Cataract, which can be defined as any opacity of the lens, occurs when the refractive index of the lens varies significantly over distances that approximate the wavelength of the transmitted light.
This variation in refractive index may be due to changes in the lens cell structure, changes in the protein components of the lens, or both.
Defined by the age of onset, a congenital or infantile cataract is visible within the first year of life; a juvenile cataract occurs within the first decade of life; a presenile cataract occurs before the age of 45; and senile or age-related cataract, thereafter.
The boundaries between the different types of cataracts are approximate; for example, some researchers consider juvenile cataracts to occur before the age of 20 years and age-related cataracts to occur after the age of 60 years.
Also, subtle cataracts may not be seen for years after they occur, especially if they are asymptomatic. The age of appearance of a cataract does not necessarily indicate its etiology.
Congenital cataracts may be hereditary or secondary to a deleterious intrauterine event (eg, rubella). Cataracts associated with systemic or genetic disease may not occur until the second or third decade (eg, cataracts associated with retinitis pigmentosa).
Even age-related cataracts, which are generally thought to be due to multiple insults accumulated over many years, have a genetic component, making certain people more vulnerable to environmental insults.
El Dr. Humberto Carreras, medical director of Vithas Eurocanarias Ophthalmological Institute, explains in this video why more and more cataracts are detected in young people.