Lens and Cataracts Flashcards
Where is the lens located?
between iris and vitreous
What is the power of the lens in adults?
15-20D
What is the power of the lens in infancy?
43-47D
What is the refractive index of the lens?
1.4
How does near accomodation work?
Ciliary muscle contraction - zonule relaxation - lens becomes more spherical and increases dioptre power
How does far accommodation work?
Ciliary muscle relaxation - increases zonular tension and lens becomes flat
Describe the histology of the capsule
outer transparent basement membrane
thinnest posteriorly and thickest near the equators
made of type IV collagen and glycosaminoglycan
anterior capsule THICKENS WITH AGE, posterior remains the same
Describe the histology of the lens epithelium
simple cuboidal cells below capsule
central zone: present on the anterior surface of the lens
pre-equatorial zone: cells undergo mitotic division through life and form the lens fibres
no epithelium on the posterior surface of the lens
Describe the histology of lens fibres
elongate and push older fibres deeper into the lens
nucleus is innermost part, present at birth
cortex = youngest part, outer part
junction of lens forms sutures:
- anterior suture: upright Y shaped suture
- posterior suture: inverted y shaped suture
What are zonules?
suspensory ligaments made of fibrillin, attached to the lens equator
What is a cataract?
progressive cloudiness of the lens causing gradual vision loss and blindness if untreated
What is the leading cause of blindness worldwide?
cataracts
Describe the grading of cataracts
immature: partially opaque
mature: completely opaque
Hypermature cataract: shrunken anterior capsule due to leakage of material outside the lens
morganian cataract: a form of hypermature cataract with cortex liquefaction causing the nucleus to sink
What are some complications of a morganian cataract?
phacoanaphylactic uveitis and phacolytic glaucoma
Describe nuclear sclerotic cataracts
characterised by yellowing of the crystalline lens due to deposition of the urochrome pigment
What phenomenon may be seen in nuclear sclerotic cataracts?
‘second sight’ elderly patients able to see close again
lens becomes harder, refractive index increases
Describe cortical cataracts
occur due to opacification of lens cortex
characterised by wedge shaped opacities
glare is the predominant symptoms especially when driving at night
describe the stereotypical nuclear sclerotic cataract pt
elderly, suddenly able to read close again
describe the stereotypical cortical cataracts
glare when driving especially at night from headlights
Describe subscapular cataracts
anterior subscapular: opacities under the anterior capsule
posterior subscapular: opacities under the posterior capsule, glare is a common symptom, difficult seeing in bright light and near vision
Describe polychromatic cataracts
characterised y needle-like opacities in the deep cortex and nucleus
What are the age related cataracts categorised into?
nuclear, cortical, subcapsular and polychromatic
What can cause acquired anterior subcapsular cataracts?
blunt trauma (flower shaped cataract)
atopic dermatitis (shield-like cataracts)
Wilson’s disease (sunflower cataracts)
post PACG - glaukomflecken
gold (drug induced)
infrared radiation (glass blower cataracts)
What can cause posterior subcapsular cataracts?
corticosteroids
diabetes (snowflake shaped cataracts)
retinitis pigmentosa
NF2
Chloroquine
What cataracts does myotonic dystrophy cause?
christmas tree like cataracts
What cataract does rubella cause?
pearly nuclear sclerotic
What cataract does down syndorme cause
Blue dot
What cataract does hypoparathyroidism cause?
polychromatic cataract
What is the gold standard for cataract Tx?
replacement of the lens with a new intraocular lens
phacoemulsification is gold std
How does phacoemulsification work?
uses an ultrasonically driven needle to chop nucleus and then aspirate lens
how does extracapsular cataract extraction work?
may be used for very hard cataracts
What are the advantages of phacoemulsification vs ECCE?
smaller incision
less astigmatism
faster recovery
reduced complications
no sutures required
How is the power of the IOL calculated?
P = A -2.5L - 0.9K
A is manufacturers constant
l is axial length measured using a-scan ultrasonography
k is average corneal power
What are the two types of IOLs?
rigid and flexible
describe rigid IOLs
made of polymethylmethacrylate (PMMA)
larger incision
higher rates of posterior capsular opacification than flexible IOL
Describe flexible IOLs
used in modern cataract surery
acrylic hydrophobic IOL: higher refractive index and lower rates of post caps opc than hydrophilic, can cause dysphotopsia
acrylic hydrophilic IOL: higher biocompatibility, but lens calcification may occur
silicone: less commonly used in modern phacoemulsification
What are some intraoperative complications of cataract surgery?
posterior lens capsule rupture
floppy iris sydrome: a flaccid iris that can complicate surgery, occurs in some patients on alpha blockers (use intracameral phenylephrine to dilate pupils)
What are some post operative complications of cataract surgery?
