Corneal Injury of the Eye
The cornea is the foremost, transparent layer of the eyeball and is a complex tissue with multiple layers. It consists of the outer epithelium, the stroma as the thickest middle layer, the Descemet’s membrane, and the inner endothelium. The cornea serves two essential functions: it protects the inner eye from external influences and is crucial for light refraction and thus for vision. With about 40 diopters, it contributes significantly to the total refractive power of the eye.
In dogs and cats, the cornea is particularly exposed and thus susceptible to injuries. A corneal injury refers to any type of damage to this sensitive structure, with the depth of the injury being crucial for prognosis and therapy. Superficial injuries only affect the epithelium, while deeper lesions can extend into the stroma or even to the Descemet’s membrane. A perforation occurs when the entire cornea is breached, which constitutes an emergency.
The anatomy of the animal eye has some peculiarities: In cats, the cornea is more curved in relation to the eye size than in dogs, making it appear optically more prominent. Certain dog breeds, especially brachycephalic breeds like Pugs or Bulldogs, have particularly exposed eyes due to their skull shape and thus an increased risk of corneal injuries.
Causes
A corneal injury of the eye refers to scratches or abrasions on the front layer of the eyeball, the cornea (physical damage). This can happen due to branches, scratching, playing with a cat, sand, splinters, thorns, or similar objects (Fig.).
Corneal injuries in dogs and cats can occur through various mechanisms. The most common causes are:
Mechanical trauma is the main cause of corneal injuries. These include scratches from branches, thorns, or grasses when brushing through undergrowth, injuries from cat claws during scuffles or play, as well as foreign bodies such as awns, grains of sand, or small wood splinters that get into the eye. Blunt trauma from bumps or blows can also lead to corneal damage.
Chemical injuries occur through contact with irritants such as cleaning agents, acids, alkalis, or other chemicals. These can cause varying degrees of damage depending on the substance and duration of exposure, with alkaline substances often being particularly dangerous as they can penetrate deep into the tissue.
Breed-specific predispositions play an important role. Brachycephalic dog breeds such as Pugs, French Bulldogs, or Pekingese, as well as cat breeds like Persians, have protruding eyes due to their skull anatomy, which are less protected by the eye socket. Additionally, these breeds more frequently suffer from eyelid malpositions and reduced eyelid closure, resulting in less moisturizing and protection of the cornea.
Secondary damage can occur due to chronic conditions such as keratoconjunctivitis sicca (dry eye), eyelid malpositions (entropion, ectropion), or distichiasis (misalignment of eyelashes). These lead to permanent irritation of the cornea and increase susceptibility to injuries and infections.
In cats, infections with feline herpesvirus (FHV-1) are also a common cause of corneal lesions, which can develop into severe ulcerations.
Symptoms
- Pain
- Spasmodic eyelid closure
- Light sensitivity
- Watery eye
- Rubbing the eye with the front paw
- Redness
Corneal injuries in dogs and cats manifest through characteristic symptoms that indicate pain and irritation of the eye. The animals typically show spasmodic eyelid closure (blepharospasm), triggered by pain and light sensitivity. Affected animals often keep the eye closed or blink excessively.
Increased tearing (epiphora) is another typical symptom. Tear production is increased by the irritation of the injury to flush out foreign bodies and clean the cornea. This leads to watery eyes and often tear stains in the fur below the eye.
Affected animals often show behavioral changes such as restlessness, increased rubbing of the eye with the paw, or rubbing the head against objects. They may also exhibit increased light sensitivity (photophobia) and seek out dark places.
Upon inspection of the eye, redness of the conjunctiva and possibly swelling of the eyelids are noticeable. The cornea itself may show clouding, which varies depending on the severity and depth of the injury. In superficial injuries, the transparency of the cornea may be preserved, while deeper lesions can lead to distinct gray or whitish opacities.
In advanced cases, purulent or mucoid eye discharge may occur, indicating a secondary bacterial infection. In deep injuries, the cornea can change shape and bulge (keratoconus) or sink in, indicating a loss of structural integrity.
Particularly serious is the appearance of a bluish sheen or a protrusion of the cornea, which may indicate a descemetocele (protrusion of Descemet’s membrane) – a condition that can occur immediately before perforation of the cornea and represents an absolute emergency.
