Cataract surgery Flashcards
(111 cards)
1
Q
What is the anatomy behind short-sightedness and how is it corrected?
A
the lens is too long so focuses the image in front of the retina. Needs correction with a CONCAVE (negative powered) lens
2
Q
How can you tell if glasses are for myopia or hypermetropia?
A
if they are concave i.e. for short-sightedness, when you look through the front, things appear small. If they are convex i.e. for long-sightedness, things appear bigger
3
Q
What is the anatomy behind long-sightedness and how is it corrected?
A
The lens is too short so focuses the image behind the retina. Needs correction with a CONVEX (positive powered) lens
4
Q
What is the leading cause of blindness in the world?
A
Cataract
5
Q
What is the general idea behind cataract surgery?
A
removal of cloudy lens and replacement with plastic artificial lens (the only effective treatment)
6
Q
What is the name of the surgical technique for removing cataracts?
A
Phacoemulsification - removal of cataractous lens using ultrasound
7
Q
Why is cataract surgery so beneficial and how common is it?
A
Gives a rapid and significant improvement in vision and quality of life. most commonly performed operation in NHS/world
8
Q
What proportion of focusing is performed by the lens?
A
third (rest is the cornea)
9
Q
What shape is the lens?
A
convex
10
Q
What are the 2 components that the lens consists of?
A
inner nucleus and outer cortex
11
Q
What covers the lens?
A
clear, thin lining (like cellophane) = lens capsule. Anterior capsule is continuous with the posterior lens capsule
12
Q
What is attached to the lens capsule and what is their function?
A
tiny ligaments = zonules, anchor lens to the ciliary muscles
13
Q
What are 2 reasons why zonules (ligaments) are needed to anchor the lens to the ciliary muscles?
A
- gives stability to the lens
2. ensures it’s in the visual axis just behind the pupil
14
Q
What is accommodation?
A
ciliary muscle contract, so zonules become relaxed, and lens becomes short and fat (more convex and strongly converging) –> allows us to read, near vision
15
Q
What happens to the lens with age?
A
the lens nucleus is a clear jelly when young but becomes harder with age; by about 45 years, the lens is less malleable. when trying to read, lens zonules relax but lens can’t change shape as much
16
Q
What is the name for the hardening of the lens and consequent difficult with near vision with age?
A
Presbyopia
17
Q
What is the treatment for presbyopia?
A
need reading glasses: additional convex lens to bring page into focus as a normal reading distance
18
Q
What is a behavioural sign of someone with presbyopia?
A
holding book further away to read
19
Q
What is a cataract?
A
opacification of the natural crystalline lens
20
Q
What are 4 types of cataract?
A
- nuclear sclerosis
- cortical
- posterior subcapsular (PSC)
- combination of all three (common)
21
Q
What colour is a nuclear sclerotic cataract?
A
lens becomes yellow/orange/brown
22
Q
What is the commonest type of cataract?
A
nuclear sclerotic cataract
23
Q
what is index myopia?
A
the nuclear sclerotic cataract means the lens nucleus acts as a stronger convex (converging) lens, so light is now focused in front of the retina
24
Q
What is the natural history of cataracts?
A
painless, gradual deterioration of vision
25
What are the symptoms specifically of nuclear sclerotic cataract?
cloudy, misty, blurred vision; colours faded due to yellow discolouration ion the lens
26
What is a symptom specific to posterior subcapsular cataracts?
causes glare: normally in visual axis, results in scattering of light -- disabling glare before acuity markedly reduced. particular difficult driving in sunny weather or at night, dazzled by headlights
27
Look at an image of what each type of cataract looks like
Nuclear sclerosis: fully blacked out, posterior subcapsular: little star in the middle (at the back), cortical: lots of wedges pointing inwards (spoke like)
28
What are 6 risk factors for cataracts?
1. age-related (>65 years)
2. secondary to ocular disease e.g. post-inflammatory: uveitis (posterior subcapsular cataract), or secondary to systemic disease e.g. DM
3. Traumatic
4. Drug induced - systemic corticosteroids (posterior subcapsular cataract)
5. congenital
6. Lower socio-economic status, smoking, drinking alcohol
29
What are 2 risk factors for posterior subcapsular cataract?
1. secondary to ocular disease e.g. uveitis
| 2. drug-induced by corticosteroids
30
What are the 2 cataract treatment options?
1. refraction: correctable with myopic spectacle lenses (as cataract alters lens refractive index, index myopia)
2. Surgery
31
What proportion of patients with cataract >65 years may require surgery?
about 30%
32
What are 3 indications for cataract surgery?
