What is the configuration of a three piece IOL
Optic postitioned slightly behind the haptics
Posterior vaulting of optic
- presses against posterior capsule enhancing lens stability
- when placed in ciliary sulcus, optic vaults away from the posterior iris, reducing the risk of iris chafing or pigment dispersion
What happens if 3 piece IOL is placed upside down?
S formation
Optic vaults forward
Myopic shift in vision
ay become trapped by dilated pupil and cause pupil block glaucoma when pupil constricts
How can single piece lenses being placed upside down affect outcome?
Flat optic-haptic plane, not vaulted
Can impact refractive outcome
Most biconvex lenses have more optical power on posterior surface to reversing the lens can lead to myopic surprise
What happened in EVS study
Endophthalmitis vitrectomy study
420 patients with endophthalmitis within 6 weeks of cataract surgery
Randomised to either initial PPV and intravitreal antibiotics
OR initial IVI antibiotics with vitrectomy at 36-60 hours if no improvement was observed
Findings of EVS
Systemic abx
VA PPV vs tap
Organism
No difference in final VA or media clarity with or without systemic abx
In initial PL or worse vision, PPV 3x increase in frequency of achieving 6/12 or better and 50% decrease in frequency of severe visual loss over tap
70% organisms isolated were Staph epidermis.
Posterior polar cataract
Inheritance pattern
Genes
Autosomal dominance
CRYAB
CIMP4B
PITX3
What type of cataract are Rubella infection, steroid use and trauma
Wilson’s disease, myotonic dystophy, Galactose-1-phosphate uridyl transferase (galactosaemia) associated with
Rubella - NS/total
Long term steorid use - PSC
Trauma - PSC, rosette cataracts
Wilson’s - sunflower cataract
Myotonic dystrophy - christmas tree cataract
Galactosaemia - Oil droplet cataracts
What probe for US biometry
10mHz probe
What happens to US biometry in silicone filled eyes?
Higher refractive index than vitreous - slows down light travelling in eye
Axial length measurement will be erroneously long - sound takes longer to travel through the oil
- results in picking IOL underpowered
- results in hyperopic surprise
What is posterior staphyloma?
Focal areas of scleral thinning with outpouching of that area
Most located peripapillary adjacent to macula 70% inside macular region
If fovea at center of staphyloma, measure AL will be longer than true AL
- results in picking IOL underpowered
- results in hyperopic surprise
Lower powered IOL
Higher powered IOL
Lower powered - more hyperopic outcome
Higher powered - more myopic outcome
Risk of contact tehcnique
Indent cornea
Shallow the AC
AL shorter than true AL
Overpowered IOL
Myopic surprise
Optical biometry
Where does measure to?
Wavelength?
Compared to US
What does it measure
2 coaxial partially coherent laser beams from infrared
Measure to RPE not ILM
780nm infrared (higher resolution
More accurate
MEasures AL, keratometry, AC depth, corneal white to white distance
Cannot pass through opaque media
Congenital cataract rule of 1/3
1/3 associated with systemic disease or illness
1/3 inherited with minimal effect on vision
1/3 idiopathic
Myotonic dystrophy
- inhertiance
Ocular findings
Risks in cataract extraction
AD
Earlier and more severe disease in successive generation (trinucelotide repeat)
Chirstmas tree cataract, ptosis, FED
retincular maculopathies
High risk fo capsular contraction and PCO, hydrophobic acrylic IOLs to reduce risk
If GA - risk fo aspiration due to reduced gastric emptying
Load
Amount of surface area of the nuclear material in contact with phaco tip
Power
Percentage of length that the phaco tip moves relative to maximal possible length
Stroke length
Distance the phaco tip travels
Chatter
How the nuclear fragment is repelled by the phaco tip - not desirable because the lens cannot be aspirated as quickly when this occurs
Duty cycle
The proportion of time phaco energy is applied during a specified period of time
(%)
Cavitation
Formation of bubbles at the phaco tip which results in lens breakdown
How does corneal oedema affect refractive outcome
IPosteiror corneal cruvature is flattened - thickening the refracting medium - more powerful
High K creates under estimation of IOL power
Increases risk of hyperopic error
In DMEK/DSEK - increase in posterior curvature of cornea followeing endothelial grafting thins the refracting medium causing it to be weaker causing hyperopic shift - stronger IOL picked to compensate
What does retained viscoelastic cause to refractive outcome
Higher refractive index
Bends light more
Myopic shift
What effect does CMO have on refractive index
Raised macula
Hyperopic shift
Light refracted behind the macula
