Most horse owners, trainers and grooms can recognize and treat everyday injuries, and can assess when to reach out for professional help. But what if the eyes are affected, and how can injuries and pathologies be recognized early, or even be avoided?
Any symptom that indicates possible eye discomfort, such as:
• Sensitivity to light
• Increased tear production or eye discharge (serous or purulent)
• Reddening of the conjunctiva
• Increased blinking or eye being held closed
• Rubbing of the eye
• Foreign bodies in the eye
• Eyelid injuries
• Cloudiness of the cornea or lens
• Pigmentation or color changes
• Asymmetry of the head or eyes
• Changes in behavior, problems with handling and riding should immediately be assessed by a trained equine veterinarian.
After a detailed examination and diagnosis, he or she will institute treatment or recommend a referral to an ophthalmologist.
The lateral orientation of the eyes and their surrounding structures (adnexa) predisposes them to traumatic injuries. Intraocular inflammation (Equine Recurrent Uveitis, ERU), neoplasia, and cataracts are also often encountered.
Common are injuries and ulcerations of the most outer transparent part of the eye, the cornea. This surface is highly sensitive. We all know how painful it is to have something in the eye. The slightest irritation or injury will cause the nerve fibers in the cornea to fire. Even a small scratch is associated with severe pain. The eye is often red, discharge can be seen, and often it is held close. Since there are no blood vessels in the cornea, the healing processes and defense against pathogens are less effective than in other parts of the body. If a corneal injury or ulceration is present, a veterinarian should determine the depth and size of the defect. An ophthalmological examination should be performed in a quiet and darkened stall. For a detailed examination of the eye the veterinarian might perform local nerve blocks. Depending on the pain level and the character of the patient, sedation might be indicated. Different reflexes are tested, tear production, the intraocular pressure is measured and the anterior and posterior sections of the eye (the pupil is dilated with special drops) are examined. In addition, samples can be obtained for e.g., pathogen and drug resistance determinations. The cornea is stained with a special dye called fluorescein. It is taken up by the cornea when the epithelium (the top layer of cells) is missing. The defect in the stroma of the cornea will glow green under an UV lamp. If the cornea is close to perforation and only the deepest layer, the endothelium, is left, the dye will not be absorbed in that area. Often these patients are less painful because the endothelium does not contain nerve fibers. Although the horse looks at us with an open eye, it is an emergency. If the cornea perforates and the aqueous humor leaks out the eye might be lost.
Therefore, a foreign body stuck in the eye should never be pulled out. It acts like a cork and closes the wound. Only a specialist who has the surgical skills to repair the cornea should perform such a procedure.
If lodged behind the third eyelid hay, sand, splinters and other debris can lead to chronic irritation and ulceration of the cornea. Part of the eye exam is the inspection of the third eyelid. Small puncture wounds can lead to introduction of bacteria and/or fungal pathogens into the corneal stroma. A stromal abscess can develop.
Deep and/or infected corneal injuries, ulcerations, and stromal abscesses often require surgical repair. Various techniques are used for this. The aim is to reduce the pathogen load, strengthen the cornea and allow blood vessels and the associated defense cells and growth factors to migrate to the area of the injury. Due to the short contact time of the various eye drops or ointments, a special catheter is often placed in the upper or lower eyelid through which medication can be continuously administered with a pump. In addition, systemic drugs are often prescribed.
In the field traumatic injuries to the eyelids are also common. Given they are immediately surgically treated, the well vascularized eyelids often heal without complications. If this is not the case, infection, scar tissue formation and deformation of the eyelids can occur. This can restrict or impede the natural closure of the eyelids possibly leading to tear film disturbances and further long-term eye problems.
A blow or other trauma occurring to the head can result in significant soft tissue injury, fractures of the various bones of the skull, and e.g., proptosis (the eye protrudes from the bony orbit) intraocular hemorrhage, and retinal detachment. These patients need immediate veterinary care. If present, shock symptoms must be treated, the circulation stabilized, and hemorrhages stopped. Strong systemic analgesics and sedatives are often indicated. A head bandage moistened with saline solution or antibiotic eye drops may be placed for the transport to a clinic. Often further work up, such as imaging (e.g., ultrasound, radiographs, computer tomography), is necessary to determine the extent of the injuries.
An acute equine recurrent uveitis (ERU) flare up is also an emergency. This autoimmune mediated, inflammatory disease affects the inside of the eye and is difficult to control. Horses often suffer multiple episodes of inflammation, which over time cause degenerative changes and can ultimately lead to blindness of the affected eye or eyes. During a flare-up, most horses show typical symptoms such as blinking, reddening of the conjunctiva, increased tearing, a cloudy cornea. Some horses will display only very mild symptoms. Downward pointing eyelashes might be the only sign displayed. Since each flare-up potentially causes more damage, it‘s important to act quickly and call the veterinarian. There are various therapeutic approaches (e.g., vitrectomy, cyclosporine implants), but despite close monitoring and treatment, there is always a risk of another episode.
Neoplasms such as squamous cell carcinoma and less commonly, sarcoids and melanomas can be found in the ocular region. These are not specifically emergencies, but it is important to regularly examine the eyes and to palpate the adnexa. This will allow detecting changes in color, shape, and consistency of the tissue at an early stage. If there is any doubt, a veterinarian should be consulted, and the rest of the body should be examined for metastases and other tumors.
In horses, cataracts are usually secondary (caused by another condition, especially ERU) or congenital. Early detection and diagnosis will lead to better outcomes if surgery is possible and indicated. Depending on the size and location of the lens opacity, it can alter the way light hits the retina and some horses will show behavioral changes. This is especially true when the turbidity increases. Therefore, these patients should be examined regularly, and the size and position of the cataract noted.
Every horse should be presented annually to the veterinarian for a general wellness exam. Management questions, such as husbandry, feeding, training schedules and goals will be discussed and a full veterinary examination, including the eyes, should be performed. This will allow detecting and treating early signs indicative of a disease process and improve the long-term performance of the patient.
To avoid emergencies and, above all, injuries to the eyes, it is important to optimize the environment of our horses. Hazards, such as protruding nails, sharp edges, and corners in the stable or on the pasture need to be detected and eliminated. Hay nets and round bales have been associated with injuries of the cornea. Wind and dust will cause irritation to the surface of the eyes and should be avoided. Stress, especially in horses with ERU, can also have a negative impact on the ocular health. If possible, horses should only be turned out with fly masks with UV protection. These can also protect against drafts while trailering. Various manufacturers produce special goggles for horses that can offer protection from eye injuries while being ridden and played.
If a horse shows symptoms suggestive for ocular discomfort, it should be isolated immediately, placed in a quiet, dark, draft-free stall, and examined by a veterinarian. A clean fly mask can protect against further contamination of the eye. If there are foreign objects on the surface of the eye, these can be flushed away with saline prior the arrival of the veterinarian. A foreign body stuck in the cornea should never be pulled out. Horses rubbing their eyes vigorously should be discouraged to avoid further injury. If possible, hemorrhage of surrounding structures should be stopped by applying pressure or placing a head bandage. Do not use medications prescribed for the eye of another horse. This can have fatal consequences.
An injury, no matter how small, can result in blindness or the loss of an eye, so act quickly and call the vet.