Unilateral Watery Eye After Interscalene Block
A unilateral watery eye (epiphora) following interscalene brachial plexus block is caused by ipsilateral Horner's syndrome, which results from blockade of the sympathetic cervical chain (stellate ganglion) by local anesthetic spread—this occurs in 100% of interscalene blocks and is a benign, self-limited side effect that resolves completely as the block wears off. 1
Mechanism and Clinical Features
The interscalene approach to brachial plexus blockade invariably produces sympathetic blockade due to the anatomical proximity of the stellate ganglion to the injection site. 1, 2 This sympathetic paralysis manifests as the classic Horner's syndrome triad:
- Ptosis (drooping eyelid)
- Miosis (constricted pupil)
- Anhidrosis (decreased sweating on the ipsilateral face)
The watery eye specifically results from loss of sympathetic tone to the lacrimal drainage system, causing impaired tear drainage through the nasolacrimal duct and overflow tearing (epiphora). 1 Additional sympathetic blockade effects include increased skin temperature, cutaneous vasodilation, and attenuated vasoconstrictor reflexes on the blocked side. 2
Timeline and Resolution
- Onset: Horner's syndrome typically appears 30-40 minutes after block placement 1
- Duration: Complete resolution occurs within 2-3 hours as the local anesthetic effect dissipates 1
- No sequelae: This is a transient phenomenon with no lasting clinical consequences 1
Clinical Significance and Patient Management
This is an expected side effect, not a complication. The key clinical actions are:
- Reassure the patient that this is normal and will resolve completely 1
- Monitor closely during the symptomatic period 1
- Document the finding as an expected consequence of successful interscalene blockade
- No treatment is required—the syndrome resolves spontaneously as the block wears off 1
Important Distinction from Complications
The watery eye from Horner's syndrome should not be confused with:
- Post-viral dry eye syndrome, which presents with weeks of conjunctival injection followed by painful dry eye symptoms 3
- Bacterial or viral conjunctivitis, which typically features discharge (purulent or watery), bilateral involvement, and photophobia 4
- Anesthetic myotoxicity, which causes diplopia (double vision) rather than tearing and may persist for up to 6 months 5, 6
Anatomical Context
The interscalene block preferentially affects the cephalad portions of the brachial plexus and caudad portions of the cervical plexus. 7 The stellate ganglion lies in close proximity to this injection site, making sympathetic blockade anatomically inevitable regardless of technique modifications. 1, 2 Even reducing local anesthetic volume to 20 mL (versus 40 mL) does not prevent cervical sympathetic spread. 8
The presence of Horner's syndrome with watery eye actually confirms successful block placement near the brachial plexus at the interscalene level. 1, 2