The most common disorder in cats is runny eyes. Infectious organisms such as the flu viruses or chlamydia cause conjunctivitis, an inflammation of the membranes lining the eyelids. This results in a discharge which is either watery and runny or thick and a greenish yellow color.

Occasionally a runny eye is caused by a disorder of the normal anatomy.

Tear glands continually produce secretions which lubricate the surface of the eyeball and flush particulate material into the tear ducts which then drain into the nose. If there's a blockage of the ducts, the tears have no choice but to spill over and run down the face. Blockage can occur if there has been previous damage to the ducts or if the cat has an abnormal anatomy.

Persian cats frequently have tear staining, partly because their tear ducts are kinked and partly because their eyeball shape prevents effective drainage. Chronic tear overspill causes a brown staining on the fur which is most noticeable in pale colored cats.

Runny eyes are also a result of tear overproduction if there is an irritation to the sensitive eyeball. The cause may be easily identified as in some longhaired cats where a clump of hair rubs the surface. Some can be much more difficult to detect; solitary aberrant hairs may grow inside the eyelid and can only be discovered by carrying out an extremely thorough examination under general anaesthetic.

The cornea is the clear outer covering of the eyeball and is a very sensitive structure. Flu infections can sometimes extend beyond the membranes and also affect the corneas. In very young kittens, the damage can be so severe that the cornea is extensively scarred and the cat grows up visually impaired or even blind.

Most corneal disease is encountered as a result of a bit of a punch up with another cat and a claw being poked in the eye. The puncture wound may be very obvious, particularly if a bit of claw is left behind in the eyeball.

In other cases there may be no apparent defects.

Mild corneal damage will heal well if the cat is supported with antibiotics but more severe damage may require surgery. Stitching the eyelids together often helps with the healing.

The iris is the structure which gives the eye its color, ranging from pink in albinos, to blue in Siamese, through all shades of yellows, coppers and greens. The iris is a muscular structure which contracts and expands in order to vary the amount of light which passes through to the back of the eye.

It has very delicate blood vessels and if a claw has managed to pierce through the cornea to the iris, the bleeding can be very dramatic.