The cornea is part of the fibrous tunic, the outermost layer of the eye, and is located at the front portion of the eyeball. It is characterized by its transparency and lack of blood vessels and pigment. The cornea helps maintain the shape of the eye and serves as its primary lens, playing a crucial role in light refraction and focusing images on the retina. It receives nutrients from the tear film on the outside and the aqueous humor on the inside.
When injuries occur, the cornea changes its characteristics and shows alterations in its surface and color. The ability to recognize these changes is key to effective communication with the veterinarian.
What Reactions Can the Cornea Have to Different Diseases?
- Corneal edema: Occurs when excess fluid accumulates within the cornea. A healthy cornea can pump water toward the interior of the eye. Some corneal injuries disrupt this ability, leading to water buildup, which disorganizes the corneal structure and causes opacity. The cornea takes on a cloudy appearance and a bluish color, more intense as more fluid accumulates.
- Corneal vascularization: A normal cornea has no blood vessels. In injuries like corneal ulcers, vessels form to assist in the healing process. When the vessels are small, special equipment is needed to detect them, but when they are numerous and thick, they are visible to the naked eye, giving the cornea a deep red color.
- Corneal fibrosis: This term refers to corneal scarring. These scars appear whitish and are remnants of previous injuries.
- Corneal pigmentation: Sometimes, black pigment deposits on the cornea, reducing its transparency. This can result from chronic irritation (such as eyelid rubbing or dry eye) or breed predispositions (e.g., pigmentary keratitis in Pugs). In cats (especially Persians and Exotic breeds), black corneal pigmentation known as corneal sequestrum may appear, which often requires surgical correction.
- Deposition of whitish substances (lipids or minerals): The accumulation of lipids and/or minerals in the cornea appears as shiny, whitish, or crystalline areas. Often this is a primary corneal issue, but it may also signal an underlying systemic disease, requiring investigation into possible endocrine disorders.
There are many other possible corneal changes, some of which are combinations of the above. For this reason, it's important to call and consult your veterinarian whenever abnormal changes are noticed. Some of these conditions may be serious and can endanger the animal's vision if not treated promptly.
What Diseases Affect the Cornea?
- Keratitis: Inflammation of any layer of the cornea, which may have various causes, including infections, allergies, systemic diseases, trauma, or mechanical irritation.
- Corneal ulcer: The most common eye injury. These are wounds, often superficial, where one or more corneal layers are lost. They are painful and can cause squinting, frequent pawing at the eye, and light sensitivity (photophobia). The eye may appear red with heavy tearing. The most common cause is external trauma, although certain ocular problems or eyelid defects may also cause them.
- Entropion and ectropion: These are abnormalities in the eyelid margin where it rolls inward toward the cornea or outward away from the eye. Both conditions compromise the eyelids’ protective function and predispose the cornea to injury.
- Dry eye (Keratoconjunctivitis sicca): A common condition in dogs. It can result from reduced tear production or a change in tear composition. Affected animals often have thick eye discharge and red eyes.
- Corneal dystrophy: A genetically based condition where the cornea accumulates substances that affect its transparency. It usually affects both eyes and causes no inflammation.
- Acquired corneal degeneration: Can occur after inflammatory processes, as a result of systemic metabolic diseases, or due to degenerative changes in the cornea. These lesions appear whitish, often accompanied by blood vessels and other signs of inflammation.
- Corneal necrosis (Corneal sequestrum): A condition mainly seen in cats, where part of the cornea becomes non-viable and turns brown or black. This condition can not only affect vision but also threaten the integrity of the eyeball. Surgery is often required to remove the affected area.
When ocular injuries are observed in our pets, it is important to visit the veterinarian promptly for an accurate evaluation. Some corneal lesions allow for a more relaxed management approach, but others may require urgent treatment to avoid the risk of vision loss or even loss of the eyeball.
At IVeM, we recommend avoiding self-treatment or manipulation of the injured eye, as this can worsen the lesion and jeopardize the animal’s vision.
