Ocular Anesthesia

From EyeWiki
Original article contributed by: Namrata Bhuta, MD, Sujata Sanjay Chahande
All contributors: Brad H. Feldman, M.D. and Namrata Bhuta, MD
Assigned editor:
Review: Assigned status Up to Date by Namrata Bhuta, MD on May 31, 2015.


Introduction

Ophthalmic surgery has been performed under a wide range of anaesthetic techniques . The type of anaesthesia for each ophthalmic surgery depends on a large number of factors like patient co-operation , the nature of the surgery and surgeon’s preference. Over  the years , ocular anaesthesia has evolved tremendously , with topical anaesthesia (which was first used in 1884) making a comeback in the last few years. In this article we are going to review the various types of anaesthesia used during ophthalmic surgeries, their techniques and their possible complications.

Background

Carl Koller first used cocaine as a topical anaesthetic for eye surgery in 1884. Later that year, retrobulbar anaesthesia was introduced with Cocaine by Knapp. The year 1904 turned out to be a landmark year for ocular anaesthesia with the development of procaine for retrobulbar anaesthesia. It was Einborn who synthesized procaine and led to its worldwide  acceptance in retrobulbar anaesthesia. Peribulbar anaesthesia was discovered late in the 1980s by Dr David and Mandal. The more recent drift is again towards topical anaesthesia, which has steadily increased with the advent of modern phacoemulsification cataract extraction.

Objectives

  1. Akinesia  of the globe and lids
  2. Anaesthesia of the globe, lids and adnexa
  3. Adequate postoperative analgesia
Photo 4.JPG

FIG 1. Anatomy of the Orbit showing the intraconal compartment of the eye.

Clinical anatomy

Extraocular muscles

The origin of recti muscles from the Annulus of Zinn and their attachment to the globe forms a cone around the globe. The intraconal components include the optic nerve , ophthalmic artery and vein , 3rd ,6th and nasociliary nerves and ciliary ganglion . Blocking the motor components causes akinesia , blocking the sensory nerves causes anaesthesia . The retrobulbar anaesthesia is injected in this intraconal compartment. Peribulbar anaesthesia is  injected in the extraconal compartment and hence is considered safer since it avoids potential damage to the intraconal structures.

Nerve supply

In order to understand various types of anaesthesia used in ophthalmic surgery, it is important to understand the nerve supply of the eye and its adnexa.

Motor supply

The occulomotor nerve supplies all the extraocular muscless (except the superior oblique and and the lateral rectus muscle) and levator palpebrae superiors . The trochlear nerve supplies the superior oblique whereas the abducens nerve supplies the lateral rectus muscle. The trochlear nerve lies outside the muscle cone and hence is not usually blocked .

Sensory supply

The trigeminal nerve is divided into  the ophthalmic branch (further divided into nasociliary, lacrimal, and frontal branches) . The nasociliary branch supplies the cornea, perilimbal conjunctiva and the superonasal quadrant  of  bulbar conjunctiva. The rest of the conjunctiva is supplied by the lacrimal, infraorbital, and frontal nerve.

Photo (1).JPG
Photo.JPG
PH 10.JPG
Photo (2).JPG
                                                                              

FIG 2. Akinesia of the right eye in all directions after instillation of Retro/Peribulbar Block as compared with the left eye .

Classification of anaesthetic technique

CLASS.PNG
                      

Techniques of anaesthesia

Local anaesthesia

Infiltration anaesthesia

It is indicated for procedures involving more than  superficial manipulations of the eye and its adnexa.

PH11.JPG

It is contraindicated in uncooperative patients and in presence of an infected field  .

Retrobulbar anaesthesia

In this technique the anaesthetic  solution is injected into the intraconal compartment  of the eye.

Method:  After preparation of the skin, a 23G needle  with 3-5 ml of anaesthetic solution is introduced intradermally at inferior temporal margin  of the  orbit, at the junction of lateral 2/3rd and medial 1/3 rd of orbital margin. The needle is then directed superiorly and medially to enter the tenon’s capsule between the lateral and inferior rectus  muscles. Once the needle has reached the retroorbital space , the syringe is aspirated to ensure that no blood vessel has been entered and the anaesthetic is injected. Immediately following this injection superpinky ((a pressure device) is placed on the eye for 10-15 minutes . Intermittent pressure with superpinky should be given to prevent occlusion of vessels..

