The Lens and Cataracts (also do lens flashcards from OP4102)

Question 1

what is the anterior radius of curvature of the lens? what about the posterior radius of curvature?

Answer 1

-8-14mm
-4.5-7.5mm

Question 2

what is the unaccommodated axis length of the lens and what speed does it grow at each year?

Answer 2

-4mm
-0.023mm/year

Question 3

what is the equatorial diameter of the adult lens?

Answer 3

10mm

Question 4

what keeps the lens in position in the eye?

Answer 4

suspensory ligaments called zonules of zinn

Question 5

what are the zonules of zinn made of? what is their diameter?

Answer 5

fibrillin, 1-2 micrometers

Question 6

what happens to the lens in accommodation?

Answer 6

1. ciliary muscles contract
2. relieves the tension of the radiating fibres of the zonule so the lens assumes a more globular shape - thicker section for light to travel through so increased dioptric power
3. sphincter pupillae muscle contracts to pupil becomes smaller and light through the thickest central part of lens reaches retina

Question 7

what does protein content do in the lens?

Answer 7

it causes its refractive power to be increased e.g. fish lenses have a much higher protein concentration as refractive index of water is much higher than in air (1.333 compared to 1.00) so their lens needs a greater refractive power

Question 8

why does the lens have a refractive index gradient?

Answer 8

A lens with a refractive index gradient means you can minimise chromatic aberrations and get a sharper image.

Question 9

why do some animals have slit pupils in the light?

Answer 9

because with a circular pupil, you’re only using two refractive zones whereas with a slit, you’re exposing more refractive index gradients - different refractive index zones will refract their corresponding wavelengths of light so having more refractive index zones available, you can minimise chromatic aberrations

Question 10

what are the three parts that make up the lens?

Answer 10

-an elastic capsule
-lens epithelium (on anterior surface of the lens found under the lens capsule)
-lens fibres

Question 11

how are adult lens fibres produced?

Answer 11

1. Cuboidal Epithelial cells
   elongate, forming columnar cells
2. Apical surface of the cell grows
   and pushes anteriorly
3. Basal surface grows and
   pushes posteriorally
4. Both processes continue to
   grow, meeting opposite fibres at
   irregular sutures

Question 12

how big is each lens fibre?

Answer 12

Each fibre 4 by 7micrometers , hexagonal in cross-section up to 12mm in length

Question 13

what forms the nucleus and cortex of the lens?

Answer 13

older lens fibres form the nucleus and the younger nucleated fibres form the cortex

Question 14

what is the difference in structure between cortical and nuclear fibres?

Answer 14

cortical fibres have a nucleus and organelles whereas nuclear fibres have no nucleus or organelles

Question 15

how does the lens capsule change with age?

Answer 15

it increases in thickness

Question 16

what percentage of the lens is protein?

Answer 16

90%

Question 17

what are the two types of proteins in the lens?

Answer 17

• insoluble - membrane and cytoskeletal
  proteins
• soluble – crystallins - responsible for
  special properties of the lens.

Question 18

what are the three main groups of crystallins in the lens?

Answer 18

• Alpha crystallin
• Beta crystallin
• Gamma crystallin

Question 19

what is alpha crystallin?

Answer 19

small heat shock protein (sHSp) - a globular protein that forms aggregates and occurs in all the major body tissues

Question 20

what are 2 properties of alpha crystallin?

Answer 20

-it is polydisperse so forms aggregates of different sizes
-it cannot crystallise

Question 21

what does alpha crystallin do?

Answer 21

Chaperones/protects target proteins in
response to stress eg increased
temperatures, oxidation etc. (protects other proteins from thermal denaturing)

Question 22

how is the state of alpha, beta and gamma crystallins different?

Answer 22

alpha and beta are oligomers (a polymer with relatively few repeating units) whereas gamma is a monomer

Question 23

why is the lens transparent?

Answer 23

it has structural regularity at the atomic and the molecular level so
-regular arrangement of lens fibres in a lamellar conformation so minimal intercellular space (cataracts disrupt this regular and precise organisation)
-the relative dehydrated state of the lens
-avascularity of the lens

Question 24

how can precise packing of crystallins in the lens be disturbed?

Answer 24

-increased water accumulation
-vacuole formation within the lens fibres
-formation of high molecular wight protein amorphous aggregates (when high weight Amorphous aggregates reach a size comparable with wavelength of light - Light scattering)

Question 25

when in the embryonic lens do crystallin appear?

Answer 25

around week 6

Question 26

how can UV light cause lens opacification?

Answer 26

1. UV absorption causes changes in crystallin structure and aggregation 2. energy of the photons in UV break chemical bonds and lead to change in molecular structure 3. causes formation of large amorphous aggregates

Question 27

what wavelengths of light does the lens absorb?

Answer 27

300 and 400 nm

Question 28

why is protein denaturation a problem in the lens?

