Interstitial keratitis is a serious condition in which blood vessels grow into the cornea and can cause loss of the normal transparency. This condition is often caused by infections and may cause severe visual impairment. Syphilis is the most common cause of interstitial keratitis, but rare causes include leprosy and tuberculosis. Most cases in the developed world occur in patients with fully established systemic infection with the spirochete of syphilis. In the US, most cases of syphilis are recognized and treated before they reach this stage. However, interstitial keratitis is the most common cause of blindness in the world, with cases caused by trachoma and onchocerciasis (river blindness) being very common in parts of Asia and Africa.
| 
