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Lens and Cataract > Chapter 7: Surgery for Cataract > Flashcards

Chapter 7: Surgery for Cataract Flashcards

1
Q

Who invented the corneal knife used for a cleaner incision?

A

Albrecht von Graefe- 1828-1870

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2
Q

Who invented intracapsular extraction?

A

Samuel Sharp - 1753

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3
Q

Who invented phaco and when?

A

Charles Kerman -1967

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4
Q

Describe retrobulbar anesthesia.

A

Lidocaine injection into muscle cone via 25G, 1.5 inch (38 mm) blunt retrobulbar needle.

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5
Q

What are the complication of retrobulbar anesthesia?

A

Retrobulbar hemorrhage, globe penetration, optic nerve trauma, EOM toxicity, inadvertent intravenous injection causing cardiac arrhythmia; inadvertent intradural injection associated with seizures/respiratory arrest/brain stem anesthesia

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6
Q

What is peribulbar anesthesia?

A

Shorter - 1 inch- 25G or 27G needle used to inject anesthetic external to the muscle cone, underneath Tenon’s capsule

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7
Q

How does peribulbar anesthesia compare with retrobulbar anesthesia?

A

Slightly less effective; eliminates risk of complications of ON injury/intradural injection

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8
Q

What can be used for supplemented anesthesia during surgery?

A

Sub-Tenon’s — small posterior incision made through anesthetized conjunctiva and Tenon’s —> small cannula used to administer anesthetic.

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9
Q

What is used for topical anesthesia for cataract surgery?

A
  • propracaine or tetracaine drops
  • cellulose pledgets soaked in anesthetic
  • lidocaine jelly
  • +/- intracameral preservative free 1%/2% lidocaine; IV sedation
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10
Q

What are the disadvantages of topical anesthesia for cataract surgery?

A

Blepharospasm, lack of amines is, potential patient discomfort

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11
Q

What type of anesthesia can be used in patients with essential or reactive blepharospasm?

A

Facial nerve block

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12
Q

List and describe the types of facial nerve blocks.

A
  1. O’Brien block = directed proximally and peripherally at the nerve trunk
  2. Van Lint block = directed proximally and peripherally at the terminal branches
  3. Atkinson block = directed between these two regions
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13
Q

What are the indications for GA for cataract surgery?

A

Paediatrics patients, dementia, head tremour, deafness, language barrier, MSK disorder (inability to lie flat), restless leg syndrome, claustrophobia

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14
Q

What infectious RFs should be identified and treated before CEIOL?

A

Coexisting lid disorders, conjunctivitis, blepharitis, hordeolum, chalazion, systemic infections

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15
Q

MOA preoperative antibiotic drops?

A

Association of pre-op gtts and reduction in ocular surface bacterial counts and lower incidence of positive aqueous cultures after surgery

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16
Q

What do you do pre-op for patients with history of herpetic eye disease?

A

Pre-op prophylactic antivirals

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17
Q

What is the most important structure to sterilize before surgery?

A

Fornix

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18
Q

Describe the process of prepping the eye before CEIOL.

A
  • 5% Povidone-iodine solution (not scrub/soap) placed in conjunctival fornix
  • prep of skin with 10% povidone-iodine
  • draping eyelashes out of operative field
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19
Q

What are some principles during surgery that aid to lower risk of endophthalmitis?

A
  • limit number of times instruments introduced into the eye
  • check for signs of lint/cilia/debris on tips of instruments
  • minimize intraoperative manipulation
  • check for wound closure
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20
Q

What % of cataract surgeries result in bacterial inoculation of AC? How does this fit with endophthalmitis rates?

A

7-35%

- ability of AC to clear itself

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21
Q

List some intraoperative complications that increase risk of endophthalmitis?

A

Posterior lens capsule tear
Vitreous loss
Prolonged surgery

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22
Q

Which study describe use of adding antibiotics to irrigating solution or injecting them into AC after CEIOL? Which antibiotic was used?

A

Endophthalmitis Study Group

- intracameral cefuroxime

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23
Q

Which substances are found in OVD?

A

Sodium hyaluronate
Chondroitin sulfate
Hydroxypropyl methylcellulose

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24
Q

What is sodium hyaluronate? Where is it found and isolated from? What is its half life in aqueous and vitreous?

A
  • bio polymer occurs in many connective tissues in the body such as synovial fluid and vitreous
  • isolated from human umbilical cord and rooster combs
  • 1/2 life is 1 day in aqueous and 3 days in vitreous
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25
Q

What is chondroitin sulfate and where is it found?

A

Sulfated glycosaminoglycan; found in cartilage

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26
Q

What is hydroxypropyl methylcellulose - HPMC? How is it metabolized? How is it eliminated?

A
  • doesn’t occur naturally
  • cellulose widely distributed in plant fibres such as cotton and wood —> addition of hydroxypropyl and methyl groups increase its hydrophilic property
  • methylcellulose non physiological compound —> not metabolized intraocularly; eventually eliminated in aqueous but can be easily irrigated from the eye
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27
Q

What are the 4 properties of OVDs?