1. When level of vision restricts normal activity
2. Patient factors - e.g. young driver
3. Ocular factors - e.g. diabetic to allow fundal examination/treatment; certain types of cataract can induce glaucoma or uveitis (if lens becomes totally white)
33
What are 5 aspects of assessing patients for surgery?
1. Activities of daily living - what can they now not do due to cataract?
2. thorough medical and social history
3. medical co-morbidities
4. drug history
5. general health - physical and mental
34
What are 2 drugs which might have implications for cataract surgery if patients are taking them regularly?
1. anticoagulants
| 2. alpha blockers (usually for urinary problems) - can make iris behave abnormally
35
What are 3 general health issues to think about pre-cataract surgery?
1. can they lie flat for 20-30 minutes
2. frightened - may prevent from keeping still
3. language difficulties - need to know about in advance for appropriate planning
36
What are 4 risks of cataract surgery that you are required to inform patients for consent?
1 .1:1000 risk of severe and permanent visual loss due to infection
2. 1:100 risk of requiring additional surgery to rectify a problem
3. 1 in 20 operations have less serious complications that may require further treatment at the time of surgery or at a later date
4. 1 in 10 patients may need laser treatment in future for opacity of posterior lens capsule (behind implant)
37
What would happen if the lens was removed in cataract surgery but not replaced?
patient would be extremely long-sighted - wouldn't even be able to read top of snellen chart
38
What type of lens do patients receive after cataract removal when treatment is on the NHS?
the replacement lens that is implanted has a fixed focus, i.e. can't correct distance and near reading vision but only one of these
39
What is the aim for post-operative vision in most patients?
vision of 6:6 i.e. emetropia - refractive outcome as near to 0 as possible (able to watch TV and drive without need to wear glasses)
40
how is the correct power of the replacement lens after cataract surgery determined?
using biometry
41
What are the 4 basic measurement that biometry requires to calculate the power of the new intra-ocular lens?
1. axial length of the eye
2. depth of the anterior chamber
3. corneal curvature
4. A-constant of the lens
42
How is biometry to work out individual patient measurements performed?
all non-invasive and non-contact, takes less than 5 minutes to perform with a small machine
43
How precise is the degree of accuracy of biometry?
Precise: axial length error of 0.5mm equates to 1.4 dioptre post-operative refractive error: big impact on patient satisfaction (i.e. if you get it even a little bit out it would make a different to how good vision is afterwards)
44
What type of anaesthesia is used in most cases of cataract surgery?
Local anaesthesia
45
What are 2 options for local anaesthesia in cataract surgery?
1. Topical: drops only
| 2. Sub-tenon injection
46
How do local anaesthetic eye drops work?
numbs the cornea which is supplied by CNVa (ophthalmic branch of trigeminal) so patient won't feel incision; lens has no nerve fibres. Local anaesthetic also put into fluid that irrigates the eye during surgery
47
What is the innervation of the cornea and lens?
Cornea: CNVa
Lens: no innervation
48
What must patients be informed of if the eye muscles aren't paralysed during cataract surgery?
patient must understand they should keep their eye as still as possible
49
How is a sub-tenon injection performed? What is the injector like?
uses atraumatic blunt cannula instead of a needle into the posterior sub-tenon space. Curved cannula, slightly less curved than the globe so the tip doesn't drag over the sclera
50
What is the effect of a sub-tenon injection?
Provides good anaesthesia with akinesia
51
What happens after anaesthetic drops has been applied to the eye in cataract surgery, to give a sub-Tenon injection?
small speculum inserted to keep the eye open, then conjunctiva in infero-nasal quadrant grasped with forceps and incision made with scissors. LA injected using curved metal cannula
52
What are you cutting through when an incision is made with scissors at the start of surgery, and why?
conjunctiva, also layer of tissue underneath known as Tenon's capsule otherwise a fluid blister will form in the conjunctiva
53
What happens after the sub-tenon local anaesthetic has been injected?
the LA will initially sting, then pressure is applied over the eye for 10 minutes and eye will become numb and muscles will be paralysed causing ptosis (as levator palpebrae superioris in upper lid paralysed, so can't squeeze eye), and 6 extraocular muscles also paralysed to produce akinesia
54
When is general anaesthesia used in cataract surgery?
selected cases
55
What kind of hospital stay do most patients having cataract surgery have?
nearly all patients are day cases
56
What part is removed and what part is left behind during cataract surgery?
the cloudy, cataractous lens is removed apart form the thin transparent posterior capsule (so nucleus and cortex are removed)
57
Where does the artificial lens (intraocular lens IOL) go once implanted into the eye?
Sits on the posterior lens capsule behind the iris
58
What is done prior to the patient coming into theatre and why?
