Clinical experiences after the insertion of a Cyclosporine-A drug delivery device in horses with Equine Recurrent Uveitis

Several studies have dealt with the etiopathogenesis-, diagnostics as well as the conservative and surgical treatment methods of equine recurrent uveitis (ERU) with different outcomes. Because of potential side effects of applied medication, the risk of doping in the case of sport horses and the problem of future uveitis episodes, a traditional medical treatment is not always feasible.This circumstance requires other promising therapeutic approaches, such as the pars plana vitrectomy (PPV) and the insertion of a cyclosporine-A (CsA) drug delivery device. The literature provides varying perspectives on both of the aforementioned methods. Besides the successful PPV, the cyclosporine-A implant is proposed and applied with an increased frequency due to its nature of being an easier and financially lucrative surgical technique. Currently cyclosporine implants cannot be obtained and applied legally in Germany, therefore any usage is signified as a serious breach of the Medicines Law. According to the literature it appears that the majority of authors consider the PPV to be an effective treatment method only for leptospira positive tested horses, but nor for eyes testing negative for leptospiral antibodies. This retrospective study included 24 ERU patients of different age, gender and breeds that were initially examined by ophthalmological specialists beforehand and treated with suprachoroidal CsA implants. These horses having the CsAI still suffered from uveitis episodes, as the implant only masked inflammatory bouts resulting in a proceeding damage of intraocular structures. This circumstance required another therapeutic approach. Undiluted vitreous humor samples of all of the 24 horses were taken and were tested for specific antibodies against 9 different serovars of Leptospira interrogans by microscopic agglutination test (MAT). The ERU-diseased eyes of 4 horses were removed and in one horse an intra-scleral eye prosthesis was inserted. Between 2013 and 2017 19/24 horses with ERU (79.2%) with CsA implants, still having uveitis episodes, were treated via single port PPV. The outcome of the PPV and the postoperative course of the horses were followed up. The evaluation of efficacy of the PPV was deduced either directly by follow-up examinations (n 8), photographic documentation and patient records or indirectly by questioning the referring owners (n = 11). 14/19 horses (73.7%) were tested positive for intraocular leptospira antibodies and 5/19 horses (26.3%) have been tested intraocular MAT negative. The absence of active uveitis was considered a success irrespective of the visual outcome of the surgical treated eyes. A total of 14/19 horses (73.7%) remained relapse-free over a period of 5 to 63 months. 10/14 horses (71.4%) with leptospiral antibodies in the vitreous humor had no further uveitis relapses postoperatively, while only 1/5 horses (20%) tested MAT negative continued to episodes of ERU. The comparison between numbers of horses with positive or negative leptospiral antibodies in vitreous humor in relation with or without recurrence of uveitis after PPV was not significantly different (P = 1.0) using two-sided Fisher's exact test. According to these findings, it is doubted to perform a PPV depending on the leptospiral antibody result. In none of the 24 horses the implant slowed down the progression of uveitic destruction and a therapeutic success could not be achieved at all. This study yields promising results that the PPV should be the selected treatment method instead of the CsA implant.