Cataract Flashcards
Where does the lens sit?
Lens sits in anterior segment of eye – with suspensory ligaments attached to ciliary body
Lens has capsule – divided into anterior and posterior aspects.
Posterior aspect has live and feeding cells which produce lens fibres
As lens fibres mature, they are compacted into central part of lens (nucleus)
What is the function of human lens?
- Refractive
o One third of optical power (approx. 18-20D out of 60D)
o Rest of refractive power by cornea - Accommodation
What is the pathogenesis of cataract?
- Protein denaturation
o When lens fibres are produced from posterior capsular epithelial cells, they are transparent but as we get older the proteins in the lens fibres denature & proteins in lens fibres is opaque (manifesting as cataract) - Oxidative damage
o Can occur naturally or artificially
What are the risk factors of cataract?
- Age
- Smoking
- Alcohol
- Dehydration
- Radiation
- Diabetic – can have cataract at younger age as their metabolism is different and oxidative damage is thought to play role here
- Steroids – e.g. asthmatic pxs often present earlier in life
What are the types of cataract?
- Involutional age-related – most common type
- Congenital
- Traumatic
- Secondary – px taking steroids
How much of global blindness is due to cataract?
40% of global blindness due to cataracts – approx. 16 million
Increasing every year
Age related condition
Classifying type of cataract based on location of opacity?
- Most cataracts are nuclear cataracts
- Cortical cataract:
o Peripheral lens fibres are less compact & more loose – can get opacified as evolutional change - Posterior subcapsular – just under posterior capsule – typically seen in steroid users & diabetics
o Ground glass opacification - Christmas tree:
o Not as commonly seen
o More often seen in involutional/age-related or diabetic pxs
o Myotonic dystrophy can lead to seeing this earlier in life – congenital disease where muscles are affected - Congenital:
o Urgent referral to local HES – can be very serious cataract - Posterior Polar:
o Thought to be developed at birth or in younger yrs of life
o Manifested later in life
o Can cause complications during cataract surgery – opacification is in posterior capsule and while removing lens that can cause a posterior capsular tear (cataract surgery complication)
o Surgeon needs to know about this – as different technique can be used to remove the cataract to try and avoid the complication of tear
What are the 5 stages of cataract surgery (before and after)? - the process to achieve optimal vision in cataract px
Clinical assessment
Preop assessment
Removal of cataract
Insert intraocular lens (IOL)
Visual aids if needed (approx 4 weeks)
Describe clinical assessment before cataract surgery?
- Visual acuity
- Refraction
- History:
o Visual needs
6/18 px who is non-driver & does not read much may not need cataract surgery
6/6 px with posterior subcapsular cataract may have disabling glare while driving for work
o Symptoms - reduced VA, glare, monocular diplopia
o Change in refraction- myopic shift or astigmatism
o Systemic drugs: Alpha antagonists -tamsulosin
Can affect pupil dilation – surgeon may need extra steps to dilate the pupil (e.g. ring or hook)
Desccribe the preop assessment before cataract surgery?
- Examination :
o Lie flat- spinal abnormalities, COPD
Can they lie flat for about 30mins?
These pxs would likely not be put on a hugh volume cataract surgery list
o Deep set eyes
Can affect where surgeon accesses eye to perform surgery – usually superiorly but can be temporally if deep set eyes
o Lids- Blepharitis, malposition (ectropion, entropion)
These need treated first before going for surgery
Blepharitis – lid inflammation, red eye
All 3 can lead to intraocular infection
o Cornea: Fuchs’ endothelial dustrophy
Beaten metal appearance – Guttata – endothelial corneal cells are genetically programmed to die at a higher rate than normal – pxs lose more cells than normal
Later stage – corneal oedema
Surgeon may need to use a different technique to protect endothelium
o Adequate pupil dilation
Poor pupil dilation: - Age related
- Alpha 1 blocker
- Diabetic
- Uvetic posterior synechiae
- Pseudoexfoliation – cause poor pupillary dilation – pupil fails to dilate – operation can be difficult
o Type of cataract
Is it a wide cataract – does surgeon need to take extra precautions/steps for this cataract? Will the usual time slot be enough or does it need more time allocated to it?
o Fundus - Macular degeneration, retinal detachment
Describe optical biometry (cataract surgery)?
- For selection of correct IOL power
o Corneal power (keratometry)
o Axial length
o Constants – specific for the lens the surgeon uses - Ultrasound
o About 1/3 cannot be measured using optical – infrared rays do not penetrate dense cataract to determine power or in cases where px cannot sit in the chair for the optical method – so ultrasound must be used in these cases
o Error prone – use probe and needs to be vertical with anterior surface of cornea – if px moves eyes a lot then this could be very difficult - Optical
o Keratometry
o 6-32 points on cornea
o 2.3mm of central cornea
o Uses infrared rays - Optical more accurate than ultrasound so is default method
- SNR – signal noise ratio should be as high as possible
o Can get inaccurate axial length readings which can have impact on IOL power calculation and then ultimate vision level px can achieve
What are the types of cataract surgery?
- (Intracapsular) Historical – no longer done
- Extra capsular cataract extraction (ECCE) – used to be common method – make big incision on superior limbus (see image)
- Phacoemulsification – method of choice now – small incision or keyhole surgery
- Laser assisted cataract extraction – gaining popularity (especially privately)
What is the IOL?
PMMA
Aspheric design IOL
Most common is multifocal lens
Using more toric lens – may see mark indicating this on lens (used in astigmatism over 2/3D with regular corneal astigmatism)
Multifocal IOL – concentric rings on lens
Describe phacoemulsification?
Incision made at limbus – 2.8mm
Anterior capsule is torn
Controlled fashion
Usually done under red reflex
Stain capsule blue then tear 6mm of anterior capsule
Use ultrasound probe to emulsify nucleus (most compact part of lens) by dividing lens into 4 parts
Then irrigate and aspiration then insert IOL (folded acrylic lens – unfolds in eye)
Clear corneal incision
Capsulorhexis
Phaco of nucleus
Irrigation & aspiration
Insertion of IOL
Describe the visual outcome of cataract surgery?
- BCVA- 90% >/= 6/12 within 3 months
- > 80% within predicted refraction
What are the intraoperative complications?
- Posterior capsular tear 2%
- Nucleus drop 0.5%
- Zonular dehiscence