OCULAR ANESTHESIAModerator : DR. Padmajothi M S Presenter: Dr. Darshan S M

Objective

To assure safe surgical procedure by achieving akinesia, anesthesia & apropriate hypotony.

SURGICAL SPACES IN THE ORBIT Subperiosteal space : between the orbital bones

and the periorbita

Peripheral orbital space (anterior space) : bounded peripherally by periorbita and internally by 4 recti

Central space (muscular cone or retrobulbar space): Anteriorly : Tenon’s capsule peripherally: 4 recti posterior : continuous with peripheral space

Sub-Tenon’s space: between sclera and tenon’s capsule

Key feutures

Topical anesthesia

Local anesthesia

Local anesthetic agents

Lidocaine 2% > Onset of action : 5-10 mins > Duration of action : 1-2hrs

Bupivacaine 0.75% > Onset of action : 15-30mins > Duration of action : 5-10hrs

Epinephrine 1:100,000 > minimise systemic absorption

of anesthetic agents > prolong the duration of action > minimise bleeding > systemic effects may b harmfull.

Hyaluronidase

Enhances diffusion of anesthetic mixture through tissues

Use 75 units per 10ml anesthetic solution

Lidocaine 2% with or without epinephrine 1:100,000 (5ml)

Bupivacaine 0.75% (5ml)Hyaluronidase ( 75 units ) Therfore the final concentrations

in the anesthetic mixture are lidocaine 1%, bupivacaine 0.37%, epinephrine 1:200,000 & hyaluronidase 7.5 units per ml

Topical anesthesia

The first modern use of topical anesthesia was by Koller in 1884 with cocaine.

Benoxinate 0.4%, an ester (commonest & safest )

Other agents : tetracaine 0.5% , 1% amethocaine proparacaine (proxymetacaine) 0.5%; short acting (20 minutes) and are the least toxic to the corneal epithelium.

Lidocaine 4% and bupivacaine 0.5% and 0.75% have a longer duration of action but an increased associated corneal toxicity

Aim

To block the nerves that supply the superficial cornea and conjuctiva

> long & short ciliary nerve > nasociliary nerve > lacrimal nerve

Technique

The patient is asked to focus on the source of the light

> Small sponge soaked with the

drops can be kept in the inferior and superior fornix or a ring saturated with drops can placed in the paralimbal region to maintain corneal clarity

ADVANTAGES

•    No risk associated at needle insertion   

•    No risk of periocular hemorrhage

•    Functional vision is maintained 

•    No postoperative diplopia or ptosis   

•    Patients are fully alert

DISADVANTAGES

•    An awake and talkative patient can be distracting for the surgeon  

  •    No akinesia of the eye    •    If difficulties or problems

occur the anesthesia may not be adequate

Retrobulbar block

Aim to block the oculomtor

nerves before they enter the four muscles in the posterior intraconal space.

Local anesthetic is delivered within the muscle cone itself.

Into Central space

Using 22 G 35 mm long needle

In the Inferotemporal quadrant

At Junction of lateral 1/3rd and medial 2/3rd of inferior orbital margin

4-5 ml of local anaesthetic agent Bupivacaine 0.75% 5

ml Lidocaine 2% 5 ml with

adrenaline Hyaluronidase 75

units/m

Palpate inferior orbital rim. Place needle perpendicular

through skin , locate needle 1/3rd distance from lateral to medial canthus

Place just superior to inferior orbital rim

Inject 0.5ml of solution s/c to reduce pain when orbital septum is pierced

Advance needle parallel to orbital floor perforating the septum

After equater of globe is passed direct needle superonasally at 30 degree angle , advance ,piercing intermuscular septum and enter muscle cone,inject 4-5ml of anesthetic

Advantages

• A retrobulbar block is reliable for producing excellent anesthesia and akinesia   

• The onset of the block is quicker than with peribulbar; it usually occurs within 5 minutes   

• Low volumes of anesthetic ,results in a lower intraorbital tension and less chemosis than with peribulbar blocks   

• Loss of visual acuity occurs in a greater number of patients compared to peribulbar blocks, though this can be volume dependent

Disadvantages

The main disadvantage of retrobulbar blocks is that the complication rate is higher than for peribulbar blocks – the reason for the development of the peribulbar block

Complications

There is a 1–3% chance that complications will occur with retrobulbar block.  

