ENT Flashcards
(90 cards)
Describe the chambers and layers of the eye
Chambers:
- Vitreous chamber
- Anterior chamber
- Cornea to iris
- Filled with aqueous humor
- Aqueous humor drains from anterior chamber thru Schlemm’s canal into venous system
- Posterior chamber
- Iris to lens and ciliary process
Layers:
- Sclera (white part)- outermost layer
- Tough, fibrous
- Cornea- visual fx
- Curvature of cornea is where we have visual power
- Tissue where cornea meets sclera is limbis
- Uveal tract- middle
- Choroid- layer of blood vessels- bleeding of choroid can cause expulsive hemorrhage
- Iris- controls light entry (changes size of pupil)
- SNS stim → dilate pupil (iris muscle contracts)
- PSNS stim → myosis (constrict) → pupil constrict (iris sphincter muscle contract)
- Ciliary body- produces aqueous humor
- Retina (innermost layer) – nerve tissue cont. w/ optic nerve . no capillaries. Completely dependent on choroid layer to provide o2 and nourishment to retina

What are the 6 extraocular muscles of the eye?
6 muscles –
- superior rectus
- inferior rectus
- medial rectus
- inferior oblique muscle
- (1-4 innervated by oculomotor nerve- CN III)
- lateral rectus muscle
- innervated by abducens nerve- CNVI.
- superior oblique muscle
- innervated by trochlear nerve- CN IV.
Sit in cone behind eye
All surround optic nerve, artery, vein, ciliary ganglion

Describe the motor innervation of the eye?
-
Cranial Nerve III- Oculomotor
- innervates the superior rectus, medial rectus, inferior rectus, and inferior oblique eye muscles
- Eye movements
- Pupil constriction
- Opens eyelid
- PSNS fibers
- innervates the superior rectus, medial rectus, inferior rectus, and inferior oblique eye muscles
-
Cranial Nerve IV- Trochlear
- innervates the superior oblique muscle
- Moves eye down and outward
- innervates the superior oblique muscle
-
Cranial Nerve VI- Abducens
- innervates the lateral rectus muscle
- Moves eye lateral
- innervates the lateral rectus muscle
Sympathetic fibers from carotid plexus travel through ciliary ganglion → innervate dilator muscles
- Ex: block ciliary ganglion → fixed/dilated pupil
PSNS- CN III
Describe the sensory innervation for the eye.
-
TRIGEMINAL nerve (CN V) – touch/pain
-
Ophthalmic branch (VI): 1st branch
- Innervates the upper eyelid, conjunctiva, and cornea
- Nosociliary branch (of opthalmic nerve)
- sensory to medial canthus, lacrimal sac, and ciliary ganglion
- Ciliary ganglion → provides sensory to cornea, iris, and ciliary body
- sensory to medial canthus, lacrimal sac, and ciliary ganglion
- Also regulates OCR (oculocardiac reflex)
- Nosociliary branch (of opthalmic nerve)
- Innervates the upper eyelid, conjunctiva, and cornea
-
Maxillary branch (V2): 2nd branch of 5
- Innervates lower lids
-
Ophthalmic branch (VI): 1st branch
-
Facial nerve: VII- Exits skull in stylomastoid foramen
- Supplies motor innervation to orbicularis muscle via zygomatic branch
- Ex: block CN VII → cant squeeze lid
- Innervates the lower lid
- Ex: block CN VII → cant squeeze lid
- Supplies motor innervation to orbicularis muscle via zygomatic branch
What is normal intraocular pressure?
- Normal: ~ 16 mmHg (+/- 5)
-
Abnormal: > 25 mmHg
- Must maintain normal IOP to maintain normal curvature of cornea
- IO perfusion pressure related to CPP
- (MAP – IOP → how eye regulates perfusion)
- Ex: High IOP → impairs BF to optic nerve (fx effected)
How is aqueous humor produced?
- Posterior chamber:
- 2/3 produced by ciliary body (~80-90%)
- → then actively moved from posterior chamber to anterior chamber by an active sodium pump mechanism.
- Active Na pump (AKA → Na-K ATPase carbonic anahydrase enzyme)
- Passive filtration: 1/3 (~20%)
- comes from passive filtration through vessels in iris. across ciliary epithelium
- Aqueous fluid is produced at a rate of 2 uL/min.
How is aqueous humor eliminated?
- Fluid drains out of eye through trabecular meshwork (spongy tissue) → - into canal of Schlemm’s and the episcleral venous system (in anterior chamber) → eventually ending up at SVC and RA.
