Local anaesthetic delivery through indwelling retrobulbar catheters for ocular pain control in horses.
Authors: Moody Leah M, Hicks Sherri L, Foote Braidee C, Hendrix Diane V, Ward Daniel A
Journal: Equine veterinary journal
Summary
# Editorial Summary: Retrobulbar Bupivacaine for Equine Corneal Pain Corneal disease in horses is both common and acutely painful, yet current pain management strategies often fall short of providing adequate relief, particularly in the early stages of disease. Moody and colleagues investigated whether local anaesthetic delivered via an indwelling retrobulbar catheter could improve pain control by conducting a randomised crossover trial in seven horses, injecting either 10 mL of 0.5% bupivacaine or saline into the retrobulbar space and measuring corneal sensitivity (using Cochet-Bonnet esthesiometry), pupil size, pupillary light responses, and eye movement reflexes over 12 hours. Bupivacaine dramatically reduced corneal touch thresholds for 6 hours—dropping to 0.08 cm at one hour post-injection compared with 4.21 cm for saline (p<0.001)—whilst also causing pupil dilation lasting 3 hours and suppressing pupillary light reflexes for 9 hours; saline had no measurable effects on any parameter. Mild adverse effects including chemosis, eyelid swelling, and transient palpebral reflex reduction were observed, and the authors acknowledge that reduced corneal sensitivity may not directly translate to clinical pain relief in diseased eyes. For practitioners managing equine corneal conditions, retrobulbar bupivacaine delivery offers a pharmacologically sound approach to periocular analgesia, though further investigation of repeated dosing safety and correlation with actual pain behaviour in affected horses remains necessary before routine clinical application.
Read the full abstract on PubMed
Practical Takeaways
- •Retrobulbar bupivacaine via indwelling catheter provides measurable corneal anesthesia for approximately 6 hours in healthy horses, potentially useful for managing pain in equine corneal disease cases
- •Expect mydriasis (dilated pupil) and reduced pupillary light responses lasting up to 9 hours post-injection; monitor for mild local swelling and reduced blink reflex as expected effects
- •This technique shows promise for corneal pain control but requires further clinical validation in diseased eyes, and repeated injection safety has not been established
Key Findings
- •Retrobulbar bupivacaine injection reduced corneal touch thresholds for 6 hours, with maximum reduction at 1 hour (0.08±0.20 cm vs saline 4.21±0.39 cm, p<0.001)
- •Bupivacaine increased pupillary area for 3 hours compared to saline, with maximum increase at 3 hours (349.75±84.80 mm² vs 194.65±27.03 mm², p=0.04)
- •Bupivacaine reduced pupillary light reflexes for 9 hours and oculocephalic reflexes for 3 hours; saline had no effect
- •Mild adverse effects included chemosis, blepharoedema, and transiently reduced palpebral reflex; reduction in corneal sensitivity may not directly translate to clinical pain control