Corneal Ulcers in Horses With Cushing’s Disease: Why They Need Urgent Care

By Dr Duncan Houston

A corneal ulcer in any horse should be taken seriously. In a horse with Cushing’s disease, also called pituitary pars intermedia dysfunction or PPID, the margin for delay is even smaller.

The concern is not just that the eye is sore. The concern is that older horses and horses with PPID may have reduced corneal sensitivity, altered immune responses, poorer wound healing, and a higher risk of non-healing or recurrent corneal ulcers. One study found corneal sensitivity decreased with both age and PPID, and the authors noted this may increase the risk of non-healing or recurrent corneal ulcers in affected horses. (PubMed)

That means a tiny scratch on the clear surface of the eye can become a much bigger problem if it is missed, under-treated, infected, or treated with the wrong medication. Horse eyes are dramatic little glass windows with a talent for turning “minor” into “please call the vet now.”

Quick Answer

A corneal ulcer in a horse with Cushing’s disease or PPID should be treated as urgent. PPID is associated with poor wound healing, recurrent infections, recurrent corneal ulcers, and reduced corneal sensitivity, which can make ulcers harder to detect early and potentially slower to heal. A horse with PPID that is squinting, tearing, cloudy-eyed, rubbing the eye, or holding the eye closed needs prompt veterinary assessment, fluorescein staining, pain relief, infection control, and close rechecks. (SquareSpace)

What Is a Corneal Ulcer?

A corneal ulcer is a wound on the cornea, the clear outer surface at the front of the eye.

In horses, corneal ulcers are commonly caused by trauma. This may include hay, grass stems, bedding, branches, dust, stable hardware, rubbing, foreign material, or a small scratch that becomes contaminated. Horses are especially vulnerable to eye trauma because their eyes are large and positioned on the sides of the head. (AAEP)

Common signs include:

A corneal ulcer is confirmed using fluorescein stain, a dye that sticks to damaged corneal tissue and helps the vet identify the ulcer. (AAEP)

Why Is a Corneal Ulcer More Concerning in a Horse With PPID?

PPID is not just a long coat problem.

PPID is a progressive endocrine disease of older horses caused by dysfunction of the pituitary pars intermedia. It leads to increased ACTH and related hormone production, and clinical signs may include delayed shedding, hypertrichosis, muscle loss, lethargy, abnormal sweating, increased drinking and urination, insulin dysregulation, laminitis, recurrent infections, poor wound healing, and recurrent corneal ulcers. (SquareSpace)

For the eye, three issues matter most.

1. Reduced corneal sensitivity

The cornea normally has excellent nerve supply. That nerve supply helps the horse detect irritation, blink, protect the eye, and support normal healing.

In horses with PPID, corneal sensitivity can be reduced. That means an ulcer may not trigger as much obvious discomfort early, or the horse may not protect the eye as effectively. The study on corneal sensitivity found lower sensitivity in horses with PPID compared with older horses without PPID, and suggested this may help explain abnormal healing characteristics in older PPID horses.

This is clinically important because owners often judge urgency by how painful the horse looks. In a PPID horse, a quieter-looking eye does not always mean a safer eye.

2. Poorer healing and immune defence

PPID is associated with recurrent infections and poor wound healing. The 2025 Equine Endocrinology Group recommendations include recurrent infections, recurrent corneal ulcers, and poor wound healing in the clinical spectrum of PPID. (SquareSpace)

That does not mean every PPID horse will heal badly. It means you should assume the eye needs closer monitoring, faster intervention, and more cautious follow-up.

3. Possible changes in tear cortisol

A separate study reported that some horses and ponies with PPID had increased tear cortisol concentrations compared with healthy aged animals. This is interesting because local ocular cortisol may influence the eye surface environment, but it should be framed carefully: it is not proof that every PPID horse has delayed ulcer healing because of tear cortisol alone. (AVMA Journals)

The safer clinical message is: PPID horses can be higher-risk eye patients, and their corneal ulcers should not be managed casually.

