Disorders of Lens Shape & Position
Coloboma Congenital Zonules absent also → lens rim relaxation Affects lower quadrants Associated with iris, choroidal, & optic nerve
colobomata Associated with giant retinal tears
Disorders of Lens Shape & Position Lenticonus
Anterior or posterior coning of lens surface ‘Oil drop sign’ against red reflex Irregular myopic lenticular astigmatism Anterior & posterior lenticonus are associated
with cataract Lentiglobus
Generalised hemispherical deformity
Disorders of Lens Shape & Position Microphakia
Small lens due to arrested lens development Microspherophakia
Small spherical lens, usually bilateral Zonule visible on pupil dilatation Iridodonesis & sometimes pupil block
glaucoma Zonular rupture common Isolated/familial or associated with Marfan’s
syndrome
Disorders of Lens Shape & Position Ectopia lentis
Subluxation or dislocation of the lens due to zonular rupture
→ Loss of accommodation → Refractive error
• Myopia or astigmatism if subluxation (lens tilt)
• Hypermetropia if dislocated Can → glaucoma & uveitis
Disorders of Lens Shape & Position Causes of a dislocated lens
Can be hereditary (Marfan’s, homocysteinuria, familial et al)
Can be acquired (trauma, couching, buphthalmos, anterior uveal tumours, spontaneous [hypermature cataract], high myopia, chronic anterior uveitis)
Lens-induced Disorders Glaucoma
Phakomorphic (caused by lens shape/size) Phakolytic (capsular leakage) Lens displacement
Uveitis Phakoanaphylactic (AI sensitivity to lens
protein) Phakotoxic (toxic reaction to lens protein)
Cataract
Lens opacity or cataract? WHO estimates worldwide
there are 15 million blind (<3/60) from cataract
CATARACT IS THUS THE MOST COMMON CAUSE OF BLINDNESS WORLDWIDE
Cataract Classification
According to stage Immature Stationary Progressive Mature Intumescent Hypermature (morgagnian)
Cataract Classification According to morphology
Capsular • Congenital - anterior polar; pyramidal• Acquired - infrared, mercury (grey),
chlorpromazine (white star) Subcapsular
• Posterior - senile or 2° e.g. myotonic dystrophy or corticosteroid use
• Anterior - glaukomflecken, miotics, Wilson’s disease (green sunflower)
Cataract Classification According to morphology
Cortical• Congenital - blue/brown dot; coronary• Acquired - senile cuneiform, Christmas tree
Nuclear• Congenital - embryonal; lamellar [± riders]
(genetic, metabolic, infective causes)• Acquired - senile nuclear sclerosis
Cataract Classification According to aetiology
Not associated with ocular or systemic disease Associated with ocular disease Associated with systemic disease
Causes Of Congenital Cataract Idiopathic (largest group - 40%) Hereditary (25%) - usually AD Remaining 35%
Maternal infection, drug ingestion, malnutrition
Inborn errors of metabolism Chromosomal abnormalities Uveitis Prematurity
50% are associated with other ocular anomalies
Cataract not Associated with Ocular or Systemic Disease
Senile cataract - 90% of >70yr age group Type
Anterior subcapsular (fibrous metaplasia) Posterior subcapsular (epithelial migration) Cortical Nuclear cataract (exaggerated aging process)
Cataract not Associated with Ocular or Systemic Disease
Risk factors for senile cataract Smoking Dehydration (e.g. diarrhoeal illness) UV light exposure ?↓ by NSAIDs
Pathology of Cataract
Changes in crystallins by deamination, glycosylation, carbamoylation, accelerated by RFs, cause Protein unfolding Disulphide cross-links Removal of positive charge from cells Exposure of hydrophobic sites Protein aggregation & ↑ insoluble protein
These pathological changes produce opacification by Altering refractive index, especially at interfaces Forming large protein aggregates
Cataract Associated with Ocular Disease
Congenital disorders Aniridia Hyperplastic primary vitreous Hereditary retinal & vitreoretinal disease
Cataract Associated with Ocular Disease
Acquired disorders Uveitis Glaucoma (glaukomflecken) Myopia Retinal detachment Neoplasia Drug Rx e.g. miotics, corticosteroids Trauma [contusion → Vossius’ ring; lens
rupture; retained IOFB; electric shock; radiation; alkali burns]
Cataract Associated with Systemic Disease
Intrauterine factors Maternal rubella - fetal risk 80% in 1st
trimester• General features - stillbirth; deafness
(90%); CVS defects; small babies; psychomotor retardation; chest infection
• Ocular features - 30-60%; cataract in 50%, uni- or bilateral, nuclear or diffuse; microphthalmos (15%); ‘salt & pepper’ retinopathy; glaucoma (10%); strabismus; nystagmus; refractive errors; optic atrophy
Cataract Associated with Systemic Disease
Intrauterine factors (continued) CMV
• General features - low birth weight; jaundice; enlarged spleen & liver; chest infection; deafness; fits; psychomotor retardation
• Ocular features - cataract; uveitis; microphthalmos; optic nerve hypoplasia; optic nerve coloboma; optic atrophy; chorioretinitis
Drug ingestion Radiation exposure
Cataract Associated with Systemic Disease
Chromosomal abnormalities e.g. Down’s syndrome (snowflake cataract)
Hereditary disorders E.g. Marfan’s syndrome Retinitis pigmentosa syndromes
Systemic drugs E.g. corticosteroids, antimitotics,
chlorpromazine
Cataract Associated with Systemic Disease
Cutaneous disorders E.g. Atopic dermatitis → anterior or posterior
stellate cataract; also associated with keratoconjunctivitis & keratoconus
Muscular disorders Myotonic dystrophy (AD) → ptosis; Christmas
tree cataract [cortical polychromatic dusting]; light near dissociation; pigmentary retinal changes
Cataract Associated with Systemic Disease
Metabolic disease (there are many associated with cataract. The important ones are:) Diabetes mellitus → bilateral white snowflake
cataract - may progress rapidly. Also accelerated senile cataract
Wilson’s disease (hepatolenticular degeneration) - green sunflower cataract. Also causes Kayser-Fleischer ring at level of Descemet’s membrane
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