Corneal ulcers and abrasions are common injuries in all horses. Racehorses are especially prone to them due to the debris thrown up by the hooves of other horses during racing. They can easily become serious, difficult to treat and vision threatening (and therefore career threatening) problems.

The cornea is the transparent surface of the front of the eyeball. It consists of the outer epithelial layer, which is only eight to ten cells thick, the stroma which makes up 90% of the thickness of the cornea, Descemet's membrane which lies beneath the stroma and the innermost endothelial layer.

Injuries which initially only involve the epithelium are termed abrasions. Deeper injuries, which involve the stroma are termed ulcers.

Signs associated with corneal ulcers (and abrasions) include blepharospasm (squinting), excess tear production, reddening of the pink conjunctiva around the eye, discharge and avoidance of bright light.

Corneal ulcers and abrasions may be obvious to the naked eye or may need to be stained with fluorescein to be visualised. Fluorescein is an orange dye, which becomes fluorescent green and binds temporarily to the surface where the epithelial layer has been lost.

Uncomplicated, superficial abrasions may heal quickly with minimal treatment. Deeper ulcers, and abrasions which become infected, can rapidly become serious problems. A wide variety of bacteria are present on the surface of the normal eye and conjunctiva. Many of these can cause disease once the cornea is injured. Some of these bacteria produce enzymes called collagenases, which destroy the substance of the stroma, leading to large, rapidly deteriorating ulcers, which have a gelatinous, "melting" appearance. If unchecked, these continue to worsen, exposing Descemet's membrane and finally leading to rupture of the eyeball.

Fungi can also infect corneal ulcers, preventing healing, leading to chronic inflammation of the cornea (known as keratitis) and severely affecting vision.

In some cases abscesses may develop in the stroma. This occurs when the epithelial cells divide and migrate over an ulcer or small puncture, sealing in bacteria, fungi or foreign material (eg small splinters of wood).

A common complication of corneal injuries is inflammation of the uveal tract (iris, ciliary body and choroid), known as uveitis. Horses are far more prone to uveitis than other species. If unchecked uveitis can lead to chronic pain, cataract formation, scarring within the eyeball, glaucoma (increased pressure within the eyeball) and damage to the retina leading to blindness.

Treatment for corneal ulcers should be aimed at preventing infection, reducing inflammation and keeping the pupil dilated. It is also important to ensure that all foreign material (eg wood, sand, grit etc) is removed from the eye, especially beneath the third eyelid.

Broad-spectrum, topical antibiotics should be used, as there are many different bacteria which can infect ulcers and prevent healing. Topical atropine will dilate the pupil, allowing normal drainage from the front chamber of the eyeball and help to prevent and control uveitis.

Systemic anti-inflammatories (especially flunixin) are important to provide pain relief and prevent inflammation.

As bright light can be painful, horses with corneal ulcers should always be kept in darkened stables or wear pacifiers with the affected eye taped over.

Serum from the horse's own blood contains globulins which are potent anti-collagenases. These counteract the destructive enzymes which lead to "melting" ulcers. In deeper, infected ulcers serum should be applied topically; or whole blood collected in EDTA tubes can be used (EDTA is an anticoagulant with anti-collagenase activity). Other anti-collagenases are available, but are more expensive and can be irritant.

Horses will often resent repeated application of topical medication for corneal ulcers. As treatment may be required up to every two hours, sometimes it is necessary to use a lavage system either through the nasolacrimal duct (through the normal tear drainage duct) or more commonly through the upper eyelid. This allows drops to be applied regularly without having to handle the eye, which may be very painful.

In more severe and deeper ulcers it may be necessary to debride the area. This involves cutting and scraping away unhealthy tissue from the edges under local or general anaesthesia.

Deep ulcers may take weeks to heal, as there is no direct blood supply to provide nutrition to the healing cells. Tiny blood vessels will slowly grow across the surface of the cornea from the edges to try to reach the ulcer. This may take three to four weeks if the ulcer is in the centre of the cornea.

In severe, non-healing ulcers and those which are so deep the eyeball is in danger of rupturing, surgery may be required. A section of the fleshy conjunctiva from around the eyeball can be dissected away and sutured over the ulcer. This provides a rich blood supply for healing as well as providing protection.

On other cases, especially where there is fungal infection present, a corneal graft may be required. This is where the diseased cornea is removed and replaced with donor cornea, either from the other eye or from another horse.

Both conjunctival and corneal grafts become pigmented with time and can, themselves affect the horse's vision.

Corneal injuries can quickly become severe, painful and vision threatening problems. They can often be difficult and expensive to treat successfully. If treatment is not successful and vision is lost in the eye then the horse is unable to compete under the rules of racing. It is important that any suspected corneal injury is examined quickly (within 24 hours) so that appropriate treatment can be instigated. The majority of corneal ulcers and abrasions which are treated quickly and appropriately will respond well and heal in a few days. However; those which are neglected, not noticed or inappropriately treated can quickly become major problems with a guarded prognosis for future racing.