How to recognize corneal ulcers in foals and know the risk factors for corneal ulcers so that you can protect your foal’s eyes.
A foal’s vision is nearly mature at birth, which is very beneficial since they are precocial species, meaning they are mobile at birth. However, a neonatal foal’s eyes are morphologically and functionally different from those of a mature horse. Foals lack a menace response (the blink reflex in response to a rapid approach of an object) at birth, which develops at 14-16 days of age. Newborn foals also have decreased corneal sensitivity, which is even more decreased in sick foals. Examination of the eyes is an important part of a newborn foal exam, which should occur when the foal is 12 hours old.
What is the Cornea of the Eye?
The cornea is the transparent ocular surface of the eye. There are five layers to the cornea, with the tear film being the outermost layer. The tear film is a surface defense mechanism for the external eye. The tear film protects, lubricates, provides nutrients, immune protection, and oxygenation to the cornea, and removes debris from the eye.
What is a Corneal Ulcer?
A corneal ulcer is a disruption, scratch, or break in the corneal layers. The cornea and its associated structures participate in the stability of the ocular surface smoothness and integrity of the eye, which is crucial to the function of the eye. When a corneal injury occurs, ocular surface components work in an intricate and complicated manner to restore corneal structure and function.
What are Risk Factors for Corneal Ulcers in Foals?
- Lack of a menace response
- Decreased corneal sensitivity
- Neonatal illness
- Entropion (rolling inward of the eyelid; usually involves the lower lid)
How to Recognize Corneal Ulcers in Foals
Corneal ulcers are an acquired condition. Most of the time they are secondary to trauma to the eye. In sick foals, corneal ulcers can be initiated by entropion, reduced blinking, and more time laying down resulting in direct contact with the ground and the cornea.
A non-exclusive list of signs of a corneal ulcer includes:
- Excessive tearing
- Squinting
- Redness
- Discoloration of the globe (gray, white, blue, green, yellow)
- Lack of smoothness to the ocular surface
Foals are tricky in that they may not show these typical signs because they have decreased corneal sensitivity.
Diagnosing Corneal Ulcer in Foals
To diagnose a corneal ulcer, the eye is stained with a fluorescein stain strip and evaluated with an ophthalmoscope to determine stain uptake. An area of the corneal will stain green.
Classification of Corneal Ulcers
Uncomplicated
Complicated
- Superficial corneal ulcer
- A non-infected corneal ulcer
- There is minimal inflammation
- Deep corneal ulcer
- An infected corneal ulcer
- There is inflammation
Treatment Goals for Corneal Ulcers in Foals
Treatment goals are aimed at preventing or controlling infection, controlling pain and inflammation, limiting unregulated proteolysis, and promoting healing.
Corneal ulcers are treated with topical eye medications and systemic medications. Topical eye medications can include but are not limited to:
- Antimicrobials
- Antifungals
- Anti-proteolysis agents (e.g., serum)
- Cycloplegic agents (e.g., atropine)
Atropine ophthalmic ointment or solution helps reduce pain and inflammation in the eye by dilating the pupil which also helps to prevent synechiae (adhesions between tissues in the eye). Colic is a side effect of atropine. Therefore, use atropine cautiously and under the guidance of a veterinarian.
Corneal ulcer type and severity dictate what medications are used and how aggressive the treatment will be. Uncomplicated corneal ulcers usually require a couple of eye medications 4-6 times daily and a systemic pain reliever. Uncomplicated corneal ulcers generally heal quickly, possibly in one week. Complicated corneal ulcers require several different eye medications, which are given frequently (every 2 hours in some cases), and systemic medications.
In some of the difficult, complicated corneal ulcer cases, your veterinarian might consult with or recommend an evaluation by a veterinary ophthalmologist (eye specialist). A sub-palpebral lavage (SPL) can be placed to allow for frequent administration of eye medications. An SPL is featured in a foal in the picture above.
Take Home Message
- Foals lack a menace response and have decreased corneal sensitivity, which can predispose them to corneal trauma.
- Sick foals are at an increased risk of corneal ulcers and should always have their eyes checked for ulcers as part of the examination.
- Corneal ulcers may go unrecognized because a foal might not show any clinical signs.
- Corneal ulcers treated early, when they are superficial, will heal well, and there should be no long-term damage.
- Complicated infected corneal ulcers are expensive to treat and can lead to blindness or complete loss of the eye.
- This article should help you better understand corneal ulcers in foals and make you aware of when you should have your veterinarian examine your foal’s eyes.
Corneal Ulcers in Foals…Frequently Asked Questions (FAQ)
How long does it take for a corneal ulcer to heal in a foal?
The corneal epithelization rate is approximately 0.6mm/day, and it may be more than that in a foal. Superficial corneal ulcers take approximately 3-7 days to heal. Complicated corneal ulcers can take weeks to heal.
Will a corneal ulcer heal by itself?
Yes, if it is uncomplicated; however eye medication is still required to prevent infection while the cornea is healing. Some non-healing ulcers require ophthalmic procedures (e.g., corneal debridement) to promote healing.
What are the complications of corneal ulcers?
Complications include ocular abscess, corneal scarring, partial or complete blindness, corneal pigmentation, corneal perforation requiring removal of the eye, endophthalmitis, and phthisis bulbi.
What is the prevalence of corneal ulcers in foals?
1-18% of healthy and sick foals.
Where can I get eye medications for my foal?
From your veterinarian.