Equine recurrent uveitis (ERU) or periodic ophthalmia frequently is a sight-threatening intraocular inflammatory disease of the eye in equids of any age in all parts of the world. Severe single attacks, as well as recurrent minor episodes, can cause opacities of the refracting media by corneal edema, proteinous, cellular exudates in the aqueous humor, inflammatory deposits, and pigment patches on the lens capsule, cataracts, and liquefacation and haziness of the vitreous.

The disease is thought to be immune-mediated. However, despite extensive clinical and laboratory tests, the cause for initiation or reactivation of the inflammatory response usually remains obscure in clinical cases. Thus, conventional treatment is symptomatic and includes mydriatics, corticosteroids, systemic anti-inflammatories, and supportive care. However, in a large number of cases, the inflammation tends to recur at unpredictable intervals. For those horses, in 1989, German re-searchers introduced a surgical treatment, using vitrectomy via pars-plana sclerotomy. Since then, more than 200 equine eyes in varying stages of the disease, but which had a history of at least two or three uveitic attacks, have undergone surgery. The goal of vitrectomy is to remove diffuse opacities and large floaters from the vitreous, thus improving vision and combating uveitis relapses.

In a follow-up study, including 43 eyes of 38 horses that had been operated on between five years and six months prior to the follow-up examination, in more than 90% of the cases no further uveitic attacks had been noted by owners or veterinarians. Although 19 horses had cataracts of some degree, it is concluded that pars-plana vitrectomy is effective in controlling the inflammatory attacks in chronic ERU