Dr Damita WijewardenaConsultant AnaesthetistNational Eye Hospital

Paediatric PatientsMultiple congenital problemsRelevant investigationsFasting guidelines?Premedication EMLA, Antiemetics, ParacetamolEUA and other surgeries

Examination of the EyeFundoscopyIOP measurementRetinoblastoma follow-up

Measuring IOP

Extraocular procedures Excision of orbital dermoids/tumours Lid surgery - excision of meibomian cysts, steroid injection of haemangiomas, tarsorrhaphy, ptosis surgery NLD surgery - syringing and probing, dacryocystorhinostomy Strabismus surgery, laser surgery/cryotherapy, episcleral dermoid excision, corneal surgery, enucleation, evisceration

Squint SurgeryOculocardiac reflexPost-operative nausea and vomitingPainMuscle relaxation

Probing of nasolacrimal ductsBacteraemiaProtection of Airway

Intraocular proceduresIntraocular procedures to reduce IOP such as goniotomy, trabeculectomy/trabeculotomy lensectomy artificial lens insertion vitrectomy vitreoretinal surgery

Adult PatientsAdults who object/have contra-indications to Local AnaesthesiaAdults undergoing extensive orbital surgeryUnco-operative patients, such as mentally retardedmovement disordersExcessive anxiety and claustrophobiaIOP needs to be controlled

Cross section of the eye

Factors determining IOPVolume of aqueous humourVolume of vitreous humourChoroidal blood volumeExtraocular muscle tone

The major controlling influence on intraocular pressure is the dynamic balance between aqueous humour production in the ciliary body and its elimination via the canal of Schlemm

(1) The ChoroidA highly vascular area in which there are extensive anastomoses between the anterior ciliary arteries and the long and short posterior ciliary arteries.

(a) Autoregulation of Choroidal blood flow

To control IOPAdequate depth of anaesthesiaGood analgesiaControl blood pressureAvoid hypertensive response to laryngoscopy and intubation

(b) Chemical control of Choroidal blood flow

To control IOP..Adequate FIO2 to maintain SpO2 greater than 96- 97%Controlled ventilation to ensure an ETCO2 of around 37 mm Hg

(c) Venous drainage of the eyeVenous drainage from iris, ciliary body and choroid 4 vortex veins pass through sclera behind the equator venous plexus of orbit cavernous sinus

To control IOP.Prevent kinking of great veinsPrevent coughing or bucking on the tubeSlight head-up tilt which is not practical

(2) Extraocular muscle toneIOP may rise markedly with pressure on the eyecontraction of extraocular musclescontraction of orbicularis oculi muscleeyelid closure

To control IOP.Use of non-depolarising muscle relaxantsPeripheral nerve stimulatorAvoid suxamethonium

(3) Vitreous HumourVolume of vitreous and its pressure effect maybe reduced by dehydrating the vitreousUrea 30% solution in water20% MannitolOral glycerol

To control IOP..Intravenous infusion of mannitol, 30 40 minutes prior to surgery

(4) Effects of different drug groupsInhalational anaesthetics decrease IOPIntravenous anaesthetics decrease IOP except for ketamineSuxamethonium transient increase in IOPNon-depolarising muscle relaxants decrease IOP

Open Eye InjuriesProblems Possible prolapse of vitreous and lensOther associated injuriesFull stomach