ENT I Flashcards
1
Q
What are the 3 main chambers of the eye?
What are the 3 layers of the wall of the globe?
A
- 3 main 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
- 3 layers of wall of globe
- Sclera
- Uveal tract
- choroid- layer of blood vessels
- Iris- controls light entry
- Ciliary body- produces aqueous humor
- Retina
2
Q
What are the different parts of the eye?
Conjunctiva
cornea
aqueous humor
Schlemm’s canal
pupil
lens
A
- Conjunctiva is clear membrane that covers the sclera in the front of the eye
- Cornea (part of sclera) is a strong clear bulge located at the pront of the eye
- Aqueous humor is a watery substance located in the anterior chamber of the eye
- Schlemm’s canal is a channel in the eye that collects aqueous humor from the anterior chamber and delivers it into the bloodstream
- pupil is formed by the iris
- lens of the eye is a flexible unit that consists of layers of tissue enclosed in a tough capsule
3
Q
What are the 6 extraocular muscles of the eye?
CN innervation?
movement?
A
- Innervated by oculomotor nerve–CN III
- Eye movements, pupil constriction, opens eyelids
- Superior rectus
- inferior rectus
- medial rectus
- inferior oblique
- Eye movements, pupil constriction, opens eyelids
- Innervated by Trochlear nerve–CN IV
- moves eye down and out
- superior oblique
- moves eye down and out
- innervated by abducens nerve– CNVI
- moves eye lateral
- lateral rectus
- moves eye lateral
4
Q
What nerve provides sensory innervation to the eye?
A
- Trigeminal nerve CN V
- Opthalmic branch- upper eyelid, conjunctiva, and cornea
- Nosociliary branch of opthalmic nerve is sensory to medial canthus, lacrimal sac, and ciliary ganglion
- Maxillary branch- lower lid
- Opthalmic branch- upper eyelid, conjunctiva, and cornea
5
Q
What is the function of Cranial Nerve II?
A
- Optic nerve
- vision
- It is part of the optic chiasm along with the artery, vein, and sympathetic nerves
- Injury to the optic nerve can cause total blindness
6
Q
Aqueous humor
How is it produced?
How is it eliminated?
A
- Production:
- 1/3 produced in the posterior chamber by the ciliary body and then actively moved from posterior chamber to anterior chamber by an active sodium pump mechanism
- 1.3 comes from passive filtration through vessels in the iris
- produced at rate of 2 µL/min
- Elimination:
- fluid drains out of the eye through a spongy tissue called the trabecular meshwork into canal of Schlemm’s and the episcleral venous system located in the anterior chamber, eventually ending up at the SVC and RA
7
Q
What is IOP measuring?
How is it measured?
A
- IOP is the measurement of the fluid pressure inside the eye
- the globe is a relatively noncompliant compartment and the volume of the internal structures is fixed, except for the aqueous fluid and choroidal blood volume
- The quantity of the aqueous fluid and choroidal blood volume regulates intraocular pressure
- IOP 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
8
Q
What can increase intraocular pressure?
What can decrease intraocular pressure?
A
- Increase:
- drugs- ketamine, succ
- position changes
- coughing
- valsalva, straining
- vomiting
- HTN
- LA
- laryngoscopy
- hypercarbia/hypoventilation/hypoxia
- lid pressure
- eye compression
- mydriasis (dilation)
- Decreased:
- drugs- most anesthetic drugs, NDMR, hypertonic solutions, dextra, mannitol
- hypotension
- hypothermia
- hyperventilation
- pupil miosis (constriction)
9
Q
Topical opthalmic drugs:
Acetazolamide (diamox)
Ecothiophate
A
- Acetazolamide (Diamox)
- topical carbonic anhydrase inhibitor
- used to treat gloucoma
- induces diuresis, decreases IOP, reduces aqueous humor production
- may cause K depeletion, want pre-op labs
- Ecothiophate
- topical plasma cholinesterase inhibitor
- used to tx gloucoma
- produces miosis
- systemic absorption may cause total body inhibition of plasma cholinesterase
- caution with Succ, mivacuronium, and toxicity with ester-type anesthetics
- very long duration of action, stop 4-6 wks preop
10
Q
Topical Ophthalmic drugs:
Phenylephrine
Acetylcholine
Timolol
A
- Phenylephrine
- topical alpha agonist
- produces mydriasis
- associated with severe HTN
- Acetylcholine
- produces miosis
- Can cause bradycardia and acute bronchospasm
- Timolol
- topical beta blocker
- used to tx gloucoma
- produces miosis; reduction of aqueous humor production
- may cause bradycardia, bronchospasm, exacerbation of CHF, hearth block
- topical beta blocker
11
Q
Topical ophthalmic drugs
Ketorolac and diclofenac
Mitomycin C
Atropine and Cyclopentolate
A
- Ketorolac and Diclofenac
- used for inflammation
- Mitomycin C
- chemotherapeutic drug
- Atropine and cyclopentolate
- cycloplegic (paralizes ciliary muscles of the eye)
- pupil dilation
- SE: agitation, disorientation, psychotic reactions
12
Q
What is the Oculocardiac reflex?
