanism involves the release of inflammatory mediators such as prostaglandins in response to surgical trauma. These mediators stimulate the iris sphincter muscle, overcoming the mydriatic effects of preoperative dilation drops.
Risk Factors for Ocular Surgery-Induced Miosis
Identifying at-risk patients is essential for implementing appropriate preventive strategies. Key risk factors include:
- Pediatric or young adult patients (stronger iris tone)
- Diabetes mellitus
- History of intraocular inflammation (uveitis)
- Use of systemic alpha-1 antagonists (e.g., tamsulosin)
- Intraoperative manipulation and longer surgical duration
- Small preoperative pupil diameter
- Pseudoexfoliation syndrome
Preoperative Pharmacologic Strategies to Maintain Mydriasis
Topical Mydriatic Agents
Preoperative dilation traditionally involves a combination of:
- Tropicamide (anticholinergic)
- Phenylephrine (sympathomimetic)
These agents are often used in combination to provide both sphincter paralysis and dilator stimulation.
Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)
Topical NSAIDs such as ketorolac, bromfenac, or nepafenac are administered preoperatively to inhibit prostaglandin synthesis and reduce the risk of miosis.
Administration Protocol:
- Initiate NSAIDs 1 day prior to surgery
- Continue dosing every 6–8 hours as directed until the time of surgery
NSAIDs have been shown to significantly reduce the incidence of intraoperative miosis and postoperative inflammation.
Intraoperative Techniques and Intracameral Agents
Intracameral Phenylephrine and Ketorolac (Omidria®)
This FDA-approved solution combines:
- Phenylephrine 1.0%: contracts the dilator pupillae
- Ketorolac 0.3%: suppresses intraoperative prostaglandin release
Administered directly into the anterior chamber via the irrigation solution, Omidria maintains pupil size and reduces postoperative pain and inflammation.
Mydriatic Rings and Iris Hooks
Mechanical dilation aids include:
- Malyugin ring: A flexible ring inserted through a corneal incision to maintain pupil expansion
- Iris retractors/hooks: Physically retract the iris in small-pupil situations
These devices are indicated when pharmacologic agents fail or in patients with fixed small pupils.
Surgical Considerations to Minimize Inflammation
Gentle Tissue Handling
Minimizing mechanical trauma to the iris and surrounding tissues reduces prostaglandin release. Techniques include:
- Controlled capsulorhexis
- Low-flow phacoemulsification
- Minimized iris manipulation
Shorter Surgical Time
Efficient technique reduces the duration of exposure to inflammatory stimuli and decreases the likelihood of miosis onset.
Postoperative Considerations
Even after successful pupil management intraoperatively, postoperative monitoring is critical. Continuation of NSAIDs post-surgery reduces the risk of rebound inflammation and cystoid macular edema, particularly in diabetic or high-risk patients.
Postoperative Medication Protocol:
- Topical NSAID for 2–4 weeks
- Topical corticosteroids to suppress residual inflammation
Emerging Therapies and Research Directions
Innovations in sustained-release NSAID delivery and novel mydriatic formulations aim to reduce reliance on manual techniques and extend the duration of pharmacologic effects. Gene expression studies targeting COX pathways in the iris may lead to individualized anti-miosis therapy in the future.
Preventing ocular surgery-induced miosis is essential to ensure procedural safety, efficiency, and visual outcomes. A proactive approach combining topical NSAIDs, preoperative mydriatics, intracameral agents, and mechanical devices—when necessary—provides a robust defense against intraoperative pupil constriction. By tailoring strategies based on patient risk factors and surgical context, we can maintain optimal mydriasis and elevate the standard of ophthalmic surgical care.