- Drainage system
- Trabecular meshwork → eventually go back into central circulation
- Anything affecting flow → cause increase IOP
- Drainage system
What can happen if elimination of aqueous humor is impaired?
- Open angle glaucoma (OAG): Sclerosis of trabecular meshwork
- chronic elevation
- Closed angle glaucoma (CAG): Obstruction of Aqueous drainage from closure of anterior chamber angle
- CAG Causes:
- Iris swelling
- Anterior displacement
- CAG Causes:
- Pts already w/ narrow angle predisposed to acute increase IOP (PAIN & emergency)
What determines intraocular pressure?
- A measurement of the fluid pressure inside eye
- The globe is a relatively noncompliant compartment and the volume of the internal structures is fixed, except for aqueous fluid and choroidal blood volume.
- The quantity of these two factors regulates intraocular pressure.
- The globe is a relatively noncompliant compartment and the volume of the internal structures is fixed, except for aqueous fluid and choroidal blood volume.
-
Determined by:
- Production of aqueous humor
- Drainage of aqueous humor
- Changes in choroidal blood volume or pressure
- Extraocular muscle tone
- Normal IOP: 10-20 mmHg (~ 16 and +/- 5)
- >25 mmHg, you have problem
What can increases and decrease IOP?
- Drugs:
- Ketamine (?) → theoretically causes issues but does not directly
- Succinylcholine (increases by 8-10 mmHg)
- d/t
- decrease in Aqueous humor outflow
- increase in choroidal BV
- increase in CVP
- d/t
- Other:
- MOST SIG INCREASE → Laryngoscopy & Emergence
- Sympathetic Blunting
- Less manipulation of AW the better (LMA less increase than DL)
- Position changes
- Coughing, valsalva maneuver, straining, vomiting, HTN, injection of local anesthesia, laryngoscopy, hypercarbia/hypoventilation/ hypoxia, lid pressure, eye compression, forceful lid squeeze (increases to 70 mmHg), pupil mydriasis (dilation)
- Increases up to 30-40 mmHg
- MOST SIG INCREASE → Laryngoscopy & Emergence
Decrease:
- Drugs:
- Most anesthetic drugs:
- VA (excluding N2O → no effect)
- Propofol
- Etomidate
- Opioids
- NDMR
- hypertonic solutions
- Dextran
- Mannitol
- Most anesthetic drugs:
- Other: Hypotension, hypothermia, hyperventilation, pupil miosis (constriction)
What are some anesthetics that have no effect on IOP?
- N2O
- Versed
- ~NDNMB
What is acetazolamide?
MOA, S/E?
Carbonic anhydrase inhibitor (topical for eye)- brand Diamox
- Treatment for glaucoma
- Induces:
- decreases IOP*
- diuresis
- reduces aqueous humor production
-
K+ depletion (+/-)
- want preop labs
- SE:
- Confusion
- Drowsiness
- Low K
- Low Na
- Acidosis
- Polyuria
What is echothiophate?
- Tx for glaucoma
- Irreversible cholinesterase inhibitor
- Produces:
- miosis
- Produces:
- Systemic absorption may cause total body inhibition of plasma cholinesterase
-
CAUTION:
- Prolong effects of:
- Succinylcholine
- Mivacuronium
- Toxicity w/ Ester LAs
- Prolong effects of:
-
Very long DOA:
- Need to stop 4-6 weeks preoperatively
-
CAUTION:
Phenylephrine eye drops? s/e?
- Produces mydriasis
- Associated w/:
- severe HTN
- Arrythmias
- Adverse CV events
- Very high [] (1 drop = 5 mg)
What are clycloplegics?
Atropine and Cyclopentolate
- Pupil mydriasis (dilation)
- Systemically absorbed
- SE: See anticholinergic symptoms
- Dry mouth
- Dry skin
- Fever
- Agitation
- disorientation, psychotic reactions
- Central anticholinergic symptoms
- SE: See anticholinergic symptoms
Effect of acetylcholine in eye drops?
- Produces miosis
- Cholinergic agonist
- Causes:
- Bradycardia
- acute bronchospasm
- hypotension
What is timolol?
- Tx of glaucoma
- B1/2 antagonist
- Produces:
- Miosis
- reduction of aqueous humor production
- SE:
- Bradycardia
- Bronchospasm
- CHF exacerbation
- heart block
- Issues w/ nursing infants
NSAID use in eye drops?
- Ketorolac and Diclofenac
- Used for inflammation
Scopalamine effect on eyes?
