lens and cataracts Flashcards
define lens
lens is a biconvex crystalline structure located between the iris and vitreous. It has a power of 15–20D in adults and 43–47D in infancy. Its high-protein (crystalline) content gives the lens a high refractive index of about 1.4.
what happens at near accomodation
The eye brings near objects into focus by contracting the ciliary muscle. This results in the relaxation of the zonules making the lens more spherical and increasing its diopter power.
what happens at far accomodation
The eye brings far objects into focus by relaxing the ciliary muscle. This increases zonular tension, making the lens flat.
histology of capsule cataract
● An outer transparent basement membrane.
● Thinnest posteriorly and thickest near the equators.
● Made of type IV collagen and glycosaminoglycan.
● Anterior capsule thickens with age, but the posterior capsule maintains the
same thickness.
histology of epithelium cataracts
● Simple cuboidal cells located beneath the capsule.
● Central zone: Present on the anterior surface of the lens.
● Pre-equatorial zone: Cells undergo mitotic division throughout life and form
the lens fibres.
● No epithelium on the posterior surface of the lens.
histology of lens fibres cataracts
● Lens fibres elongate, pushing the older fibres deeper into the lens.
● The nucleus is the innermost part, which is present at birth, and the cortex is
the outer part, which contains the youngest fibres.
● The junction of lens fibres forms sutures:
Anterior suture: Has an upright Y-shaped suture. Posterior suture: Has an inverted Y-shaped suture.
histology of zonules cataracts
Suspensory ligaments, made of fibrillin, attached to the lens equator.
what is cataract maturity
progressive cloudiness of the lens causing gradual vision loss and blindness if untreated. It is the leading cause of blindness worldwide.
grading of cataracts
● Immature cataract: Partially opaque.
● Mature cataract: Completely opaque.
● Hypermature cataract: Shrunken anterior capsule due to leakage of material/water outside the lens.
● Morgagnian cataract: A form of hypermature cataract with cortex
liquefaction causing the nucleus to sink. Complications include phacoanaphylactic uveitis and phacolytic glaucoma.
classification of age-related cataracts
nuclear, cortical, subcapsular and polychromatic cataracts.
what is nuclear sclerotic
signs
patho
EARLY - yellowing of the crystalline lens due to the deposition of the urochrome pigment.
LATE - brown
increase in refractive index of the nucleus and increased spherical abberation- myopic shift leading to ‘second sight’ phenomenon
lens becoming harder, the refractive index increases, allowing for some elderly patients to read without glasses.
what is cortical cataracts
opacities start as clefts and vacuoles between lens fibres due to hydration of the cortex.
Subsequently opacification results in typical cuneiform (wedge-shaped) or radial spoke-like opacities
opacification of the lens cortex.
wedge-shaped opacities
predominant Sx of cortical cataracts
glare - especially from headlights while driving at night.
this is due to light scattering
anterior subcapsular cataract
opacities under the anterior capsule
under the lens capsule and ass w fibrous metaplasia of the lens epithelium
posterior subcapsular cataract
Opacities just in front of the posterior capsule. Glare is acommon symptom.
vacuolated , granular or plaque-like appearance on oblique slit lamp biomicroscopy
black on reteroillumination
Patients may complain of difficulty seeing in bright light and near vision.
description of polychromatic ‘xmas tree’ cataract
Characterized by needle-like opacities in the deep cortex and nucleus
acquired anterior subcapsular cataracts examples and their ass
● Blunt trauma ● Atopic dermatitis ● Wilson disease ● Post-congestive angle closure glaucoma ● Gold ● Infrared radiation
● Blunt trauma (flower-shaped cataract)
● Atopic dermatitis (shield-like cataract)
● Wilson disease (sunflower cataract)
● Post-congestive angle closure glaucoma (glaukomflecken)
● Gold (drug induced)
● Infrared radiation (glass-blower cataract)
posterior subcapsular cataracts examples and their ass
● Corticosteroids ● Diabetes (snowflake shaped) ● Retinitis pigmentos ● NF2 ● Chloroquine - myotonic dystrophy - stellate
other cataracts myotonic dystrophy rubella down syndrome hypoparathyroidism
● Christmas tree-like cataract appearance: Myotonic dystrophy
● Pearly nuclear sclerotic cataract: Rubella
● Blue dot cataract: Down syndrome
● Polychromatic cataract: Hypoparathyroidism
Gold standard Mx for cataracts
phacoemulsification
This technique uses an ultrasonically driven needle (phaco tip) to chop the nucleus and then aspirate the lens material.
other type of Mx for cataracts
Extracapsular cataract extraction (ECCE): May be used for very hard cataracts.
advantages of phacoemulsification
● Smaller incision ● Less astigmatism ● Faster recovery ● Reduced complications ● No sutures needed
what is intraocular lens power
IOL power is determined by measuring the curvature of the cornea and eye length. Power (P) is calculated using the following equation:
P = A − 2.5L − 0.9K
where:
● A is a constant supplied by the manufacturer.
