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Boards: Other Topics (Endocrine, CPR, Euthanasia, etc) > Ophthalmology > Flashcards

Ophthalmology Flashcards

1
Q

Main goal of ophthalmic anesthesia

A

prevent unwanted increases in IOP

Increased IOP = pressure on optic N = vision loss

Also want to prevent sudden increases in IOP in patients with partial/imminent loss of globe integrity to avoid complete rupture ie desmetocele, trauma, deep corneal ulcer

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2
Q

Aqueous Humor

A

similar to blood plasma but low protein, fills space in front of eyeball btw lens and cornea, maintains IOP, provides nutrients to eye

Comprises anterior, posterior chamber

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3
Q

Vitreous humor

A

clear gel that fills space btw lens, retina; provides nutrients to eye and helps eye hold shape

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4
Q

Dorsal Rectus M

A

CNIII

Elevation, medial rotation of globe

Intraconal

Deficit: ventrolateral strabismus

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5
Q

Medial Rectus M

A

CNIII

Adduction of Globe

Intraconal

Deficit: ventrolateral strabismus

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6
Q

Ventral Rectus m

A

CNIII

Depression, lateral rotation of globe

Intraconal

Deficit: ventrolateral strabismus

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7
Q

Superior elevator palpebral/levator palpebrae superioris

A

CNIII

Retracts superior eyelid

Intraconal

Deficit: Ptosis

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8
Q

Retractor Bulbi m

A

CNIII

Pulls globe into socket

Intraconal

Deficit: exophthalmus

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9
Q

Ventral Oblique m

A

CNIII

Elevation, lateral rotation

Intraconal

Deficit: VL strabismus

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10
Q

Dorsal Oblique m

A

CV IV

Medial Rotation of Globe

Intraconal

Deficits: Rotational strabismus, looking down

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11
Q

Lateral Rectus m

A

CN VI

Abduction

Intraconal

Deficits: Medial Strabismus

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12
Q

What else is supplied by CN III?

A

Parasympathetic visceral motor innervation to pupillary constrictor m anisocoria

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13
Q

CN V - branches

A

ophthalmic

maxillary

ciliary

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14
Q

Ophthalmic Br of CN V

A

exits via orbital fissure: lacrimal N, nasociliary, frontal N

Br of nasociliary = infratrochlear = medial canthus

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15
Q

Maxillary Br of CN V

A

exits via round foramen: zygomaticofacial N = lateral canthus

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16
Q

Sympathetic Innervation of Eye

A

T1-T3 SC segments -> vagosymapthetic trunk –> cranial cervical ganglion –> ophthalmic br CN V

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17
Q

Blood Supply to the Eye

A

Ocular perfusion pressure determines blood supply to retina, optic nerve
 OPP = MAP – IOP

Cats: no collateral circulation, exclusively maxillary a

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18
Q

PLR

A

(II in, III out): assessment of parasympathetic pathway

  1. CN II from retina –> optic tract +/- decussation at optic chiasm
  2. pretectal nucleus
  3. parasympathetic nucleus CN III (CB)
  4. project via CN III to ciliary body
  5. postganglionic neurons in ciliary body project to pupillary constrictor m to mediate constriction of pupil
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19
Q

Pupil Dilation

A
  1. Autonomic centers in brainstem
  2. lateral tectogemento-spinal tract
  3. synapse SC segments T1-T3
  4. Vagosympathetic trunk
  5. cranial cervical ganglion
  6. pupillary dilator m
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20
Q

Palpebral Reflex

A

Maxillary: lateral (zygomaticofascial)
Ophthalmic branch: medial (infratrochlear)

Palpebral: trigeminal N to trigeminal sensory nucleus –> facial motor nucleus –> CN VII to orbicularis oculi

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21
Q

Menace Response

A

(II in, VII out)
Not a reflex: learned behavior, requires pathways involving cerebral cortex, cerebellum

Medial retina (optic nerve); continuing through the contralateral geniculate nucleus, motor cortex, pontine nucleus; to cerebellum; terminating at both facial nerves

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22
Q

Corneal Reflex

A

mediated via nasocillary n (ophthalmic br of trigeminal), same pathway as palpebral