- Mydriasis (dilation)
- Can causes central anticholinergic syndrome
Scopalamine drug card:
-
CLASS= tertiary amine anticholinergic that crosses BBB; used for motion sickness, PONV, sedation, bronchodilation; biliary & ureteral SM relaxation; NOT used for reversal of NMB
- (Most potent anti-sialagogue (+++) & sedative anti-cholinergic) (+++)
-
MOA:
- Competitively inhibit ACh at the muscarinic receptors & decrease PNS activity (preventing decrease cAMP & cGMP);
- causes sedation by blocking Ach effects @ M1;
- increase HR by blocking the ACh effects @ M2;
- relaxes bronchial smooth muscle & decrease secretions by blocking Ach effects @ M2 & M3; also decrease GI secretions;
- Pharmacokinetics= lipid soluble; onset- 10 min; DOA- 2 hrs; E1/2- 4 hrs- may last 3-7 days; metabolized by the liver with <1% excreted unchanged in urine
- SE= sedation, post-op delerium; increase HR (+), CO, IOP; OH; arrhythmias; blurry vision; decrease secretions (+++) & GI motility; urinary retention; central anti-cholinergic syndrome, bronchodilation (+)
- CI= glaucoma, GI/GU obstruction; caution elderly
- Dose= 0.3-0.6 mg IV q 4-6 hrs, patch over 72 hours
What is the oculocardiac reflex?
Aka Trigeminal-vagal reflex
- Reflex triggered:
- → pressure on globe, pain, and / or traction on extraocular muscles, retrobulbar block, orbital injections, trauma, and hypoventilation (hypercarbia and hypoxemia)
- Ex: *traction on medial rectus muscle
- Pressure on periosteum
-
Afferent limb arises from ophthalmic division of trigeminal nerve → goes to gasserian ganglion and sensory nucleus of trigeminal nerve near the 4th ventricle
-
Afferent limb synapses with motor nucleus of vagus nerve → efferent impulse that travels to heart (via vagus nerve) → leads to:
- Decreases HR
- Decrease contractility
-
Afferent limb synapses with motor nucleus of vagus nerve → efferent impulse that travels to heart (via vagus nerve) → leads to:
- → pressure on globe, pain, and / or traction on extraocular muscles, retrobulbar block, orbital injections, trauma, and hypoventilation (hypercarbia and hypoxemia)
What is the oculocardiac reflex associated with?
- Bradycardia
- atrioventricular block
- ventricular ectopy
- negative inotropy
- asystole
- Occurs most often during strabismus surgery (peds pts)
- Pulling/traction of medial rectus muscle
- May be seen more often under topical anesthesia
- Occurs most often during strabismus surgery (peds pts)
How can you reduce the occurrence of the OCR?
- Maintain normal ETCO2, SpO2
- Pretreat with anticholinergic
- (atropine or glycopyrrolate)→ have ready
- Considerations:
- *Pts typically elderly (increasing HR decreases coronary perfusion pressures)
Treatment of OCR?
- Stop stimulus
- Assess ventilation:
- Correct hypoxia/hypercapnia (can worsen reflex)
- Admin: 100% FiO2
- normal ETCO2? SpO2?
- Correct hypoxia/hypercapnia (can worsen reflex)
- Deepen patient
- Atropine 7 ug/kg increments or Glycopyrolate
- Worsen → Epi
- Local anesthetic (lidocaine) into muscle
Preop assessment of ophthalmic patient?
- High risk population/low risk surgery
- Elderly, co-morbidities
- These Pts cannot typically have outpt sx:
- Severe cardiomyopathy, pulmHTN
- Home O2
- Super morbid obese
- Known DAW
- OK to do just 1 mg Midaz
- Chronic conditions that may make it difficult to lie still and /or supine
- SOB, chronic cough, nasal drip, reflux, nausea
- Parkinson’s, Alzheimer’s or claustrophobia, mentally disabled, back pain, OSA
- These Pts cannot typically have outpt sx:
- Pediatric patient cooperation
- Non-english speaking, deaf
- Might have to consider more than MAC case
- EKG not indicated per AHA/ACC
- NEED to educate pt on what to expect. pt needs to stay still, will have blue drape over face
- 30% of eye injury during ophthalmic surgery with anesthesia were related to patients moving.
- Blindness was the outcome in all cases!
- Most problems occurred under GA, 25% under MAC.
- **Ensuring pt immobility during the procedure are therefore of the utmost importance


