Ophthalmic Flashcards
What is the leading cause of blindness worldwide?
Cataracts
- Leading cause of poor vision in the USA
What is the leading cause of new blindness cases among adults 20-74yo?
Diabetes
Eyeball
Globe
Adult volume = 30mL
Visual Axis
Optic axis - imaginary line from cornea midpoint to retina or macula midpoint
Axial length measures the visual axis
Normal Visual Axis Length
23-23.5mm
Hyperopia
Farsighted
Globe < 22mm long
Myopia
Nearsighted
Axial length >24mm
↑risk globe puncture
Anterior Segment
Two chambers:
- Anterior
- Behind the cornea
- Filled w/ aqueous humor produced by ciliary body - Posterior
- Contains the lens
Posterior Segment
Vitreous humor
Retina
Macula
Optic nerve root
Optic Nerve
Cranial nerve II
Optic nerve orbital portion 25-30mm long & travels posteriorly w/in the muscle cone
4mm diameter
NOT A TRUE CRANIAL NERVE
Central retinal artery & vein surround the nerve
What is the optic nerve?
Outgrowth of the brain
Covered by meninges - pia, arachnoid, dura
Anything injected into the nerve sheath can travel directly to the brain via CSF
Oculomotor Nerve
Cranial nerve III
Innervates the superior rectus, inferior rectus, inferior oblique, medial rectus, & levator
1° motor nerve to the extraocular orbit muscles
Sends PSNS fibers to the ciliary ganglion - innervate iris sphincter muscles to cause pupil constriction
SNS motor fibers control pupil dilation
Trochlear Nerve
Cranial nerve IV
Provides motor fibers to the superior oblique muscle
Only orbital cranial motor nerve that enters the orbit from outside the muscle cone
Travels in medial direction to innervate the superior oblique muscle
Trigeminal Nerve
Cranial nerve V
Sensory & motor
Intracranial portion forms the trigeminal ganglion
- Ophthalmic, maxillary, & mandibular divisions
Ophthalmic Nerve
Trigeminal nerve branch
Provides pain, touch, & temperature sensation to the cornea, ciliary body, iris, lacrimal gland, conjunctiva, nasal mucosa, eyelid, eyebrow, forehead, & nose
- Lacrimal, frontal, & nasociliary
Frontal = largest branch
Nasociliary sends nerve fibers medially & to the ciliary ganglion
Maxillary Nerve
Trigeminal nerve branch
Provides pain, touch, & temperature sensation to the upper lip, nasal mucosa, & scalp muscles
Abducens Nerve
Cranial nerve VI
Motor function to the lateral rectus muscle
Facial Nerve
Cranial nerve VII
Provides motor function to the facial muscles
Upper & lower branches
Upper branch innervates the orbicular muscle, superficial facial, & scalp muscles
Vagus Nerve
Cranial nerve X
Motor function to the intrinsic muscles in the larynx & heart
PSNS visceral innervation
*Efferent pathway for oculocardiac reflex
Extraocular Muscles
- Superior rectus - moves the eye upward
- Inferior rectus - moves eye downward
- Medial rectus - moves eye nasally
- Lateral rectus - moves eye laterally
- Superior oblique - rotates eye on horizontal axis towards the nose
- Inferior oblique - rotates eyeball on horizontal axis temporally
Superior Rectus
Cranial nerve III
Supraduction
Inferior Rectus
Cranial nerve III
Infraduction
Medial Rectus
Cranial nerve III
ADduction
Lateral Rectus
Cranial nerve VI
ABduction
Superior Oblique
Cranial nerve IV
Intorsion, depression
Inferior Oblique
Cranial nerve III
Extorsion, elevation
Normal IOP
10-20mmHg
What determines IOP?
