The major causes of blindness include cataracts, age-related macular degeneration, diabetic retinopathy and glaucoma, according to the Centers for Disease Control and Prevention. As of 2013, the leading cause of blindness in the world is cataracts, which occur when the lenses in the eyes become clouded.
Cataracts occur due to protein clumping together on the lens, which can get larger, making it difficult to see, notes the National Eye Institute. Several of the many causes of cataracts include smoking, diabetes and aging. Cataracts can also develop after surgery for other eye problems or in people who have diabetes. The condition causes a gradual increase of symptoms over time, including dull or blurry vision and a brownish tint to vision.
Age-related macular degeneration occurs when the blood vessels that supply the macula get damaged, harming the macula, according to MedlinePlus. The two types of age-related macular degeneration are dry and wet, with dry being the most common. The cause of age-related macular degeneration is unknown, but factors that increase the risk of developing it include consuming a high-fat diet, having a family history of the condition, and being a woman.
Diabetic retinopathy occurs when the blood vessels of the retina get damaged, which may cause them to swell and leak fluid, explains the National Eye Institute. All people with diabetes are at risk of developing the condition, and the risk increases the longer a patient has diabetes. Diabetic retinopathy causes gradual vision loss and usually affects both eyes.