A
  1. Viscosity
  2. Elasticity
  3. Pseudoplasticity
  4. Surface tension
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28
Q

What is viscosity?

A
  • Resistance to flow; thinness/thickness of a fluid

- determined by MW and concentration

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29
Q

What does a higher viscosity mean?

A

Better tissue displacement and staying in place

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30
Q

What is elasticity?

A

Ability of material to return to original shape after being stressed

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31
Q

What does it mean to be a higher elasticity OVD?

A

Excellent at space maintaining

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32
Q

What is pseudoplasticity?

A

Ease with which material can change from being highly viscous at rest to watery at increasing rates of shear stress

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33
Q

What is an example of an everyday pseudoplasticity material?

A

Toothpaste

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34
Q

What is the use of pseudoplasticity in OVD during CEIOL?

A

At zero shear force, OVD is lubricant and coats tissues well; when forced thru small gauge cannula it functions as a liquid

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35
Q

What is surface tension?

A

How surface of fluid tends to stick to another surface

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36
Q

What is coatability?

A

Inversely proportional to surface tension

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37
Q

What does it mean for an OVD to have low surface tension?

A

Better at coating tissue, but harder to remove from the eye

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38
Q

What are the 2 categories of OVD?

A

Cohesive and dispersive

39
Q

Compare and contrast the properties of cohesive vs dispersive OVDs.

A
  • cohesive: long chain, high MW, high viscosity.

- dispersive: short chain, low MW, low viscosity, low surface tension.

40
Q

Describe how cohesive OVDs behave in the eye.

A
  • maintain space well at no/low shear rates; at high shear rates they are easily displaced.
  • easier to remove from the eye because they stick together and are aspirated in long pieces = like spaghetti
  • minimal coatability therefore provide less tissue protection
41
Q

Describe how dispersive OVDs behave in the eye.

A
  • excellent coating and protection at high shear rates

- more difficult to remove from the eye bc don’t stick together and aspirated in short fragments = like macaroni

42
Q

Which OVD type is more likely to be retained in the eye, causing angle obstruction/reduced outflow and high IOPs post-op?

A

Dispersive

43
Q

List the cohesive OVDs.

A
  • Healon, Healon GV by Abbott

- Amvisc, Amvisc Plus, Provisc by Alcon

44
Q

List the dispersive OVDs.

A
  • OcuCoat by Bausch and Lomb
  • Viscoat by Alcon
  • Healon Endocoat by Abbott
45
Q

What are some combination OVDs? Describe them.

A
  • Discovisc by Alcon —> combines dispersive and cohesive properties
  • Healon5 by Abbott —> long, fragile chain with high MW that changes behaviour at different flow rates ==> lower flow rate more viscous/cohesive and higher flow rate, acts like pseudodispersive agent
46
Q

Which OVD can cause extremely high IOP post-op?

A

Healon5

47
Q

List the 3 main functions of OVDs.

A
  • space maintenance ability
  • coatability
  • optical clarity
48
Q

Describe the functions of space maintenance ability of OVDs.

A
  • keeps AC formed
  • expands AC, can do safe manipulations away from k endothelium and posterior lens capsule
  • viscomydriasis
  • keeps plane of anterior lens capsule flat for better control of CCC
  • makes lens implantation less traumatic to zonular fibres and posterior capsule
49
Q

Describe the functions of coatability of OVDs.

A
  • protects K endophthalmitis

- vitreous tamponade if posterior capsule tear to prevent vitreous prolapse anteriorly.

50
Q

Describe the functions of optical clarity of OVDs.

A
  • can place on K surface to maintain clarity, prevents drying of K epithelium
  • provides slightly magnified view of anterior segment structures
51
Q

List the main components of phacoemulsification.

A

Hand piece
Foot pedal
Irrigation system
Vacuum pump

52
Q

What is the function of the phaco handpiece?

A
  • likened to jackhammer, vacuum, garden hose.

- simultaneous emulsification and aspiration of the lens while keeping tip cool and maintaining AC depth.

53
Q

What is the mechanical energy of phaco produced by?

A

To and fro oscillation generated by pizoelectric crystals in the handpiece

54
Q

What is the amplitude of the movement of the phaco handpiece?

A

Stroke length

55
Q

How is stroke length related to phaco power?

A

Increased stroke length increases power

56
Q

Describe how the phaco tip results in nucleofractis.

A
  • as tip moves forward, compression of gas atoms in solution occurs
  • as tip moves backward, expansion of gas atoms occurs forming gas bubbles (=cavitation)
  • bubbles subject to same compression and expansion
  • when bubbles implode —> release heat and shock waves —> disassembles lens nucleus
  • nonaxial vibrations (torsional or elliptical) can further augment mechanical breakdown of nucleus
57
Q

What are the 3 positions of the foot pedal?

A
  • position 1: irrigation
  • position 2: aspiration at a constant or variable rate
  • position 3: phaco power at fixed or variable level
58
Q

What happens with fixed versus variable foot pedal position 3?

A
  • fixed: power level may be set from 0 to 100%, and chosen power delivered immediately when foot pedal depressed to position 3
  • linear ultrasound: surgeon controls amount of phaco power delivered by varying depth of depression of foot while it is in position 3
59
Q

Define cavitation.