Complications:

OCULAR COMPLICN.PNG

Advantages and disadvantages of retrobulbar anaesthesia RETRO.PNG

Peribulbar anaesthesia

In this procedure, the anaesthetic is injected into the extraconal compartment of the eye. Thus , most of the complications associated with retrobulbar anaesthesia are avoided.

Photo 3.JPG

Hence, it is a much safer, equally efficient and less painful anaesthesia.

Technique: This technique involves  giving two injections of long acting anaesthetic at least 20 minutes before the surgery. The first injection is given inferiorly with a 23 g needle at the junction of outer one third and inner two third of the lower orbital rim(5cc). The second injection is given superonasally beneath the superior orbital notch(3cc). Immediately following this injection superpinky is placed on the eye for 10-15 minutes. Intermittent pressure with superpinky should be given to prevent occlusion of vessels.

PERI.PNG

Subconjunctival anaesthesia

Photo 1.JPG

Can be utilized in almost every operation on the eyeball. However it should not be used in the presence of infection.

In this technique, a sharp 26 G needle mounted on a syringe is introduced subconjunctivally and the anaesthetic solution is injected beneath the bulbar conjunctiva at variable distance from limbus.

Subtenon infiltration anaesthesia:

Photo 2.JPG

The tenon’s capsule is the anterior extension of the visceral layer of the Dura. It fuses  with the conjunctiva about 2-3 mm away from the limbus.

Thus 2-3 mm beyond the limbus region the subtenon's space is continuous with the retrobulbar space. Anaesthetic injected in this space reaches the retrobulbar space. This the mechanism of action of subtenon's block.

In this technique, forceps are used to elevate the conjunctiva and tenon’s  capsule and the needle is directed posteriorly  and anaesthetic is injected in the subtenon’s space between the tenon’s capsule and sclera in the equatorial region of the superotemporal quadrant of the eyeball. This results in blocking of the ciliary nerves.

Intracameral anaesthesia:

Intracameral  anaesthesia is instilled by injecting non preserved 1% lignocaine (lidocaine) in the anterior chamber  through paracentesis or side port incision. It anaesthetises the iris and the ciliary body and hence reduces pain and IOP fluctuations during small procedures like IOL redialling. The drug must be washed after 15-30 seconds by irrigation through viscoelastics or basal salt solution as it may reach the retina and cause gradual decrease in vision.

Nerve blocks

Facial nerve blocks

To prevent the squeezing action of eyelids during cataract extraction, temporary paralysis of the orbicularis oculi muscle is affected by blocking the facial nerve, by one of the following methods of Facial block:

  1. Van Lint's block
    • In this method, only the terminal branches of facial nerve are blocked, thus avoiding total facial paralysis. A 23 g needle with anaesthetic solution is placed subcutaneously posterior to the intersection of horizontal line along the most inferior margin of the orbit and a vertical line along the most lateral margin of the orbit. The anaesthetic solution is then injected superiorly and inferiorly in a V shaped pattern.
  2. O' Brien's block
    • It is also known as facial nerve trunk block. The block is done at the level of the neck of the mandible near the condyloidprocess just anterior to the tragus of the ear. This offers more complete akinesia .
  3. Atkinson's block
    • This was introduced  to overcome the disadvantage of Van Lint and O’Brien’s block. Van Lint  causes ballooning and distortion of the lids and ocular adnexa while that of O’Brien produces postoperative pain at site of anaesthesia  . The superior branch of the facial nerve is blocked by injecting the anaesthetic solution at the inferior margin of zygomatic bone subcutaneously with a 23g needle .Firm pressure is then applied to produce a more rapid and complete block.
  4. Nadbath block
    • In Nadbath block, the facial nerve is blocked at the stylomastoid foramen. It involves blocking of the  facial nerve as it emerges from the  stylomastoid foramen and  before it  enters  the parotid gland. The patient is likely to experience pain.
  5. Spaeth block:
    • Injection is given proximal to classic approach of O’Brien over the mandibular condyle, thus catching the facial nerve before it divides.

Blocking of other nerves

  • Infratrochlear nerve block

The infratrochlear nerve supplies branches to the skin, conjunctiva, and eyelids near the medial canthus. Its nerves run to the caruncle, lacrimal sac and nose. It has to be blocked in all lacrimal apparatus operation.