Aqueous humor dynamics - balance b/w production & elimination
Changes in choroidal blood volume - vascular meshwork in the posterior chamber
↑venous blood pressure
Extraocular muscle tone
Aqueous Humor
Thin, watery fluid that fills the space in the anterior chamber b/w the cornea & iris
- Nourishes the cornea & lens
- Gives the anterior eye form & shape
Continually produced by the ciliary body (lies behind the iris)
Drains out via trabecular meshwork into the aqueous veins & then into orbit veins
↑IOP
Eyelid muscle contraction Blinking 5mmHg Squinting 26mmHg Cardiovascular or respiratory variables (CVP, ABP, PaCO2) *Laryngoscopy & intubation External pressure Positioning - prone Succinylcholine Topical anticholinergics
↓IOP
Volatile anesthetics IV anesthetics (exception: Ketamine) Non-depolarizing muscle relaxants Benzodiazepines Narcotics
Succinylcholine
↑IOP 5-10mmHg for 5-10 minutes
MOA unclear
Result from prolong extraocular muscle contraction?
No consistent method to prevent increase
Pediatric laryngospasm dose 4mg/kg IM or 1-2mg/kg IV (10mg)
Oculocardiac Reflex
Afferent transmission via Trigeminal nerve V
Efferent transmission via Vagus nerve X
Pull on muscle → bradycardia
Causes - pain, pressure, or eyeball manipulation
Traction on medial rectus muscle common
Oculocardiac Reflex S/S
Cardiac dysrhythmias (bradycardia, sinus arrest, V-fib, AV block, ventricular ectopy) Negative inotropy
During what surgery does the oculocardiac reflex most commonly occur?
Pediatric strabismus surgery
Oculocardiac Reflex Treatment
Anticholinergics pre-treatment (?)
Stop the stimulus or release pressure
Administer Atropine 10mcg/kg or Glycopyrrolate
LA infiltration into medial rectus muscle
Detached Retina Surgical Repair
Small gas bubble injected into posterior chamber to hold retina in place
Sulfur hexafluoride most commonly used
- Inert, poorly diffusible gas
- Less soluble in blood than nitrogen & N2O
- DOA 10 days
Bubble expands 2x in 24 hours
Discontinue N2O 20 minutes prior to injection to allow washout
Avoid N2O 10-14 days after sulfur hexafluoride
Echothiophate
IRREVERSIBLE cholinesterase inhibitor Glaucoma treatment Systemic absorption → ↓plasma cholinesterase activity Lasts 3-6 weeks after discontinuation Succinylcholine prolonged 20-30 minutes Extend ester local anesthetics duration
Topical Eye Medications
Enter bloodstream via outer eye membrane & lacrimal apparatus
Close eyes 60 seconds after gtt instilled to improve absorption
Avoid blinking
Block tear outflow canal (place finger over medial canthus)
What are the most commonly performed intraocular procedures?
Cataract & vitreoretinal surgeries
Ocular Regional Anesthesia
Peribulbar block
Retrobulbar block
Facial nerve block
Peribulbar Block
Inject LA outside the muscle cone
Injection above and/or below orbit
Provides eye analgesia & akinesia
Typically more patchy - requiring additional supplementation throughout the case (request surgeon admin more LA)
Relatively low complication rate
Safer choice d/t less hemorrhage & central spinal risk
Peribulbar Block
Disadvantages
↑volumes injected 6-8mL ↑IOP Slower onset (5-10 minutes) Possible globe perforation Vertical diplopia (myotoxicity from LA)
Peribulbar Block
Technique
Patient looks straight ahead
Avoid vasculature & optic nerve
Dull, short-beveled 25-27G 22mm needle
Insert needle lateral aspect of the inferotemporal quadrant & superior-nasal
ASPIRATE slowly before injection
Inject 6mL local anesthetic
Lidocaine + Bupivacaine (+/- Epi 1:400,000)
Retrobulbar Block
Inject LA inside the muscle cone
Provides eye analgesia & akinesia* (better akinesia for surgeon)
↑complication rate as compared to peribulbar block
Hemorrhage risk d/t anesthetic injection inside the muscle cone
Retrobulbar Block
Technique
Insert 25G needle through lower lid at lateral third junction & medial 2/3 inferior orbital edge
Advance 25-35mm (19-31mm safest) toward orbit apex
ASPIRATE & inject 2-5mL local anesthetic
Lidocaine & Bupivacaine most common
Retrobulbar Block
Complications
1:500 blocks Trauma to optic nerve Vision loss *Retrobulbar hemorrhage Globe perforation Oculocardiac reflex Brainstem anesthesia (injection into optic nerve sheath) - Central LA spread to CSF causing hemodynamic instability & respiratory depression w/in 5min IV or intra-arterial injection Seizure Respiratory or cardiac arrest *Usually occur w/in 15 minutes after block
Retrobulbar Block
Contraindications
Bleeding disorders
Anticoagulation
Extreme myopia
Open eye injury
Sub-Tenon (Episcleral) Block
Local anesthetic placed into potential space b/w tenon’s capsule & sclera
Inferonasal conjunctival fornix most commonly used
Direct needle posteriorly following globe curve
Superficial injection allows LA to spread circularly around scleral globe portion (3-5mL)
Larger volume (8-11mL) allows spread to extraocular muscle sheaths
Deep injection - posterior intra & extraconal spaces (2-5mL) most common
Facial Nerve Block
Facial nerve periocular branches
Prevent excessive blinking during eye surgery
What are indications for general anesthesia?
