Answer: This skin or membrane is in fact third eyelid (called the nictitating membrane) which is well developed in the cat and can be seen in the inner corner of the eye as a small pink flap. Properly, it’s called the ‘haw’. Although the condition does look alarming , the movement of this membrane across both eyes does not signify a loss of sight or some other eye disorder, but generalized loss of condition.
Fat is laid down in the body mainly beneath the skin and around the kidneys, but there is also a pad of fat at the back of the eyeball where it lies in a socket in the skull, the orbit. This pad of fat, which is semi-liquid at body temperature, help provide protection for the eyeball if it should be pushed back on to the underlying hard bone of the skull, i.e. it cushion the impact of blows to the eyeball. However, when a animal is debilitated (following diarrhea or some other disorder associated with loss of weight and condition) the reserves of fat being to be broken down to provide essential energy. The reduction in the amount of fat in the orbit allows the eyeball to skin further into the socket. This ’sinking’ of the eyeball permits the third eyeball to move further then usual across the front of the eye. When the animal gains weight and replaces its fat reserves the eye moves forwards again and the third eyelid is pushed back into its normal position at the inner of the eye.
With debility then, both eyes are affected in this way, though not necessarily to the same degree. Where there is membrane across only one eye it may be due to the more serious condition involving never damage or the growth of a tumor, or there might be a foreign body (e.g. a grass seed) in the eye, and therefore advice should be sought immediately.