Patients pupils dilated fully with eyedrops to ensure as much as possible that the lens is visible during surgery
59
How is the patient positioned during cataract surgery?
Patient is flat on their back, on a specially designed comfortable trolley; can be adjusted for previously identified breathing difficulties. Head rests on rubber pillow with dimple in the centre/small rubber ring
60
How is the patient prepped before starting surgery once in the theatre? 3 things
- Surrounding skin and eyelid prepped with povidone-iodine
- sterile paper towel is placed over the head/upper body ensuring mouth and nose not obstructed.
- Part of drape contains clear steridrap to access the eyes --> cut made, speculum inserted
61
Where is the surgeon in relation to the patient during cataract surgery? How do they view the eyes?
Surgeon usually sits at the head of the patient, uses operating microscope to perform surgery
62
One anaesthetic has been applied what is the first step in cataract surgery?
The incision: precise, 2.8mm into superior peripheral cornea with triangular blade
63
What is the next step after the first incision and what happens as a result?
Another smaller side port incision is made in the peripheral cornea 90 degrees from first incision. Aqueous humour comes out and the anterior chamber flattens
64
What is the name of the single layer of cells that lines the inside of the cornea and what is its function?
Corneal endothelium; prevents aqueous getting into the corneal stroma by active pumping mechanism (otherwise would go white)
65
Why is it important that instruments don't damage the corneal endothelium if all the aqueous humour comes out?
endothelium doesn't regenerate (unlike corneal epithelium) - so would decompensate and become white below a certain number of endothelial cells
66
What is done to ensure no damage to corneal endothelium occurs from instruments after the first incision is made?
anterior chamber kept as deep as possibly by injecting visco-elastic liquid into it: sodium hyaluronate
67
What is the next step of cataract surgery after the first incision is made and sodium hyaluronate is injected?
the central part (5-6mm) of the anterior lens capsule is removed to allow access to the nucleus of the lens. With end of needle or with forceps, small cut is made into the anterior capsule and it is removed by pulling it around in a circular fashion
68
What is the name of the process by which the central part of the anterior lens capsule is removed, after the first incision?
Continuous circular capsulorhexis
69
What happens after capsulorhexis?
saline is injected under the edge of the anterior capsule, to separate the hard lens nucleus from the peripheral soft cortex: hydro-dissection
70
What is the name of the process by white saline is injected under the edge of the anterior capsular after capsulorhexis to separate the lens nucleus and cortex?
Hydro-dissection
71
What is the purpose of hydro-dissection during cataract surgery?
allows the lens to be rotated
72
What happens after capsulorhexis and hydro-dissection?
Phacoemulsification: nucleus removed using ultrasonic probe
73
Describe the ultrasonic probe used to perform phacoemulsification.
Metal probe surrounded by a silicone sleeve that fits snugly through the 2.8mm corneal incision. End of the probe is a high speed vibrating ultrasonic tip
74
How does the probe remove the nucleus of the lens?
the metal tip vibrates to form two deep grooves in the lens nucleus at 180 degrees (i.e. a cross) but without perforating the posterior lens capsule. the grooves are split apart into 4 segments and each segment is then aspirated
75
What happens after the probe has segmented and aspirated the lens nucleus?
saline enters the eye through the silicone sleeve of the probe, ensuring the anterior chamber doesn't collapse (see pictures of phako probe and phako machine)
76
What is the final step of phacoemulsification?
the soft, peripheral lens cortex is also removed by being aspirated. This leaves behind a clear posterior lens capsule
77
Describe what the artificial acrylic intra-ocular lens is like.
Very small convex lens of about 6mm diameter
78
After phacoemulsification, what is the structure left behind known as?
Capsular bag: you have the anterior lens capsule with a central hole, that is continuous with the transparent posterior lens capsule
79
What is done after phacoemulsification?
inject/implant intraocular lens through the incision (hole in anterior capsule) so that the lens lies on the clear, posterior lens capsule
80
How are most IOLs inserted into the capsular bag now and why?
most are injected, allows us to have a very small incision
81
How do some IOL lens injectors come? What is done if they aren't like this?
pre-loaded; scrub nurses load them otherwise
82
How is the IOL inserted into the capsular bag using an injector device?
