VN March 2023

Vetnuus | Maart 2023 38 I have decided to discuss slow-release episcleral cyclosporin implants for this rhinoceros edition. Although not directly related to rhinos, I have used it with good results in a patient with ocular Habronemiasis. Cyclosporine was isolated from the fungus Tolypocladium inflatum in 1972. It is a potent immunosuppressive drug used for the treatment of immune-mediated ocular disease. It is a calcineurin inhibitor that reversibly inhibits T-cell proliferation and prevents proinflammatory cytokines’ release. The drug also enhances the function of suppressor T lymphocytes. CsA is also directly lacrimogenic, reduces corneal melanosis and vascularization, and stimulates canine conjunctival goblet cells to secrete mucin. Common indications for using CsA in veterinary ophthalmology are chronic superficial keratitis and keratoconjunctivitis sicca in dogs as well as immune-mediated keratitis in horses. Unfortunately, topical medication for these conditions is required chronically, if not for the remainder of the patient’s life. This chronic treatment is sometimes difficult, especially in horses and impossible in most game species. Therefore, adequate control of this chronic disease is challenging. Sustained release ocular drug delivery devices, or implants, have been developed, allowing a low dose of medication to be released to the eye for an extended period. A major advantage of such drug delivery devices in veterinary medicine is that ocular therapy does not rely on patient or owner compliance. Intraocular delivery of medications has been successfully achieved using suprachoroidal space implant devices. These implants are difficult to implant and do not offer direct drug delivery to the anterior segment of the eye or cornea. In comparison to these suprachoroidal implants, silicone matrix implant devices placed in the episcleral space have been demonstrated to deliver drugs such as CsA to the cornea in a sustained release manner. The device is very easy to implant and can be done on standing equine patients. Cyclosporine silicone matrix implants have been demonstrated to be well tolerated in animals and release a high amount (2–5 lg/day) of the drug over the initial five months, followed by a steady-state release of 1–2 lg/day up for at least 400 days. Conjunctival habronemiasis was described in a square-lipped rhinoceros by Horrowitz IH in 2016. This case presented with intermittent signs of bilateral conjunctivitis and conjunctival proliferation. Periodic improvement was noted, especially in winter, but the condition had deteriorated over the years. Treatment with various topical, intralesional, and systemic antibiotics and glucocorticosteroids was largely ineffective, as were repeated dewormings. No primary cause for these lesions was found in biopsies, although a severe infiltrate of numerous eosinophils was observed. After the further worsening of the condition, aggressive resection of the proliferating tissue was performed, and submitted biopsies yielded a diagnosis of severe allergic conjunctivitis, eosinophilic granuloma, and habronematid larval infection. In this case, it was concluded that the presentation was most likely due to a hypersensitivity reaction to the dead or dying larvae. Fly repellent is now regularly applied around the eye of this rhinoceros, and a protective face mask has been fitted. Ongoing periodic relapses are treated with oral Ivermectin, topical antibiotics, and steroids. This patient was in a zoo, allowing medication to be given regularly. In 2018 a privately owned rhinoceros from Mpumalanga, South Africa, was presented with a history of chronic mucopurulent discharge and a conjunctival mass in the right eye. A raised, granulomatous, ulcerative lesion on the ventromedial palpebral conjunctiva was identified. Some “sulfur”-appearing nodules were also present in this granulomatous tissue. Conjunctival cytology revealed normal as well as degenerative conjunctival epithelial cells as well as eosinophils. The clinical appearance was very similar to ocular Habronemiasis seen n horses. Due to the impossibility of frequent application of topical corticosteroids, it was decided to debride the mass and do a cyclosporine implant in the area. Dr Izak Venter, Digital Veterinary Ophthalmology Services (DVOS) Episcleral cyclosporine implants and ocular Habronemiasis in a rhinoceros Technical I Ophthalmology Column Figure 1 . Severe proliferative reaction of the conjunctiva of the right eye of a square-lipped rhinoceros. [Veterinary Ophthalmology. 2016; 19(2): 161-166]