High blood sugar levels cause the lens to swell and become misshapen and cloudy. This makes it difficult for it to filter light to the retina, resulting in glared or blurry vision. Elevated glucose levels over a long period of time can cause permanent damage to the lens and lead to reduced visual acuity. Cataracts are treatable with surgery and intraocular lenses, but this is not true for many other diabetic eye diseases. Indeed, diabetic retinopathy is the leading cause of permanent blindness in industrialized countries.