Chapter 16 Ophthalmic Surgery

What is the function of the Orbit of the eye?
Protects the eyeball and surrounding structures.

What does the optic foramen (orbital apex) transmit?
Optic nerve
Optic artery
Optic Vein
SNS nerves from carotid plexus

What is the fibrous outer layer of the eye?
Sclera

What is the anterior portion of the sclera that is transparent?
Cornea

What is the middle vascular layer of the eye that contains the iris, ciliary body and choroid?
Uvea

What controls the iris sphincter to dilate and constrict the eye and ciliary muscles?
Sympathetic dilates iris
Parasympathetic controls iris constrictor and ciliary muscles

What is mydriasis?
Dilation of pupils

What is miosis?
Constriction of pupils

What part of the eye is neurosensory and converts light into neural impulses that are carried via the optic nerve to the brain?
Retina

What part of the eye covers the globe surface and lines the eyelids?
Conjunctiva

What part of the eye is very absorbant (where meds are absorbed)?
Conjunctiva

What is the arterial blood flow to the eye?
Internal and external carotid arteries

What is the venous drainage of the orbit of the eye?
Drainage of the orbit via the superior and inferior opthalmic veins

What is the venous drainage of the eye?
Central retinal vein

Where do the veins of the eye empty into?
Cavernous sinus

What nerve of the eye controls pupil sphincter and ciliary muscle?
Oculomotor nerve to ciliary ganglion

What nerve supplies superior oblique muscle?
Trochlear nerve

What nerve supplies lateral rectus muscle?
Abducens

WHat other 2 nerves supply musculature of the eye?
Trigeminal & Facial nerves

where is aqueous humor formed?
2/3 formed in posterior chamber
1/3 formed from vessels of the iris via passive filtration

What is the rate of production of aqueous humor?
What is the total volume?
2.5 microLiters/min
Total vol= 250 microliters

WHat process forms aqueous humor?
Active secretory process
-carbonic anhydrase and cyctochrome oxidase systems

WHat is actively transported into aqueous humor at ciliary epithelium?
What follows?
Na+
HCO3- and Cl- follows

How does aqueous humor osmotic pressure compare to plasma?
Aqueous humor osmotic pressure is greater than plasma

What are the 4 steps of aqueous humor flow?
Ciliary body (produced here)
Posterior chamber via pupil
Anterior chamber
Drains to venous system through canal of schlemm

WHat is normal IOP?
10-22 mmHg

How much can position changes affect IOP?
1-6 mmHg

WHat can an acute rise in IOP cause?
Glaucoma

Once eye cavity is entered, IOP becomes what?
Atmospheric

Under GA, acute increase in IOP may cause what?
Permanent vision loss

What are the 3 main factors that affect IOP?
External pressure on the eye
Scleral rigidity
CHanges in intraocular contents which are semisolid or fluid

What things associated with anesthesia will increase IOP?
Laryngoscopy/intubation
Hypoventilation, hypoxia, increased CO2
Succinylcholine

WHat things associated with anesthesia will decrease IOP?
Hyperventilation
Hypothermia
Inhalation agents
Etomidate
Nondepolarizing NMB

How do nondepolarizing NMB decrease IOP?
By relaxing extraocular muscles

How does Succs increase IOP?
Tonic contractions of extraocular muscles
Choroidal dilation of vasculature
Relaxes orbital smooth muscle
Increases resistance of outflow of aqueous humor from eye
– causes extrusion of aqueous humor in open globe injury

How much can Succs increase IOP?
By 10-20 mmHg for up to 5 min

WHat can you pretreat with to give SUccs to avoid an increase in IOP?
Nondepol. NMB
Benzos
Beta blocker
Acetazolamide

What eye surgery should Succs be avoided in?
Strabismus

What other medications decrease IOP?
Ganglionic blockers
Trimethaphan
Acetazolamide (interferes with Na+ pump, reducing aqueous humor formation)

How do hypertonic solutions affect IOP?
Decrease it by elevating plasma oncotic pressure which reduces formation of aqueous humor.

WHat are hypertonic solutions?
Dextran
Mannitol
SOrbitol
Urea

What does pressure on the globe or traction of the extraocular muscles stimulate?
The vagus nerve and causes bradycardia

What is the reflex that attaches your eye to your heart?
Oculocardiac reflex

WHat is the afferent limb of the oculocardiac reflex?
Trigeminal nerve (V)

What is the efferent limb of the oculocardiac reflex?
Vagus nerve (X)

WHat are possible causes of the oculocardiac reflex?
Retrobulbar block
Ocular trauma
Direct pressure on remaining tissue following enucleation

What increases risk of the oculocardiac reflex?
Hypoventilation (increased EtCO2)
Hypoxemia
Acute onset, strong, sustained traction

What is the treatment of bradycardia d/t oculocardiac reflex?
Stom stimulation
Assess anesthetic depth and ventilation
Atropine
Lidocaine infiltration at site

What is acetycholine give for as optdhalmic agent?
For lens extractions
Produces miosis

What are the systemic effects of acetylcholine?
Bradycardia
Salivation
Bronchial secretions
Bronchospasm
Hypotension

WHat is Echothiophate used for?
Glaucoma treatment
Miosis
Decrease IOP (decrease resistance to aqueous humor flow)