Answer 28

due to the chaperone role of alpha crystallin

Question 29

give 5 symptoms of catarct

Answer 29

* Blurred or hazy vision * Problems with NV first * Problems driving at night * Glare * Like looking through mist

Question 30

give 3 general signs of cataract

Answer 30

* Opacity of natural lens of the eye * Can be classified according to position of the opacity * Most common is nuclear sclerosis which is age related

Question 31

what are the first wavelengths of light to get lost in a cataract?

Answer 31

the short wavelengths so you stop being able to see warmer tones

Question 32

what is the most common cataract type? what does it look like?

Answer 32

cortical cataract so looks like spikes coming into the center and in retro illumination you can see glare associated with this in the patient's vision

Question 33

what is a posterior sub capsular cataract?

Answer 33

where the back of the lens becomes opacified - common in people with disease like diabetes or uveitis and patients even in their 20s can develop this hence not age related

Question 34

give 5 rare types of catarcat

Answer 34

-christmas tree or polychromatic -anterior capsular -traumatic -posterior pole -diabetic snowflake cataract

Question 35

what is a Christmas tree cataract?

Answer 35

also polychromatic cataract - due to changes in the lens, can be due to lipid changes as well as protein changes and its more rare

Question 36

is anterior or posterior rupture to lens worse? why?

Answer 36

Anterior rupture of capsule is much worse than posterior rupture as the aqueous has more liquid than the vitreous

Question 37

what is significant about management for posterior pole cataracts?

Answer 37

need a specific surgical technique as they are very common to rupture but most patients with this usually have good va so not worth risk of surgery

Question 38

why does diabetic cataract look the way it does?

Answer 38

snowflake cataract where multiple layers of the lens have different opacities

Question 39

why does diabetes cause cataract?

Answer 39

due to rapid osmotic changes in the lens due to poor diabetic control

Question 40

what are the 2 causes of anterior capsular cataract?

Answer 40

-trauma -idiopathic

Question 41

what are traumatic cataracts also known as?

Answer 41

stellate or rosette

Question 42

what can cause posterior pole cataract

Answer 42

congenital with AD inheritance link

Question 43

why grade cataracts and how does it work?

Answer 43

Grading cataracts are used for research purposes to categorise the cataract and explain to people what they may look like - not used clinically to make surgical decisions - n grading, c grading and p grading where the higher the level of cataract, the higher the grading.

Question 44

why give cataract patients a questionnaire? How does it work?

Answer 44

because va is not always the best way to measure how cataract impacts daily life due to other affects like contrast. Negative score means you're good, positive score = worse cataract that's affecting your life and people with symptomatic cataract have a score of 0. Patients post surgery should increase their score by a mean of ~3.5. You want to know their best corrected symptoms

Question 45

what is the cataract questionnaire called?

Answer 45

CATProm-5

Question 46

what ocular assessment would you do for someone with cataract? what is an extra thing ophthalmologists would do?

Answer 46

* Visual acuity * Contrast sensitivity? * IOP * Anterior eye check – look for signs of blepharitis – increased risk of endophthalmitis – lid hygiene recommended * Lens check * Posterior eye Biometry

Question 47

give 8 examples of ocular conditions that would affect cataract surgery and how they would affect it

Answer 47

* Corneal scarring – poor view * Anterior chamber depth - difficult surgery * Previous trauma – causes zonules to be weakened or damaged * Intra-ocular injections – zonular damage, risk of posterior lens touch * Pseudo- exfoliation – weak zonules * Diabetes – poor dilation, risk of bleed if NVI * Fuchs endothelial dystrophy – risk of post op corneal decompensation * Deep sockets – difficult access for surgery

Question 48

what systemic checks would you need to do before cataract surgery?

Answer 48

* Blood pressure – needs to be controlled prior to surgery * Blood sugar if patient is diabetic * Review of medication – some will affect how the eye behaves in surgery * Allergies * Ability to mobilise and lie flat for surgery * Other health checks only needed if a general anaesthetic is being carried out

Question 49

give 6 medical problems that may affect cataract surgery with examples

Answer 49

* Poor mobility – unable to get on and off the bed easily * Spinal problems – unable to lie flat for surgery * Dystonia – unable to keep still for surgery * Thromobcytopenia – may require medication prior to surgery * Dementia or learning difficulties – not co-operative * Use of alpha-blockers such as Tamsulosin / Doxazocin– will cause intra-operative floppy iris syndrome (IFIS) (where the iris shrinks during surgery)

Question 50

what is biometry?

Answer 50

collecting and analysing data using stats methods where you sit at the machine and it can calculate multiple lenses that will be good for the power of the eye. Cl wearers should not wear their Cls 2 weeks prior to this appointment

Question 51

give 3 reasons that youd have to repeat biometry

Answer 51

* Axial length below 21 mm and above 26mm * If there is more than 0.3mm difference between the two eyes * if the cataract is more than 4 years old

Question 52

what kind of IOL is supplied under the NHS?

Answer 52

a monofocal one (px can be fitted with one distance and one reading if patient has had experience of this with contact lens wear)

Question 53

when do NICE recommend you use a toric IOL?

