What causes a cataract to grow?

Aging and... The biggest factor is aging, but ultraviolet light (sunlight, tanning boothes) and smoking are big factors as well. Some medical diseases such as diabetes, and some medications, such as steroids can also lead to increasing cataracts. More info: cataract surgery michigan.
Not quite growth. Cataracts are mostly a change in the character of the very specialized proteins that make up the natural clear lens. When these change, the transmission of light becomes impaired. We call this the growth of a cataract but it is really a change in the makeup rather than growth meaning enlargement. It is mostly an aging process with a breakdown in the normal mechanisms that maintain transparency.
Cataract cause. Cataract cause: Cataract occur from change in lens proteins which cause whitening/clouding of clear lens composition: can be due to an infection or inflammation from birth (ie, rubella), old age/genetics, steroid use, trauma, poor diet; smoking & Diabetes increases risk. More info: eyedoc2020@blogspot.com.
Age. Cataract is when the natural lens inside the eye becomes cloudy or opaque. Treatment is indicated if it is affecting your ability to see and perform normal activities of daily living. The clouding usually starts in the late 50's and surgery is usually indicated in the late 60's - 70 years of age. Typically aging is what causes a cataract to progress, but trauma, diabetes, uv light can also.
Cataract . Cataracts can progress due to age, diabetes, steroid usage or other medical conditions.