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23
Q

IOP

A

Depends on balance btw inflow, outflow of aqueous humor

Also affected by extraocular m tone, choroidal blood flow, CVP

Goldman Equation: IOP = (AH formation rate/AH outflow rate) + episcleral venous pressure

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24
Q

AH Flow

A

Produced by Ciliary Bodies

Conventional Outflow Pathway
Unconventional Outflow Pathway (Uveoscleral)

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25
Q

Conventional AH Outflow Pathway

A

AH enters venous vascular system via scleral venous plexus (analogous to Schlemm’s canal in humans)

drains into vortex veins

orbital vasculature

episcleral venous system

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26
Q

Unconventional AH Outflow Pathway

A

HORSES

Exits anterior chamber via diffusion through iris stroma, CB musculature
* Flows caudally to enter suprachoroidal then scleral/choroidal vasculature
* Involves ciliary m, superciliary regions, choroidal spaces

From there, drains either through scleral pathway or vortex pathway

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27
Q

Scleral Pathway for Unconventional AH Outflow

A

drains across sclera to be reabsorbed by orbital vessels

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28
Q

Vortex pathway for Unconventional AH Outflow

A

AH enters choroid itself to drain through vortex vessels, less dependent on IOP

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29
Q

Choroid Blood Flow

A

arterial BPs, CVPs

Intraocular (choroidal) blood volume determined by arterial inflow, venous outflow, tone of intraocular vasculature

Autoregulation of choroidal blood flow minimizes effects of systemic ABP on choroidal blood volume, IOP

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30
Q

Hypoxemia, hypercapnia effect on IOP

A

induce VD, increase intraocular blood volume, increase IOP

Hyperventilation may not decrease IOP DT effects of IPPV on CVP

not demonstrated in horses DT differences in aqueous flow

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31
Q

Effect of Resp Alkalosis, hyperbaric oxygen

A

induce VC –> decreased AH formation via decreased CAH activity, decreased choroidal blood volume, IOP

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32
Q

Normal IOP: dog

A

 Dog 10-26mm Hg

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33
Q

Normal IOP: cat

A

 Cat 12-32mm Hg

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34
Q

Normal IOP: horse

A

 Horse 23.5-28.6mm Hg

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35
Q

Normal IOP Cattle

A

 Cattle 16-39mm Hg

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36
Q

Consequences of Increased IOP

A

lens/vitreous prolapse, choroid hemorrhage, subsequent retinal detachment

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37
Q

Physical Causes of Increased IOP

A

Pressure on eyelids (facemask)
ET Intubation
Excessive restraint, struggling
Jug vein pressure
Head below body
Cataract sx

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38
Q

Physiologic Causes Increased IOP

A

Vomiting
Pre-existing glaucoma
Coughing
Tenesmus, straining
Hypoxemia
Hypercapnia

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39
Q

Pharmaceutical Causes Increased IOP

A

Succinyl choline
Ketamine (??) - dose dependent
Etomidate (myoclonus)
Positive Inotropies/VPs

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40
Q

Most Anesthetics Effect on IOP

A

anesthetic drugs decrease IOP, likely via multiple mechanisms: m relax, decreased venous and arterial BP, increased aqueous outflow, central depression of diencephalic centers controlling IOP

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41
Q

Pupil Size - mammals

A

smooth muscle units, autonomic innervation
* Sympathetic –> iris dilator m –> mydriasis = pupil dilation
* Parasympathetic –> iris constrictor m –> miosis = pupil constriction

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42
Q

Pupil Size - birds, most reptiles

A

striated pupillary muscles
* VOLUNTARY ACTIVE CONTROL OF PUPIL DILATION
* Unresponsive to topically applied parasympatholytic/sympathomimetic agents

WILL respond to NMBA

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43
Q

Globe, Pupil Position for Ophthalmic Anesthesia

A

Most anesthetics will constrict pupil - use atropine or epi, important to facilitate cataract sx

Globe usually needs to be central: ketamine, NMBAs

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44
Q

Tears

A

Protects, mechanical removal of debris and bacteria from ocular surface, lubricates cornea to maintain transparency, nourishes cornea

