What are UV rays? These are rays emitted by the sun. There are several types, and they are more or less dangerous because they are more or less well filtered by the atmosphere. Rays that are not filtered by the atmosphere (UVA and UVB) can be dangerous for the skin (horses with white marks, sunburn), but also for the eyes! The dangerousness of UV rays depends on geographical location, altitude and time of day (most dangerous between 10 a.m. and 2 p.m.).
UV rays: what are the risks for my horse's eyes?
Fortunately, most UV rays are filtered out. UVC is filtered by the atmosphere and UV A and B are filtered by the eye, thanks to several anatomical structures.
The horse's cornea
It's a superposition of very thin layers of cells. The only transparent tissue in the body, it is the cornea that enables vision. Located at the front of the eye, the horse's cornea absorbs part of the UV rays received, protecting the lens and retina. Although its upper layer is constantly being renewed, these cells are sensitive to cumulative effects. Overexposure of the cornea to UV rays can lead to inflammation and a burning sensation: this is keratitis.
The lens
It lies behind the cornea and iris. Its role is to focus light onto the retina. Particularly sensitive, it also absorbs a large proportion of UV rays. But the longer the eyes are exposed to unprotected light, the more the lens ages. It loses its transparency, opacifies, and ultimately increases the risk of developing cataracts. Its filtering function is essential. Horses that have undergone cataract surgery, had the lens removed or replaced by an implant, must be protected from UV radiation to protect the retina.
The horse's retina
It covers the back of the eye. The horse's retina is responsible for transmitting light signals to the brain. The sun's rays are thought to accelerate retinal aging.
The eyelids
They provide mechanical and physiological protection for the eye through the blinking reflex and the spreading of tears over the cornea. They are highly exposed to external elements, notably UV rays.
Horses' eyelids are susceptible to cancer. According to the Skin Cancer Foundation, 10% of all human skin cancers are located on the eyelid. Exposure to UV rays, especially UVB rays, is the main cause of eyelid tumours. UV exposure is cumulative. In other words, you can't undo the damage your skin or eyes have suffered in the past. You can, however, reduce the risk of making things worse. So start now to take additional protective measures against the sun, especially for horses with a history of eye pathology (cataracts, uveitis, keratitis, ulcers, etc.).
How can I protect my horse from UV rays?
Today, there are many aids available to protect horses' eyes from insects. Few, however, filter out UV rays. Equine eye protection often darkens the eyes. This is good for limiting glare, but extremely harmful if UV rays are not filtered. As the pupil dilates more in the shade, the quantity of UV rays passing through is even greater if they are not filtered. Read the instructions carefully before buying a mask or rigid goggles for work. For rigid goggles for working horses, the color of the lenses has virtually no effect on the level of UV protection. Whether the lenses are transparent, gray or brown, with or without a mirror effect, is of far less importance than the anti-UV coating integrated into the lenses. However, pay attention to the shape and size of the frame of rigid glasses: the closer they are to the head, the more effective they will be against UVs.
Article written by Estelle Guilbaud - Optometrist specializing in equine vision