early: corneal oedema, elevated IOP and acute endophthalmitis
late: PCO, irvine gass syndrome (CMO post cataract surgery), retinal detachment (especially if high myopia)) and delayed endophthalmitis
What is endophthalmitis?
inflammation of the vitreous and aqueous humour usually caused by infection
characterised by progressive vitiritis
how is endophthalmitis prevented?
povidone-iodine 5% antiseptic to clean eyes perioperatively
What are the features of endophthalmitis?
vitritis (floaters and blurred vision)
pain
hypopyon
corneal haze
How is endophthalmitis managed?
intravitreal antiobiotics or pars plana vitrectomy
What did the early vitrectomy study gorup find?
early vitrectomy is only beneifical in patients with light-perception only vision
What is acute endophthalmitis?
usually occurs within first week of surgery
due to patients own’ periocular flora,
STAPH EPIDERMIS
What is delayed endophthalmitis?
between 6 weeks to several months
PROPIONIBACTERIUM ACNES
What are some other causes of endophthalmitis?
post trauma: staphylococcus or Bacillus cereus (worst prog)
Fungal: candida: occurs in immunocompromised patients most common cause of endogenous endophthalmitis
What is the most common complication of late cataract surgery?
posterior capsule opacification, due to posterior migration of lens epithelial cells
What are the features of posterior capsule pacification?
gradual loss of vision and glare, patients may think cataract has recurred
Elschnig pearls: grape like collection of swollen lens epithelial cells
simmering rings: white annular proliferation of residual cells
How is posterior capsule opacification managed?
Nd: YAG laser
Describe the inheritence of bilateral congenital cataracts
AD
describe the inheritence of unilateral congenital cataracts
sporadic
What are some secondary causes of congenital cataracts?
galactosaemia
lowe syndrome
fabry disease
mannosidosis
down syndrome
TORCH intrauterine infection
Describe galactosaemia
AR conditon due to absence of galactose-1-phosphate uridyltransferase
features: infant with liver dysfunction, failure to thrive and OIL DROPLET CATARACT
Ix: stool for reducing substances
Mx: dietary restriction of lactose and galactose
What is low syndrome?
XLR condition
due to abnormality in amino acid metabolism
features: seizures, cataracts, posterior lenticonus congenital glaucoma
What is fabry disease?
spoke shaped posterior cataracts and corneal verticillata
What is mannisidosis?
AR condition due to deficiency in alpha mannosidase
spoke shaped posterior cataracts
What are the torch infections?
toxoplasmosis other (VZV, synphilis, parvovirus b19) rubella cmv HSV
What is the management for congenital cataracts?
observation if small, < 3mm and partial dense
unilateral: part time occlusion, pharmacological mydriasis of good eye can help prevent amblyopia (delays cataract surgery)
What is the surgery for congenital cataracts?
pars plana lensectomy, posterior capsule capsulorhexis and anterior vitrectomy where appropriate
how is a bilateral dense congenital cataract treated?
treat within 8-10 weeks
How is a unilateral dense cataract treated?
surgical treatment within 6 weeks due to higher risk of amblyopia
What are some post operative complications of managing congenital cataracts?
PCO - can lead to ambylopia
secondary glaucoma: open angle glaucoma, can occur years after surgery, closed angle may occur immediately post op
endophthalmitis
retinal detachment
What is anterior lenticonus?
bilateral thinning of the anterior capsule with anterior lens protrusion into the anterior chamber
associated with alport syndrome (type IV collagen disorder)
What is posterior lenticonus?
deformity in the posterior surgace of the lens that is usually unilateral
associated with congenital cataract
associated with lowe syndrome
What is ectopia lentis?
ectopia lentis refers to the dislocation / displacement of the lens from its normal position
most common cause is trauma, can be associated with ocular or systemic disease
What are some ocular causes of ectopia lentis?
simple (familial) ectopia lentis
- occurs congeitally or later in life
- AD or AR
- Bilateral symmetric lens dislocation superotemporally
pseudoexfolation syndrome
hypermature cataracts
high myopia
What are some systemic causes of ectopia lentis?
marfan syndrome
Describe marfan syndrome
most common inherited cause of ectopia lentis
AD due to mutations in fibrillin-1 gene on chromosome 15 (FBN1 gene)
bilateral superotemporal lens dislocation
accommodation is not affected because zonules are intact
ectopia lentis is most common ocular feature
systemic features: tall stature, typically with dolichostenomelia (long limbs), mitral prolapse, aortic aneurysm, regurgitation and dissection and kyphoscoliosis
What is homocystinuria?
the second most common inherited cause of ectopia lentis
inheritance is AR due to cystathionine beta-synthase deficiency
bilateral inferonasal lens dislocation is typical
systemic features: coarse blond hair, malar flush, blue irides and intellectual disability
