2-27,28 - Cataracts Flashcards
Treatment of cataracts
Surgically remove + replace w/ IOL
- Intracapsular cataract extraction (ICCE) = Remove lens + capsule, add AC-IOL attached to iris or ciliary sulcus
- Extracapsular cataract extraction (ECCE) = REmove lens substance only (post. capsule remains), add PC-IOL using post. capsule as base.
- Phacoemulsification = Vibrations emulsify lens, suck out lens, continue w/ ECCE
Anterior-subcapsular Cataracts
- General information
- General mechanism
- Opacities beneath ant. lens capsule
- Associated lens epithelium fibrous metaplasia (to myofibroblast) (triggered by injury)
- Leads to ASC fibrous plaques -> contraction wrinkles lens capsule + disrupt tissue order
- 5% of cataracts are ASC, not age-related
Cortical cataracts
- General information
- Mechanism
- Anywhere within cortex, usually starts infero-nasal
- Due to ionic imbalance -> localised lens fibre swelling (disrupt organized packing)
- Starts as clefts + vacuoles between fibres (pools of fluid displaces fibres causing degen)
-> then becomes typical cuneiform (wedge) or radial (spoke-like) opacities
-> then becomes Morgagnian globules (protein leak) -> then cortical liquefaction - Nucleus can appear sunken
- Due to age + DM
- Most common, least visually significant (unless at visual axis)
Mechanism:
Cannot regulate volume
E.g. Na/K pump inactive or membrane permeability increase
Leads to:
- Imbalance of H2O inward vs outward
- Localised H2O accumulation
- Fibre cell swell -> membrane damage -> clefts -> vacuoles
- Cuneiform + wedge-shaped opacities
Nuclear cataract
- General information
- Mechanism
- At centre of lens
- Biochemical but not structural changes (unlike cortical)
- Modifications to crystallin proteins w/ age -> diff. n value
- Yellowish hue due to urochrome pigment deposition (dark brown if advanced)
- Risk factors = age, UV, smoking
- Associated w/ myopic shift
Mechanism:
- Protein absorbs light -> make ROS e.g. H2O2, O2.-, .OH
- ROS scavenger system e.g. Glutathione (GSH) not working
- Lots of ROS (especially at nucleus where furthest from ambient levels in AH) -> lens crystallin protein cross-link -> protein aggregation -> refractive index mismatch -> opacities
Posterior subcapsular cataracts
- General information
- General mechanism
- Just in front of post. lens capsule
- Due to lens epithelial cells migrating along post. capsule (swelling as they move)
- Forms grainy/plaque-like PSC depositions (solitary plaques = “wedl” or “bladder” cells)
- Risk factors of DM and corticosteroid use
- Severely affects vision
LOCS III grading method
- Mainly for study purposes
- Uses 0.1 increments between grades
- Doesn’t have ant. subcapsular due to rarity
WHO grading: Nuclear cataract
NUC-0 = No cortical cataract
NUC-1 = Cortical transparency > Centre
NUC-2 = Equal opacification
NUC-3 = Nuclear more opaque than peripheral cortex
WHO grading: Cortical cataract
After dilation, you
- Divide lens into 8 sections
- Add up circumference of involved cortical cataract
Grade:
- Trace cortical = <1/8
- COR-1 = 1/8 to ¼
- COR-2 = ¼ to ½
- COR-3 = >½
if reach central 3mm, add “+ CEN”
WHO grading: Posterior-subcapsular cataract
Using retro,
- Find largest central opacity
- Measure vertical height (adjust slit beam height to match it)
Grade:
- Trace = <1mm
- PSC-1 = 1mm
- PSC-2 = 2mm
- PSC-3 = 3mm
Maturity classification of Cataracts
Only applicable when cataracts is white which is severe end-stage cortical (unlikely to happen in NZ)
Either:
- Mature Completely white opaque lens
- Hypermature (cells burst from swelling, gives wrinkly lens appearance)
- Morgagnian (Liquefaction of cortical fibres so intact brown nucleus sinks down)
Note: Nucleus likely brown from concurrent nuclear cataract.
Senile cataracts
- Age-related (noticed around 50-60yrs, exponential incidence after that)
- Nuclear (most common) + cortical + PSC
- Arbitrary amount of opacity used to classify
Penetrating vs blunt trauma cataract
Penetrating:
- Sharp obj. E.g. metalic FB
- Focal nonprogressive opacities
Blunt:
- Days or years to develop
- Transient, static, or progressive possible
- Rosette ASC/PSC most common (“sunflower” cataract)
- Vossius ring possible (iris imprint on lens)
Electric shock cataract
- Diffuse milky-white opacity
- Snowflake-like opacities, sometimes in star-like distribution
Infrared radiation cataracts
- Chronic exposure to IR from heating glass or molten metal
- “Glassblower’s cataract”
- Any layer of lens affected
- Can cause true exfoliation of ant. lens capsule
Ionizing radiation cataracts
- Exposed to stuff like X-rays, CT scans (often medical workers)
- PSC opacities, sometimes cortical
- Months to years to manifest
