The four recti muscles (superior, medial, lateral and inferior) originate from a tendinous ring (the annulus of Zinn) and extend anteriorly to insert beyond the equator of the globe. Bands of connective tissue are present between the rectus muscles forming a conical structure.

These bands hinder the passage of local anaesthetic.

The superior oblique muscle is situated outside this conical structure and is the most difficult muscle to anaesthetise completely, particularly with a single inferotemporal peribulbar injection. Performing a medial injection as well may help to prevent this.

The extraocular muscles are supplied by the

• Third (inferior oblique, inferior recti, medial and superior)
• Fourth (superior oblique) and
• Sixth cranial nerves (lateral rectus).

The sensory supply to the globe is via the long and short ciliary nerves, which are branches of the nasociliary nerve, (which is itself a branch of the ophthalmic division of the trigeminal nerve).

These nerves enter the fibrotendinous ring and need to be fully blocked to anaesthetise the eye for surgery.