Why Delay Is Dangerous

Corneal ulcers in horses can worsen quickly, especially if they become infected, deepen, or start to melt. Complicated ulcers may need medication every few hours, close monitoring, referral, or surgery. AAEP notes that complicated ulcers are ideally referred because the eye may need medication every few hours and close monitoring, while early aggressive treatment can give a good visual prognosis. (AAEP)

The risk is even higher when the horse has:

The real danger is not just the scratch. It is the combination of corneal damage, infection risk, inflammation, delayed healing, and the wrong treatment at the wrong time.

Severity Framework: How Worried Should You Be?

In a horse with PPID, I would lower the threshold for veterinary assessment. These are not the horses where you want to “see how it looks after the weekend.”

What Else Can Look Like a Corneal Ulcer?

A painful, watery, cloudy eye is not always a simple corneal ulcer.

Important rule-outs include:

This is why fluorescein staining, eyelid examination, eye pressure measurement, and sometimes cytology or culture matter. The treatment for uveitis, glaucoma, fungal keratitis, and a simple superficial ulcer can be very different.

How Do Vets Diagnose a Corneal Ulcer in a PPID Horse?

A proper eye exam usually includes:

University of Melbourne equine antimicrobial guidelines state that a thorough ophthalmic exam is needed to identify corneal ulcers and assess predisposing factors, and that culture and cytology should be considered from affected areas when corneal disease is present. (Faculty of Science)

Why Fluorescein Staining Matters

Fluorescein stain is one of the most important tools in horse eye medicine.

If the corneal surface is damaged, the stain highlights the ulcer. This helps confirm the diagnosis, monitor healing, and guide treatment. AAEP describes fluorescein stain as a tool that adheres to corneal defects and allows the veterinarian to identify damage. (AAEP)

This matters because some medications are dangerous if an ulcer is present.

Corticosteroids can be useful for some inflammatory eye diseases, but they are contraindicated when a corneal ulcer is present. MSD Veterinary Manual states that the cornea should be stained with fluorescein before corticosteroid use, and that corticosteroids are contraindicated topically and systemically when a corneal ulcer is present. (MSD Veterinary Manual)

The practical rule is simple: do not put steroid drops or old eye ointment into a horse’s eye unless a vet has checked the cornea first.

How Are Corneal Ulcers Treated in Horses With PPID?

Treatment depends on whether the ulcer is simple, infected, deep, melting, fungal, non-healing, or associated with other eye disease.

Simple superficial ulcers

A simple ulcer may be treated with:

MSD Veterinary Manual describes simple ulcer management as preventing infection and controlling pain, with broad-spectrum topical antibiotic therapy, atropine when appropriate, systemic NSAIDs, and rechecks because corneal infections are common in horses. (MSD Veterinary Manual)

In a PPID horse, a “simple” ulcer still deserves respect. The recheck is not optional decoration. It is how you know the eye is actually healing.

Complicated ulcers

A complicated ulcer may show stromal loss, infiltrate, malacia, deepening, infection, a melting appearance, poor healing, or worsening discomfort.

Treatment may involve:

MSD Veterinary Manual notes that complicated ulcers may need cytology, bacterial and fungal culture, antibiotics every 2 to 6 hours, antifungal treatment, anti-collagenase therapy, atropine, systemic NSAIDs, frequent monitoring, and referral when ulcers are deep or progressive. (MSD Veterinary Manual)

Melting ulcers

A melting ulcer is an emergency.

This is when enzymes break down corneal collagen, causing the cornea to soften, deepen, and become structurally unstable. The eye can deteriorate quickly.

Anti-collagenase agents such as serum, EDTA, or N-acetylcysteine may be used as part of therapy, along with aggressive antimicrobial treatment and close monitoring. MSD Veterinary Manual lists anticollagenase therapy every 2 to 6 hours as part of complicated corneal ulcer management. (MSD Veterinary Manual)

Fungal ulcers

Horses are more prone to fungal corneal disease than many owners realise.

