| (Section)/
Technique |
Entry point for cannula or incision |
Procedure/Remarks |
| (i)
Retrobulbar |
Avascular area Inferotemporal quadrant (or nasal side of medial rectus muscle). |
The syringe needle is initially inserted horizontally in an axial direction through the lower eye-lid (just above the lateral orbit margin) up to the eye-equator plane, and then the needle is inclined upwards and pushed posterior to the bulb. Both [109] the motor and the sensory nerves are affected; the oculomotor (III) and abducent (VI) motor nerves paralyse all the extraocular muscles except the superior oblique. Ciliary ganglion is also blocked. The entire eyeball is anaesthetised as a result of blocking of the nasociliary and the long ciliary nerves.
(For detailed procedural techniques see Refs [53,54]) |
| (ii)
Peribulbar |
Avascular area.
Nasal side of medial rectus (or inferotemporal quadrant). |
For the needle-tip to end up beyond the equator-plane, the syringe needle is inserted horizontally through the conjunctiva or the lower eye-lid, in an axial direction above the infraorbital margin. It is angled upwards for delivery. Here [48] the injectate is deposited within the orbit and does not enter the geometric confines of the cone of the rectus muscle. During this procedure, LA affects both the motor nerve supply of the superior oblique muscle, and also the orbicularis muscle (due to the spread of LA through the orbital septum.
(For detailed procedural techniques see Refs [53-55]) |
| (iii)
sub-Tenon’s |
Incision of tented conjunctiva, infero-nasal quadrant. |
A small incision is made infero-nasally through the conjunctival and ST layers. Using a ST curved blunt cannula placed through the incision to the ST space; 3.5–5ml of LA is injected. Ocular massage is optional. Iris and anterior segment anaesthesia is achieved,48 and is better than sub-conjunctival injection alone. The degree of abolition of extraocular muscle movement is proportional to the volume and depth of the injectate. With age [19], the posterior Tenon’s capsule degenerates and fenestration probably aids diffusion of anaesthetic into RB cone.
(For detailed procedural techniques see Refs [20,62]) |
| (iv)
Topical |
Drops administered to cornea and fornix |
Either drops or gel is applied to the surface of the conjunctiva and cornea preoperatively. Trigeminal nerve-endings in the cornea and conjunctiva only are
Blocked [52]. Intra-ocular structures in the anterior segment are not anaesthetised.
(For detailed procedural techniques see Refs [38,69]) |
| (v)
Intracameral |
Injected though corneal incision during surgery. |
Preservative free anaesthetic (usually 1% lidocaine) is injected into the anterior chamber at the beginning of the operation through one of the corneal incisions required for phacoemulsification. It provides sensory blockage of the axis and the ciliary body
(For detailed procedural techniques see Refs [38,110]) |
