Insights into Suitable Nerve Blocks of Eye of Animals

Insights into Suitable Nerve Blocks of Eye of Animals

-Harshit Saxena

UG Scholar, B.V.Sc. & A.H.-Final Year

CoVSc & AH – DUVASU Mathura

 

Nerve Blocks of Eye are routinely practiced not only in Veterinary Occular Surgical procedure but also in order to Eye examinations. As of all nerve blocks the primary aim is to produce analgesia and to omit pain during the surgical procedures but when in comes to Occular nerve blocks along with analgesia the aim is also to restrict blinking reflexes and hence producing akinesia. Appropriate anaesthetic management contributes to the success or failure of ophthalmic surgery. Though General Anaesthesia may produce similar effects but Quicker patient rehabilitation and fewer complications in patient population are the main reasons why many ophthalmic surgeons are now choosing local anesthesia (LA) over GA.

Nerve Blocks of Eye Includes-

1. Peterson Orbital Nerve Block
2. Auriculopalpebral Nerve Block
3. Retrobulbar Nerve Block
4. Supraorbital Nerve Block

#Topical corneal anaesthesia also holds separate relevance.

1. Peterson’s Orbital Eye Block

# The eye block was developed by Peterson in 1966.

 

 

     Indication-

1. Extirpation of eye, enucleation, conjunctival flaps and any type of ocular surgery are the main indications.
2. Desensitization of the eye for foreign body removal.
3. With additional modification, such as the addition of an auriculopalpebral block to abolish motor activity, surgery of the eyelids is possible (e.g. mass removal).
4. The Peterson technique may also be necessary for some horn procedures in adult bovids.

 

Nerves Blocked

1. Mandible branch of Trigeminal
2. Maxillary branch of Trigeminal supplying to the lower eyelid
3. Ophthalmic branch of Trigeminal supplying to upper eyelid, 3^rd eyelid, median canthus and eyeball.
4. Oculomotor, trochlear and abducens nerves providing the motor supply to the ocular muscles.

 

 

Site  & Technique

 

In Cattle 10cm long curved 18 gauge needle is inserted in caudal notch formed by supraorbital process & zygomatic arch , passed craniomedial to the coronoid process of mandible until it strikes the wing of sphenoid just rostral to foramen orbitorotundum. 15 ml of 2% lignocaine is deposited.

 

    Advantages

1. Safer than the Retrobulbar block Retrobulbar block as there is less risk of globe penetration and hemorrhage.
2. Additionally, potential catastrophic injection of the meninges surrounding the optic nerve is minimized using this technique.
3. More effective than alternative techniques if performed correctly.
4. Less edema and inflammation with this block than with infiltration of local anesthetics into the eyelids and orbit.
5. Auriculopaplpebral Nerve Block

Indications

1. Mostly used in the large animals for examination of the eye, in blepharospasms and for the removal of foreign bodies by causing partial paralysis of muscles of eyelids.
2. Management of surgical conditions of Eyelids & Eyeball in conjunction with Retrobulbar nerve block.
3. The nerve block controls eyelid movements.

# The auriculopalpebral block is purely a motor block and does not remove sensation

 

Nerves Blocked

 

AP nerve is a motor branch of the facial nerve supplying to the orbicularis oculi muscle of the eyelid and therefore block produces akinesia only

 

 

 

Technique & Site

 

The injection site is directly anterior to base of of the Auricular muscle at aboral end of the zygomatic arch. The needle is inserted obliquely and dorsally to contact the bone and is pushed until its point lies at dorsal border of zygomatic arch. 10 ml of 2% lignocaine is injected at this site as the needle is slowly withdrawn.

 

Advantages

 

1. Provides excellent eyelid akinesis.
2. Can be used in conjunction with sedation and other regional blocks.

 

3. Retrobulbar Nerve Block

                   

Indications

1. The retrobulbar nerve block (RBNB) involves injecting local anaesthetic directly within the periorbita, and in general practice, can be utilised for standing enucleations.