Fungal keratitis can range from non-ulcerative disease to rapidly progressive keratomalacia or stromal abscessation. The horse’s ocular surface is exposed to environmental fungi, and fungal involvement is more likely when the corneal surface is damaged or host defence is altered. University of Melbourne guidelines note that bacterial, fungal, or mixed infections can occur in corneal ulcers, with regional variation in pathogens. (Faculty of Science)

In a PPID horse, fungal concern should be taken seriously if there is a cloudy, white, yellow, plaque-like, melting, or poorly responsive ulcer, especially in regions where fungal keratitis is common.

Why a Subpalpebral Lavage System May Be Needed

Some horse eye ulcers require medication very frequently. Every 1 to 2 hours is not unusual in severe cases.

That is a lot of handling. It is also a lot of chances for the horse to object, especially if the eye is painful.

A subpalpebral lavage system is a small tube system placed by a vet that allows medication to be delivered to the eye without repeatedly forcing the eyelids open. It can make treatment more reliable and much safer for the horse and handler.

MSD Veterinary Manual notes that subpalpebral lavage placement may be necessary for complicated corneal ulcers, and the University of Tennessee notes vets may choose this system when a horse is difficult to treat or requires long-term treatment. (MSD Veterinary Manual)

Should PPID Treatment Change During an Eye Ulcer?

The corneal ulcer needs direct eye treatment, but the PPID should not be ignored.

PPID management commonly involves pergolide, diet and metabolic care, insulin assessment, laminitis prevention, dental care, parasite control, and general senior horse management. The 2025 Equine Endocrinology Group recommendations describe pergolide mesylate, along with appropriate dietary management and general wellness care, as the mainstay of PPID treatment. (SquareSpace)

The eye ulcer will not heal just because the horse is on pergolide. But uncontrolled PPID, poor body condition, laminitis pain, insulin dysregulation, chronic infection, or poor general health can make the whole patient harder to manage.

A good plan should ask:

Cornell lists commonly used PPID tests as baseline ACTH and insulin, TRH-response testing, and dexamethasone suppression testing, with follow-up including clinical signs and ACTH or insulin monitoring. (Cornell Vet College)

When Is This an Emergency?

A horse with PPID and any painful eye sign should be treated with urgency.

Call a vet immediately if you see:

The University of Tennessee states that squinting and excessive tearing indicate a painful eye, and that equine eye diseases can progress quickly enough that delayed treatment can worsen the problem and risk vision loss. (College of Veterinary Medicine)

What Should You Do Right Now?

1. Call your vet

Tell them your horse has PPID or suspected PPID. Mention the horse’s age, current PPID medication, whether they are squinting, whether the cornea is cloudy, and whether there is discharge.

2. Do not apply old medication

Especially do not use steroid-containing drops or ointments unless your vet has examined the eye and confirmed there is no ulcer. Steroids can slow epithelial regeneration and are contraindicated when a corneal ulcer is present. (MSD Veterinary Manual)

3. Prevent rubbing

Rubbing can turn a small ulcer into a bigger one. Use a safe, clean, well-fitted fly mask only if it does not press on the eye and does not hide worsening signs.

4. Reduce irritation

Move the horse away from dust, wind, rough hay, branches, sharp objects, and heavy flies where practical.

5. Take clear photos

Photograph both eyes from the front and side in good light. This helps monitor change, but photos do not replace fluorescein staining.

6. Ask about fluorescein staining

This is one of the first practical steps to confirm or rule out a corneal ulcer.

7. Ask about recheck timing

For a PPID horse, rechecks are especially important. If the eye is not clearly improving within the expected timeframe, the plan may need to change quickly.

8. Review PPID control

This is not the emergency priority in the first painful eye moment, but it should be part of the broader plan once the horse is stable.

Common Mistakes Owners Make

Mistake 1: Waiting because the eye is “only a little watery”

In a PPID horse, subtle signs can still matter. Reduced corneal sensitivity may make the eye look less painful than expected.