First Aid
Generally, any eye injury should be treated by a veterinarian as quickly as possible.
- If you can see a single foreign object like thorns, carefully remove it.
- Avoid touching the eyeball if possible.
- Do not use tweezers, cotton swabs, or similar tools.
- If you are unable to remove a foreign object immediately, leave it to a veterinarian. They may slightly sedate your pet for the treatment.
- For foreign objects like sand, rinse the eye thoroughly with warm water.
- Do not use eye medications without veterinary instructions.
Diagnosis
The diagnosis of a corneal injury begins with a thorough anamnesis, where the veterinarian asks about possible causes and the timeline of symptoms. The clinical examination initially includes a careful inspection of the eye under good lighting conditions, looking for signs of redness, swelling, and discharge.
The fluorescein test is the most important diagnostic method when corneal injuries are suspected. A green dye is applied to the eye, which binds to damaged corneal tissue. Under blue light, the damaged areas glow intensely green, making even the smallest epithelial defects visible. The test is painless and provides important information about the location, size, and depth of the injury.
The slit lamp examination allows for a detailed view of the individual corneal layers. With this special microscope, the veterinarian can more accurately determine the depth of the injury and detect even the smallest foreign bodies or deposits. Additionally, it can be assessed whether deeper structures such as the Descemet’s membrane or the endothelium are affected.
In complex cases, additional diagnostic procedures may be employed. Measuring intraocular pressure (tonometry) is important to detect complications such as secondary glaucoma. A microbiological examination with swab and culture can be performed if an infection is suspected to identify the pathogen and enable targeted antibiotic therapy.
In special cases, optical coherence tomography (OCT) can also be used, providing high-resolution cross-sectional images of the cornea and allowing precise assessment of the layer structure.
The diagnosis also includes the assessment of possible complications such as uveitis (inflammation of the middle layer of the eye), hypopyon (pus accumulation in the anterior chamber), or incipient endophthalmitis (infection of the eye’s interior).
Further veterinary measures
Minor, superficial injuries to the cornea of the eye usually heal without complications within 1-2 days.
Deep corneal injuries should always be presented to a veterinarian.
Germs may have entered the eye, and the risk of consequential damage inside the eye, such as inflammation, infections, adhesions, and corneal clouding, is very high.
The veterinarian will examine the eye more closely using a magnifying glass and a slit lamp.
Antibiotic treatment and possibly pain medication, as well as special medications to prevent adhesions inside the eye, are essential.
Supplement
The treatment of corneal injuries depends on the severity and depth of the injury, as well as the presence of complications. The therapeutic spectrum ranges from conservative measures to surgical interventions.
For superficial injuries, drug therapy is the primary focus. Local antibiotics in the form of eye drops or ointments (e.g., ofloxacin, tobramycin) are used to prevent or treat bacterial secondary infections. They are usually applied several times a day over a period of 7 to 14 days. In case of proven or suspected fungal infections, antifungal preparations are used.
For pain relief and anti-inflammation, nonsteroidal anti-inflammatory drugs (NSAIDs) such as meloxicam are administered systemically. Local pain relievers like proxymetacaine should only be used for diagnosis, not for long-term therapy, as they can delay healing.
For deeper injuries or ulcerations involving the stroma, collagenase inhibitors such as acetylcysteine can be additionally used to slow down the enzymatic breakdown of corneal tissue. In certain cases, the use of autologous serum (eye drops derived from the animal’s blood) can be beneficial, as it contains growth factors that promote healing.
Surgical interventions are necessary for deep injuries, descemetoceles, or perforations. Common techniques include:
- The conjunctival flap, where a piece of the conjunctiva is drawn over the defect to protect the cornea and supply it with blood vessels
- Temporary tarsorrhaphy, where the eyelids are partially sutured to protect the cornea
- For large defects, a keratoplasty (corneal transplantation) or the use of biological membranes such as amniotic membrane may be necessary
Accompanying local therapy, wearing an Elizabethan collar is often necessary to prevent self-injury from scratching. For severe pain or uncooperative patients, short-term sedation may be necessary.