A
  • formation of gas bubbles arising from aqueous in response to pressure changes at phaco tip.
  • bubbles expand and contract, and implosion of bubbles result in emulsification of lens material
60
Q

What is more efficient wrt cavitation: continuous ultrasound versus intermittent?

A

Intermittent

61
Q

Define chatter.

A
  • when ultrasonic stroke overcomes vacuum (“holding power”) —> causes nuclear fragments to repel until vacuum reaches levels to neutralize tip’s repulsive energy —> once again attracts material
62
Q

What does chatter inhibit?

A

Followability

63
Q

What can be done to diminish chatter? How?

A

Reduction in phaco power —> decreases stroke length of tip excursion, thereby reduces forces that push the fragment away from the tip

64
Q

Define energy.

A

Energy = Power x time

65
Q

How do you decrease energy?

A

Decreasing either phaco power or length of time that phaco power is on

66
Q

Define frequency.

A

Speed at which phaco needle moves back and forth

67
Q

What does ultrasonic frequency refer to?

A

Above range of human audibility; >20,000 Hz

68
Q

What is the frequency of the phaco handpiece?

A

27,000-60,000 Hz

69
Q

What is a pizoelectric crystal?

A

Type of transducer used in handpiece that transforms electrical energy into mechanical energy

70
Q

How is linear motion generated at the phaco tip?

A

When a tuned, highly refined crystal is deformed by the electrical energy supplied by the console

71
Q

Define power.

A

The ability of the phaco tip to vibrate and cavitation the adjacent lens material

72
Q

How is phaco power noted?

A

Percentage of maximum stroke length of the phaco needle

73
Q

How is phaco power generated?

A

Foot position 3

74
Q

Define stroke.

A

Linear distance that the tip traverses to produce impact on lens material

75
Q

What is the stroke length in phaco?

A

0.05 to 0.10 mm

76
Q

What happens with chatter?

A

Phaco tip pushes nuclear fragments away even as the aspiration attracts them

77
Q

What can heat buildup from the delivery of phaco power cause?

A

Wound burns and damage to the corneal endothelium

78
Q

What factors can be altered to increase cutting efficiency?

A

Size and angle of phaco tip; modes of intermittent rather than continuous phaco such as pulse and burst

79
Q

What can be used to minimize heat generation with phaco?

A

Torsional and elliptical movement of the phaco tip

80
Q

What are the available bevels of phaco tips?

A

0, 15, 30, 45, 60 degrees

81
Q

What are the available end configurations of phaco tips?

A

Round, ellipsis, bent, flared

82
Q

What are the advantages and disadvantages of steeper bevels?

A
  • steep and oval port: larger surface area with greater holding force and greater cutting efficiency
  • disadvantages: more difficult to occlude to achieve full vacuum
83
Q

What is pulsed phaco? What is “pulse”?

A

Setting the number of pulses per second while in position 3

  • pulse = interval of phaco power turned on alternating with interval in which phaco power is turned off.
  • amount of phaco delivered depends on foot pedal excursion in position 3
84
Q

What is the advantage of a pulsed phaco, where there is delivery of phaco power for only a portion of the cycle?

A

Reduces repulsion of material by the vibrating tip and improves followability

85
Q

What is a duty cycle?

A

In pulsed phaco, the ratio of on:off pulses

86
Q

What is the duty cycle if phaco power on equals the time of phaco power off?

A

50%

87
Q

What is burst mode phaco?

A

Delivery of preset power (0-100%) in single bursts that are separated by decreasing intervals as foot pedal is depressed through position 3 —> at end of position 3 excursion, phaco power is no longer delivered in bursts, but it is continuous

88
Q

What is the advantage of burst mode phaco?

A

Allows phaco needle to be buried into lens, an essential step in chopping techniques

89
Q

What is torsional phaco and its advantages? Name an example.

A

Pizoelectric crystals of phaco handpiece produces an oscillatory (torsional) movement which is amplified by use of a bent Kelman phaco tip —> greater side to side movement at tip allows for greater shearing forces to assist nucleus disassembly
- Ozil Torsional by Alcon

90
Q

What system utilizes a combination of transverse and longitudinal phaco modalities?

A

Elliptical cutting - enhances nucleus emulsification

- Ellips by Abbott

91
Q

Where is the irrigation of phaco?

A

Thru sleeve around U/S tip with some egress of fluid thru incisions

92
Q

What is the function of phaco irrigation?

A
  • Coaxial irrigation with balanced salt solution cools phaco tip, preventing heat buildup and consequent damage to adjacent tissue
  • maintenance of AC
93
Q

How does the surgeon adjust IOP and and AC depth?

A

Changing height of irrigation bottle, with gravity increasing the force generated to increase IOP
- newer machine have collapsible saline bag which is compressed by pressure plates - sensors on plates provide continuous feedback allowing for active control fluidics and resulting in a more stable AC

94
Q

What can be added to irrigation solutions during surgery?

A
  • pupil dilators

- antibiotics

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