Subcapsular cataracts are known to be caused by a variety of factors: aging, diabetes (either type 1 or type 2), long term taking of steroid medication, radiation exposure and others. In fact, this type of cataract can be more common in air pilots who've spent significant time at high altitudes, because cosmic radiation is stronger in the upper atmosphere.
The name subcapsular refers to the location where these cataracts begin, in back of the lens. The lens is surrounded by a capsule of tissue and this variety of cataracts, also called posterior subcapsular cataracts, begins with water from the aqueous part of the eye leaking into the capsule.
The leakage results from the failure of so-called pump proteins in the capsule membrane meant to regulate concentrations of the minerals sodium and potassium. Those mineral concentrations in turn control where water goes, by osmosis, and in this case it's in the wrong direction. A small amount of water can be compartmentalized and kept away from the lens but this fails as the condition progresses. Water coming into contact with the crystalline proteins of the lens causes them to dissolve and lose their molecular shapes, which we and the sufferer see as cloudiness in the eye.
That cloudiness especially affects reading, even with good lighting. Lights themselves are seen with halos or glare. This type of cataract can progress quickly, more so than any other, with visual impairment becoming serious within months, not years. Because of their rapid progression, changes in corrective lenses are not a practical option for subcapsular cataracts the way they are for other types. When the degree of vision impairment is serious and affects a person's daily activities, surgery is necessary.
The most common approach to subcapsular cataracts, in practice since the 1960s, is called phacoemulsification. This means that ultrasound waves are focused on the lens to liquefy (emulsify) the cloudy part of it, after which the liquid is removed with suction. The lens may also be completely removed and an artificial intraocular lens (IOL) put into its place, as this will not dissolve or become cloudy when exposed to the water of the eye. The surgery can be done on an outpatient basis and the patient may or may not be awake, depending on their preference and that of the surgeon.
The patient must be very careful to protect their eyes from any kind of trauma during the recovery period of about two weeks. Glasses or contact lenses may be required, depending on if standard IOLs were inserted or if advanced IOLs that correct for near- and farsightedness were used. Cataract surgery is the most common operation in the US.