Primary O2 source for avascular cornea

  1. Reflex Tears
  2. Basal Tears
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45
Q

Tear Production and Anesthesia

A

Produced by Lacrimal Gland

Depressed produced of both types of tears by anesthesia EXCEPT IM ketamine (increased d tear production) for up to 24hr

PSNS: increased tear production
SNS: decreased tear production

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46
Q

reflex tears

A

produced IRT irritants by optic nerve (bright light), trigeminal nerve (wind, temperature changes, conjunctival/corneal irritation)

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47
Q

Basal Tears

A

impt for normal tear film function, produced constantly

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48
Q

Schrimer Tear Test

A

Quantitative eval of tear function

Normal: 15-20mm/min in most species
* STT Type 1: reflex tears
* STT Type 2: basal tears utilizing topical ax, drying of ventral conjunctival fornix

Tear production decreases with age

49
Q

Oculocardiac Reflex (Ashner’s Reflex)

A

Triggered by: globe pressure or traction, retrobulbar block, ocular trauma/pain, traction on extraocular muscles
 Possibly more likely to occur when p hypercapnic, quickly changing/high levels of globe/m traction

Bradycardia, ectopic beats/dysrhythmias, asystole, vfib

More acute onset and more sustained pressure/traction, more likely OCR is to occur

50
Q

Afferent Pathway of Oculocardiac Reflex

A

ciliary nerves to ciliary ganglion

ophthalmic br of trigeminal n (CNV)

sensory nucleus of trigeminal N/motor nucleus of Vagus in fourth ventricle

51
Q

Efferent Pathway of OCR

A

vagal nucleus into efferent vagal fibers/vagal cardiac depressor n –> negative dromotrophy, inotropy

52
Q

Treatment of OCR

A

dc stimulation, +/- atropine if needed
 Atropine admin to tx/prevent OCR in people controversial
 Can be effective if OCR persists, but dosage/timing of atropine affects ability to block reflex

53
Q

Topicals: cholinergic agonists

A

Tx glaucoma by increasing aqueous outflow
 Direct agents mimic ACh, indirect = anti ACh-E

SE: systemic absorption –> bradycardia, AV block, bronchoconstriction

Ex: pilocarpine (direct), few to no systemic effects

54
Q

Potential Effect of Indirect Cholinergic Agents

A

Anti AChE: additive effect with organophosphates,

54
Q

Potential Effect of Indirect Cholinergic Agents

A

Anti AChE: additive effect with organophosphates, prolong duration levels of succinylcholine - d/c 2-4wks prior to succ use

55
Q

Topicals: Cholinergic Antagonists (eg atropine)

A

Induce mydriasis (pupil dilation) – paralyze pupillary sphincter

Topical atropine will increase IOP, effect of atropine IV ???
No effect of systemic glyco on IOP/pupil size

Tachycardia, ileum (horses) if systemic absorption

56
Q

Topical Adrenergic Agonists

A

peripheral VC, mydriasis
* Systemic hypertension, tachycardia
* Subconjunctival phenylephrine: hypertension, pulmonary edema in horses

topical a2s will decrease IOP: MOA not well understood

Timolol used in past

57
Q

Osmotic Agents for Ophtho Patients

A

 PO, IV –> fluid shift –> decrease vol of vitrous body, allows for better drainage by opening iridocorneal angle , decrease IOP
 Use: emergency tx, short term control of glaucoma
 Ex: Glycerol, mannitol

58
Q

Topicals: carbonic anhydrase inhibitors

A

Ex: acetazolamide, dorzolamide

Decrease IOP via decreased AH production

Important to remember where carbonic anhydrase is
* Systemic effects: may cause renal chloride retention; K/HCO3 excretion (decreased HCO3 resorption) = metabolic acidosis, hyperchloremia, hypokalemia

Topical CAIs: minimal systemic effect when used short term in dogs, cats, horses

59
Q

Glycerol

A

Osmotic agent used for emergency glaucoma tx
* PO admin, slower onset
* Relatively non toxic, emesis reported
* Metabolized to glucose = caution in diabetic patients