What are the systemic effects of echothiophate?
Irreversible cholinesterase inhibitor
Plasma cholinesterase activity 5% of normal
Activity normalizes after 4-6 wks

WHich anesthesia medications are affected by echothiophate?
Succs
Ester local anesthetics

What is Cocaine used for as ophthalmic drugs?
Nasal packs
Vasoconstriction
Blocks reuptake of NE

What is epinephrine used for in opthalmic procedures?
Open angle glaucoma treatment
(may cause anxiety, angina, tachycardia)

What is phenylephrine used for in opthalmic pts?
Mydriasis
Capillary decongestant
(may cause HTN, Tachycardia, Headache, temrulousness)

What is Timolol used for?
Glaucoma Treatment
-decreases IOP by decreasing aqueous humor production

What are the side effects of Timolol?
Nonselective Beta blocker
Bradycardia, Hypotension, Asthma exacerbations, myasthenia gravis exacerbations

What is Betaxalol used for?
Glaucoma Treatment
Beta-1 antagonist
Minimal side effects

What is cyclopentolate used for?
Anticholinergic to dilate pupils
Mydriasis

What are the side effects of cyclopentolate?
Dysarthria
Disorientation
Frank psychosis
Seizures in children

What are anesthesia requirements for opthalmic surgeries?
Safety
Akinesia
Profound analgesia
Minimal bleeding
Obtundation of oculocardiac reflex
Smooth emergence

What block is used where local anesthetic is injected into muscle cone behind the globe near the ciliary nerve?
Retrobulbar block

WHat branch is blocked with separate injection that causes akinesia of eyelids?
Facial nerve motor branch

What enhances the spread of local anesthetic by increasing tissue permeability?
Hyaluronidase

What is the Honan cuff?
Orbital compression balloon that facilitates the block by decreasing IOP and promoting periorbital spread of local anesthetic

What are some complications of the retrobulbar block?
Optic nerve trauma
Retrobulbar hemorrhage
Increased IOP
Oculocardiac reflex
Intravascular injection
Apnea

What are the advantages of doing a retrobulbar block?
Decrease incidence of coughing and straining
Decreased PONV
Minimal sedation required – SDS
Analgesia
Akinesia

What is brainstem anesthesia from a retrobulbar block?
Direct injection or spread of local anesthetic along optic nerve sheath to CSF

What are s/s of brainstem anesthesia?
Anxiety
Apnea
(usually resolves in 1 hr)
Must have emergency intubation equipment available

What are S/S of retrobulbar hemorrhage?
Eye tenses and pushes forward
Proptosis -bulging

What is the Treatment for retrobulbar hemorrhage?
Gentle pressure for 20 min
Lateral canthotomy- relieve nerve compression
Reschedule surgery

How is topical anesthesia done for the eye?
Local anesthetic is absorbed through conjunctiva and blocks sensory innervation of cornea

What are the disadvantages of topical anesthesia for eye procedures?
Eye movement
Anxiety
Allergic reactions

What should be avoided in GA for eye surgery?
Ketamine – causes nystagmous

Why is open globe surgery considered full stomach?
What precautions should be taken
Because it is usually caused by trauma
No awake intubation
Paralysis required- so intraocular contects dont extrude
RSI

What are the goals with open globe anesthesia?
Prevent aspiration
Prevent sudden increase in IOP

What preop meds should be given to open globe surgery?
Reglan
H2 antagonists

What should be done for induction of open globe pts?
Cricoid pressure
Sedative + non-depolarizing paralytic
Succinylcholine with pretreatment to control fasciulations with nondepol.
Awake extubation

What are anesthesia concerns with open globe surgeries?
Avoid pressure on eye form facemask
Avoid increase etCO2 or hypoxemia b/c increased risk of oculocardiac reflex
Anti-emetics

What is the most common pediatric opthalmic procedure?
Strabismus surgery

What is triggered during strabismus surgery?
Oculocardiac reflex

The incidence of what is increased with strabismus surgery?
MH b/c associated with myopathies

What should be avoided with strabismus surgery?
Succinylcholine b/c of tonic contracture of extraocular muscle, interferes with forced duction test

What are the advantages of LMAs for strabismus surgery?
No paralysis required
Smooth emergence

What reflex causes PONV?
Oculogastric reflex

How do you prevent PONV?
Antiemetics
Limit narcotic use- use tylenol
Adequate hydration
Lidocaine infiltration at operative site- blocks afferent impulses/post op pain

What is intraocular surgery done for?
Glaucoma drainage
Vitrectomy
Keratoplasty (corneal transplant)
Cataract extraction

What type of anesthesia is used for intraocular surgery?
Local or General

What should be used for paralysis for intraocular surgery?
Nondepolarizing neuromuscular blockers causes akinesia

How should ventilation be controlled with intraocular surgery?
Avoid hypercarbia b/c it stimulates the oculocardiac reflex
consider deep extubation with IV lidocaine

What is an injection of air, gas or silicone bubble to tamponade?
Retinal detachment

What should be avoided with retinal detachment repairs?
Shut of N2O 15 min prior to injection
Avoid N2O for 5 days

What drugs are used for retinal detachment?
Sulfer hexafluoride
Perfluoropropine
Octaflurocyclobutane

What can be given for retinal detachment to decrease IOP?
Mannitol or acetazolamide

Do retinal detachment repairs require muscle relaxation?
No b/c it is extraocular case

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