- capsular bag filled with visco-elastic liquid to expand it so 2.8mm enlarged to just over 3mm
- injector goes through the incision
- foldable, acrylic IOL injected through hole then unfolds, lies on clear posterior lens capsule
83
What stabilises the IOL and how?
two loops/haptics stabilise the lens and allow it to sit in the visual axis behind the pupil
84
What happens after the IOL has been inserted and why?
visco-elastic is removed from the anterior chamber, otherwise likely to block trabecular meshwork so aqueous humour can't leave the eye --> postoperative rise in intraocular pressure
85
What happens after the IOL has been inserted AND the visco-elastic has been removed from the anterior chamber?
steroid and antibiotic injected into the anterior chamber to reduce post-operative inflammation and prevent infection
86
What is the final step in cataract surgery after the steroid and antibiotic have been inected into the anterior chamber?
saline injected around each wound to swell up wound edges and prevent wound leak (sutures not requires)
87
How will patients often be allowed to go home?
with a pad and clear plastic shield placed over the eye
88
What instructions should patients be given about care of their eye(s) following cataract surgery? 4 things
1. next day, remove pad and shield
2. use steroid and antibiotic drops for 4 weeks
3. wear plastic shield at night for 2 weeks to prevent accidental injury in the night
4. tell them to return for outpatient visit after 4 weeks
89
What happens when a patient returns for an outpatient visit 4 weeks after cataract surgery?
stop drops, tell to go to local optometrist for reading glasses. Then either discharged or placed on waiting list for surgery for other eye if visually significant cataract
90
What is the one key peri-operative complication of cataract surgery?
Rupture of posterior capsule, leading to vitreous loss or dropping of lens nucleus into the vitreous
91
How often in cataract surgery does rupture of the posterior capsule occur?
3% of cases
92
What happens if the posterior capsule is ruptured after the cataract is removed?
can't put in the IOL (as it will fall through the posterior capsule); IOL will have to be put in more forward position - not ideal, compromise
93
What will happen if the posterior lens capsule is ruptured before the cataract is removed?
the lens nucleus will fall through the hole in the posterior capsule, into vitreous and sit on the retina - known as 'dropping the nucleus'
94
What happens if dropping of the nucleus occurs during surgery?
operation stopped, patient will require further surgery a few days later by vitreo-retinal surgeon, to remove the nucleus and implant the IOL
95
What are 7 post-operative complications of cataract surgery and their relative frequencies?
1. endophthalmitis: 0.1%
2. haemorrhage
3. uveitis
4. glaucoma
5. macular oedema
6. retinal detachment
7. opacification of posterior lens capsule
96
Which of the post-operative complications is a late complication?
posterior lens capsule opacification
97
Which is the most feared post-operative complication of cataract surgery and why?
endophthalmitis: ophthalmic emergency as delay in treatment may lead to total blindness
98
What causes endophthalmitis post-operatively?
usually from bugs from eyelids being washed into the eye at the time of surgery; most frequent organism is Staph. epidermidis
99
What are the symptoms of endophthalmitis?
- initially asymptomatic but day 3-4 eye becomes red, very painful with considerable loss of vision
- hypopyon due to pus cells settling at bottom of anterior chamber, due to fibrin in anterior chamber
100
What is the management of endophthalmitis? 3 aspects
- Patient admitted
- Vitreous sample taken to try and identify responsible organism
- Intravitreal antibiotics injected
101
What are the usual outcomes of endophthalmitis?
many patients lose vision; if highly virulent bug, could lose eye
102
Over what time frame might patients develop posterior capsule opacification following cataract surgery?
Months or years
103
What are the symptoms of posterior capsule opacification?
Is gradual and painless, as if the cataract has regrown
104
Is it possible for a cataract to truly regrow?
no as the nucleus of the lens cannot grow back
105
What does cause posterior lens capsule opacification after cataract surgery?
if not all peripheral cortical lens fibres are removed, can slowly regrow across the clear posterior lens capsule behind the IOL, causing the capsule to become opaque
106
What is the treatment for post-cataract surgery opacification? How does this treatment work?
if vision is significantly reduced, then laser treatment (Nd: YAG laser) used to make hole in posterior capsule to clear the visual axis
107
How often is the Nd: YAG laser required following cataract surgery?
5-10% of all procedures
108
What is the procedure like when Nd: YAG is used to correct posterior capsule opacification after cataract surgery?
painless laser treatment, takes 15 minutes, outpatient treatment
109
When is it safe to perform Nd: YAG laser treatment following cataract surgery?
months to years after surgery (NOT at time of surgery)
110
What are 6 benefits of cataract surgery?
1. small wound, no sutures
2. fast healing and rapid visual rehabilitation
3. colours appear more vivid
4. reduction in number of falls (elderly patients)
5. can be driving and back to work within a week
6. usually results in excellent return of vision if no other ocular pathology present
111
What proportion of patients following cataract surgery can see
a) 6/12 or better overall
b) 6/12 or better in patients with with ocular comorbidities
c) 6/12 or better in patients without ocular co-morbidities
a) 91%
b) 80%
c) 95%