60
Q

Mannitol

A

Emergency glaucoma tx

  • Not metabolized to significant degree –> urine excretion, osmotic diuresis so will decrease urine output
  • Rapid expansion of EC volume, overloading of CV system

may precipitate formation of pulmonary edema in patients with CV dysfunction, patients under GA, patients with renal dysfunction
–PPV during, immediately after admin of mannitol may help prevent formation of PE vs SpV

61
Q

Topical Prostaglandin Analgoues

A

Ex: latanoprost

Most commonly used now for glaucoma tx in dogs
* Increase uveoscleral (unconventional) outflow of AH
* Minimal to no systemic effects

62
Q

Topical, subconjunctival corticosteroids

A

prednisolone acetate

May incur systemic effects of hepatopathy, alopecia, marked decreases in cortisol production
* Dose, duration dependent

Implicated in late term abortions in llamas when applied late gestation

NSAIDS! Can become Cushingoid

63
Q

Topicals: NSAIDS (diclofenac)

A

Increased IOP, likely decreased effectiveness of topical prostaglandin analogue glaucoma tx

Topically, may delay wound healing, cause corneal irritation

For overall analgesic purposes, systemic admin usually more effective

Systemic effects possible with longer duration
* Cats: decreased GFR after 7d admin topical 0.1% diclofenac = caution using these agents in at-risk population

64
Q

Effect of Inhalants on IOP

A

Historically, methoxyflurane = inhalant of choice for ophthalmic px DT greater ocular m relaxation, hypotonic/centrally rotated eye, slower recovery

Consensus: decreased to no effect

65
Q

Effect of Inhalants on Tear Production

A

Tear production decreased: duration depends on study (up to 24h), may be related to time under GA

66
Q

Effect of N2O On ophthalmic sx

A

DO NOT USE IF INTRAOCULAR INJ OF GAS BUBBLE

Diffusion of nitrous oxide into gas bubble will cause it to expand, increase IOP = loss of vision DT central retinal artery occlusion

Prior to inj, N2O should be discontinued for 15-20’
For repeat ax episodes, recommended that N2O not be administered for at least 5 days after intraocular air inj, 10d after sulfur hexafluoride inj

67
Q

Barbiturates IOP

A

Decrease

68
Q

Propofol IOP

A

Mixed effects on IOP - increases then decreases

69
Q

Alfax IOP

A

Mostly indicate increases in IOP, decreased tear production, miosis lasting approx 10’ post induction

70
Q

Etomidate IOP

A

Humans: mydriasis, decreases IOP

If etomidate-myoclonus occurs, increases IOP

Current recommendation: admin benzo prior to etomidate induction to patients at risk of globe rupture

71
Q

Dissociatives and IOP

A

Ketamine may cause increased IOP DT extraocular m ctx, effects = variable

Tiletamine alone = muscular clonus

Telazol did not induce extraocular myoclonus

72
Q

Alpha 2s and IOP

A

In general, tend to decrease IOP

73
Q

Mattos-Junior et al 2021 (VAA)

A

dexmedetomidine alone or in conjunction with torb, meperidine, methadone, nalbuphine or tramadol resulted in decreased IOP in dogs for 120’

74
Q

Phenothiazines - Effect on IOP, tear production

A

No changes to decrease

75
Q

Signs of Ocular Pain

A

Blepharospasm, discharge, photophobia, rubbing of eyes, eye/facial guarding, avoidance

76
Q

Topical Corneal Anesthesia

A

 Proparacaine
 If topical locals used long term, can delay healing; also cause pain when administered
 Intracameral inj of PF lido: no AE on IOP, corneal thickness

77
Q

Succinylcholine Effect on IOP

A

Increases IOP

ctx extraocular muscles, distortion of globe with axial shortening, choroidal vascular dilation secondary to increase arterial pressure, ctx orbital smooth muscle

78
Q

Effects of non-depolarizing NMBA on IOP?

A

no effect, decreases IOP

79
Q

Pupil Dilation in Birds, Reptiles

A

Topical vecuronium +/- atracurium showed to be effective mydriatic agents in raptors, psittacines, vultures

Vecuronium: fewest SE when admin to 3 species of psittacines and most consistent/greatest pupil dilation vs pancuronium, d-tubcurarine

Intracameral inj of d-tubocurarine in pigeons, pancuronium = effective but not preferred bc more AE (apnea, salivation) than topical applications

80
Q

Topical Local Anesthetic

A

Preservative-free formulations preferred: preservatives can damage corneal epithelium

SE: Irritating, transient conjunctival hyperemia, damage corneal epithelium, delay wound healing, mask signs of dz/discomfort

Best for diagnostic use: DO NOT USE LONG TERM

81
Q

Which locals are used for ophthalmic topical preparation?

