Cats’ eyes come in many colors due to different breeds. The various colors of cat’s eyes also bring great joy to our breeding. For example, black cats’ eyes are generally green, and Landrace cats’ eyes are blue. Yes, it has been scientifically proven that iris pigmentation and blue light reflection determine a cat’s eye color. However, cats’ eyes may also experience some abnormalities, such as turning red, which may be a sign of eye disease.

Red eyes of cats is also a common symptom of cat eye diseases. We can also see many owners coming to the hospital for treatment because of symptoms of red eyes of cats. In fact, there are many diseases that cause red eyes of cats. Eyes Redness can be roughly divided into two types: "redness on the surface of the eyeball" and "redness inside the eyeball." Redness on the surface of the eyeball can be roughly divided into two types: redness on the surface of the eyeball and redness on the cornea. No matter how it is classified, it is easy to determine whether the redness is on the surface of the eyeball or inside the eyeball just by visual inspection. However, there are many different diseases that cause red eye symptoms, and correct judgment is required. Moreover, it is not limited to distinguishing between the surface of the eyeball and the inside of the eyeball. If the diseased site can be further distinguished in detail, the cause of the disease can be naturally determined.

1. Congestion

Hyperemia is caused by external stimulation or inflammation, which increases the amount of blood flowing through the small blood vessels and capillaries on the conjunctiva. Congestion is divided into conjunctival congestion and ciliary congestion. The distinction between the two can be an important basis for determining the cause of congestion. Conjunctival congestion can disappear after the administration of vasoconstrictor drugs (epinephrine, etc.), while ciliary congestion cannot disappear after the use of vasoconstrictor drugs, which can be identified accordingly.

　1.1 Conjunctival congestion

Characteristics: Superficial congestion, bright red, and the direction of blood vessels can be clearly seen.

Diseases that may cause this symptom:

　①Conjunctivitis (bacterial or viral conjunctivitis, etc.)

The diagnosis can be confirmed through conjunctival contact smear microscopy and microbial culture identification of eye secretions. In conjunctivitis, you can generally see swelling of the eyelids on the nasal side, flushing and congestion of the conjunctiva, blindness, tears, and discharge of serous and purulent secretions from the inner corners of the eyes. The affected cat scratches the eyes with its front paws from time to time, causing pain and itching. Over time, conjunctival hyperplasia, adhesion, and secondary keratitis can be seen.

　②Mild corneal damage

Diagnosis can be made through tear volume measurement, corneal and conjunctival staining tests (fluorescein staining, rose bengal staining), slit lamp examination, blood tests (when endocrine abnormalities are suspected), etc.

　1.2 Ciliary congestion

Characteristics: It is deeper than conjunctival congestion, purple-red in color, individual blood vessels are not obvious, and is generally more severe than conjunctival congestion.

Diseases that may cause this symptom:

　①Severe corneal damage

The diagnostic method is the same as conjunctival congestion.

　②Uveitis

Diagnosis can be made by confirming anterior chamber flare, blood tests (routine blood test, CRP value test, antinuclear antibody test, antiglobulin test, viral antibody titer test, etc.

　③Glaucoma

Diagnosis is made by measuring intraocular pressure and examining the anterior chamber angle with gonioscopy.

　④Retinal detachment

Diagnosis is through fundoscopy and eyeball ultrasound examination.

　⑤Intraocular tumors

Diagnosis through slit lamp and eyeball ultrasound examination.

2. Corneal neovascularization

Another main cause of eye redness is corneal neovascularization. The cornea itself has no vascular tissue. Through the metabolism of corneal epithelial cells and the collagen fibers of the corneal stroma, it maintains a regular layered structure and maintains its transparency.

Characteristics: Angiogenesis can be seen from the limbus to the corneal epithelium, which is caused by damage to the corneal epithelium due to various reasons.

Diseases that may cause this symptom:

　① Dry eye syndrome (KCS, corneal epithelial damage caused by decreased tears)

　②Chronic irritation to the cornea such as meibomian gland cyst or ectopic eyelashes

　③Mild scleritis

3. Eyelashes that are too long

Inverted eyelashes stimulate eye redness, which is also a common cause. If you usually see long eyelashes, you can consider trimming them. If your eyelashes are red, put some pet eye drops on them. They will be fine in a few days and it will be no big deal.

4. Foreign body redness

There is a foreign object in the cat’s eyes that makes the eyes red. If a cat is playing naughtily outside and a foreign object enters its eyes, the symptom will be redness. For treatment, just use ordinary eye drops for care, or flush the cat's eyes with saline.

When a cat’s eyes are red, we should also pay attention to the occurrence of other symptoms, such as whether the cat sheds tears and excessive eye feces, which will help us judge the cat’s disease.