Comparing Blind and Ultrasound-Guided Retrobulbar Nerve Blocks in Equine Cadavers: The Training Effect.
Authors: Hermans Hanneke, Lloyd-Edwards Ralph A, Ferrão-van Sommeren Aukje J H, Tersmette Anne A, Schouten Jacobine C M, Serra Bragança Filipe M, van Loon Johannes P A M
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Retrobulbar nerve blocks remain a cornerstone of standing ophthalmic surgery in horses, yet debate persists about whether blind placement or ultrasound guidance offers superior safety and efficacy. Hermans and colleagues conducted a cadaveric study with two inexperienced operators performing retrobulbar injections across three groups: blind technique (16 blocks), ultrasound-guided technique (14 blocks), and blind technique following ultrasound training (14 blocks), with needle position and dye distribution assessed via CT imaging and dissection. Whilst ultrasound-guided blocks achieved 75% optimal needle placement compared to 37.5% for untrained blind technique, this difference failed to reach statistical significance; moreover, ultrasound guidance reduced intraocular injection from 18.75% to 0%, though the small sample size prevented this from being statistically conclusive. The finding that ultrasound-trained operators improved their blind technique accuracy to 71.4% suggests that familiarity with retrobulbar anatomy—rather than imaging guidance per se—may be the critical factor for safer block placement. For practitioners, these results indicate that investing time in anatomical training substantially narrows the safety gap between techniques, though ultrasound guidance may offer additional confidence and a non-invasive learning pathway, particularly valuable in a teaching environment or for operators early in their learning curve.
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Practical Takeaways
- •US-guided retrobulbar blocks appear safer (fewer intraocular injections) than blind technique, though statistical significance was not reached in this cadaver study
- •Training on ultrasound-guided technique may improve overall needle placement skills even when returning to blind technique
- •For practitioners performing standing ophthalmic surgery, US guidance warrants consideration despite lack of definitive statistical superiority, given the trend toward fewer complications
Key Findings
- •US-guided RNB achieved 75% optimal needle positioning versus 37.5% with blind technique in inexperienced operators
- •Intraocular injection rate was 18.75% with blind RNB versus 0% with US-guided and 7.1% after US-guided training
- •US guidance showed trend toward improved accuracy but no statistically significant difference between blind and US-guided techniques
- •Training on US-guided technique improved subsequent blind RNB performance to 71.4% optimal positioning