A

Proparacaine, bupivacaine (potentially less toxic, shorter acting), tetracaine 4x more toxic/more irritating

LAST possible in small patients but unlikely

82
Q

Auriculopalpebral NB

A

Terminal branch of facial N (CN VII)

Motor innervation to orbicularis oculi
* NO SENSORY! Blockade = eliminates forceful blepharospasms

Horses: no effect on tear production, IOP

Crosses dorsal dorsal aspect of zygomatic arch midway btw lateral canthus and base of ear

83
Q

Lacrimal NB

A

Br ophthalmic CN V

Lateral 1/3 of upper eyelid, lacrimal gland, local CT, temporal angle of orbit

Dorsal rim of orbit medial to lateral canthus

84
Q

Supraorbital NB

A

Supraorbital foramen, br ophthalmic CN V

Successful completion of block will desensitize forehead, middle 2/3 upper eyelid, +/- some terminal branches of auriculopalpebral N

Horses: thumb at medial canthus, middle finger at lateral canthus – first finger falls into supraorbital foramen

Enucleation, SPL placement, palpebral lac repair

85
Q

Infratrocholar NB

A

Br ophthalmic CN V

Medial canthus, partially responsible for innervation of third eyelid, lacrimal gland, connective tissue

Horses: notch in orbital rim just above medial canthus

86
Q

Zygomaticofacial NB

A

Br maxillary CN V

Lateral ¾ of lower eyelid, lower 2/3 lower eyelid, skin, CT

Lateral cantos

87
Q

Retrobulbar Block

A

Indications: intraocular sx, corneal surgery, evisceration/enucleation
* DT risk of optic N damage, primarily used for enucleation

88
Q

Structures Blocked with Retrobulbar

A

cornea, uvea, conjunctiva via blockade of ciliary nerves
II, III, IV, V, VI

Densitizes globe/palpebrae, akinesia, transient vision loss, pupil dilation, decreases IOP

Prevents globe movement, OCR

89
Q

Limitations of the Retrobulbar Block

A

Does not block orbicularis oculi or lids

some branches of ophthalmic, maxillary br of CN V pass extraconally

90
Q

Retrobulbar Block Approaches

A
  1. Cats - DM (1mL)
  2. Dogs - VL (2-3mL)
  3. Horses - spinal needle perpendicular to skin 0.25” behind bony orbit, needle directed ventrally until “pop” + enter retrobulbar space, 10-12mlL
  4. Large ruminants - 4pt, 5-10mL/site
  5. Calves, SR - 2pt, 2-3mL/site
91
Q

What is the indication of a successful retrobulbar block?

A

PROPTOSIS = INDICATION OF SUCCESSFUL BLOCK

92
Q

Risks Retrobulbar Block

A

retrobulbar or orbital hemorrhage, inadvertent arterial inject (acute sz), damage to optic n, intrathecal inj (acute CNS toxicity, death), globe rupture, brainstem ax, cardiac arrest, chemosis, corneal abrasions, ecchymosis

93
Q

Contraindications to Retrobulbar Block

A

orbital infection/severe inflammation, excessive movement, +/- coagulopathy, hypersensitivity to LA, space-occupying lesion in orbit

94
Q

Peterson Block

A

Cattle; less reliable DT need for careful needle placement

Efficacy depends on accurate placement of injected anesthetic at site of emergence of nerves from foramen orbitorotundum (ventral to optic foramen)

95
Q

Structures Blocked with Peterson Block

A

block CN II, III, VI; maxillary br of CN V (zygomatic N, zygomaticofacial br to get lower eyelid innervation); pterygopalantine and infraorbital N (ax nasal passages, noses)

96
Q

Approach for Peterson Block

A

needle just in front of rostral border of coronoid process of mandible, caudal to notch formed by zygomatic arch and supraorbital process
* Direct needle slightly ventrally, posteriorly for length of needle or until strike bone

