Retrobulbar lidocaine injection via the supraorbital fossa is safe in adult horses but produces regionally variable periocular anaesthesia.
Authors: Yang Vanessa Y, Eaton Joshua Seth, Harmelink Katherine, Hetzel Scott J, Sanchez Adriana, Lund Jane R, Smith Lesley J
Journal: Equine veterinary journal
Summary
# Editorial Summary Retrobulbar anaesthesia via supraorbital injection is a well-established technique in equine practice, yet surprisingly little objective evidence existed regarding its safety profile and actual anaesthetic coverage until this 2021 study. Researchers administered 10 mL of 2% lidocaine retrobulbarly to eight sedated mares and monitored corneal sensation, periocular anaesthesia, intraocular pressure (IOP), and adverse effects over 24 hours, using the contralateral untreated eye as control. Whilst the injection proved broadly safe, several clinically significant findings emerged: IOP increased substantially (peak 6.0 mm Hg above baseline at 30 minutes), six of eight eyes developed mild-to-moderate chemosis lasting 2–24 hours, and one eye experienced severe chemosis with subsequent superficial corneal ulceration—highlighting genuine risk in compromised eyes or those predisposed to glaucoma. Anaesthetic coverage proved regionally inconsistent, with reliable corneal and dorsomedial periocular numbness for approximately 2 hours, but inadequate ventral and lateral anaesthesia beyond 30 minutes, and unpredictable optic nerve blockade. For practitioners, this means retrobulbar injection alone is insufficient for eyelid surgery or enucleation and must be combined with supplementary local anaesthetic techniques; careful case selection is essential to avoid IOP complications, and owners should be counselled regarding chemosis as a common post-procedure expectation.
Read the full abstract on PubMed
Practical Takeaways
- •Retrobulbar lidocaine injection is safe in normal equine eyes but should be avoided or used cautiously in horses with structural ocular disease or glaucoma due to transient IOP elevation
- •Plan for common and potentially severe chemosis development 2-4 hours post-injection; monitor closely for corneal ulceration risk, particularly in compromised eyes
- •Retrobulbar injection alone provides incomplete periocular anaesthesia and should be combined with supplemental local blocks (auriculopalpebral, infratrochlear, supratrochlear) for eyelid surgery or enucleation procedures
Key Findings
- •Retrobulbar lidocaine injection (10 mL, 2%) significantly increased intraocular pressure for up to 2 hours, peaking at 30 minutes (mean increase 6.0 mm Hg)
- •Six of eight treated eyes developed mild to moderate reversible chemosis lasting 2-24 hours; one eye developed severe chemosis with superficial corneal ulceration
- •Corneal sensitivity significantly decreased for 6 hours after injection, with maximum effect at 10 minutes (-44.4 mm)
- •Periocular anaesthesia was regionally variable: dorsal and medial areas anaesthetised for up to 2 hours, but ventral and lateral sensitivity not effectively reduced beyond 30 minutes
- •Optic nerve function was not consistently reduced following injection