Filamentary keratitis is an anterior ocular condition affecting the corneal surface with mucous strands or "filaments." These filaments are composed of degenerated epithelial cells and mucin, which form thin strands that adhere to the corneal surface and cause irritation.

The filaments occur due to altered or decreased tear film production and an abnormal corneal epithelium. Symptoms include dry eye pain and discomfort such as a sandy or gritty sensation in the eyes, photophobia, or blurry vision.

Risk factors include severe dry eye, exposure keratopathy, Sjögren syndrome, blepharoptosis, chronic anticholinergic use, and previous corneal surgeries.