OPHTHALMICS

patient has ECG monitoring to recognize the arrhythmias. For hypotension, epinephrine, 50–100 µg i.v. (0.5–1 ml of 1:10,000) over 1 minute has been recommended with titration of further doses as required. Undiluted epinephrine 1:1000 should never be given intravenously unless the patient has cardiac arrest because of the risk of ventricular arrhythmias. Rapid intravenous infusion with crystalloid, 20 ml/kg, should then begin. An adult may require 2–5 litres of crystalloid.

Eye and orbit Hari Jayaram Ian Calder

Secondary management Secondary management is with an antihistamine (chlorphenamine, 10–20 mg by slow intravenous infusion) and corticosteroids (intravenous hydrocortisone, 100–500 mg slowly). Although of benefit for the allergy aspect they are not useful for the life-threatening immediate reaction that usually responds to epinephrine. H2blockers are not indicated. Bronchodilators may be required for persistent bronchospasm. If so, give salbutamol, 5 mg by nebulizer or 250 µg slow i.v., or aminophylline, 250–500 mg slow i.v. For intractable hypotension, poorly responding to epinephrine or norepinephrine by infusion, vasopressin, 1–5 units/hour, may be helpful.

Anatomy Orbit: each orbit is pyramidal in shape with its base anteriorly and its apex posteromedially directed towards the optic canal. The average dimensions are 40 mm wide, 35 mm high and 25 mm deep. The angle between both lateral walls is 90° and between lateral and medial walls of the same side is 45° (Figure 1). The medial walls are almost parallel to the sagittal plane. Needles introduced in this plane travel a greater distance towards the orbital apex and can potentially cause more damage, compared with those inserted laterally along the orbital wall.

Investigations Investigations are carried out once the patient has been stabilized. Mast cell tryptasee is the principal protein released by mast cell degranulation in anaphylactic and anaphylactoid reactions. The basal tryptase level concentration is 0.8–1.5 ng/ml. The halflife is about 2.5 hours. About 99% of the body’s total enzyme is located in the mast cell. Tryptase is not present in basophils so the concentrations are not affected by haemolysis. As soon as possible after resuscitation, 10 ml of clotted blood is collected and again at 1 hour and at 6 hours. The serum is separated and stored at 4ºC if the sample is to be analysed within 48 hours or stored at –20ºC for later analysis. Tryptase levels above 15 ng/ml suggest an anaphylactic reaction. Complement should be measured when the blood is collected, from an EDTA gel sample to show evidence of complement consumption.

Globe: the globe is located anteriorly within the orbit in a superolateral position; its dimensions vary. Myopic eyes are longer with thin sclera, and are at greater risk of needle perforation. An axial length over 26 mm should hazard caution. A ‘socket’ is formed by Tenon’s capsule, which extends from the optic nerve menin-

Angular relationships of medial and lateral orbital walls

Optic canals

Angle of lateral orbital wall

45˚

Follow-up and prognosis All suspected anaphylactic reactions should be reported to the Committee on Safety of Medicine via a yellow card. The doctor who administers the drug is responsible for ensuring the reaction is reported. The patient should be referred to an immunologist for skin testing later. The patient should be given a full explanation, a record should be made in the patient’s case notes and a letter sent to their general practitioner. The patient should be given a written record of the reaction and be encouraged to carry a Medic-Alert bracelet. Recovery from anaphylaxis is usually rapid and complete. Long-term sequelae are rare and result from cardiac and neurological damage incurred during the initial episode. ‹

Hari Jayaram is a Basic Surgical Trainee in Ophthalmology. He qualified from the Universities of Cambridge and Oxford and is currently working in the Department of Neurosurgery at the National Hospital, Queen Square, London.

FURTHER READING Association of Anaesthetists of Great Britain and Ireland (AAGBI) and British Society for Allergy and Clinical Immunology. Suspected anaphylactic reactions associated with anaesthesia. London: AAGBI, 2003. Ewan P W. ABC of allergies – anaphylaxis. Br Med J 1998; 316: 1442–5. The emergency medical treatment of anaphylactic reactions by first medical responders and community nurse. www.resus.org.uk/pages/reaction.htm

ANAESTHESIA AND INTENSIVE CARE MEDICINE 5:9

45˚

Ian Calderr is Consultant Anaesthetist at the National Hospital, Queen Square, and the Royal Free Hospital, London, UK. He qualified from Liverpool University and trained in Liverpool and London. His research interests lie in airway management.