Can also use technique in calves, SR

97
Q

SE Peterson Block

A

accidental inj into CSF = death

98
Q

Peribulbar Block

A

Extraconal, requires 2-4x vol of RB blocks
* Large vol required for adequate intraconal distribution may exceed max LA dose in small dogs, cats

Block placed in space btw boney orbit and ophthalmic m

Approaches: single VL, single medial, double inj of DM/VL, DM single (cats)

99
Q

Sub-Tenon’s Technique

A

Indications: cataract sx, corneal/intraocular sx

Sterile insertion of blunt cannula along curvature of sclera into Tenon’s space via small incision in conjunctiva, Tenon’s capsule several mm from limbus

100
Q

Indications for Sub-Tenon’s

A

Blocks short ciliary n (pupil dilation), long ciliary n (analgesia)

101
Q

Complications of Sub Tenon’s

A

chemosis, ecchymosis, retrobulbar hemorrhage, globe perforation, central spread of LA

102
Q

Bartholomew, Smith, Bentley and Lasarev 2020 (VAA)

A

use of retrobulbar bupivacaine for enucleation in dogs not assoc with increased d risk major, minor complications

103
Q

Scott, Vallone, Olsen, et al 2020 (VAA)

A

Preop RB block 0.75% ropi inj (1mL/10kg) provided analgesia in dogs following enuc at extubation - intraop, postop pain control did not differ from placebo inj with saline

Lack of differences btw groups may have been influenced by sample size limitations

104
Q

Rabbogliatti, De Zani et al 2021 (VAA)

A

cadaver study, complete regional ax seems more likely using combined ventrolateral/dorsolateral peribulbar techniques with 20mL/ea (40mL total)

105
Q

Greco, Costanza, Senatore et al 2021 (VAA)

A

CT-based method for assessment of canine RB cone volume for ophthalmic ax, larger retrobulbar cone volume with brachycephalic, dolicocephalic than mesocephalics. Weight = strongest predictor

106
Q

Horner’s Syndrome

A

Loss of sympathetic innervation to the head

miosis, enophthalmos, protrusion of third eyelid, prolapsed third eyelid

107
Q

Ddx Ptosis

A

Anything that causes globe to be smaller or recede into orbit

Problems with CN VII in LA, Horner’s, dehydration, oculomotor deficits

108
Q

Electroretinogram

A

measures electrical response of light-sensitive cells in eyes, most commonly used before cataract sx

a, b, c wave; b/a ratio

109
Q

ERG: a wave

A

generated by cones, rods in outer photoreceptor layer
* Amplitude measured from baseline to trough

110
Q

ERG: b wave

A

generated by bipolar, Müller cells of inner retina
* Amplitude measured from trough of a wave to peak of b wave

111
Q

ERG: c wave

A

not usually included in animal protocols, technical challenging in normal dogs
* Generated by retinal pigment epithelium

112
Q

ERG: b/a ratio

A

index of inner to outer retinal function

113
Q

ERG: implicit time

A

Assoc with b wave

time btw stimulus onset, maximum amplitude

114
Q

Anesthesia Effect on ERG

A

Generally decreased amplitude, increased implicit time for rod and cone driven responses

Also affected by hypoxemia, hypercapnia

115
Q

How Anesthetists can minimize effects on IOP

A

 Premedication with no vomiting, retching, struggling
 Careful restraint not to put pressure on eye or occlude jugular veins
 If using mask, ensure not pressing on eyes
 Body position can also affect IOP
* Head below heart level vs head above or at heart level
 Can place temporary tarsorrhaphy or tape lids shut to protect eyes

116
Q

Eye Lubricant

A

aqueous-based formulations preferred
 Petroleum-based ointments gain access to intraocular structures = severe uveitis, further compromise vision/comfort

117
Q

Important Considerations in Rodents

A

(mice, rats, hamsters

lens opacification during prolonged sedation, ax

Transient, caused by lack of blinking, subsequent evaporation of fluid from shallow anterior chamber
 Mitigated by application of eye ointment

Boards: Other Topics (Endocrine, CPR, Euthanasia, etc) (8 decks)

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