Sub-Tenon’s injection in equine cadaver eyes: MRI visualization of anesthetic fluid distribution and comparison of two different volumes.

The research compares the distribution and localization of two different volumes of anesthetic fluid in equine cadaver eyes during a sub-Tenon’s injection. The study aims to identify the optimal volume for the injection. It concludes that there is no significant difference in the distribution of 7 and 10 mL volumes of anesthetic, with both volumes proving potentially efficient for use in equine ophthalmic surgeries.

Methodology

• The research involves performing a single sub-Tenon’s injection of 2% lidocaine in 10 equine cadaver heads (20 eyes).
• Two different volumes of the anesthetic fluid, 7 ml and 10 ml, are used for the injection on opposite sides of the cadaver heads.
• The distribution of the anesthetic in the eye is then examined using sagittal, dorsal, and transverse MRI sequences.
• The observations are performed independently by three board-certified radiologists, ensuring a non-biased evaluation of the fluid’s distribution.

Results

• The study observes the extension of the injection fluid mainly along the dorsal and temporal quadrants of the globe, within the subconjunctival space, the anterior and posterior sub-Tenon’s space, and the muscle sheaths along the extraocular muscles.
• Anesthetic fluid accumulation directly surrounding the optic nerve is observed in three out of the 20 cadaver eyes.
• The comparison of 7 ml and 10 ml volumes of anesthetic show no significant difference in the circular distribution.
• However, more retrograde leakage of the anesthetic is observed with the 10 ml volume compared to the 7 ml.
• The evaluation also shows no significant differences in observations made by the three independent observers.

Conclusion

• The research concludes that Sub-Tenon’s anesthesia potentially offers an alternative to retrobulbar anesthesia for ophthalmic surgeries in equines.
• It concludes that an injection volume of 7 ml to 10 ml should be appropriate based on the study’s results.
• However, the study also recommends further investigation into the distribution of the anesthetic solution in live tissues, the clinical effects, and the potential for complications in a live, clinical setting.