● L is the axial length of the eye, measured using A-scan ultrasonography.
● K is the average corneal power reading in diopters.
what is rigid IOL
● Made of polymethylmethacrylate (PMMA).
● Requires a larger incision. more than 5mm
● Higher rates of posterior capsular opacification (PCO) than flexible IOL.
what is flexible IOL
types
● Used in modern cataract surgery.
- smaller incision
● Three types
Acrylic hydrophobic IOL: Has a higher refractive index and lower rates of PCO than its hydrophilic counterparts. However, can cause dysphotopsia (troublesome glare). greater reaction in uveitic eyes
Acrylic hydrophilic IOL: Has higher biocompatibility. However, calcification of the lens (causing lens opacities) may occur. better with uveitic eyes
Silicone IOL: Less commonly used in modern phacoemulsification.
complications of intraoperative surgery
- Posterior lens capsule rupture.
- Floppy iris syndrome: A flaccid iris that can complicate surgery. It usually occurs with some patients on alpha blockers (e.g. tamsulosin). Intracameral phenylephrine can be used to dilate pupils in high risk patients
complications of postoperative surgery
Early: Corneal oedema, elevated IOP and acute endophthalmitis.
Late: PCO (most common complication), Irvine-Gass syndrome (CMO post cataract surgery), retinal detachment (especially in patients with high myopia) and delayed endophthalmitis.
what is endopthalmitis
inflammation of the vitreous and aqueous humour, usually caused by infection. It is characterized by progressive vitritis.
staph epidermidis is common
main prevention of endopthalmitis
povidone-iodine 5% antiseptic
prophylatic ABx
features of endopthalmitis
Progressive vitritis (blurred vision, floaters), pain, hypopyon and corneal haze.
Mx of infective endophthalmitis
Intravitreal antibiotics ie ceftazidime - gram negative and vancomycin - coagulase negative or
pars plana vitrectomy.
In acute endophthalmitis, the Early Vitrectomy Study Group found that early vitrectomy is only beneficial in patients with light perception-only vision
what is acute endophthalmitis
● Usually occurs within the first week of surgery.
● This is due to the patient’s own periocular flora. The main causative
organism is Staphylococcus epidermidis.
Most common source: bacteria from patient’s lids/conjunctiva
what is delayed endopthalmitis
features
● Onset varies from 6 weeks to several months.
● Main causative organism is Propionibacterium acnes.
• Indolent uveitis/vitritis
• White capsular plaque, painless
other causes of endophthalmitis
● Post-trauma: Staphylococcus or Bacillus cereus (has the worst prognosis).
● Fungal (Candida): Occurs in immunocompromised patients. Most common
cause of endogenous endophthalmitis.
most common complication of late cataract surgery
posterior capsular opacification
what is posterior capsular opacification
The posterior capsule opacifies due to posterior migration of lens epithelial cells.
features of posterior capsular opacification
● Gradual loss of vision and glare; patients often think their cataracts have recurred.
- capsular fibrosis
● Elschnig pearls: Grape-like collection of swollen lens epithelial cells - proliferation of epithelial cells in the posterior capsule which usually has none
● Sommering rings: White annular proliferation of residual cells.
Mx of posterior capsular opacification
Capsulotomy with Nd:YAG laser.
secondary causes of congenital cataracts
galactosaemia
lowe syndrome
fabry disease
mannosidosis
down
TORCH
what is galactosaemia
features
Ix
Mx
- AR condition due to absence of galactose-1-phosphate uridyltransferase.
- Features: Infant presenting with liver dysfunction, failure to thrive and oil-droplet cataract.
Investigation: Stool for reducing substances.
Management: Dietary restriction of lactose and galactose.
what is lowe syndrome
XLR condition due to an abnormality in amino acid metabolism.
Features: Seizures, cataracts, posterior lenticonus and congenital glaucoma.
what is fabry disease
XL lysosomal storage disorder
periodic burning pain in extremities, telangectasias
Spoke-shaped posterior cataracts and corneal verticillata.
what is mannosidosis
inheritance
feature
AR condition due to deficiency in alpha mannosidase.
Spoke-shaped posterior cataracts.
features of down syndrome
Single palmar crease, low set ears, large tongue, epicanthal folds and blue dot cataract.
what is TORCH
Toxoplasmosis, other (VZV, syphilis, parvovirus B19), rubella, CMV, HSV.
Mx of congenital cataracts
● Observation, for small, <3 mm diameter, partial dense cataracts.