  Retrobulbar hemorrhage    Ocular perforation (< 0.1%

incidence, but 1 in 140 injections in myopic eyes)[

Subarachnoid or intradural injection, leading to brainstem anesthesia in 1 in 350–500 patients   

Muscle complications: ptosis from levator aponeurosis dehiscence, entropion and diplopia following extraocular muscle injection    

Oculocardiac reflex, usually produced by pressure on the globe (vasovagal bradycardias are more common)

RETROBULBAR HEMORRHAGE Most common ,due to inadvertant puncture

of vessels within retrobulbar space. Simultaneous appearance of an excellent

motor block of the globe, closing of the upper lid, proptosis and a palpable increase in intraocular pressure.

It can lead to stimulation of the oculocardiac reflex.

the best course of action to postpone surgery for 2-4 days after hemmorhage

PUNCTURE OF THE GLOBERisk factors : High myopia (axial

length greater than 26 mm),Sharp injection needlePrevious scleral buckling Inexperience in performing local

blocks Poor patient complianceSIGNS: Sudden loss of

vision,hypotonia,poor red reflex

PERIBULBAR ANESTHESIAThe injection is outside the muscle cone

Spreads by way of diffusion to block the orbital nerves, including the IV nerve.

25 G ,25 mm long needle

Place needle perpendicular through skin

Locate needle 1/3rd distance from lateral to medial canthus

Technique 1st injection

Place just superior to the inferior orbital rim

Advance parallel to orbital floor,peforating orbital septum

Hub of needle should not go beyond inferior orbital rim.

Aspirate to avoid blood vessel and inject 3ml of anesthetic solution .

Apply pressure to prevent hemorrhage and facilitate diffusion of anesthetic

2nd injectionLocate needle by supraorbital

notch, place needle just Inferior to the superior orbital rim, advance needle straight back ,inject 3ml of anesthetic.

ADVANTAGES

The risk of complications associated with peribulbar block is low   

Peribulbar block has all the advantages of retrobulbar block

DISADVANTAGES Peribulbar blocks have all the

disadvantages of retrobulbar blocks, but less frequently

   The quality of akinesia and anesthesia may

not be as good as with retrobulbar block    Often more than one injection is required   

The block takes much longer to work—it can take up to 30 minutes   

The Honan balloon may be uncomfortable for the patient   

Chemosis occurs in 80% of cases, which makes operating conditions difficult   

In 5.8% of both retrobulbar and peribulbar blocks, ptosis can remain for up to 90 days

PARABULBAR ANESTHESIASub Tenons block /pin point

anesthesia/medial episcleral block.

Post limbal, sub Tenon’s incision (1 mm)

Inferonasal quadrant - good fluid distribution,avoids damage to vortex vein

Short ciliary nerves are blocked

The conjunctiva is anesthetized first with drops of the local anesthetic of choice.

The commonest approach is by the infranasal quadrant

The eye is cleaned and the patient asked to look upwards and outwards.

Aseptically, the conjunctiva and Tenon’s capsule are picked up 3–5 mm away from the limbus using nontoothed forceps.

A small incision is made through these layers using scissors (Wescott scissors) exposing the sclera.

A sub-Tenon’s cannula is inserted

The cannula is advanced posteriorly halfway between the horizontal and vertical equators of the globe.

3 to 5milliliters of local anesthetic are injected; the greater the volume, the greater the akinesis.

Lignocaine 2% is the gold standard(2.5ml); bupivacaine 0.5% and articaine 2% .

Hyaluronidase can be added.

ADVANTAGES Less painful than peribulbar block    Better analgesia than topical anesthesia    Complications rarely serious    No increase in intraocular pressure occurs

with the administration of local anesthetic    Surgery can begin almost immediately

  Lasts for 60 minutes and supplemental anesthetic agent can be given  

The globe can be voluntarily moved at the surgeon’s instruction   

Low dose and low volume of anesthetic agent are used

DISADVANTAGES The local anesthetic agent must be injected

into the capsule – double perforation of the capsule results in anesthetic leaking out, which decreases the effectiveness of the block   

Although it is an advantage that the globe can be moved under instruction, it is important the eye is not moved at other times – the use of stabilizing sutures is advised   

Post-op morbidity: Chemosis and subconjunctival haemorrhage.