Disease summary:

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  Age-related cataract is a complex disorder of the ocular lens involving environmental and genetic risk factors. In addition to decreased visual acuity, early symptoms include myopic shift, astigmatism, monocular diplopia, glare, color shift, and reductions in contrast-sensitivity, light transmission, and visual field. Despite surgical treatment, age-related cataract remains a universally important cause of progressive low vision and blindness.

  
  
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  Clinical presentations are morphologically described as nuclear cataract, cortical cataract, posterior subcapsular cataract (PSC), or mixed cataract.

  
  
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  Age-at-onset is usually within the sixth to eighth decades; however, in some populations, onset may occur as early as the third to fourth decades (eg, India).

Differential diagnosis:

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  Presenile cataract may present in the second to fifth decades and can be associated with genetic or metabolic disorders, including myotonic dystrophy-associated cataract, hereditary hyperferritinemia cataract syndrome (HHCS), adult i blood group phenotype, female carriers of X-linked forms of cataract (eg, Nance Horan “cataract-dental” syndrome [NHS]; Lowe oculocerebrorenal syndrome [OCRL]), oil droplet cataract and diabetic cataract. Other adult-onset forms of cataract may result from local ocular disease (eg, uveitis, retinal dystrophy or degeneration, glaucoma, ocular tumors), certain drugs (eg, chronic corticosteroid regimens), radiation exposure, electrocution, metal ion deposits (eg, siderotic cataract), and trauma.

Monogenic forms:

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  Many Mendelian forms of cataract are known. Most present with an early onset, ranging from birth or infancy (congenital or infantile) through the second decade (juvenile) either in association with other ocular and/or systemic abnormalities, or as an isolated lens phenotype often with autosomal dominant inheritance. Mutations in genes encoding crystallins and gap-junction (or connexin) proteins account for approximately 70% of autosomal dominant cataract.

Family history:

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  A positive family history has been indicated as a risk factor for cortical cataract, nuclear cataract, and mixed nuclear and cortical cataract but has not been replicated for PSC.

Twin studies:

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  Heritability estimates for cortical cataract lie in the range of 53% to 58% mostly due to dominant genetic effects, and those for nuclear cataract are approximately 48% due to additive effects.

Environmental factors:

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  Cortical cataract and PSC are associated with UV-B exposure, diabetes, alcohol consumption, and topical or oral steroid use. Nuclear cataract is strongly linked with tobacco smoking. Other risk factors include female gender, myopia, metabolic syndrome, severe dehydration or diarrhea and malnutrition.

Genome-wide associations:

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  The strongest genetic association is obtained at the EPHA2 locus on chromosome 1p36 with cortical cataract in Caucasian and Chinese populations and with cortical cataract and PSC in Southern India (Table 147-1). An unidentified locus on chromosome 6p12-q12 has been associated with cortical cataract in Caucasians. Genetic testing for single-nucleotide polymorphisms (SNPs) is not clinically validated for diagnosis.

Pharmacogenomics:

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  No clinically valid testing is available. Protective effects of statins and nutritional supplements including daily multivitamins, antioxidants, and n-3 fatty acids, remain controversial.