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

This study investigates the impact of radio-frequency current-induced hyperthermia on the eyes of horses and ponies. The findings suggest that although this treatment can cause temporary damage, including depigmentation and ulcerative keratitis, vision is not permanently affected and all layers of corneal tissues were integral 8 days after exposure to hyperthermia.

Methodology

• The researchers induced hyperthermia in the eyes of 13 light horses and 8 ponies by using radio-frequency current. The right eye was given a single central corneal lesion whereas the left eye was given 2 separate limbal lesions.
• Temperature profiles for this procedure were separately studied from the eyes of a horse and a pony.
• Following the treatment, the effects were observed for up to 6 months using different techniques such as indirect ophthalmoscopy, biomicroscopy, and fluorescein staining.

Immediate Observations

• Immediately after the treatment, opaque imprints of the electrodes from the current field device were visible on the eyes.
• The eyes displayed cases of ulcerative keratitis from day 2 to day 6, and anterior uveitis from day 3 to day 7 post-treatment.
• There were occasional instances of a mucopurulent discharge and variable degrees of conjunctival hyperemia, which is an excess of blood in the vessels of the conjunctival tissues.

Long-Term Observations

• There were small scars at the sites where the electrodes were positioned vertically. Hyperthermia treatment resulted in depigmentation at pigmented limbal sites.
• However, no instance of compromised vision was observed in any of the test subjects permitted to live beyond a week of treatment.
• On a microscopic level, the researchers noted that denudation and subsequent repair of the corneal epithelium were concurrent with the presence and eventual absence of fluorescein staining.
• The corneal tissue showed signs of inflammation, edema, disorganization of collagenous fibers, and temporary disruption of the corneal endothelium, all of which contributed to temporary corneal opacity. However, all layers of corneal tissue had completely repaired 8 days post-treatment.
• Some of the later changes observed were choroidal hydrops, vascular damage in conjunctival vessels, stromal neovascularization, and corneal fibroplasia, which refers to the growth of fibrous tissue on the cornea.