A cataract is opacification or thickening of the lens. The most common cause is advanced age. Other causes include congenital, post traumatic, diabetes and radiation. Rarer causes are not listed here. Visual deterioration occurs with increasing degrees of severity. The diagnosis is made clinically. Ocular ultrasound is performed when there is suspicion of posterior globe pathology but visualization of the back of the eye is obscured by the opaque lens. Treatment is surgical removal of the lens which is usually replaced by an intraocular lens implant.