Interstitial keratitis is a broad descriptive term that has become synonymous with syphilitic eye disease. It is a serious condition in which blood vessels grow into the cornea. Some of the causes are autoimmune diseases, like rheumatoid arthritis and sarcoidosis. It can also be caused by infections such as leprosy, Lyme disease and tuberculosis.

The condition presents with a mixed grayish-white nebula covering a deep layer of the cornea, which affects visual acuity. The onset of this condition is often slow. Treatment usually takes a long time and it often results in a remaining scar and nebula, which obstructs visual acuity.

Symptoms include eye pain, excessive tearing and photophobia. Local corticosteroid drops can help to minimize scarring to help preserve the clarity of the cornea. If the cornea is scarred, the only way to restore vision is with a corneal transplant. However, surgery is not always successful: the presence of blood vessels in the diseased cornea brings white blood cells to the area, increasing the risk of transplant rejection. Furthermore, the underlying disease must also be treated. If diagnosed and treated early, the prognosis for recovery is good.

In TCM, interstitial keratitis is referred to as hùn jīng zhàng (混睛障, murky eye nebula). This condition is frequently caused by externally contracted wind heat atacking upwards and invading the cornea. Other causes include excessive heat in the zang-fu organs, toxic heat of the liver and gallbladder rising upward to atack the eyes, fre congestion in the eye and qi and blood stasis. Visual examination of the eye will show the nebula as cloudiness in the cornea combined with the blood vessels. Other causative factors include constitutional defciency or spleen and stomach defciency that results in a loss of its transportive and transformative functions. This in turn, can result in internal damp heat sweltering the eyes and afecting the cornea. Finally, unresolved latent toxins hidden internally can injure the yin fuids, causing defcient fre to rise upward and burn the cornea.