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- A cataract is any opacity or discoloration of the lens, localized or generalized; the term is usually reserved for changes that affect visual acuity (1,2).
- Etymology: from Latin catarractes, for “waterfall”; named after foamy appearance of opacity
- Leading cause of blindness worldwide, estimated 20 million people (1,2)
- Types include the following:
- Age related: 90% of total
- Metabolic (diabetes via accelerated sorbitol pathway, hypocalcemia, Wilson disease)
- Congenital (1/250 newborns; 10–38% of childhood blindness)
- Systemic disease associated (myotonic dystrophy, atopic dermatitis [AD])
- Secondary to associated eye disease, so-called complicated (e.g., uveitis associated with juvenile rheumatoid arthritis or sarcoid, tumor such as melanoma or retinoblastoma)
- Traumatic (e.g., heat, electric shock, radiation, concussion, perforating eye injuries, intraocular foreign body)
- Toxic/nutritional (e.g., corticosteroids)
- Morphologic classification:
- Nuclear: exaggeration of normal aging changes of central lens nucleus, often associated with myopia due to increased refractive index of lens (Some elderly patients consequently may be able to read again without spectacles, so-called second sight of the aged.)
- Cortical: outer portion of lens; may involve anterior, posterior, or equatorial cortex; radial, spoke-like opacities
- Subcapsular: Posterior subcapsular cataract has more profound effect on vision than nuclear or cortical cataract; patients particularly troubled under conditions of miosis; near vision frequently impaired more than distance vision
- System(s) affected: nervous
Some degree of cataract formation is expected in all people >70 years of age.
See Congenital cataract; may present as leukocoria
See Congenital cataract (i.e., medications, metabolic dysfunction, intrauterine infection, and malnutrition).
- ~48% of the 37 million cases of blindness worldwide result from cataracts (1,2).
- Leading cause of treatable blindness and vision loss in developing countries (1,2)
- Predominant age: depends on type of cataract
- Predominant sex: male > female
- Cataract type and prevalence are highly variable based on population demographic.
- An estimated 50% of people 65 to 74 years of age and 70% of people >75 years of age have age-related cataract.
Etiology and Pathophysiology
- Age-related cataract:
- Continual addition of layers of lens fibers throughout life creates hard, dehydrated lens nucleus that impairs vision (nuclear cataract).
- Aging alters biochemical and osmotic balance required for lens clarity; outer lens layers hydrate and become opaque, adversely affecting vision.
- Usually unknown etiology
- Drugs (corticosteroids in 1st trimester, sulfonamides)
- Metabolic (diabetes in mother, galactosemia in fetus)
- Intrauterine infection during 1st trimester (e.g., rubella, herpes, mumps)
- Maternal malnutrition
- Other cataract types:
- Common feature is a biochemical/osmotic imbalance that disrupts lens clarity.
- Local changes in lens protein distribution lead to light scattering (lens opacity).
- Congenital (e.g., chromosomal disorders [Down syndrome])
- Genetics of age-related cataract are not yet established but likely multifactorial contribution.
- Cigarette smoking
- Ultraviolet (UV) sunlight exposure
- Prolonged high-dose steroids
- Positive family history
- Use of UV protective glasses
- Avoidance of tobacco products
- Effective control of diabetes
- Care with high-dose, long-term steroid use (systemic therapy > inhaled treatment)
- Protective methods using pharmaceutical intervention (e.g., antioxidants, acetylsalicylic acid [ASA], hormone replacement therapy [HRT]) show no proven benefit to date.
Commonly Associated Conditions
- Diabetes (especially with poor glucose control)
- Myotonic dystrophy (90% of patients develop visually innocuous change in 3rd decade; becomes disabling in 5th decade)
- AD (10% of patients with severe AD develop cataracts in 2nd to 4th decades; often bilateral)
- Neurofibromatosis type 2
- Associated ocular disease or “secondary cataract” (e.g., chronic anterior uveitis, acute [or repetitive] angle-closure glaucoma or high myopia)
- Drug induced (e.g., steroids, chlorpromazine)