● In unilateral cases, part-time occlusion or pharmacological mydriasis of the
good eye can be helpful to avoid amblyopia. These interventions are useful in delaying the need for cataract surgery until the eye growth becomes stable.
● Surgery: Involves pars plana lensectomy, posterior capsule capsulorhexis and anterior vitrectomy where appropriate. In addition to correction of refractive errors.
● A bilateral dense cataract requires surgical treatment within 8–10 weeks.
● A unilateral dense cataract requires surgical treatment within 6 weeks due to
a higher risk of amblyopia.
postop complications of congential cataracts
- Posterior Capsular Opacification: A dangerous complication, as it can lead to amblyopia.
- Secondary glaucoma: Open-angle glaucoma can occur years after surgery. Angle closure may occur immediately postop. Incidence is higher if surgical treatment was performed within the first month of life.
- Endophthalmitis.
- Retinal detachment.
what is anterior lenticonus
Bilateral thinning of the anterior capsule with anterior lens protrusion into the anterior chamber.
- Alport syndrome (type IV collagen mutation disorder).
- AD
- sensorineural deafness and renal disease
what is posterior lenticonus
Deformity in the posterior surface of the lens that is usually unilateral. Associated with congenital cataract. Associated with Lowe syndrome.
what is ectopia lentis
dislocation/displacement of the lens from its normal position. The most common cause is trauma
ocular causes of ectopia lentia
● Simple (familial) ectopia lentis Occurs congenitally or later in life Inheritance: AD or AR Bilateral symmetric lens dislocation superotemporally ● Pseudoexfoliation syndrome ● Hypermature cataracts ● High myopia
systemic causes of ectopia lentis
marfan
homocystinuria
marfan syndrome causing ectopia lentis
● Most common inherited cause of ectopia lentis.
● Inheritance: AD due to mutations of fibrillin-1 gene on chromosome 15
(FBN1 gene).
● Bilateral superotemporal lens dislocation is typical. Accommodation is not affected because ZONULES ARE NOT BROKEN
● Systemic features
- Tall stature, typically with dolichostenomelia (unusually long limbs) - Mitral prolapse, aortic aneurysm, regurgitation and dissection
- Kyphoscoliosis
homocystinuria causing ectopia lentis
● The second most common inherited cause of ectopia lentis.
● Inheritance: AR due to cystathionine beta-synthase deficiency.
● Bilateral inferonasal lens dislocation is typical.
- ZONULES BROKEN
Skeletal abnormalities, mental disability, risk of thrombotic complications (especially with anaesthesia)
● Systemic features
- Coarse blond hair
- Malar flush
- Blue irides
- Intellectual disability
• Treatment of homocystinuria: low methionine, high cysteine diet
nuclear sclerotic cataract is assessed by
oblique slit-lamp biomicroscopy and not by retroillumination
secondary cataracts - cataracts that develope as a result of some other primary ocular disease
anterior uveiits
acute agnle closure glaucoma
hereditary fundus dystrophies
drugs associated with cataracts
- Steroids
- Chropromazine • Gold
- Amiodarone
- Busulphan
- Allopurinol
anaesthetic options
sub-tenon block - 5mm from limbus into subtenon space - akinesia is variable
peribulbar block - akinesia and anaesthesia good but perforation of eyeball is risky
topical anaesthesia - absent akinesia
signs of ruptured posterior lens capsule
sudden shallowing of AC
presentation of delayed onset postop endophthalmitis
painless visiual deterioration ass w floaters
mutton fat keratic precipitates
anterior stellate cataract
phenothiazine, amiodarone
RFs of cataracts
UV exposure, smoking, sugar level, steroid use
Mx of delayed endophthalmitis
• Difficult eradication (intracameral vancomycin),may require Intraocular lens explant & Capsulectomy (to get rid of the plaque)
metabolic causes of ectopia lentis
• Abnormal elastin (Marfan’s)
• Metabolism: Homocysteinuria,
Sulfite oxidase, hyperlysinaemia)
genetic causes of ectopia lentis
• Weil-Marchesani Syndrome - converse of marfan
short stature, bradyactlyy, stubby fingers, ectopia lentis inferior
microsphelakia - subluxation anteriorly
• Pierre Robin syndrome
wilson mytonic dystrophy trisomy 21 outdoor exposure posterior subcapsular cataract nuclear sclerotic anterio stellate cataract
- Wilson’s disease = sunflower cataract, which is anterior sub capsular.
- Myotonic dystrophy = Christmas cataract
- Trisomy 21 = Cerulean Blue dot cataract
- Outdoor exposure = cortical cataract
- Posterior subcapsular cataract = most likely to produce symptoms of glare in bright light
- Nuclerar sclerotic = myopic shift “able to read the newspaper without wearing glasses again”
- Anterior stellate cataract: phenothiazine, amiodarone