Mistake 2: Using leftover steroid drops

This is one of the most dangerous mistakes. Steroids can be useful for some inflammatory eye diseases, but they are unsafe when a corneal ulcer is present. (MSD Veterinary Manual)

Mistake 3: Assuming all cloudy eyes are cataracts

A cloudy cornea can mean corneal oedema, ulceration, infection, uveitis, glaucoma, or stromal abscess. Cataracts are inside the eye lens. Owners cannot reliably separate these from the paddock.

Mistake 4: Missing fungal infection

A non-healing, worsening, yellow-white, plaque-like, melting, or painful ulcer may need cytology, culture, and antifungal treatment. Fungal keratitis in horses is a severe problem that needs prompt and aggressive treatment. (College of Veterinary Medicine)

Mistake 5: Stopping treatment as soon as the eye looks better

The cornea may still stain positive. Pain may improve before the ulcer has fully healed. Treatment and tapering should follow veterinary rechecks.

Mistake 6: Treating the eye but ignoring the PPID

The ulcer needs direct care, but PPID control, insulin status, nutrition, laminitis risk, and general senior horse health all affect the bigger picture.

Prevention for PPID Horses

You cannot prevent every corneal ulcer, but you can reduce risk.

For PPID horses, prevention is less about wrapping them in bubble wrap and more about making sure small eye changes are not ignored.

Normal Irritation vs Red Flag Eye Signs in PPID Horses

The clinical checkpoint is this: pain, cloudiness, discharge, one-sided signs, rubbing, or persistence changes the level of concern.

Will My Horse Be Okay?

Many horses with PPID and corneal ulcers do well when the ulcer is found early, treated correctly, and rechecked closely.

The prognosis is better when:

The prognosis becomes more guarded when the ulcer is deep, infected, melting, fungal, recurrent, non-healing, or associated with uncontrolled PPID, severe pain, or poor treatment compliance.

Related Horse Eye Topics To Link Internally

This article fits well with related educational articles on:

FAQs About Corneal Ulcers in PPID Horses

Is a corneal ulcer in a horse with PPID an emergency?

Yes, it should be treated as urgent. PPID horses may have reduced corneal sensitivity, poor wound healing, recurrent infections, and recurrent corneal ulcers, so delaying care can increase the risk of complications. (SquareSpace)

Can PPID make a horse’s eye ulcer heal more slowly?

It can. Research has shown reduced corneal sensitivity with age and PPID, and decreased corneal sensitivity is associated with impaired wound healing. PPID is also linked with poor wound healing and recurrent corneal ulcers in clinical guidance. (PubMed)

Can I use old eye drops if my horse has had ulcers before?

No. Do not use old eye drops unless your vet has examined the eye. Steroid-containing drops can be dangerous if a corneal ulcer is present, and the current eye problem may not be the same as the last one. (MSD Veterinary Manual)

How do vets know if a horse has a corneal ulcer?

Vets commonly use fluorescein stain to identify defects in the cornea. They may also examine the eyelids, check for foreign bodies, measure eye pressure, and perform cytology or culture if infection or a complicated ulcer is suspected. (AAEP)

Does pergolide treat the corneal ulcer?

No. Pergolide helps manage PPID, but the corneal ulcer still needs direct eye treatment. PPID control is part of the broader health plan, while the ulcer may need topical medication, pain control, rechecks, culture, antifungals, anti-collagenase therapy, or referral depending on severity.

The Bottom Line

A corneal ulcer in a horse with Cushing’s disease or PPID is not something to watch casually.

PPID horses may have reduced corneal sensitivity, poorer healing, recurrent infections, and a higher risk of recurrent or non-healing ulcers. That means the eye may be more serious than it first looks, and the horse may not show pain as clearly as expected.

The safest rule is simple: if a PPID horse has a watery, squinting, cloudy, swollen, painful, or one-sided eye problem, call your vet promptly. Early fluorescein staining, correct medication, close rechecks, and careful PPID management give the horse the best chance of keeping the eye comfortable, functional, and sighted.

If you are unsure whether your horse’s eye signs are mild irritation, a corneal ulcer, PPID-related healing concern, uveitis, glaucoma, or an emergency, ASK A VET™ can help you understand what signs matter and when veterinary care is needed.