Reaction of normal equine eyes to radio-frequency current-induced hyperthermia.

In the main study, hyperthermia was induced by radio-frequency current to obtain a single, central, corneal lesion in the right eye and 2 separate limbal lesions in the left eye of 13 light horses and 8 ponies. Intracorneal and intralimbal temperature profiles for the procedure were obtained in a separate study from the eyes of a horse and a pony treated in the same manner. After treatment of the principal eyes and 6 sham-treated eyes, clinical observations were conducted for up to 6 months, using indirect ophthalmoscopy, biomicroscopy, and fluorescein staining. Immediately after hyperthermic treatment of the eyes, dense opaque imprints of the electrodes of the localized current field device were present. Ulcerative keratitis persisted variably from day 2 through day 6 after treatment; anterior uveitis was present from day 3 through day 7. A mucopurulent discharge occurred infrequently, and conjunctival hyperemia was variable. Depigmentation resulted from hyperthermic treatment at pigmented limbal sites. Small scars persisted at 1 central site and 6 limbal sites where the electrodes were positioned vertically. Vision was not compromised in any of the horses permitted to live beyond a week. Microscopically, denudation and subsequent repair of the corneal epithelium correlated with the presence and then the absence of fluorescein staining. Stromal inflammation, edema, disorganization of collagenous fibers, and temporary disruption of corneal endothelium contributed to transitory corneal opacity. Time required for repair of corneal tissues varied, but all layers were integral 8 days after exposure to hyperthermia. Later changes included choroidal hydrops, vascular damage in conjunctival vessels, stromal neovascularization, and corneal fibroplasia.