Mod9: Anesthesia for Ophthalmic Surgery

Question 1

_{Ocular Anatomy}

Protective fibrous outer layer of the eye

^{White part of the eye}

Answer 1

Sclera

Question 2

_{Ocular Anatomy}

Function of the Sclera

Answer 2

Provides sufficient rigidity to maintain globular shape of the eye

Question 3

_{Ocular Anatomy}

Anterior portion within the sclera

Answer 3

Cornea

Transparent, permits light to enter for translation to the brain

Question 4

_{Ocular Anatomy}

Colored part of the eye

Answer 4

Iris

Surrounds the Pupil

Divides posterior chamber from anterior chamber

Question 5

_{Ocular Anatomy}

Opening through the cornea that controls light levels entering eye?

Answer 5

Pupil

Question 6

_{Ocular Anatomy}

Alpha-1 stimulation

^causes:

Answer 6

Mydriasis

Dilation (sympathetic innervation)

Question 7

_{Ocular Anatomy}

Parasympathetic innervation

^causes:

Answer 7

Miosis → constriction

Question 8

_{Ocular Anatomy}

Structure that Produces aqueous humor

(Watery substance between lens/cornea)

Answer 8

Ciliary body

Question 9

_{Ocular Anatomy}

Space at the junction of the sclera and cornea in the eye

(Drains aqueous humor)

Answer 9

Schlemm’s canal

Question 10

_{Ocular Anatomy}

Structure that converts light impulses to neural impulses that travel via optic nerve to brain

Answer 10

Retina

Question 11

_{Ocular Anatomy}

Vascular layer of the eye lying between the retina and the sclera

Answer 11

Choroid

Provides O2/nourishment to outer layers retina

Question 12

_{Ocular Anatomy}

Mucous membrane covering globe

Lining eyelids

Answer 12

Conjunctiva

Topical administration drugs

Question 13

_{Ocular Anatomy}

6 muscles move eye within the globe

Answer 13

Intraocular muscles

Question 14

_{Ocular Physiology}

Formation of Aqueous Humor

^{Where and How?}

Answer 14

Posterior chamber by ciliary body (2/3rd)

Active secretory process involving carbonic anhydrase

Passive filtration from vessels on anterior surface iris

Question 15

_{Ocular Physiology}

Drainage of Aqueous Humor

^How?

Answer 15

Via network connecting venous channels empty into SVC/RA

Travels though pupillary aperture to anterior chamber

Exits via Fontana’s spaces into the canal of Schlemm

Connecting venous channels empty into SVC

Question 16

_{Ocular Physiology}

Pathway of Aqueous Humor

^{See picture}

Answer 16

Pathway of Aqueous Humor

Question 17

_{Ocular Physiology}

Glaucoma

^{Pathophysiology}

Answer 17

Impaired aqueous humor drainage

leading to increase intraoccular pressure and possible damage to eye structures

Question 18

_{Ocular Physiology}

Treatment of Glaucoma

^{Two folds:}

Answer 18

1. Promote miosis/trabecular stretching

=> Increase aqueous drainage/outflow

^{Drainage of aqueous humor is facilitated by miosis}

2. Decrease aqueous humor production

Question 19

_{Ocular Physiology}

Treatment of Glaucoma

^{Common topical medications}

Answer 19

Beta-blockers (Timoptic/Betoptic)

Anticholinesterases (Echothiophate)

Carbonic anhydrase inhibitors (Acetazolamide)

Cholinergic agonist (Pilocarpine)

Question 20

_{Ocular Physiology - Treatment of Glaucoma}

Beta-blockers (Timoptic/Betoptic)

^{How do they work here? Concerns?}

Answer 20

↓ aqueous production

_Concerns:

Bradycardia, bronchospasm, CHF

Question 21

_{Ocular Physiology - Treatment of Glaucoma}

Anticholinesterases (Echothiophate)

^{How do they work here? Concern?}

Answer 21

Produce miosis

_Concern:

Prolong succinylcholine duration → paralysis

_{Anticholinesterases primary mechanism of action is to inhibit true cholinesterase.}

_{Recognize that cholinesterase inhibitors act indirectly by raising the concentration of acetylcholine at synapses.}

Question 22

_{Ocular Physiology - Treatment of Glaucoma}

Carbonic anhydrase inhibitors (Acetazolamide)

^{How do they work here? Concern?}

Answer 22

↓ aqueous production

_Concern:

Diuresis K+ /HCO3 → hypokalemia/ hyperchloremic metabolic acidosis

_{Acetazolamide (Diamox) is classified as a weak diuretic.}

_{It works by inhibiting carbonic anhydrase.}

_{Acetazolamide is used primarily to decrease intraocular pressure.}

_{Inhibition of carbonic anhydrase in the ciliary process of the eye reduces the formation of aqueous humor, which in turn leads to a decrease in intraocular pressure.}

_{When administered chronically to lower intraocular pressure, there may be an associated renal loss of bicarbonate and potassium ions}

Question 23

_{Ocular Physiology - Treatment of Glaucoma}

Cholinergic agonist (Pilocarpine)

^Effect:

Answer 23

Produces miosis

Question 24

_{Ocular Physiology - Treatment of Glaucoma}

Anticholinergics

→

Answer 24

Pupillary dilation/mydriasis

TOPICALLY may precipitate open angle glaucoma (Atropine > Glycopyrrolate).