About 1 ml of anaesthetic is injected against the bony orbital wall just below the trochlea in the superomedial angle of the orbit.

  • Supraorbital nerve block

The supraorbital notch or the foramen is located by palpation and 1ml of anaesthetic solution is injected into the supraorbital notch or the foramen.

  • Lacrimal nerve block

1 ml of anaesthetic solution is injected just above the zygomaticofrontal suture above the tubercle of the zygomatic bone.

  • Infraorbital and zygomatic nerve

The needle is introduced through the skin below the middle third of the lower lid 1 cm below the orbital rim and 1ml of anaesthetic solution injected.

Topical anaesthesia

In the last few years the shift in anaesthesia in ophthalmic surgery has been towards topical anaesthesia. Cataract surgeries have now become sutureless with the advent of phacoemulsification and rapid visual rehabilitation is expected. Topical agents like  0.5 % proparacaine are used to anaesthetise the nerves.  All the complications associated with orbital injections can be avoided. It is the ideal choice for same day surgery, where patients can be immediately discharged post operatively. However, the anaesthesia is limited to conjunctiva, cornea and anterior sclera.  The iris and ciliary body are not anesthetized. Reliance on patient cooperation along with epithelial toxicity is a key disadvantage in the use of topical anaesthesia.

General anaesthesia

Indications for g.a. in ophthalmic surgery

  • Extensive operation in which local anesthesia is impractical
  • Operations on patients who may prove uncooperative during local anesthesia
    • Children
    • Psychosis or poor comprehension
    • Deaf
  • Operation on infected fields where local anesthesia is contraindicated


Whereas general anaesthesia gives complete control over the patient and avoids the complications of an orbital injection, there is increased nausea, vomiting , cardiovascular and pulmonary stress.

Most G.A drugs reduce IOP except ketorolac and succinylcholine .

Build up of gases like carbon dioxide intraocularly during G.A. may cause expulsion of  intraocular contents. Gases used during vitrectomy and retinal detachment may interact with nitrous oxide used for G.A

Anaesthetic solutions

Local anaesthestics are combined with various other drugs like adrenaline and hyaluronidase in order to enhance their effects or supplement their actions.

  • Lignocaine (lidocaine) 2% - 4% : Fast onset of action and effects last for an hour.
  • Bupivacaine 0.5% - 0.75% : slow onset of action but lasts for 3-4hrs
  • Hyaluronidase (7.5 units/ml) helps facilitate spread of anaesthetic through tissues by increasing permeability of fibrous septa . It improves the speed of onset and quality of nerve block.
  • Adrenaline (1:1,00,000) helps in slower absorption of anaesthetic and longer action of anaesthetic. It also reduces the incidence of haemorrhages and of intraoperative vitreous bulging . However, adrenaline in very high doses causes toxic effects to macula and also central retinal artery spasm..
  • Small amount of 8.4 % sodium bicarbonate is added to raise the pH of the commercially available solution (because with increased pH, the amount of drug present in base form is increased which promotes more effective nerve block , less burning and also shortens onset time).


Each anaesthetic technique comes with its unique set of  advantages and disadvantages . The decision for the type of anaesthesia should be made after taking into consideration all these factors including the duration of anaesthesia, patient cooperation, type of surgery and surgeon's preference.

References

[1] [2] [3] [4] [5]

[6]
  1. Comparison of different techniques of Anaesthesia by Dr. Sujata Chahande and Dr. Ashok Patel, 1998; Bombay University;1-53
  2. VV Jaichandran; Ophthalmic regional anaesthesia;Indian Journal of Anaesthesia 2013 Jan- Feb ;57(1):7-13
  3. Hansen EA ,Mein CE, Mazzoli R. Ocular anaesthesia for cataract surgery : A direct subTenon's approach . Ophthalmic Surg. 1990;21:696-9
  4. Wolff.E.Philadelphia and London : WB Saunders ; 1996. Anatomy of the Eye and Orbit ;p31
  5. Kumar CM, Dowd TC.Complications of ophthalmic regional blocks: Their treatment and Prevention.Ophthalmologica;2006;220:73-82
  6. Preoperative preparation and anaesthesia :Manual of Small Incision Cataract Surgery by K.P.S.Malik, Ruchi Goel;2003 :5-9