Eva I. A. Baake et al. Pferdeheilkunde -Equine Medicine 35 (2019) 220 Long-term ophthalmologic examinations of eyes with equine recurrent uveitis after pars plana vitrectomy Pferdeheilkunde -Equine MedicineSummary: Equine recurrent uveitis (ERU) is an ocular disease in horses of different breeds with a prevalence between 2.7 and 7.6 % in Europe and vitrectomy is a common method of treatment. The objective of the study was to evaluate the long-term retention of vision and control of uveitis after pars plana vitrectomy performed between 2005 and 2013 on eyes with a history of equine recurrent uveitis (ERU). Vitrectomy in eyes with ERU can influence the recurrent nature of the disease. Previous studies indicated success rates regarding the further absence of uveitis between 73.6 and 97.7 %. Owners of the horses were contacted and an ophthalmological reexamination including tonometry, induction of mydriasis, slit lamp biomicroscopy and direct ophthalmology was performed in 116 horses (147 eyes vitrectomized). Visual acuity was examined by the dazzle reaction and the menace response. Aspects such as gender, age and breed of the horses, as well as leptospiral status and preexisting damage of operated eyes are described. A total of 246 eyes were accessible for follow-up information, whereas 147 eyes were available for ophthalmologic reexaminations. If only the reexamined eyes are considered, an improvement of the condition was seen in 133 eyes (91 %) and 14 eyes (9 %) showed at least one uveitic recurrence after vitrectomy. A positive menace response and a positive dazzle reaction were observed in 128 of the 147 reexamined eyes (87 %). The number of episodes prior to vitrectomy, the gender of the horse and the leptospiral status of the eye showed no significant correlation with the prevalence of recurrences. Coat color, breed and age of the horse operated, and preexisting ocular alterations showed a significant influence on the chance of postoperative recurrences of uveitis. Horses with a coat color other than "chestnut" and "black and brown" had significantly more recurrences and odds ratio for these horses developing recurrences was also significantly higher. The present study shows that a large number of reexamined eyes remained visual (87 %) and a large proportion of the eyes (91 %) showed an improvement of the condition after vitrectomy. Results of this study suggest that genetic factors, age and preexisting ocular alterations influence the long-term prognosis of eyes with ERU after vitrectomy.Citation: Baake E. I. A., von Borstel M., Rohn K., Boevé M. H., Ohnesorge B. (2019) Long-term ophthalmologic examinations of eyes with equine recurrent uveitis after pars plana vitrectomy.

Summary: Equine recurrent uveitis (ERU) is an ocular disease characterized mainly by recurrent episodes of inflammation, alternating with quiescent episodes of various durations. There are numerous aetiological theories for the cause of ERU, but to date, the "classic ERU" is most commonly associated with an intraocular leptospiral infection. The pars plana vitrectomy has, so far, been the most promising treatment of ERU and is thought to be more successful in eyes with detectable leptospiral antibodies in the microscopic agglutination test (MAT) and therefore a preselection is recommended. The objective of this study was to investigate whether different laboratories have an influence on the frequency of detection of leptospiral DNA and leptospiral antibodies from vitreal samples of horses with ERU and if these results are in accordance with cultural testing of the vitreal samples. Vitreal samples were obtained from 93 eyes of 78 horses of various breeds and age with a clinical history of ERU. The vitreal samples were taken at the beginning of the vitrectomy to keep the dilution of the vitreal samples as low as possible. The samples were split and sent to three different laboratories in Germany (L1, L2 and L3). Laboratory 1 (L1) performed a polymerase chain reaction (PCR) and a MAT, laboratory 2 (L2) carried out a PCR and laboratory 3 (L3) performed a MAT, a cultural examination and an enzyme-linked immunosorbent assay on the vitreal specimens. The amount of dilution was evaluated by comparing the urea content of 34 vitreal samples with the urea content of the serum of each of the horses at the time of sampling. Furthermore, a serial dilution was performed with undiluted vitreal material of two enucleated eyes and sent to L1 for MAT and PCR. The results of the PCR indicated a strong conformity between L1 and L2 (Kappa 0.95), both laboratories concurrently revealed 52 positive and 31 negative results and only two specimens showed deviating results. The MAT in L1 was positive in 51% of the vitreal samples tested, whereas only 41% of the vitreal samples were tested positive in L3. The conformity was, moreover, serovar-and breed-dependent. The Kappa was 0.67 when only including serovar Grippotyphosa, and was 0.82 for serovar Pomona (Tab. 5). Warmblood horses displayed a Kappa of 0.56 between L1 and L3, whereas the Kappa for the Icelandic horses was 0.91 between L1 and L3. The cultivation of leptospires was successful in 16 % of the vitreal specimens. The dilution of vitreal samples was measured to range between 1 and 2.1 with a standard deviation of 1.68. Overall, 67 vitreal samples were tested simultaneously in all three laboratories. A positive result in at least one of the tests performed occurred in 57 % (38), whereas 43 % (29) of the vitreal specimens were tested negative in all five tests performed (PCR in L1 and L2, MAT in L1 and L3, and culture in L3). The variation of agreement of the MAT between serovar Grippotyphosa and serovar Pomona and between Warmblood and Icelandic horses in L1 and L3 might be account...