However, premedication doses administered systemically are not associated with increases in IOP

Question 25

_{Ocular Physiology - Glaucoma} **Normal eye** ^{Flow of aqeous humor}

Answer 25

(see picture) Note: Flow of fluid from (aqeous humor) from the inner chamber to the outer chamber This fluid is free to drain through the drainage channel of the CANAL OF SCHLEMM at the outer edge of the iris

Question 26

_{Ocular Physiology - Glaucoma} **Eye with Glaucoma** ^{Flow of aqeous humor}

Answer 26

(See picture) Note: Flow of fluid stays within the eye and pressure rises The Iris presses againts the lens, blocking the drainage of fluid

Question 27

_{Ocular Physiology} Measurement of fluid pressure within the eye ^{Known as:}

Answer 27

Intraocular Pressure

Question 28

_{Ocular Physiology - Intraocular Pressure} **Determinants** of Intraocular Pressure

Answer 28

**Aqueous humor** volume **(major)** ^{Coupling of production/drainage} **Choroidal** blood volume

Question 29

_{Ocular Physiology - Intraocular Pressure} ## Footnote **Normal Intraocular Pressure**

Answer 29

**12 - 20 mmHg** Becomes atmospheric when globe is opened

Question 30

_{Ocular Physiology - Intraocular Pressure - Increases Intraocular Pressure} **Jeopardized retinal perfusion** ^{could lead to:}

Answer 30

Retinal ischemia | (Ultimately =\> Blindness)

Question 31

_{Ocular Physiology} ## Footnote **Factors Increasing Intraocular Pressure**

Answer 31

Anything that↓ Drainage/outflow aqueous humor ^{(Glaucoma, increased CVP)} ↑ Blood volume Anesthetic events Hypercarbia Hypoxemia ↓ Globe size without proportional change in volume of contents External pressure on globe

Question 32

_{Ocular Physiology - Factors Increasing Intraocular Pressure} **↓ Drainage/outflow aqueous humor** ^{possible causes:}

Answer 32

Glaucoma ↑ CVP

Question 33

_{Ocular Physiology - Factors Increasing Intraocular Pressure} **↑ Blood volume** ^{How does it inc IOP?}

Answer 33

**Impedance blood flow from eye to right atrium** ↑ CVP (most profound) ↑ ABP (extreme) Venous effect \> arterial _{[Obstruction between eye & right atrium impedes drainage = increases intraocular pressure]}

Question 34

_{Ocular Physiology - Factors Increasing Intraocular Pressure} **Anesthetic events** _{that increase intraocular pressure?}

Answer 34

Laryngoscopy Intubation Coughing Bucking Vomiting T-burg position

Question 35

_{Ocular Physiology - Factors Increasing Intraocular Pressure} **Hypercarbia** ^{How does it cause increased intraocular pressure?}

Answer 35

...

Question 36

_{Ocular Physiology - Factors Increasing Intraocular Pressure} **Hypoxemia** ^{How does it cause increased intraocular pressure?​}

Answer 36

...

Question 37

_{Ocular Physiology - Factors Increasing Intraocular Pressure} **↓ Globe size** _{without proportional change in volume of contents} ^{How does it cause increased intraocular pressure?}

Answer 37

...

Question 38

_{Ocular Physiology - Factors Increasing Intraocular Pressure} ## Footnote **External pressure on globe**

Answer 38

Tight mask fit Tumor Contraction ocular muscles (recti/orbicularis oculi) Scleral rigidity Retrobulbar hemorrhage/detachment Improper prone position

Question 39

_{Ocular Physiology} ## Footnote **Anesthetic Agents Decreasing IOP**

Answer 39

**Volatile agents (↓↓)** N2O (↓) **Barbiturates** and **benzodiazepines (↓↓)** Narcotics (↓) NDMR (0/↓)

Question 40

_{Ocular Physiology - Anesthetic Agents Decreasing IOP} **Volatile agents (↓↓)** ^{How do they decrease IOP?}

Answer 40

**↓ BP & choroidal blood volume** **Relaxation ocular muscles** ^{=> Lowers wall tensions} **Pupillary constriction** ^{=> Promotes aqueous outflow} **Proportional to depth of anesthesia**

Question 41

_{Ocular Physiology - Anesthetic Agents Decreasing IOP} ## Footnote Why will the Surgeon need access to the eye very early on in the case?

Answer 41

The more exposure to anesthetic agents, the further away the surgeon will assess the intraoccular pressure that the pt actually lives in

Question 42

_{Ocular Physiology - Anesthetic Agents Increasing IOP} **Succinylcholine (↑↑)** ^{How much increase in IOP does it cause?}

Answer 42

↑ IOP **5-10 mmHg** for **5-10 minutes** Repeated depolarization → Prolong contracture → ↑IOP Extraocular muscles contain cells with multiple NMJ ^{(unlike other skeletal muscle)}

Question 43

_{Ocular Physiology - Anesthetic Agents Increasing IOP} **Succinylcholine (↑↑)** ^{Concerns regarding use:}

Answer 43

**Spurious IOP** measurements during Exam Unde Anesthesia **Extrusion** of ocular contents **open globe** ^{(surgical incision/trauma)} **Abnormal forced duction test for 20 min** ^{=> Measures cause EOM imbalance with strabismus => Influence type surgery performed repair}

Question 44

_{Ocular Physiology} **Anesthetic Agents** with **Questionable effect** on **Increased IOP**

Answer 44

**Ketamine** **Etomidate**

Question 45

_{Anesthetic Agents with Questionable effect on Increased IOP} **Ketamine** ^concerns:

Answer 45

=\>↑ ABP =\> No muscles relaxation (nystagmus)

Question 46

_{Anesthetic Agents with Questionable effect on Increased IOP} **Etomidate** ^concerns:

Answer 46

=\> Myoclonus hazardous with open-globe injury