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Background: Iris cysts in horses are often asymptomatic and noticed incidentally. However, cysts can cause local corneal oedema and erratic behaviour like shying, decreased performance and head-shaking., Objectives: To describe the use of diode laser as a noninvasive treatment option for iris cysts in the horse and to document factors influencing its efficacy, associated complications, long-term outcome and rate of recurrence., Study Design: Retrospective case series., Methods: Case records of horses treated for iris cysts by diode laser at the Utrecht University Equine Clinic were reviewed between 2008 and 2020. Diagnosis was based on ophthalmic and ultrasonographic evaluation. Long-term follow-up was obtained in two phases, a telephone survey with the owner and a photographic re-evaluation of the treated eyes., Results: Thirty-five horses were included, with a total of 46 eyes treated. One day after diode laser treatment (short-term), 35/46 treated eyes had a good decrease in cyst size, 7/46 had a moderate effect, 1/46 had a minimal effect, 1/46 had no effect, and in two cases the effect was unspecified. The decrease in size after diode laser treatment in polycystic eyes (odds ratio [OR] 0.381, 95% CI 0.1530-0.724), p = 0.001), thick-walled cysts (OR = 0.139; CI = 0.023-0.726, p = 0.02) and hyperplastic corpora nigra (OR = 0.081; CI = 0.004-0.528, p = 0.03) was significantly less satisfactory, with ORs of 0.381, 0.139 and 0.081, respectively. Minor complications, such as mild reactive uveitis, were reported in 8/46 (17%) eyes. On long-term follow-up (median 19 months; IQR 25.5), clinical signs had diminished or disappeared in most cases (93%) and 83% of the owners would recommend the treatment. Based on long-term photographic re-evaluation (median 32.5 months; IQR 49.75), 2/16 cases of recurrence were seen., Main Limitations: Retrospective design, follow-up by telephone questionnaire and photographic re-evaluation. Loss to follow-up in the photographic re-evaluation., Conclusions: Both short- and long-term results indicate diode laser treatment is a useful and safe option for iris cyst size reduction, with a low risk of recurrence. Presurgical ultrasonography is recommended to assess the feasibility of treatment and to allow for better surgical planning., (© 2022 The Authors. Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.)

Background: Topical dexamethasone and prednisolone are currently the mainstay treatment for equine ophthalmic inflammatory diseases, such as equine recurrent uveitis. Comparative pharmacokinetic studies in horses are lacking and current guidelines are mainly based on empirical data and extrapolation from other species., Objectives: To investigate the penetration and local concentrations of topically applied dexamethasone and prednisolone in normal equine ocular fluids and serum., Study Design: Prospective randomised experimental pharmacokinetic study., Methods: Twenty-one Shetland ponies without ophthalmic disease were treated bilaterally topically every 2 hours during 24 hours to obtain steady state drug concentrations. One eye was treated with 0.15 mg of dexamethasone disodium phosphate (0.1%), and the other eye was simultaneously treated with 1.5 mg of prednisolone acetate (1%). Serum samples were taken prior to the induction of general anaesthesia. Aqueous and vitreous humour samples were taken during euthanasia at time points after administration of the last dose (t = 5 min, t = 15 min, t = 30 min, t = 60 min, t = 90 min, t = 120 min, t = 180 min). Each pony was randomly assigned to one time point, and three ponies were sampled per time point. Dexamethasone and prednisolone concentrations were measured by liquid chromatography-mass spectrometry., Results: The mean dexamethasone concentration in aqueous humour was 32.4 ng/mL (standard deviation [SD] 10.9) and the mean prednisolone concentration was 321.6 ng/mL (SD 96.0). In the vitreous and in serum samples concentrations of both corticosteroids were below the limit of detection (LOD 2.5 ng/mL)., Main Limitations: The study group was limited to subjects without evidence of current ophthalmic disease. A limited number of time points were measured., Conclusions: Potentially effective dexamethasone and prednisolone concentrations were measured in the anterior chamber, but vitreal concentrations were negligible. Systemic uptake was low. Therefore, treatment with only topically administered corticosteroids is deemed insufficient in horses in cases of posterior uveitis. Further studies evaluating other routes of administration are warranted., (© 2021 The Authors. Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.)