Answer 53

when corneal astigmatism is >2.5D

Question 54

give 2 more complex IOLs you can use in cataract surgery

Answer 54

-EDOF which mean your need to use reading glasses would be less -Multifocal lenses

Question 55

what is an EDOF IOL?

Answer 55

extended depth of focus lens so has a single extended focal point which allows greater range if focus and reduces dependence on near vision correction

Question 56

what are the negatives of using a multifocal IOL

Answer 56

* Prone to ghosting and halos * Difficult to adapt * Need to manage patient expectations

Question 57

what is a multifocal IOL?

Answer 57

a lens with multiple points of focus produced either by diffractive rings or variable refractive materials

Question 58

what are the topical anaesthesia is uses in cataract surgery?

Answer 58

Local anaesthetic drops and intracameral lidocaine

Question 59

what happens in sub-tenons block and why can't it be done on both eyes at once?

Answer 59

Small incision made in the inferior medical canthus and a blunt canular takes anaesthetic to posterior eye because it will block extra ocular muscles, lid movement and optic nerve function, therefore cannot block both eyes

Question 60

what oral sedation can you use for any local anaesthetic procedure?

Answer 60

diazepam or temazepam

Question 61

give reasons why GA is avoided in cataracts

Answer 61

Elderly patients with small vessel dementia can be progressed with general anaesthetic - avoid unless really needed

Question 62

what should not be a reason to give GA for cataract surgery?

Answer 62

anxiety

Question 63

when might you use GA with cataract surgery?

Answer 63

-learning difficulties -dimentia -movement disorders

Question 64

what do the surgeons feet do in cataract surgery?

Answer 64

one foot controls the phaco machine and the other controls the microscope (binocular microscope)

Question 65

what are the 10 steps in cataract surgery?

Answer 65

1. Incision 2. Viscoeleastic 3. Caspularhexis 4. Hydrodissection 5. Sculpt 6. Segment (quadrant) removal 7. Irrigation aspiration 8. Lens insertion 9. Removal of visco elastic 10. Antibiotic and wound hydration

Question 66

learn the steps of cataract surgery slides 32 - 36 on cataract surgery pptx in block 8 under lecture slides

Answer 66

okay

Question 67

what are the most common intra-operative complications in cataract surgery?

Answer 67

* Extension of the rhexis * Zonular dehisence * Posterior capsular rupture * Loss of vitreous * Dropped nucleus

Question 68

what are the most post operative complications in cataract surgery?

Answer 68

* Prolonged inflammatory response including macular oedema * Corneal decompensation * Refractive surprise

Question 69

what can increase risk of intraoperative complications?

Answer 69

* White cataract * Multiple Intravitreal injections * Ocular co-morbidity * High refractive error – both myope and hypermetrope * Poor co-operation

Question 70

how common are intraoperative cataract complications?

Answer 70

uncommon - approx 1% of cases

Question 71

how do ypu deal with prolonged inflammatory response in post op cataract surgeries?

Answer 71

All patients will have antibiotic and steroid post operatively for us to 4 weeks

Question 72

when is prolonged inflammatory response post cataract op even more common?

Answer 72

* where surgery has been prolonged or complication has occurred * Common where ocular co-morbidity especially co-existed ocular inflammatory disease

Question 73

how do you deal with post op uveitis?

Answer 73

-flare in AC and CMO in oct 4 weeks post op is normal -asymptomatic Px dont need treatment -symptomatic can have NSAID 3 times a day and steroid 2x a day for a further 4 weeks but if this persists then refer to secondary care

Question 74

how do you deal with corneal decompensation (oedema post op)

Answer 74

-be concerned if va is reduced -treat with mild topical steroid, can consider 5% (hypertonic) saline for further 4 weeks -refer to secondary care if does not want to resolve

Question 75

when may you not do phaco? what other surgeries are there?

Answer 75

if the nucleus is very dense with Small incision manual cataract surgery (SIMCS) ECCE and ICCE (extra and intra capsular cataract extraction) is where you flap the cornea open and just remove the cataract - this was the old way of doing it before phaco.

Question 76

how is a capsular rupture dealt with in cataract surgery?

Answer 76

* Manage vitreous loss * If nuclus is dropped will require vitrectomy to remove * Lens placed in sulcus, anterior IOL or scleral suture

Question 77

what can cause higher risk of corneal decompensation post cataract op?

Answer 77

-if prolonged surgery or endothelial injury during surgery -if there's pre-exisiting corneal pathology – Fuchs endothelial dystrophy

Question 78

what defines refractive suprise post cataract surgery?

Answer 78

+/- 1.00D deviation from expected combined spherical error (SE)

Question 79

what can cause refractive surprise post cataract op?

Answer 79

-using the wrong biometric formula -if viscoelastic trapped behind the IOP causing capsular distension

Question 80

how can you correct refractive surprise post cataract op?

Answer 80

* Glasses * Contact lenses * YAG capsulotomy * IOL exchange

Question 81

when might you have to make alterations to biometry formula?

Answer 81

-if they have had previous refractive surgery -if they had a silioconfilled eye