Pediatric patient Uncooperative patient Severe claustrophobia Inability to communicate Inability to lie flat Open-eye injuries Procedures w/ duration > 2 hours
General Anesthesia
Disadvantages
Nausea/vomiting ↑IOP Aspiration Complications 2° to medical problems (i.e. cardiovascular disease) Time \$\$$
Medication Considerations
Synergistic effects
Pediatric/elderly dosing
Circulation time
Intraop Management
Block sedation (short-acting agents) Sedation not required w/ adequate block Rotate HOB 90-180° Standard monitors Oculocardiac reflex Temperature Fluids Consider "light" GA w/ stimulation Hypotension Oxygen & cautery → airway fire risk Corneal abrasion risk Retinal artery occlusion
Postop Management
PONV (especially pediatrics)
Postop eye pain unusual - indicates corneal abrasion or acute intraocular HTN (treat w/ Mannitol or Acetazolamide)
Elderly patients w/ MI history ↑risk ischemic events even under LA - consider periop β blockers
Strabismus
Ocular misalignment
Intervention before 4mos to allow normal stereoscopic visual development
↑MH risk associated w/ underlying myopathy
Avoid triggers
What is the most common ophthalmic condition requiring surgical repair in children?
Strabismus
Strabismus Surgical Correction
Lengthens/shortens ocular muscles to straighten eyes & allow binocular vision
30-60 minutes
General anesthesia
Minimal EBL
PONV prevention - hydration, ↓opioids, avoid N2O, Propofol, LA infiltration near extraocular muscle, antiemetics (Decadron 0.1mg/kg or Zofran 0.1mg/kg)
Painful procedure - Tylenol 15mg/kg, Toradol 0.5mg/kg, & Fentanyl 1-3mcg/kg
Penetrating Eye Injuries
Full stomach precautions
Aspiration risk
Prevent ↑IOP
Open Globe
Full-thickness cornea (transparent outer covering) or sclera (white outer covering) defect Emergency surgery w/ GA Succinylcholine risk vs. benefit Laryngoscopy & intubation ↑IOP Antibiotics - Vancomycin & Zosyn
Aspiration Prevention
Do NOT attempt to evacuate contents w/ NG tube preop
Admin Metoclopramide IV, H2 antagonists (Ranitidine), and/or non-particulate antacid prior to induction
Do NOT attempt regional anesthesia LA injection ↑IOP
Attempt RSI w/ cricoid pressure & avoiding PPV
Extubate awake, spontaneously breathing, & head turned to side
Prevent ↑IOP
AVOID
AVOID direct pressure on eye AVOID Trendelenburg position AVOID regional anesthesia AVOID ↑CVP AVOID drugs ↑IOP AVOID agitation in young children
Ophthalmic Anesthesia Complications
Retrobulbar hemorrhage Globe puncture Optic nerve sheath trauma IV injection Ocular ischemia Extraocular muscle palsy & ptosis Facial nerve blocks Oculocardiac reflex Corneal abrasion Central retinal artery occlusion d/t prolonged pressure
Complications
Retrobulbar Hemorrhage
Results from trauma to an orbital vessels
Moves eyeball forward
Venous hemorrhage - slow onset
Arterial - rapid onset & pronounced proptosis
Treatment:
- Digital pressure
- Lateral canthotomy (cut lateral canthus) ↑orbital space → place hemostat in temporal direction along lateral canthus 4-6mm & clamp hemostat, use scissors to incise the crush marks left by hemostat, control local bleeding
Complications
Globe Puncture
↑IOP caused by injection (sharp or dull needles)
Risks include myopic eye, scleral thinning, scleral buckling, & sclera bulging
Prevention - avoid supranasal gaze position, direct needle away from globe axis during insertion, insert needle slowly w/ bevel towards globe, never forcefully inject LA, use modified techniques