A
- Trigeminal-vagal reflex
- Pressure on the globe of the eye, pain, or traction on the extraocular muscles causes bradycardia, atrioventricular block, ventricular ectopy, negative inotropy or asystole
- Can also be caused by:
- retrobulbar block
- orbital injections
- trauma
- hypoventilation
- Occurs most often during strabismus surgery
- esp under topical anesthesia
13
Q
Oculorcardiac Reflex:
How can you reduce occurence?
How can you treat?
A
- To reduce occurence:
- maintain normal ETCO2, SpO2
- pretreat with anticholinergic (atropine or glyco)
- Treatment
- stop stimuus
- assess ventilation
- Atropine 7µg/kg
- LA (lidocaine) into muscle
14
Q
What should your pre-op assessment include for an opthalmic case?
A
- May be high risk population
- Elderly have co-morbidites
- may not be able to lie still or supine w/some chronic conditions
- SOB, cough, nasal drip, reflux, OSA, back pain
- Pediatric patient may be difficult to get to cooperate
15
Q
How should you prepare for an opthalmic case?
A
- make sure pre-op ophthalmic drops are given
- continue home medications
- educate pt about being awake/still during to surgery
- avoid over-hydration
- control HTN
- control BS
- No steroid coverage needed
- dry secretions
- treat reflux
- good operative positioning.
18
Q
Retrobulbar block:
Procedure
complications
A
- Procedure:
- LA instilled by injection posterior to eye directly into the orbital cone
- 2% lidocaine/0.75% bupivicaine, 1:1 ration, 2-3 ml
- hyaluronidase assed for tissue penetration
- provides akinesia and analgesia
- Complications
- Retrobulbar hemorrhage (most common)
- Globe perforation
- OCR
- sz
- resp arrest
19
Q
Peribulbar block:
compared to retrobulbar
onset time
complications
Technique
A
- Safer than retrobulbar block b/c muscle cone is not penetrated (it goes into the extraconal space)
- Slower onset of action (10 min vs 5 min)
- requires higher volumes of LA
- Lower incidence of complete akinesia of eye
- Globe perforation and failure of block are most common complications
- Technique:
- blunt needle is inserted thru skin and advanced along the orbit floor directed parallel to the globe, thru the lower lid, toward the sphenoid bone. Local anesthetic is instilled into the extraconal space (outside the muscle cone) and will slowly penetrate toward the optic nerve.
20
Q
Sub-tenon block:
Where is it done?
What does it do?
SE
A
- LA injected under Tenon’s fascia
- Analgesia for the iris and anterior eye
- SE: some conjunctival edema
21
Q
What block provides anesthesia to the eyelids?
Complications?
A
- Facial nerve block (CN VII)
- Complications:
- facial droop
- vocal cord paralysis
- respiratory distress
25
Q
What is Gloucoma?
A
- Increased IOP
- Open-angle
- Sclerosis of trabecular tissue- develops slowly and bilaterally
- Angle btwn iris and cornea is correct, but drainage canals become clogged
- Tx: miosis, decrease production of aqueous humor, and trabecular stretching
- Angle closure or closed angle
- peripheral iris moves into direct contact with cornea, mechanically obstructing aqueous flow
- acute process
- Tx: immediate surgery
- peripheral iris moves into direct contact with cornea, mechanically obstructing aqueous flow
28
Q
What is Retinal detachment?
What are the surgical treatments?
A
- A separation of the retina from its attachments to its underlying tissue within the eye
- most are result of a retinal break, hole, or tear
- Surgical treatments:
- scleral buckle
- vitrectomy
- pneumatic retinopexy
- cryotherapy