 

1. In the referral setting, the RBNB is used in numerous procedures including standing corneal surgeries (keratectomies and grafting), eyelid surgeries, laser ablation of granula iridica cysts and cytophotocoagulation for management of glaucoma.

 

Nerves Blocked

1. Sensory nerves (including branches of the ophthalmic nerve (CN V), lacrimal n., supraorbital and infratrochlear n., and maxillary nerve (CN V; zygomatic n.)) which provide sensation to the eyelids and periocular skin, are not consistently blocked by the RBNB.
2. The branches of the ophthalmic nerve which provide innervation to the eyeball (long and short ciliary nerves) are consistently blocked by the RBNB.
3. As a result of this inconsistent anaesthesia of the sensory branches of CN V supplying the eyelids, additional nerve blocks are required for desensitisation of the eyelids, commonly the supraorbital nerve for the upper eyelid and a line block for the lower eyelid and canthi.

 

Technique & Sites

3. The injection: 2 to 3.5 ml of the anaesthetic solution in a syringe with a sharp 23-gauge 24 mm needle (not 38 mm). The needle should not have an acute bevel.
4. Feel the lower orbital rim and pass the needle through the skin or the conjunctiva at the junction of its lateral (outer) and middle thirds. The bevel of the needle should be pointing upwards. The needle should be passed straight back below the eye for 15 mm; it should be parallel to the floor of the orbit and angled down . You might feel the resistance as you pass through the orbital septum.
5. Change the direction of the needle so that the tip is pointing upwards and inwards towards the back of the skull. Feel the resistance as the needle passes through the muscle cone. The needle should be advanced not more than 24 mm from the skin in total

 

1. Inject slowly and look for dilation of the pupil and drooping of the upper lid.
2. Close the eyelids gently, cover with a pad, and immediately apply firm, gentle pressure for 5 to 10 minutes. This can be done manually or with a special balloon inflated to 30 mmHg.
3. Supraorbital Nerve Block

 

Indications

1. The block is mostly employed in horses, cattle and buffaloes.
2. It is indicated for operations on the upper eyelid, trephining of the frontal sinus and management of the wounds of the forehead.

 

Technique & Site

1. The foramen is felt as small depression midway across the supra orbital process on the ventral line running upward from the median angle of the eye.
2. A 20 gaze, 2-3 cm long needle is inserted into the foramen and about 5 ml of the local anaesthetic is injected.
3. In case of the cattle the injection is made above the median canthus and spread the anaesthetic laterally along the supra orbital

# Corneal Anaesthesia

Topical anesthetics such as tetracaine and proparacaine are use to examine the cornea of the eye as well as for corneal scrapings, swabs of the eye and other minor surgical procedures. It can also be helpful when performing an eye enucleation. Local anesthetics are cytotoxic so therefore should not be used for long-term analgesia. The onset of analgesia is within one minute and duration of action is approximately 15 to 30 minutes. The metal shaft of a 25-gauge needle may be broken off to help facilitate the installation of the local anesthetic into the eye.

Contraindications/Risks

1. Allergy to a necessary anesthetic, and nystagmus. Other contraindications are just those of the particular surgery that is to be performed.
2. Long eye (in the anterior to posterior axis, evidenced by high myopia), staphyloma (abnormal protrusion at a weak spot in the wall of the eye), enophthalmos (posteriorly or deep set eyes), and extended surgery duration are relative contraindications to retrobulbar and peribulbar anesthesia.
3. Chances of damage to nerve are low but present.
4. Bleeding may occur during injecting a anaesthetic that bring secondary complication.

Conclusion

Local Anaesthesia of Eye through nerve blocks produce excellent ocular analgesia a prerequisite or any Surgical procedure. It restricts undue complications  of General Anaesthesia like those that comes at revival.

A veterinary Surgeon should necessarily acquaint himself to various nerve blocks of eye for carrying out Occular Surgical Procedures as sugeries like of Glaucoma, Cataract, Cherry Eye, Eye Enucleation & Extirpation are routinely involved in cases of both Large & Small animal practice.