300

© 2004 The Medicine Publishing Company Ltd

OPHTHALMICS

Conal space and fibrous septa

Orbital apex Superior orbital fissure

Extraconal space

Lacrimal nerve (V1) Frontal nerve (V1) Trochlear nerve (IV)

Intraconal space

Levator palpebrae superioris Superior rectus Superior oblique

Periorbita Lateral check ligaments Tenon’s capsule

Medial check ligaments Common muscle sheath

Superior ophthalmic vein

Suspensory ligament Spini recti lateralis

2

Lateral rectus

ges posteriorly to within millimetres of the corneoscleral limbus anteriorly. This layer is pierced by the extraocular muscle tendons, which pass to insert into the sclera. The globe itself has three layers. The outermost fibrous sclera (which envelops the globe except the anterior transparent cornea), the vascular pigmented layer (choroid, iris and ciliary body), and the innermost sensory retina. The conjunctival mucosa lines the inner surface of the eyelids and the anterior aspect of the eyeball.

Superior division of III Nasociliary nerve (V1) Inferior division of III Abducent nerve (VI)

Medial rectus Optic nerve in optic canal Ophthalmic artery Inferior rectus Inferior ophthalmic vein

3

branch of V2). The nasociliary division of V1 gives branches to the ciliary ganglion, medial aspect of eyelid skin and conjunctiva, ciliary body and cornea.

Orbital apex: the four recti muscles arise from a common tendinous ring formed from periosteum at the orbital apex, which lies medial to the globe. This ring encloses the optic canal and the medial portion of the superior orbital fissure. The cone formed by the recti muscles passing towards the globe, helps define an incomplete extraconal (peribulbar) and intraconal (retrobulbar) space (Figure 2). The relationship of the important anatomical structures to this muscular cone is shown in Figure 3.

Lacrimal gland is located in the superolateral orbit. Drainage is via superior and inferior puncta near the medial lid margins. Each punctum leads to the respective canaliculus, which passes medially to the lacrimal sac. This drains via the nasolacrimal duct to the inferior meatus of the nose. Injection between the caruncle and canthal fold will avoid these structures, and anaesthetize the medial aspect of the eyelids and cornea.

Fibrous septa: there is no strict anatomical separation of the extraconal and intraconal spaces. A matrix of connective tissue gives support, allows dynamic function and controls the spread of injectate within fibro-adipose compartments (Figure 2).

Anaesthesia Injection into avascular regions such as the medial or preferably inferolateral compartment, can provide adequate regional anaesthesia while minimizing complications. The superomedial compartment must be avoided, because of the risk of damaging the vasculature, muscles and optic nerve at the orbital apex. Current guidelines suggest the use of fine, short needles (25 mm or less), though the issue of blunt versus sharp is still being debated. ‹

Blood vessels: the main supply is from the ophthalmic artery. This is a branch of the internal carotid after it emerges from the cavernous sinus. It initially lies within the subarachnoid space, but pierces the optic nerve sheath meninges after leaving the optic canal. It first runs inferolateral to the nerve, but then moves above and towards the superomedial orbit with a tortuous course. Behind the medial upper lid, the facial and supraorbital veins pass posterolaterally as the superior ophthalmic vein. The venous plexus on the anterior orbital floor contributes to the inferior ophthalmic vein.

FURTHER READING Rubin A P. Complications of local anaesthesia for ophthalmic surgery. Br J Anaesth 1995; 75: 93–6. Snell R S, Lemp M A. Clinical anatomy of the eye. 2nd ed. Oxford: Blackwell Science, 1998. The Royal College of Anaesthetists and The Royal College of Ophthalmologists. Local anaesthesia for intraocular surgery, 2001.

Nerves: the abducent nerve (VI) supplies lateral rectus, trochlear nerve (IV) supplies superior oblique, and the other muscles are supplied by the oculomotor nerve (III), which also gives a branch to the upper lid levator. The skin and conjunctiva of the upper lid are supplied by the lacrimal and frontal branches of V1 (extraconal), and those of the lower lid by the infraorbital nerve (terminal

ANAESTHESIA AND INTENSIVE CARE MEDICINE 5:9

Common tendinous ring

301

© 2004 The Medicine Publishing Company Ltd