There are a number of causes of cat eye infections. To be able to identify what is afflicting a cat, the physical appearance of the infection of the eye must be considered, and also the symptoms that are accompanying the infection.
Anatomy of the Cat's Eye
Understanding the parts of the cat's eye will aid in defining what is being affected by the infection. The main parts of the cat's eyes are:
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Cornea: this is the exposed surface of a cat's eye. It is the first layer of the eye, and is transparent.
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Sclera: the whites of the eyes. The muscles responsible for eye movement are attached to the sclera.
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Iris: this is the colored part of the eye, and occupies all the visible part of the eye.
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Pupil: the pupil is located inside the iris, and appears as a black, vertical slit that changes size depending on the amount of light present.
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Third eyelid: the third eyelid is not visible under normal circumstances. However, it can sometimes be seen if a cat is suddenly woken. The third eyelid is located at the bottom of the eye, and is semi-transparent.
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Conjunctiva: this is a normally pink membrane that lines the eyelids. The conjunctiva is responsible for secreting mucus to keep the eye moist and movable.
Conjunctivitis
Conjunctivitis is the inflammation or infection of the conjunctiva and sclera. The infection can be cause by viruses, bacteria or fungi. Conjunctivitis is the most common eye infection in cats, and the symptoms are:
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redness of the conjunctiva cause by fluid buildup
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eye discharge (thick yellow, or green)
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third eyelid is partially visible
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pawing or rubbing of the eye
Conjunctivitis has the potential to spread to other structures of the eye, and can also be a sigh of immunodeficiency virus infection. Conjunctivitis can spread to other cats.
Herpes Virus Infection
The herpes virus is a common cause of conjunctivitis. If your cat has the herpes virus, it will show these symptoms along with those associated with conjunctivitis:
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corneal ulcers
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nasal discharge
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sneezing
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oral ulcers
Once a cat has acquired the herpes virus infection, it will become a lifelong carrier. However, this doesn't mean that it will continually show symptoms. Symptoms can flare up with the onset of stress.
Uveitis
Uveitis is the inflammation of the uvea. The uvea is the dark tissue of the eye that contains blood vessels. Uveitis can be caused by infections from viruses, bacteria, parasites, fungi and bacteria. It can also be caused by immunodeficiency diseases, cancers and trauma or injury to the eye. The symptoms of uveitis are:
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redness of the eyes
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cloudy or dull appearance of the eyes
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squinting of the eyes
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unevenly colored, or discolored iris
Uveitis can be indicative of other diseases that can be affecting the rest of a cat's body. Uveitis has the potential to permanently damage a cat's vision, and can also cause blindness.
Cryptococcosis
Cryptococcosis is caused by fungal infection. The disease is caught from a cat's environment, and along with uveitis it is not limited to affecting the eye. The problems associated with this infection are:
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peripheral blindness
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detached retinas
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inflamed retinas
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nasal discharge
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skin lesions
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behavioral changes