S/S ↑resistance to injection, pupil dilation/ paralysis, ↑IOP, hemorrhage
Complications
Optic Nerve Sheath Trauma
Optic nerve sheath surrounds the optic nerve
- Outer sheath contains dura mater
- Inner sheath consists arachnoid & pia mater
Subarachnoid space contains CSF & continuous w/ optic chiasm
Dura splits into 2 layers at optic foramen
Inner layer forms optic nerve dural covering & forms orbital epidural space
*Observe contralateral pupil block
Contralateral pupil constricted → dilated after block → assume subarachnoid/subdural injection & prepare for respiratory arrest
Complications
Ocular Ischemia
Retinal vascular occlusion or thrombosis reported after ocular blocks
↓pulsatile ocular blood flow after blocks
Optic nerve atrophy reported after regional block or GA
Transient optic nerve injury symptoms - include contralateral amaurosis or respiratory arrest or vascular occlusion/thrombosis → vision loss
Complications
Extraocular Muscle Palsy & Ptosis
Inferior muscle palsy reported after retrobulbar anesthesia
Persistent vertical diplopia (double vision)
Surgical intervention indicated
Prevention - avoid needle contact w/ extraocular muscles, avoid deep orbital penetration, avoid angling needle toward visual globe axis
LA myotoxicity may cause postop diplopia and/or ptosis
Complications
Facial Nerve Block
Cranial nerve VII
Bell’s palsy 2° to direct nerve trauma
S/S - dysphagia, hoarseness, coughing & respiratory distress
Vagus, glossopharyngeal, & spinal accessory nerves close proximity
Prevention:
- Avoid large volume LA
- Avoid Nadbath block technique in certain patients
- Airway concerns → intubate
Bells Phenomenon
When the eyeballs move upward & outward in response to the eyes being forcefully closed
Protective reflex to prevent corneal injury
AKA “belling”
Requires MAC 1.8 to abolish this reflex
Fluorescein
EUA Dye used to visualize the retina images & leaks around corneal surgical sites Dose 5-7mg/kg IV push fast (similar to Adenosine) Wear gloves when prepare & admin
Retinoblastoma
Ocular retina cancer 1° affects children < 4yo Tumor present in the eye or bilateral Curable, but ↑risk cancers later in life Monthly check-ups EUA → laser or cryotherapy
Amblyopia
Lazy eye
Children 0-7yo
Initial treatment w/ eye patches or dilation drops on the stronger eye to force the weaker eye to work
Corneal Transplant Melts
Corneal transplant rejected or suture to the eye has come undone, leaving an opening to the eye
General anesthesia
LMA or ETT dependent on melt severity
Surgical treatment - few sutures or completely remove the original transplant & replace w/ new one
Canaliculi Repairs
Inner or outer canthus repair
Common in younger children from dog bites or scratches
Fairly quick procedure
Performed by plastic surgery resident
Endopthalmitis
Tissue or fluid infection INSIDE the eyeball
Surgery performed after patient not responded to conservative measures → infection now in the vitreous
Vitrectomy performed by retina surgeon to remove infected vitreous gel & inject antibiotics into the eye
Possible peribulbar block however not effective in severe infections
Tetracaine
Local anesthetic gtt Numbing eye drops - Eye only holds 0.5mL - Admin 2-6 drops divided in doses 1-2min apart Utilize w/ PRN sedation
Diamox
Acetazolamide
Carbonic anhydrase inhibitor used to lower IOP
↓aqueous humor production in anterior eye
Adult dose 150-500mg
Mix w/ NS
Admin at end procedure
IV incompatible w/ Zofran
Contraindicated in patients w/ Sulfa allergies