For cats with herpesvirus-associated corneal lesions, additional antiviral therapy with preparations such as ganciclovir or idoxuridine is indicated.
Prognosis and aftercare
The prognosis for corneal injuries depends significantly on the depth and extent of the injury, the speed of treatment, and potential complications. Superficial epithelial defects usually heal completely within 3-5 days with adequate treatment, without leaving permanent damage. Deeper injuries affecting the stroma, however, require 1-2 weeks or longer to heal and may leave scars that, depending on their location, can impair vision.
Aftercare plays a crucial role in the success of healing. Regular veterinary check-ups are essential to monitor the healing process and adjust therapy if necessary. Daily checks may be necessary in the first few days, with intervals later extended according to the healing progress.
Correct application of prescribed medications by the pet owner is necessary. Eye drops and ointments must be administered at the prescribed frequency and throughout the entire treatment period, even if improvement has already occurred. If there are difficulties with administration, techniques for gentle restraint of the animal should be applied.
Protection against self-injury using a collar must be maintained until the cornea has fully healed. This can be uncomfortable for the animal but is essential for successful healing.
Complications that may occur during the healing phase include secondary infections, scarring, chronic keratitis, symblepharon (adhesions between the cornea and conjunctiva), or secondary glaucoma. If signs of deterioration such as increasing redness, increased discharge, or clouding occur, a veterinarian should be consulted immediately.
In the long term, regular ophthalmological check-ups may be advisable after healed corneal injuries, especially for animals with predisposing factors such as brachycephalic skull shape or chronic eye diseases. Preventive measures such as correction of eyelid malpositions or treatment of dry eye can reduce the risk of recurrent injuries.
Summary
Corneal injuries in dogs and cats are common and potentially serious eye conditions that require immediate veterinary care. The transparent cornea, as the frontmost layer of the eye, is particularly exposed and thus susceptible to injuries from mechanical impacts, foreign bodies, or chemical substances.
Clinical symptoms include blepharospasm, increased tear flow, photophobia, and behavioral changes such as increased rubbing of the eye. Diagnosis is made through careful clinical examination, particularly using a fluorescein test and slit lamp examination, to assess the location, size, and depth of the injury.
Treatment depends on the severity of the injury and ranges from local antibiotics and pain medications for superficial defects to surgical interventions such as conjunctival flaps or keratoplasty for deep injuries or perforations. Consistent aftercare with regular veterinary check-ups and correct medication administration is crucial for successful healing.
The prognosis depends significantly on the depth of the injury and the speed of treatment. While superficial epithelial defects usually heal without consequences, deeper injuries can lead to scarring and impairment of vision. Special attention is required for animals with predisposing factors such as brachycephalic breeds or those with chronic eye diseases.
Preventive measures such as avoiding dense undergrowth during walks, correcting eyelid malpositions, and regular ophthalmological check-ups can help reduce the risk of corneal injuries and maintain the animals’ eye health in the long term.
Outlook on current research
Research in the field of veterinary ophthalmology is continuously advancing, improving the treatment of corneal injuries in dogs and cats. Innovative therapeutic approaches aim to accelerate healing and optimize functional and aesthetic outcomes.
A promising area of research is the application of growth factors and stem cells to promote corneal regeneration. Studies on the topical application of mesenchymal stem cells have shown that they can accelerate the healing of corneal defects and reduce scar formation. These cells release bioactive substances that have anti-inflammatory effects and promote tissue regeneration.
Advances in biomaterial research have led to the development of novel corneal replacement materials. Synthetic keratoprostheses and biocompatible collagen matrices offer alternatives for cases where conventional therapy is not successful. These materials are continuously being improved to enhance their tissue integration and long-term stability.
The use of amniotic membrane as a biological wound dressing is gaining increasing importance. This membrane from the placenta contains anti-inflammatory factors, inhibits scar formation, and promotes epithelialization. New preservation methods such as lyophilization (freeze-drying) make the amniotic membrane more durable and easier to use.
In the field of drug therapy, new formulations are being developed that allow for longer retention on the eye and better penetration into the corneal tissue. Nanoparticles as carriers for antibiotics or anti-inflammatory substances can optimize drug release and reduce application frequency, thus improving compliance.
Research on feline herpesvirus and its role in corneal diseases in cats is leading to more targeted antiviral therapies. New active ingredients with improved efficacy and fewer side effects are being developed to better treat this common cause of corneal lesions in cats.
Advances in diagnostic imaging, particularly in high-resolution optical coherence tomography (OCT), allow for increasingly precise assessment of corneal structure and healing progress. These non-invasive procedures enable detailed visualization of individual corneal layers and can thus contribute to the optimization of therapy.
The interdisciplinary collaboration between veterinary ophthalmologists, materials scientists, and cell biologists opens up new perspectives for the treatment of complex corneal injuries and could lead to individualized therapeutic concepts in the future, tailored to the specific needs of each patient.
Frequently asked questions (FAQs)
- How do I recognize if my pet has a corneal injury?
Look out for increased blinking, tearing, redness of the eye, light sensitivity, or if your pet is rubbing its eye more frequently. If you suspect an injury, you should consult a veterinarian immediately. - How long does it take for a corneal injury to heal?
The healing time depends on the depth of the injury. Superficial injuries usually heal within 3-5 days, while deeper injuries may take 1-2 weeks or longer. - Can my pet go blind after a corneal injury?
With timely and adequate treatment, the prognosis is generally good. However, untreated or very deep injuries can lead to scarring and visual impairments up to vision loss. - Why does my pet need to wear a collar?
The collar prevents your pet from scratching or rubbing the injured eye, which could disrupt the healing process and lead to further damage. - How do I administer eye drops to my pet?
Gently hold the head, pull the lower eyelid down slightly, and apply the drops into the conjunctival sac. Avoid direct contact between the dropper tip and the eye. - Are certain dog or cat breeds more susceptible to corneal injuries?
Yes, brachycephalic breeds such as Pugs, Bulldogs, and Persian cats have protruding eyes due to their skull anatomy and thus an increased risk of corneal injuries. - Can I prevent corneal injuries in my pet?
Avoid dense undergrowth when walking, keep your cat’s claws trimmed, and have eyelid abnormalities corrected. Regular veterinary check-ups can also detect risk factors early. - What is a fluorescein test and is it painful for my pet?
The fluorescein test is a painless examination where a green dye is applied to the eye, which binds to damaged areas of the cornea and makes them visible under blue light. - Can a corneal injury heal on its own?
Tiny superficial injuries may sometimes heal on their own, but there is always a risk of complications such as infections. Therefore, veterinary examination and treatment are strongly recommended. - What complications can occur with a corneal injury?
Possible complications include bacterial or fungal infections, descemetocele (protrusion of the deep corneal layer), corneal perforation, uveitis (inflammation of the middle layer of the eye), or chronic keratitis with scarring.
Literature
- Hertslet, Shirin; Jawinski, Gabriele: Perforating corneal injuries – diagnosis and initial treatment. kleintier konkret 2011; 14(S 01): 13-16, Enke Verlag
- Löwe, G. and Löwe, O. (2021). Emergencies in Dogs and Cats – A Veterinary Guide. Kynos-Verlag. 208 p.
- Ledbetter EC, Gilger BC. Diseases and Surgery of the Canine Cornea and Sclera. In: Gelatt KN, Gilger BC, Kern TJ, editors. Veterinary Ophthalmology. 6th ed. Hoboken: Wiley-Blackwell; 2021. p. 1082-1164.
- Pot SA, Gallhöfer NS, Matheis FL, Voelter-Ratson K, Hafezi F, Spiess BM. Corneal collagen cross-linking as treatment for infectious and noninfectious corneal melting in cats and dogs: results of a prospective, nonrandomized, controlled trial. Veterinary Ophthalmology. 2014;17(4):250-260.
- Jégou JP, Tromeur F. Superficial keratectomy for chronic corneal ulcers refractory to medical treatment in 36 cats. Veterinary Ophthalmology. 2015;18(4):335-340.
- Lacerda RP, Peña Gimenez MT, Laguna F, Costa D, Ríos J, Leiva M. Corneal grafting for the treatment of feline corneal sequestrum: a retrospective study of 18 eyes (13 cats). Veterinary Ophthalmology. 2017;20(4):344-349.
